Ecological Assessment of the Freshwater Wetlands in the Nicholson-Gregory Catchment,
North-Western Queensland.
Report No. 04/10
July, 2005
Prepared by Aaron Davis and John Dowe
Australian Centre for Tropical Freshwater Research
James Cook University, Qld, 4811
Phone: (07) 47814262
Fax: (07) 47815589
Email: [email protected]
TABLE OF CONTENTS
EXECUTIVE SUMMARY.................................................................................................................................... 3
1.0
INTRODUCTION ....................................................................................................................................... 4
2.0
STUDY AREA .............................................................................................................................................. 5
3.0
WETLAND ENVIRONMENTS OF THE NICHOLSON-GREGORY CATCHMENT ........... 6
3.1
3.2
3.3
4.0
The Conservation Status of Wetland Ecosystems in the Nicholson-Gregory Catchment............. 7
Species of Conservation Concern.................................................................................................. 8
Cultural Values.............................................................................................................................. 9
WETLAND MANAGEMENT ISSUES ............................................................................................... 10
4.1 Grazing ........................................................................................................................................ 10
4.2 Introduced Weeds........................................................................................................................ 10
4.2.1
Aquatic Weeds ................................................................................................................................. 10
4.3 Feral Pigs..................................................................................................................................... 11
4.4 Potable Water Quality, Pollution and Contaminants................................................................... 11
5.0
CATCHMENT CONDITION ASSESSMENT ............................................................................... 12
5.1 Hydrology of the Nicholson-Gregory Catchment ....................................................................... 12
5.1.1
Surface Waters ................................................................................................................................ 19
5.1.2
Groundwaters .................................................................................................................................. 19
5.1.3
Groundwater Discharge and Recharge Relationships .............................................................. 19
5.1.4
Water Resource Development, Flow Modification and River Regulation.............................. 19
6.0
WATER QUALITY .................................................................................................................................. 20
7.0
FRESHWATER FISH COMMUNITIES ............................................................................................ 24
7.1 Fish Survey Methodology ........................................................................................................... 24
7.2 Fish Survey Results ..................................................................................................................... 25
7.3 Significant Fish Species of the Nicholson-Gregory Catchment .................................................. 32
7.4 Habitat Condition ........................................................................................................................ 34
Introduced Fish Species ................................................................................................................. 36
7.4.1
7.4.2
Recreational Fishing ...................................................................................................................... 38
7.4.3
Fish Kills .......................................................................................................................................... 39
7.5 Conclusions ................................................................................................................................. 40
8.0
RIPARIAN VEGETATION........................................................................................................................
8.1 INTRODUCTION ................................................................................................................................
8.2 Methods ...........................................................................................................................................
8.3 Results .............................................................................................................................................
8.4 Summary of Survey Sites ................................................................................................................
8.4.1
Gregory River – The Knob ................................................................................................................
8.4.2
Gregory River – Six Mile ...................................................................................................................
8.4.3
Gregory River – Greogry Downs Public Camping Area ..............................................................
8.4.4
Gregory River – Gregory Downs Station (Planet Downs) ..........................................................
8.4.5
Gregory River – West of Tirranna Roadhouse ...............................................................................
8.4.6
Beams Brook – Brinawa Crossing ...................................................................................................
8.4.7
Beams Brook – Downstream of Black Gully Junction ..................................................................
8.4.8
Beams Brook - Brookdale ..................................................................................................................
8.4.9
Beams Brook – Upstream of Albert River Junction .......................................................................
8.4.10 Lawn Hill Creek – Big Lagoon ........................................................................................................
8.4.11 Lawn Hill Creek – Lawn Hill Station .............................................................................................
8.4.12 Lawn Hill Creek – Bluewater Waterhole Crossing ......................................................................
8.4.13 Running Creek - Almora ....................................................................................................................
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8.4.14 One Mile Creek - Punjaub ................................................................................................................
8.4.15 Elizabeth Creek – Lawn Hill Station ..............................................................................................
8.5 Summary .........................................................................................................................................
8.6 Aquatic Weeds ................................................................................................................................
9.0
MACROINVERTEBRATES .................................................................................................................. 59
9.1 Macroinvertebrate Assessment Methodology and Data Analysis ............................................... 60
9.2 Results ......................................................................................................................................... 62
9.3 Discussion ................................................................................................................................... 65
The Natural Values of Karst and Spring Environments ............................................................ 66
9.3.1
10.0 OTHER AQUATIC FAUNA .................................................................................................................. 67
10.1 Reptiles........................................................................................................................................ 67
10.2 Cane Toads .................................................................................................................................. 67
11.
CONCLUSIONS ........................................................................................................................................ 68
12.
RECOMMENDATIONS ......................................................................................................................... 70
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EXECUTIVE SUMMARY
•
The Nicholson-Gregory River catchment contains a diverse range of wetland environments
displaying natural, cultural and social values that span local, state and national scales.
•
The vast majority of threatened bioregional habitats that occur within the catchment are
associated with the region’s wetland environments, specifically the area’s riparian, floodplain and
spring habitats.
•
Despite the high natural values associated with the catchment’s wetland ecosystems there
remains a distinct lack of quantitative scientific data regarding their basic ecology and the key
processes which drive ecosystem form and function.
•
The Gregory River’s unique status as a large, perennial watercourse in arid/semi-arid Australia is
due to the groundwater influence of Australia’s largest karst terrain, the Barkly Karst. Despite
this distinctiveness, the isolation of the Gregory River karst area has seen minimal research
devoted to aquifer characteristics such as the location and extent of recharge zones as well as
long-term discharge behaviour.
•
The level of water resource development and consumptive surface-water usage in the catchment
is currently minimal. The degree and nature of future water resource development is however a
key issue that will dictate prospective ecosystem health. Considering the limited current
entitlements and the high natural values of the region, the impending Water Resource Plan will
apparently consider limited consumptive growth of water entitlements across the basin, although
the exact nature and magnitude of future allocations is yet to be specified.
•
A compilation of fish survey effort highlights the high freshwater fish diversity of the NicholsonGregory catchment. This apparent high diversity has been compared to some catchments such as
those of Cape York Peninsula and the Northern Territory-Kimberley region that are generally
regarded as highly speciose on a national scale.
•
The more seasonal off-channel wetlands of the Nicholson-Gregory catchment (swamps,
waterholes etc) face considerably greater pressures from feral pig and cattle activity than the instream aquatic habitats of perennial systems such as Lawn Hill Creek and the Gregory River.
•
While instream habitat degradation in many of the major systems across the basin has been
minimal, the fish fauna of the Nicholson-Gregory catchment still faces a number of emerging and
potential threats. The effects of recreational fishing on fish stocks (via legal and illegal methods)
are uncertain but could cause localized impacts. The potential effect of introduced fish species is
another issue requiring greater attention and public education.
•
A riparian zone condition assessment; The Tropical Rapid Appraisal of Riparian Condition
method (TRARC) was applied to 15 sites throughout the Gregory River-Lawn Hill Creek
catchment. Based on the TRARC scores, five sites were in the poor category, eight sites were in
the average category and two sites in the good category.
•
There is a need to establish long term monitoring of aquatic/riparian ecosystems across the basin.
The usefulness of any baseline information at sites relies heavily upon subsequent long-term data
collection to reliably account for the natural (and largely climate driven) variability that
characterises the local environment.
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1.0
INTRODUCTION
The Southern Gulf of Carpentaria contains an array of natural environments of value at local, state,
national and international scales, many of which are associated with the riverine and wetland ecosystems
of the region. There remains a long-standing perception or expectation that the isolation of the Southern
Gulf environment has meant that it has remained largely untouched in relation to the maintenance of
natural environmental values. Many impacts have certainly been restricted due to low population levels
and limited accessibility and relative to many other regions of Australia, the Southern Gulf has largely
avoided the worst effects of issues such as land clearing and river regulation. In recent times however,
road infrastructure has improved, there have been concurrent increases in tourism, especially naturebased recreation, as well as rising interest in the feasibility of a variety of developmental projects.
Stakeholder concerns over this increased accessibility, the sustainability of some current practices and
uncertainty over the direction of future development has underlined the need for a more coordinated
approach to resource management.
Much of the social and economic foundation of the southern Gulf is tightly associated with the area’s
water resources. The region contains an associated array of wetland environments, the diversity and
extent of which exceed those of all other Queensland bioregions with perhaps the exception of Cape York
Peninsula (Morgan, 1999b). Despite the undoubted significance of the wetland environments the region
supports, there has been little in the way of systematic documentation of the diversity of aquatic
ecosystems across the region. Apart from some notable exceptions driven largely by issues such as
uranium mining (i.e. East Alligator River, Northern Territory), remoteness, sparse population densities
and seasonal accessibility issues has seen research into the ecology of northern Australian wetland
ecosystems remain limited. Not surprisingly, the lack of adequate biophysical data on the distribution of
native habitats and the processes affecting their condition is a widely stated impediment to integrated,
whole of landscape approaches to land management in the Southern Gulf Region (SGCI, 2000; GRPAC,
2000).
This report has been produced by the Australian Centre for Tropical Freshwater Research (ACTFR) as
part of the Southern Gulf Environmental Information Program (SGEIP). The SGEIP is an initiative of the
Queensland Department of State Development and Information (DSDI) to the support the ecological
sustainability of Gulf communities. It’s intention is to provide reliable, accurate and accessible
information to all stakeholders and communities in the Southern Gulf region (existing ACTFR reports
can be accessed at http://www.actfr.jcu.edu.au/sgeip/). This report focuses upon riverine and wetland
management issues raised by stakeholders. The majority of issues addressed are specific to the Nicholson
River watershed, particularly the identified need for baseline data describing the status and condition of
water resources and wetland environments in the Lawn Hill Creek and Gregory River sub-catchments.
This report has two main goals, the first being to collate what existing information is available from
previous research in the area. The second is to establish an array of indicators to benchmark ecological
condition at a range of sites throughout the catchment.
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2.0
STUDY AREA
The Nicholson-Gregory catchment (area: 52, 234 km²) is situated along the western edge of the Gulf of
Carpentaria. The intermittent Nicholson River is the longest system (ca. 390km) in the watershed with its
major tributaries including the permanently flowing Gregory River and Lawn Hill Creek. The upper
catchments of a number of these systems such as the Gregory and Nicholson Rivers and Lawn Hill Creek
extend well into the Northern Territory (approximately 15, 760km² of total catchment area). In the
northwest of the catchment the Nicholson River drains the steep, erosional ridges and ranges of the
Mount Isa Inlier. In the southwest, the Gregory River and Lawn Hill Creek drain the dissected limestonedolomite slopes, canyons and plateaus of the Barkly Tableland. The lower reaches of these major streams
all flow through the low relief of the broad, depositional Gulf Plains (NRM&E, 2004).
Pastoral activity in the form of cattle grazing is the predominant land use for the catchment. The high
natural and cultural values of the area have seen tourism in the Nicholson basin recently develop as a
major and rapidly growing industry. Popular local attractions include Boodjamulla (Lawn Hill) National
Park and the associated World Heritage Listed Riversleigh Fossil Site as well as the scenic and
recreational amenity provide by the area’s river environments (NRM, 2003). Areas such as Escott and
Burketown in the lower end of the catchment also support thriving ecotourism industries based primarily
around recreational fishing attractions, particularly species such as barramundi. Substantial parts of the
catchment lie within the North West Minerals Province, regarded as one of the most prospective regions
in the world for metals, industrial minerals and gemstones (SGCI, 2000). The Zinifex (formerly Pasminco
Century) deposit, some 65km west of Gregory Downs is currently the main operational mining project in
the area, focusing upon extensive zinc, lead and silver reserves. Numerous Resource Reserves also exist
within the catchment and future exploration could occur depending on trends in commodity markets.
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3.0
WETLAND ENVIRONMENTS OF THE NICHOLSON-GREGORY CATCHMENT
The tropical freshwater ecosystems of northern Australia have received minimal scientific scrutiny
compared to Australia’s temperate freshwater environments. This consequent knowledge gap is
especially pronounced for northern monsoonal wetland systems. A number of areas in the GregoryNicholson catchment have at least received some degree of localized, discrete scientific attention (i.e.
Lawn Hill National Park, Musselbrook Creek, Century Zinc etc.). The overall ecology of the region is
however poorly known and extensions beyond sporadic and localized taxonomic inventories into processoriented studies are rare (a not uncommon situation across much of arid and tropical Australia).
Nevertheless, it is generally regarded the Nicholson-Gregory catchment contains an abundance of natural
assets of high natural/biological value.
The national significance of the region’s wetland resources in highlighted by the inclusion of an extensive
array of local ecosystems on the Register of National Estate and the Directory of Important Wetlands in
Australia (i.e. Blackman et al., 1996; Anon., 2004). Considering the relatively small size of this
catchment, the number and diversity of significant wetlands is exceptional. These sites include a
spectrum of wetland environments spanning spring-fed upland stream systems, the middle reaches of
large perennial rivers, seasonal shrub-scrub wetlands on alluvial black soil floodplains and complex
coastal delta wetlands merging across a freshwater/saltwater gradient. The following information
summarises descriptions of the five wetland complexes listed in the Directory of Important Wetlands in
Australia, as taken from Blackman et al. (1996):
ƒ
ƒ
ƒ
ƒ
ƒ
The Gregory River (26, 639ha): ‘The Gregory river is the largest perennial river in arid and semi
arid Queensland. The area encompasses the internationally significant Riversleigh fossil beds
associated with the Carl Creek Limestone formation. This area has high recreation potential and
the river levees are of considerable aboriginal site significance’.
Thorntonia Aggregation (298, 888ha): includes the ANCA listed Lawn Hill Gorge wetland
(1133ha) and a large part of the Riversleigh fossil field. A good example of a pristine wetland
system with permanent deep water in a semi arid environment. Probably the only perennial
streams in arid Queensland. The area includes a large part of the Carl Creek Limestone formation
containing the internationally significant Riversleigh fossil field. The area is notable for its floral
rainforest influences and contrasts between fringing communities and surrounding semi-arid
country.
Musselbrook Creek Aggregation (45, 157ha): ‘probably the best example of a structurally diverse
suite of wetlands developed on meadow podosolic soils in the Doomadgee plains province. In
particular the wetlands characterized by Acacia stenophylla are particularly significant, such
swamps are localized in occurrence and apparently restricted to the northwest part of the Gulf
plains. The extensive swamps within the aggregation provide extremely rich waterfowl habitat.’
Bluebush Swamp (879ha): ‘a good example of a palustrine scrub-shrub wetland in an alluvial
plain of the Armraynald Plain Province of the Gulf Plains Bioregion. Feeding nesting and
breeding habitat for waterfowl in late wet season, autumn and spring. One of a number of
wetlands dominated by Acacia stenophylla’.
Nicholson Delta Aggregation (63, 640ha): ‘the best example of a deltaic, alluvial system in the
southwest portion of the southern Gulf of Carpentaria. Riverine systems with emergents, aquatic
beds, open water and associated deep water habitat, together with associated seasonally rich
lacustrine and palustrine wetlands with open water, aquatic beds, emergents and forested
wetlands characterise the alluvial systems of the area. The rich array of permanent, semipermanent and seasonal wetlands provides drought refuge for waterbirds as well as breeding,
roosting, feeding and moulting habitat’.
The Register of National Estate is Australia’s national inventory of natural and cultural heritage places
deemed worthy of keeping for the future. The Riversleigh Fossil Site, Lawn Hill Gorge and Boodjamulla
(Lawn Hill) National Park and Adjacent Resource Reserves are current registered sites in the Australian
Register of National Estate. The areal extent of these sites contains all or part of a number of these
significant local wetland complexes (i.e. Lawn Hill Gorge, Gregory River, Thorntonia Aggregation). The
Nicholson Musselbrook and Thorntonia Aggregation wetlands are currently indicative sites on the
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Register of National Estate, meaning these locations are at some stage of the assessment process in
deciding whether these sites merit registration as part of the National Estate.
The wetlands of the Nicholson-Gregory catchment have also been recognised for their significance at
national and regional levels through their operation as important biological refugia in the arid and semiarid regions of Australia. The Gregory and Nicholson River wetlands for example have been rated as
significant refugia due to their importance to waterbirds and migratory waders (Morton et al., 1995). The
permanent water and fringing forest habitats of Lawn Hill Creek and the Gregory River have been rated
as important short-term refugia for water dependent species in a semi-arid environment during times of
drought (Dames & Moore, 1994; Morton et al., 1995; Anon. 2004). Interestingly, Lawn Hill Creek has
also been recognised as a highly significant long-term evolutionary refugia from climatic change (Morton
et al., 1995; Anon., 2004). The riverine and spring-dependent forest communities of Lawn Hill Creek
harbour biota (primarily plant species) exhibiting considerable rainforest affinities. These species are
presumed to be relicts from wetter paleo-climatic periods such as when the Riversleigh fossil suite was
preserved.
3.1
The Conservation Status of Wetland Ecosystems in the Nicholson-Gregory Catchment
Sattler & Williams (1999) review of the conservation status of Queensland’s regional ecosystems
identified a number of ecosystems in the Nicholson-Gregory catchment that were either of concern or
endangered. Endangered status refers to an ecosystem where less than 10% of pre-European extent
remains in an intact condition across the bioregion, or its distribution has contracted to less than 10% of
its former range. Additional to basic proportional current extent, the total extent of ecosystems can have
considerable bearing on conservation status. Rare ecosystems (original extent <1000ha or patch sizes
generally <100ha) subject to a threatening process are regarded as endangered. Similarly naturally
restricted ecosystems (original extent < 10,000ha) reduced to between 10 and 30% of original extent are
considered endangered. An of concern ecosystem is one of which 10-30% of pre-European extent
remains in an intact condition. Similar to the endangered classification system, a rare regional ecosystem
not subject to a threatening process is regarded as of concern, while a naturally restricted ecosystem
subject to a threatening process is also considered to be of concern.
The vast majority of these threatened environments are associated with the floodplains or riparian
fringing communities of larger watercourses and springs (i.e. Lawn Hill Creek, Widdallion Creek,
Gregory River). The endangered ecosystems of most relevance to the Nicholson-Gregory area include
the River Red Gum (Eucalyptus camuldensis), Melaleuca spp. and Swamp Box (Lophestomenon
grandiflorus) fringing wetlands (RE1.3.7, R.E.1.3.8, R.E.2.3.26) associated with the larger watercourses
of the region (i.e. Gregory River and Lawn Hill Creek). The Swamp Bloodwood (Corymbia phytocarpa)
open forest ecosystems associated with sandstone springs (RE1.10.6) are another notable endangered
ecosystem in the area.
A number of other notable wetland ecosystems in the Gregory-Nicholson area are considered to be of
concern (Morgan 1999a, 1999b). For example, the localized and patchily distributed Myall (Acacia
stenophylla) swamp forests (RE 2.3.13) are a significant wetland association apparently restricted to the
north-west part of the Gulf Plains (Blackman et al., 1996). These regionally significant waterbird habitats
are currently subject to significant grazing pressure as well as disturbance by pigs (Morgan, 1999b). This
ecosystem type is quite poorly known and requires survey to confirm condition.
Many of these communities are typically naturally restricted in distribution and as would be expected in a
dry area, grazing pressure is often focused upon these environments with associated threatening processes
such as a variety of feral weed invasions (Morgan, 1999a). Feral pigs, fishing and unregulated tourism all
represent additional pressures disturbing these ecosystems (Morgan, 1999b). The fact that many of these
threatened ecosystems additionally have minimal or non-existent coverage in protected areas underlines
the need for integrated landscape scale approaches to management.
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3.2
Species of Conservation Concern
A considerable number of species with some level of formal conservation concern occur throughout the
Nicholson-Gregory catchment (for a detailed list see Morgan 1999a & 1999b). Rather than
comprehensively discussing all threatened species possibly occurring in the catchment that may utilise
wetland environments to some extent, of particular interest are those obligate riparian/wetland species
which depend almost solely upon these particular habitats for their continued survival.
The riparian zones of major watercourses for example provide specialist habitat that supports populations
of a number of bird species with restricted ranges or of conservation concern such as the Crimson Finch
(Neochmia phaeton) listed as Vulnerable under the Queensland Nature Conservation Act 1992. This
species is closely associated with water, particularly riparian grasses and Pandanus habitats (Todd et al.,
2003). This species is divided into two geographically distinct sub-species. N. p. evangelinae is restricted
to the east and west coast of Cape York Peninsula, while the other sub-species N.p. phaeton is relatively
widespread and abundant within savannah woodlands from western Australia across to north-west
Queensland. While the species as a whole is listed as vulnerable at state level, it is the Cape York subpopulation N. p. evangelinae that is viewed as ‘most threatened’ due to range contractions and threats to
remaining habitat from cattle grazing and altered fire regimes (Todd et al., 2003). This Cape York subspecies is also listed as Vulnerable under the Commonwealth Environment Protection and Biodiversity
Conservation Act (EPBC) 1999.
The riparian zones of the Gregory and O’Shannassy Rivers and Lawn Hill Creek are also notable in
providing a habitat stronghold for the Carpentarian population of the Purple Crowned Fairy Wren
Malurus coronatus (Russell, 1993), a species listed as Vulnerable under the Qld. Nature Conservation
Act 1992. The western sub-species of the Purple Crowned Fairy Wren, Malurus coronatus coronatus,
found in the Kimberly region has suffered a severe distribution reduction due largely to severe long-term
pastoral degradation of riparian habitats in the area. This sub-species also listed as Vulnerable under the
recent EPBC Act 1999. Despite over a century of pastoral activity in the Nicholson-Gregory catchment,
the riverside vegetation is still in a condition capable of maintaining healthy populations of the eastern
sub-species of the Purple Crowned fairy Wren, Malurus coronatus macgillivrayi (Rowley, 1993). The
specialised habitat requirements, limited dispersal capabilities and isolated populations of this species still
render it quite vulnerable to localised extinctions in the event of any habitat degradation (Rowley &
Russell, 1993). Rowley (1993) suggested the presence or absence of this species could be regarded as a
useful indicator of the well-being of riparian river frontages.
A number of reptile species exist throughout the catchment which also warrant conservation concern.
Due in large part to substantial widespread population declines associated with commercial hunting
(which ceased in 1974), the estuarine crocodile Crocodylus porosus is listed as Vulnerable under the Qld.
Nature Conservation Act. This species occurs primarily in the lower reaches of a many of the region’s
watercourses. Of particular interest is the Gulf Snapping Turtle (Elseya lavarackorum), another resident
wetland species of considerable conservation concern. This species is listed as nationally Endangered
under the EPBC Act 1999. Belonging to the taxonomically problematic Northern Snapping Turtle
(Elseya dentata) species complex, it is one of the continent’s largest freshwater turtle species. This
species was recently identified as a relictual extant population of a formerly widespread pleistocene taxon
and represents Australia’s first ‘living fossil’ freshwater turtle (Thomson et al., 1997). To date, the known
distribution of this species remains confined to the Nicholson and Gregory Rivers including Lawn Hill
Creek and Louie Creek, although future survey may well reveal a wider distribution than currently stated
(White, 1999).
A number of fish species including the freshwater sawfish (Pristis microdon) and various shark species
such as the northern river shark (Glyphis sp. C) and speartooth shark (Glyphis sp. A) with varying levels
of threatened species status also possibly occur in the Nicholson-Gregory catchment, particularly in the
lower reaches of rivers. These species will be discussed in more detail in a later section of the report.
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3.3
Cultural Values
The people living in the Nicholson-Gregory catchment are particularly reliant on the maintenance of
wetlands and watercourses to provide a range of social, economic and natural functions. The availability
of surface waters in what is predominantly a semi-arid landscape has obvious significant utility to local
pastoralists. Domestic water supplies for most pastoral holdings and small urban communities are also
commonly drawn directly from watercourses without the use of water treatment facilities. The local
waterways and associated riparian areas also provide a facility for recreation and most landholders fish
the various local wetlands on a regular basis. Local residents across the region often have a long-standing
association with the land, sometimes spanning several generations, so sentimental attachments to natural
resources can be high.
Aboriginal people also ascribe a variety of additional significant cultural/natural values to many
components of the natural landscape. At present, there is little in the way of systematic mapping and
documentation of indigenous cultural heritage at a regional level in the Southern Gulf. Boodjamulla
(Lawn Hill) National Park is one prominent locality known for its significant indigenous cultural values.
Predictive modeling suggests the main areas for indigenous cultural heritage will likely be in riverine
corridors (0.5 km either side) or around more permanent waterholes (WWF, 1999).
Many of the indigenous residents in northern Australia, including the Southern Gulf catchments live in
traditional areas and still depend on traditional wildfood sources to a large extent for nutrition and income
substitution (Vardon et al., 1997, SGCI, 2000, WWF, 1999). While much indigenous traditional
hunting/gathering in the southern Gulf tends to concentrate on coastal-marine fisheries (SGCI, 2000),
utilisation of freshwater natural resources is also prevalent. In the Cape York Peninsula for example,
Herbert et al., (1995) noted significant indigenous utilization of freshwater resources including fish
(barramundi, black bream, saratoga, eel-tailed catfish, fork-tailed catfish, sleepy cod etc.), redclaw
crayfish, giant freshwater prawn (cherabin), freshwater turtles and freshwater mussels. A similar situation
exists in the Gregory-Nicholson catchment where indigenous collection of traditional resources from
local wetlands is common. Traditional hunting/gathering practices also fulfil a profound role in
transmission of cultural institutions that underpin indigenous culture such as reinforcement of kinship
bonds through resource sharing, passing on traditional practices, fulfilling customary custodial
responsibilities, or asserting native title rights. Therefore many wetlands throughout the catchment will
be inextricably bound into the culture and lifestyle of local indigenous peoples.
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4.0
WETLAND MANAGEMENT ISSUES
A number of resource management issues have considerable relevance to the condition and integrity of
wetland environments in the Nicholson-Gregory catchment. Most of these issues apply not only to the
Nicholson-Gregory catchment, but across the entire Southern Gulf of Carpentaria and much of northern
Australia as a whole (see Finlayson, 1995; SGCI, 2000; GRPAC, 2001).
4.1
Grazing
Over-grazing in wetlands and adjacent to watercourses is one of the primary resource management issues
across the Southern Gulf of Carpentaria (WWF, 1999; SGCI, 2000; GRPAC, 2000). This is generally a
seasonal issue with grazing impacts often concentrated in vulnerable areas such as riparian zones and
river frontages when cattle seek out remaining feed as the dry season progresses (GDRP, 2000). Such
areas typically have high erosion potential and face additional grazing associated impacts such as
trampling and weed infestation. Unrestricted stock use of waterholes as they dry can also result in
deteriorating water quality via increased siltation and turbidity, elevated nutrient and faecal input and
grazing of aquatic macrophytes (Leggett & Byron, 1998; SGCI, 2000). All of these processes can have
deleterious effects on water quality and instream habitat values.
4.2
Introduced Weeds
Significant stakeholder concern exists regarding the threat posed by introduced weeds to pastoral
production and the integrity of native ecosystems (SGCI, 2000). Weed invasion is another of the primary
land degradation problems facing the Southern Gulf region. The distribution and abundance of weed
species across the Gulf is generally poorly known (GRPAC, 2000). The low population levels, vast tracts
of land and limited resources devoted to the issue pose a continual dilemma for weed management. The
large majority of the prominent environmental weeds in Australia have a particular propensity for
invading wetland environments (Storrs & Finlayson, 1997). It is therefore not surprising that most of the
troublesome weeds in the Southern Gulf region (rubbervine, calotrope, mesquite, parkinsonia etc.) have a
particular affinity for severe infestation of river frontages, riparian wetlands and waterways (GRPAC,
2000).
Perhaps the weed of greatest current environmental concern is rubber vine (Cryptostegia grandiflora), a
species which has invaded many northern Australian river systems. This aggressive species dominates
tree canopies and eventually kills host trees. Prickly acacia (Acacia nilotica), noogoora burr (Canthium
pungens), calotrope (Calotropis procera) and parkinsonia (Parkinsonia aculeate) are also often locally
significant (Morgan, 1999a, 1999b). Calotrope is probably a pest species that merits further management
attention. A declared noxious weed in Western Australia and the Northern Territory, this species is
currently widespread in the NT, particularly in the Daly, Katherine, Roper and Victoria River areas where
populations are expanding (Smith, 2002). A native of Asia and Africa, this species thrives on poor soils,
especially where overgrazing has reduced competition, and forms dense thickets which degrade pastoral
lands, hinders mustering and is reportedly toxic to stock (Smith, 2002). This species is rapidly becoming
a prevalent river frontage weed across many parts of the southern Gulf. The recent proliferation of this
species along creeks and drainage lines in the adjacent Leichhardt catchment is readily observable on any
drive between Burketown and Normanton along the ‘Great Top Road’.
4.2.1
Aquatic Weeds
A number of prominent aquatic weed species already pose significant problems for wetlands and
waterways in some Gulf of Carpentaria catchments. Salvinia (Salvinia molesta), water hyacinth
(Eichhornia crassipes) and water lettuce (Pistia stratiotes) have infested some Northern Gulf streams
such as the Mitchell River catchment (Burrows, 2004). Similarly salvinia and water hyancinth have
already been documented in catchments adjacent to the Nicholson-Gregory watershed. These infestations
are usually associated with storage impoundments in the upper reaches of the Leichhardt catchment such
as the Lake Julius reservoir near Mount Isa (Blackman et al., 1996; Smith, 2002).
Australian Centre for Tropical Freshwater Research
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There are also significant and well-founded concerns regarding the emerging threat to Southern Gulf
wetlands via spread of aquatic weed species such as hymenachne (Hymenachne amplexicaulus) and
mimosa Mimosa pigra (Environment North, 1998; Morgan, 1999b; GRPAC, 2000). Mimosa, sometimes
referred to as giant sensitive tree, is a well-established menace to floodplain environments in the Northern
Territory, necessitating the implementation of extensive and expensive eradication programs (Storrs &
Finlayson, 1997). A prolific seed producer, mimosa is readily dispersed by water and animal vectors with
strong evidence also linking outbreaks to vehicle movements (Finlayson et al., 1997). Considering the
steady growth of tourism across northern Australia, this is a particular concern. The dispersive
capabilities of this weed were underlined with the recent discovery of a Mimosa pigra outbreak in Peter
Faust Dam near Proserpine (North Queensland), the first record of this species outside the Northern
Territory. This weed has the potential to become one of the most troublesome weeds for the wetland
environments in the Gulf of Carpentaria.
4.3
Feral Pigs
Some of the highest feral pig (Sus scrofa) population densities in Australia possibly occur in the northern
and southern Gulf regions of Queensland (Jim Mitchell, pers. comm.). This species is generally
considered to be the most damaging vertebrate pest animal across the Southern Gulf region (SGCI, 2000).
Little is known of their specific ecological effects, particularly in savannah environments but significant
impacts (both direct and indirect) may include habitat degradation, predation, weed and disease
transmission, erosion, negative influences on ecological processes (succession and species composition)
and competition with native animals (Mitchell, 2003). Pigs have been consistently noted as causing
severe damage to riverine vegetation as well as contributing to bank erosion, increased water
sedimentation and poor water quality at a range of ecosystems within the Nicholson-Gregory catchment
(Dames & Moore, 1994; Morgan 1999a, 1999b).
The distribution and population dynamics of feral pigs are apparently seasonally driven in Australia’s
wet-dry tropics (Ridpath, 1991; Mitchell, 2003). During the wet season pigs disperse throughout most
habitats in a region, but contract to areas with available water during the dry, often reaching very high
localized densities (Mitchell, 2003). The effects of pig activity tend not be great at a whole of landscape
scale, but may have a concentrated and severe ecological impact within restricted microhabitats such as
swamps, rivers and creek lines where soil moisture persists during the dry season (Mitchell et al., 2004).
As noted by Mitchell et al. (2004) the preference of pigs to dig in swamps and creeks may have
especially significant ramifications if these habitats are threatened ecosystems or represent refuges for
rare or endangered biota. Such a situation certainly exists for a number of the notable wetland
environments in the Nicholson-Gregory catchment. High levels of pig disturbance have been noted in a
number of endangered or bioregionally significant wetlands such as the fringing riparian forests of the
Gregory River and Lawn Hill Creek and the Acacia stenophylla shrub-scrub swamps of the Gulf Plains
(Blackman et al., 1996; Morgan, 1999a&b). While aerial baiting and aerial shooting have been identified
as reasonably effective control techniques, total eradication of pigs in most areas is virtually impossible
(Mitchell, 2003). Cryptic habits and a high reproductive potential make feral pigs inherently difficult to
manage.
4.4
Potable Water Quality, Pollution and Contaminants
Various land uses such as mining, urbanization, agriculture and tourism all have an associated potential
for water pollution. In a catchment where stakeholders are heavily reliant on surface waters, the
suitability and availability of freshwater resources is of critical importance. Two issues of concern to
local stakeholders regarding potable (drinking) water supplies in the catchment are 1) the downstream
effects of unregulated tourist activities near watercourses, and 2) urban waste disposal activities adjacent
to town water supplies in the Doomadgee community.
Given that domestic water supplies are usually extracted directly from watercourses and treated water
only offered in some town areas, a growing public health issue is the pollution of watercourses due to
uncontrolled tourist visitation to streams and rivers (SGCI, 2000; GRPAC, 2000). This has become an
issue particularly in the vicinity of the Gregory River near the Gregory Downs township where camper
numbers at the water’s edge in peak tourist times can be significant, and improvements in transport
Australian Centre for Tropical Freshwater Research
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infrastructure will possibly exacerbate the issue in the future. Public toilets are often not available or not
well patronised, so people often use creek beds and banks. Locals also report incidents of people
discharging contents of portable caravan and campervan toilets in the vicinity of waterways or driving
their vehicles into the river for cleaning purposes. Such reports obviously raise concerns among local
residents regarding the suitability of local water supplies for human consumptive purposes.
The situation at the Doomadgee township is similar, with concerns raised regarding possible leaching
effects from historic (and recent) waste disposal activities adjacent to town water supplies. The ‘old town
dump’ in this case, while downstream (ca. 1km.) of where town water supplies are pumped from the
Nicholson River, still drains into the Doomadgee Weir impoundment from which the community
drinking water is drawn. Potential pollutant ingress from the old town dump site as well as recent local
council disposal of waste (primarily old construction material) at the site has elicited concerns from
residents. The results of two ACTFR potable water quality surveys in relation to both of these issues is
provided in Appendix 1.0.
5.0
CATCHMENT CONDITION ASSESSMENT
Subsequent reporting in this document will aim to provide a comprehensive overview of the nature and
status of various aspects of the wetland environments and water resources in the Nicholson-Gregory
catchment. The aim of a number of the specific condition assessments (i.e. fish, riparian vegetation and
macroinvertebrates) will be the development of quantitative, broad scale, repeatable surveys of riverine
and wetland condition that can be used for future reference purposes.
5.1
Hydrology of the Nicholson-Gregory Catchment
5.1.1
Surface Waters
Due to its almost universal role across most physical, chemical and ecological processes, stream-flow
hydrology is generally regarded as the key driver of riverine and wetland ecosystem function (Bunn &
Arthington, 2002). The Gulf of Carpentaria and Timor Sea drainage divisions extending from
Queensland’s Cape York Peninsula to Western Australia’s Kimberley region encompass Australia’s true
wet-dry monsoonal tropics, a region contributing almost 40% of the total discharge of all Australian
rivers (Bishop & Forbes, 1991). The Gulf of Carpentaria region itself has a tropical monsoonal climate
with marked seasonality in rainfall the most distinguishing feature of the regional climate (Dames &
Moore, 1994). Weather is driven by north-west monsoons with around 80% of annual rainfall occurring
from December to March. Prior to the onset of the more established rain systems of the monsoonal trough
there is a pre-wet transitional period (October to November) denoted by a gradual build-up in humidity
and the irregular occurrence of thunderstorms (McDonald & Alpine, 1991; Dames & Moore, 1994). The
monsoon onset usually corresponds to a sudden transition from these scattered random convections to a
large-scale organized convection (Cook & Heerdegen, 2001).
The amount and duration of wet season rain in northern Australia typically decreases with increasing
distance from the coast (Cook & Heerdegen, 2001). The rainfall gradient existing in the southern Gulf
ranges from 900mm on the southern and western coastlines of the Gulf to ca. 400mm at Cloncurry
(SGCI, 2000). While inland areas are effected by monsoonal rains, the monsoon influence is not as
pronounced as for regions in closer proximity to the coast. Because of this decreasing rainfall gradient,
the more inland regions of the Gregory-Nicholson catchment (Lawn Hill, Gregory Downs) could be more
precisely described as semi-arid with monsoonal influences (Dames & Moore, 1994). The El Nino –
Southern Oscillation phenomenon exerts significant influence on inter-annual weather variability across
the region, producing marked fluctuations in the amount, timing and distribution of rainfall. Accordingly,
there is considerable year-to-year climatic variation ranging from ‘failed’ wet seasons, to ‘normal’
conditions to above average rainfall and tropical cyclone activity. As noted by Dames & Moore (1994),
the variability associated with resultant quasi-cycling of aridity and flood condition calls into question the
relevance of hydrologic and meteorological descriptions such as ‘average conditions’.
Australian Centre for Tropical Freshwater Research
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The northern river systems covering Australia’s true wet-dry monsoonal tropics share a similar but
distinguishing suite of climatic conditions and drainage characteristics that have seen them termed the
‘northern flood-drought’ rivers (Bishop & Forbes, 1991). Stream flows are highly variable and seasonal,
with typical summer flooding and relative low flows for the remainder of the year. Due to these marked
seasonal changes in discharge displayed by a typical northern Australian ‘flood-drought’ system, many of
even the largest rivers virtually cease to flow during the dry season, often persisting as a series of remnant
pools until the return of the wet season (Bishop & Forbes, 1991). While a number of the creeks and rivers
of the Nicholson-Gregory catchment share many of these characteristic monsoonal features such as
marked seasonality in peak flows and high inter-annual variability, another additional and quite
distinctive catchment characteristic is the perennial streamflow of the Gregory River and some of its
component tributaries such as the O’Shannassy River, Lawn Hill Creek and Louie Creek (Drysdale et al.,
2002). These systems constitute some of the largest permanently flowing streams in arid/semi-arid
Australia (Blackman et al., 1996; NRM, 2003).
The information afforded by long-term streamflow records are increasingly being recognised as
providing immense value to decision-makers and researchers alike. The Queensland Department of
Natural Resources and Mines (NRM) is the lead government agency responsible for monitoring the status
of surface-water and groundwater resources. Following an expansion of the state gauging station network
in the late 1960’s – early 1970’s, a substantial number of gauging stations were operational on most of
the major river and creek systems in the Nicholson-Gregory catchment, both intermittent and perennial.
However in the late 1980’s following a statewide rationalisation of gauging station operation, the vast
majority of sites within the catchment were closed. Table 1 provides an overview of most of the
Nicholson-Gregory catchment gauging stations that have substantial data records available along with a
small subset of relevant hydrological statistics. It is unfortunate that these broad scale closures occurred
in the late 1980’s considering many of these stations would probably just now be yielding data records
approaching a sufficient magnitude for meaningful use in resource management decisions. Extended time
scales/data records are obviously needed to meaningfully monitor variable river systems and reliably
quantify normal conditions.
Australian Centre for Tropical Freshwater Research
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Table 1
Nicholson-Gregory catchment gauging station details
Gauging Station
Lat./Long.
(deg:min)
Period of
Record
Catchment
Area (km²)
Mean Annual
Flow (MAF):
Megalitres
Coefficient
of Variation
(MAF)
Max. & min. annual
flows: Megalitres.*
Average Number of
cease to flow days/year
912101a: Gregory River
at Gregory Downsª
18:38/139:15
01/10/196901/10/2002
12690
693917
1.10
3,701,682 (1973/74)
123,140 (1984/85)
0
912103a: Lawn Hill
Creek at Lawn Hill No. 2
18:35/138:34
01/10/192501/10/1988
3905
104267
1.15
504,061 (1973/74)
4,122 (1979/80)
7.4
912104a: Widdallion
Creek at Lawn Hill
18:36/138:30
01/10/196801/10/1988
28
170170
1.30
820,611 (1973/74)
807 (1968/69)
101.9
912105a: Gregory River
at Riversleigh ª
18:58/138:48
01/10/196801/10/2002
11489
760792
1.01
3,675,596 (1973/74)
140,753 (1968/69)
0
912106a: Musselbrook
Creek at Stockyard Ck.
18:28/138:15
01/10/196801/10/1988
1682
361533
1.15
1,320,932 (1973/74)
24,632 (1984/85)
201.8
912107a: Nicholson
River at Connelly’s Hole
17:52/138:15
01/10/196801/10/1988
13887
1085031
1.22
4,373,318 (1973/74)
8,307 (1979/80)
203.9
912108a: O’Shannassy
River at 17.7km
19:06/138:45
01/10/196801/10/1988
5836
309230
1.3
1,744,995 (1973/74)
26,159 (1984/85)
1.2
912110a: Thornton River
at Rosehill Bore
19:21/138:17
01/10/197001/10/1988
1785
71677
1.58
459,634 (1973/74)
1,911 (1979/80)
201.5
912111a: Goonooma
Creek at Norfolk
19:14/138:17
25/07/197001/10/1988
1107
25354
1.50
124,305 (1973/74)
0 (1984/85)
325.7
912112a: Seymour River
at Main Road
19:20/139:00
01/10/197001/10/1988
289
23696
1.57
157,256 (1973/74)
108 (1977/78)
292.5
912113a: Elizabeth
Creek at Mining Camp
18:13/138:21
01/10/197401/10/1988
670
141688
1.11
434,383 (1975/76)
10,267 (1977/78)
256.5
912115a: O’Shannassy
River at Morestone
19:36/138:22
01/10/197001/10/1988
425
54984
1.70
404,958 (1973/74)
1,632 (1979/80)
312.8
* Minimum values are the lowest recorded annual discharges at sites in years with minimal missing record.
ª Currently active gauging stations.
Australian Centre for Tropical Freshwater Research
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One of the more notable flow statistics is that of average number of ‘cease to flow days’ per year
recorded at each station (i.e. when instantaneous stream discharge falls below 0.001m³/s). A number of
stream systems such as the Thornton, Seymour and upper O’Shannassy Rivers typically flow for only a
short period. In contrast, the perennial flow of the Gregory River is obvious as evidenced by the absence
of cease to flow conditions at the two Gregory River gauging stations.
The 7.4 days per year of no flow conditions at the Lawn Hill Creek site suggests a degree of
intermittency but is in fact an artefact of gauging station location. The Lawn Hill Creek system as a
whole has not ceased to flow during the period of gauging station record. A complex of bifurcations and
junctions occur both upstream and downstream of the Lawn Hill Creek gauging station site such that
Widdallion Creek, an adjacent system to the north has periodically captured flow from Lawn Hill Creek
for some distance (skirting the gauging station) before it rejoined the Lawn Hill Creek channel
downstream. These flow patterns between Lawn Hill and Widdallion Creek have been extensively
modified through time by both local pastoralists (in the form of small weirs) and periodic flood events.
The subsequent results of these flow alterations constitute one of the few ‘environmental flow’ issues
now existing in the catchment. The combined effects of a weir dividing Lawn Hill and Widallion Creeks
and the geomorphic changes wrought by recent flood events has now seen flow into Widdallion Creek
virtually cease for some time to the detriment of the system’s environmental values. There are some
concerns regarding this process from local residents who desire a resumption of perennial flow down
Widdallion Creek as per the historic situation (for a detailed overview see Earthworks, 2004).
The 1.2 days of cease to flow record per year at the O’Shannessy River at 17.7 km site (Station 912108a)
is also interesting. This system is usually regarded as perennial due to spring outputs, at least in the lower
reaches. In the twenty years of data available at this site, the only ‘no flow’ days recorded occurred in the
last twenty-five days of record leading up to gauging station closure in 1988. The possible influence, if
any, of spring outputs further downstream of the gauging station on flow rates in lower stream reaches
cannot be gleaned from available data.
5.1.2
Groundwaters
Catchment geomorphology is the fundamental process underpinning much of the distinctive hydrology
characterizing the Gregory-Lawn Hill catchment. The perennial stream systems that traverse the Gulf
Plains and drain northwards into the Gulf of Carpentaria all issue from the northeast portion of the
Barkley Tableland, an extensive plateau forming part of the Georgina Basin. Catchment geohydrology of
the upper reaches is dominated by the extensive middle Cambrian Thorntonia Limestones and
Camooweal Dolomite formations, and to a lesser extent the elevated Proterozoic sandstones of the
adjacent Constance Sandstone formation (Blackman et al., 1996). One of Australia’s most extensive
exposed carbonate terrains, the Barkly Karst has developed on the northeastern portion of this tableland,
covering approximately 13,000 km² and extending well into the Northern Territory (Drysdale et al.,
1998; Drysdale et al., 2002; Anon., 2004). Karst terrain is an environment where the dominant landscape
forming process is solution weathering of rocks and minerals through the chemical action of natural
waters (Drysdale et al., 1998; Humphreys, 2000). Due to their solubility, karst landscapes tend to be most
fully developed on carbonate and evaporate rocks such as limestone, dolomite and gypsum.
Well-developed groundwater systems are commonly associated features of karst landscapes, and
perennial spring seepage from the north-eastern portion of the Barkly Karst is responsible for the
permanent flow found in many local stream systems. The discharging springs that feed the various
perennial streams exhibit relative chemical homogeneity, indicative that spring-waters are essentially
derived from a common regional groundwater aquifer (Drysdale et al., 2002). Many of the characteristic
properties of karst wetlands make them quite vulnerable to degradation and can present considerable
management challenges (Humphreys, 2000). Diffuse and often spatially extensive recharge or drainage
characteristics means management may have to extend well beyond wetlands or karst features
themselves. Many conventional hydrological monitoring and modeling techniques are also often
inappropriate for karst systems which can require specialized investigative and monitoring approaches.
It is worth noting that the distinctive geomorphology and associated hydrology of karst systems
(fractured carbonate rocks, extensive interconnected networks of cavities and conduits etc.) make these
Australian Centre for Tropical Freshwater Research
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environments particularly susceptible to pollutant ingress (Kacaroglu, 1999). Once contaminants are
introduced, groundwater velocity is usually much higher in karst aquifers as opposed to non-karstic
(granular or fractured) aquifers (e.g. karst groundwater velocities can be hundreds of time faster than that
of alluvial aquifers). Sources of contamination can be detected considerable distances from points of
origin within very short periods of time. The relatively high water velocities typical of karst aquifers also
limits the time available for groundwater self purification where pollutants can be retarded or attenuated
by various physical, biological and chemical processes such as acid-base reactions, adsorption, ion
exchange, precipitation or volatilization. While contaminant dispersivity can be high, degradation
processes and residence times for pollutants can be long, with containment and remediation difficult once
pollutants enter the aquifer. The primary human activities posing highest risks for karst groundwater tend
to be associated with urbanization, industry, agriculture and forestry (Kacaroglu, 1999). While most of
these issues may not be immediately relevant to the Gregory-Lawn Hill catchment, they may bear
consideration for any future developments in the region. Solid and liquid (i.e. municipal wastewater)
wastes related to infrastructure developments (settlement, urbanization and tourism) can easily pollute
karst groundwaters. Solid wastes dumped into sinkholes or similar karstic depressions are subject to
leaching by percolating water with subsequent leachate possibly containing high concentrations of
organic and inorganic compounds, heavy metals, total dissolved solids or microbiological contaminants
(Kacaroglu, 1999). Sinkpoints in karst areas have traditionally been popular dumping points for various
waste products (Kacaroglu, 1999), a past practice which can be seen in some localised points of the
nearby Cammooweal Caves area. Pastoral activities (cattle grazing) have also been implicated in the nonpoint source pollution of groundwaters through elevated nitrate and fecal bacteria levels in karst regions
of the U.S.A. (Boyer & Pasquarell, 1995; Howell et al., 1995). The effect of catchment activities in the
vicinity of the Gregory-Lawn Hill karst aquifers on subsequent groundwater quality remains virtually
unknown, but this knowledge gap does suggest some need for a more proactive approach to aquifer
investigation and preservation.
In addition to the mineral dissolution processes defining karst landscapes, constructional karst features
formed by carbonate deposition are another unique karst characteristic (Humphreys, 2000). The
travertine deposition processes associated with water movement through the surfacewater-groundwater
interface of a limestone karst landscape is one of the more notable (and well studied features) of the
Barkly Karst (see Drysdale et al., 1998; Drysdale et al., 2002 for detailed overviews). Absorption of
biogenic carbon dioxide by rainwater percolating through soils creates carbonic acid which aggressively
dissolves the minerals (calcite and dolomite) constituting the limestone bedrocks. With the passage of
these percolating waters through the karst and its groundwater table, dissolved ions (calcium, magnesium,
bicarbonate) are taken into solution. Emerging karst springwaters are rich in dissolved carbon dioxide and
calcium carbonate. With dissolved carbon dioxide levels hundreds of times higher than that of the
ambient atmospheric conditions, the resurgent springwaters equilibriate with the atmosphere via carbon
dioxide outgassing. This surfacewater soon becomes supersaturated with calcium carbonate and once
various kinetic thresholds are reached, minerals in solution are precipitated out as travertine.
The hydrochemical evolution of emergent karst waters is controlled by a variety of physical, chemical
and biogenic factors which can result in travertine accretion occurring for many kilometres downstream.
This chemical sedimentary deposition is responsible for forming an array of structures such as terraces,
barrages, cascades and ‘tuffa’ deposits such as the spectacular ‘Indarri Falls’ travertine dam in Lawn Hill
National Park, one of the largest and spectacular karst phenomena in Australia (Drysdale & Gale, 1997).
Such structures can significantly alter local hydrology and geomorphology by transforming riverine
reaches into essentially lacustrine (lake) environments (Drysdale & Gale, 1997).
The behaviour and long-term prognosis for the Gregory-Lawn Hill catchment’s spring fed streams has
been a subject of considerable conjecture and surmise since the earliest resource surveys (see
Whitehouse, 1940). Even today, some people voice concern that streamflow levels in systems such as the
Gregory River are declining or ‘the lowest they’ve seen’. Despite being one of Australia’s largest karst
environments, the Gregory region’s isolation and remoteness has resulted in little being known regarding
the system’s general hydrological characteristics, such as rates of aquifer discharge and recharge, extent
of recharge zones and relationships with other aquifers (Drysdale et al., 1998).
Australian Centre for Tropical Freshwater Research
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Whitehouse (1940) noted anecdotal reports of substantial declines in spring activity throughout the
Gregory River-Lawn Hill Creek area in the relatively short time interval since white settlement (even in
larger systems). A number of older homesteads in the upper reaches of the Gregory catchment, for
example, had been established beside ‘good springs that have since failed completely’ (Whitehouse,
1940). Whitehouse also noted the upstream limits of permanent water in some large systems such as the
O’Shannassy River had receded substantially over time periods of only around two decades. Many of
these upper reaches which previously held permanent water were always now dry and fringed with
‘masses of dead Pandanus and Melaleuca’, purportedly due to water stress. The paleo-climatic insights
offered by generations of abandoned fossil travertine formations in upstream reaches many of the
perennial streams also suggest substantial declines in spring discharges over much longer time frames,
although this interpretation of travertine deposition is ongoing and yet to be fully investigated (Drysdale,
2001; Drysdale et al., 2002).
5.1.3
Groundwater Discharge and Recharge Relationships
The Gregory-Lawn Hill karst aquifer is fed almost entirely by diffuse autogenic recharge (Drysdale,
2001; Drysdale et al., 2002). An autogenic karst aquifer system is one which derives its water only from
rainfall precipitation (Ford & Williams, 1989). Variations that occur in base-flow discharges are probably
broadly related to significant fluctuations in the volume of wet season rainfall recharge. This relationship
between spring base-flow volumes and magnitude of the preceding wet-season’s rainfall has at least been
noted for some of the smaller spring-fed systems in the catchment (Drysdale, 2001; Drysdale et al.,
2002). Karst hydrology is a complex study area and it is therefore difficult to investigate the relationships
between spring output responses and antecedent rainfall recharge in great detail given the limited data
available. A multitude of compounding effects such as variable flow paths and residence times, hydraulic
conductivity, karstic porosity as well as other issues associated with throughput control and storage of
water in a karst aquifer all need to be addressed (see Ford & Williams, 1989).
Gauging Station 912101A (Gregory River at Gregory Downs) provides the most comprehensive and
longest duration streamflow record available in the Gregory-Lawn Hill catchment. Figure 2 displays the
minimum monthly discharge occurring each calendar year for the period of record available at this site
(ca. 33 years). The particular month yielding minimum flows can obviously vary each year, but almost
invariably occurred in either October or November of most years (i.e. at the end of a typical dry season
just preceding the onset of the wet season).
Australian Centre for Tropical Freshwater Research
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Yearly minimum monthly discharge (Megalitres) for the period 1970-2002 at Gauging
Station 912101a (Gregory River at Gregory Downs)
35000
30000
25000
20000
15000
10000
5000
0
19
70
19
74
19
78
19
82
19
86
19
90
19
94
19
98
20
02
Minimum Monthly Flow (ML)
Figure 2
Year
While this graph represents only a coarse overview of dry-season base-flow behaviour and permits only
generalized conclusions, it does demonstrate base-flow volumes (even in larger systems such as the
Gregory River-O’Shannassy River complex) can vary significantly through time. The relatively high
baseflow volumes of the mid to late 1970’s are notable, coinciding with what are generally regarded as
exceptionally wet years by Australian rainfall standards (see Suppiah, 2004). The graphical
representation of Figure 2 suggests even large systems may be quite responsive to recent rainfall. The
cumulative effects of these high rainfall years through the early 1970’s may have substantially recharged
local aquifers for a time, followed by a gradual baseflow recession in drier subsequent years. Just how
strong an association exists between antecedent rainfall and consequent dry-season baseflow is difficult
to conclusively comment upon considering the limited nature and relatively short extent of available data.
The duration and intensity of wet season rainfall rather than simple magnitude is an additional
complicating factor. Prolonged, low intensity ‘soaking’ rainfall spread over a substantial time interval
may provide much for more effective aquifer recharge than high intensity rainfall events where
substantial surface runoff may occur (Drysdale et al., 1997). There is little doubt water issuing from
springs may vary greatly in ‘age’ in many cases with some water having spent considerable time in the
aquifer.
Substantial variations in dry-season base-flow volumes through time were noted in some of the earliest
resource surveys carried out in the catchment. Whitehouse (1940) noted with interest the marked
differences in dry season base-flow volumes that can occur through time at sites along the Gregory River.
Instantaneous gauged flow volumes at Riversleigh and Gregory Downs in May/June 1919 were 155 and
184 cusecs (4.389 & 5.218 m³/s) whereas subsequent measurements in June of 1931 yielded greatly
substantially volumes of 113.5 and 75 cusecs (3.214 & 2.124m³/s) respectively (Whitehouse, 1940). On
both occasions these measurement series were taken at least several months after any substantial rainfall
in the catchment and were regarded as useful estimates of spring outputs.
Drysdale et al. (2002) raised the possible influence of decadal scale fluctuations in regional recharge as a
contributing factor to the apparent declines in spring activity and output noted by Whitehouse’s early
surveys. This is a salient consideration when assessing streamflow behavior in this particular climatic
environment. Decadal scale variations in rainfall are a characteristic and very relevant feature of the longterm Australian rainfall record, due in large part to the influence of a number of global climatic
mechanisms including the El Nino–Southern Oscillation (ENSO) and central Pacific sea surface
temperature oscillations (McMahon & Finlayson, 2003, Suppiah, 2004). Accordingly, many Australian
rivers display concurrent long-term trends or quasi-cycling patterns, exhibiting sequences of consecutive
Australian Centre for Tropical Freshwater Research
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years where streamflows are significantly above or below the long-term ‘average’ (McMahon &
Finlayson, 2003). Historical accounts (i.e. Whitehouse, 1940) and a brief recent data record suggest that
while a number of local systems are perennial and never cease to flow, there exists aspects of baseflow
behaviour that are nonetheless quite dynamic through time. Considering the geographic location of the
Gregory-Lawn Hill catchment and the recognized climatic vagaries the region is subject to, marked longterm variability in streamflow behavior, including concomitant base-flow variations from an autogenic
karst aquifer would not be unexpected. The 33 years of streamflow record available here unfortunately
only offers a brief glimpse at the long-term climatic/streamflow variability that may occur within the
catchment.
Once the Nicholson, Gregory and Lawn Hill Creek systems have left the geomorphic confines and
foothills of the Mount Isa Inlier and Barkly tableland, the streams traverse the broad, alluvial Gulf Plains.
Upon this low gradient environment both the Gregory and Lawn Hill systems undergo a number of
bifurcations in certain reaches resulting in a complex anastomosis of flow paths. The Gregory River
divides into two channels carrying nearly equivalent flow volumes around 90km from its confluence with
the Nicholson River. The western channel of this division (the Gregory River) continues on to a
confluence with the Nicholson River. The eastern channel (Beames Brook), in contrast, continues on to
terminate in the head on the Albert River estuary near Burketown. There are also a number of additional
smaller flow divisions such as One-Mile Creek and Running Creek in these lower reaches. Lawn Hill
Creek also undergoes a similar division into multiple flow paths for significant lengths in the reaches of
its lower catchment. The actual hydrology of this floodplain area is not particularly well known and
anecdotal reports from local landholders suggest that flow patterns across the plains may be quite
dynamic through time. A complex of active and abandoned streamlines traverse the plain, and those that
carry water or the relative proportionate flow in these various channels may vary depending on factors
such as the geomorphic processes associated with wet-season flood events or dry-season baseflow levels.
The low stream capacities on these floodplains result in widespread flooding during the wet-season.
A historic, quantitative study of streamflow behavior on these plains noted remarkably uniform losses of
water along the course of both Beames Brook and the Gregory River to the point both systems flow was
substantially reduced by the time they reached their respective endpoints in other systems (Whitehouse &
Ogilvie, 1949). The major component of this loss was suggested to be seepage loss to the groundwater
underflow. The significant contribution from the perennial streams of the catchment to shallow
groundwater flows is notable for playing an important role in supporting coastal wetland environments
(NRM, 2003). The terminal, coastal wetland aggregations of the Nicholson Delta provide a rich complex
of permanent, semi-permanent and seasonal wetland habitats merging across a freshwater/saltwater
gradient and are in themselves of considerable natural significance (Blackman et al. 1996).
This division of flow into multiple pathways on the plains has implications for a number of ecological
processes. The potential levels of riparian-water interaction may be greater on the plains in relation to the
single large stream channels in upper reaches. The division of flow paths on the low gradient Gulf Plains
may also have ramifications for levels of impacts associated with the effects of exotic and pastoral
animals (as will be discussed further).
5.1.4
Water Resource Development, Flow Modification and River Regulation
Future water resource development in the Nicholson-Gregory catchment is one of the key issues that will
dictate the overall condition and functioning of local wetland environments. Alteration of natural flow
regimes coincident with water resource development is generally regarded as one of the more chronic and
pervasive threats to the ecological sustainability of riverine and wetland environments (Bunn &
Arthington, 2002). The widespread hydrologic alteration seen across much of southern Australia is
however generally absent in northern environments (Finlayson et al., 1997). Water resource development
and consumptive water use is currently minimal in the Nicholson-Gregory catchment. With the exception
of a relatively minor storage constructed on the Nicholson River near Doomadgee (1500ML capacity),
the streams draining this catchment (and those of most Southern Gulf drainages) remain primarily
unregulated. Existing surface water entitlements across the Nicholson catchment currently represent
around 0.13 % of mean annual flow (NRM, 2003), although this figure is perhaps a simplistic way to
view the issue. It is also unlikely that all current entitlements are being used to their full capacity. Soil
Australian Centre for Tropical Freshwater Research
Page 19
investigations of the Gregory River region indicate predominantly moderate to low agricultural suitability
due to the presence of shallow rocky soils and Blaken clays (DNR, 1999), therefore substantial
development of irrigated cropping would seem unlikely. Some areas of calcareous red earths situated
along the Gregory River do have high agricultural potential, although their extent is yet to be defined.
The Queensland Department of Natural Resources and Mines recently initiated the development of a
Water Resource Plan (WRP) for the Gulf Rivers (NRM, 2003). Taking into account the current limited
consumptive demands and the high natural values of the Nicholson-Gregory catchment, the WRP
planning process will apparently consider limited growth of entitlements except for urban, mining, stock
and domestic purposes (NRM, 2003). That said, water harvesting has been identified as an option for
some parts of the Nicholson basin and some pending water applications are apparently very large (NRM,
2003). The Gregory River is also apparently one of 18 Queensland rivers currently under consideration
for designation as a ‘Wild River’ in upcoming legislation (Teambeattie.com, 2004). Such designation
would have a number of management implications including limitations on additional developments and
water allocations, minimal flow regulation, protection of associated wetland complexes etc. Final
designation of ‘Wild River’ status depends on an extensive community consultation process before a
formal legislative adoption.
Even in primarily unregulated systems, incremental water resource development including land use
changes, minor water diversions and water harvesting of in-channel and floodplain flows can have a
substantial effect on the natural flow regime (Arthington et al., 1998). It is perhaps questionable whether
sufficient data exists to properly assess potential impacts of water resource development in the Nicholson
-Gregory catchment. The impacts of abstraction in the complex and dynamic fluvial floodplain
environment in particular would seem difficult to anticipate on a landscape scale. Floodplain
environments are inherently sensitive to changes in flow regime, where even small changes in water level
can lead to major changes in areal inundation patterns (Kingsford, 2000).
6.0
WATER QUALITY
The need to gain a better understanding of water quality characteristics in Gulf catchments has been
reiterated in a number of recent natural resource management initiatives (i.e. GRDP, 2000; SGCI, 2000).
From the early 1990’s onwards, an array of programs have collected a variety of water quality data
throughout the Nicholson-Gregory catchment. For example:
ƒ
ƒ
ƒ
Dames & Moore (1994) utilised spot water samples as well as rising stage samplers to monitor
general water quality, trace metals and nutrients over the period 1991-1994 in a number of creek
systems in close proximity to the Century Zinc mine project (ie. Page, Mitton, Archie, Coglan,
Louie and Lawn Hill Creeks and the Gregory River).
Recent studies on karst hydrology have collected a variety of water quality data predominantly
focused upon karst spring-water and groundwater characteristics (i.e. Drysdale et al., 1998;
Drysdale et al., 2002). These studies concentrated primarily on physico-chemical changes in
water quality downstream of spring complexes in the upper reaches of the Gregory, Lawn Hill,
O’Shannassy and Louie Creek systems. Parameters investigated included pH, conductivity, major
ions, calcite saturation, dissolved carbon dioxide and bicarbonate concentrations (i.e. variables
relevant to the evolution of travertine depositing rivers).
Since 2000, the Queensland Department of Primary Industries (QDPI) Long-term Fisheries
Monitoring Program has also routinely collected water quality information once a year at
approximately seven sites within the Nicholson catchment. This includes six sites on the Gregory
River and one site on the lower reaches of the Nicholson River. These spot water samples focus
on a range of standard water quality parameters such as pH, turbidity, conductivity, salinity,
temperature and dissolved oxygen. This water quality dataset has not yet been analyzed or
reported upon to any extent.
Australian Centre for Tropical Freshwater Research
Page 20
Not surprisingly, considering the varying functions and generally disparate nature of this work, much
available water quality information consists of incohesive and sporadic datasets, built using various
collection methodologies and standards of quality control. The most significant water quality dataset
available in terms of sampling regularity and geographic extent is that associated with the Department of
Natural Resources and Mines (NRM) gauging station and ambient monitoring network. Fifteen gauging
station sites within the Nicholson-Gregory catchment have water quality data consistent with this state
gauging station network. The period of water quality record available at many sites is somewhat limited
in terms of sampling effort and duration, with the vast majority of gauging stations closed in the late
1980’s. Only two main sites (two Gregory River gauging stations) remain operational and currently
collect water quality information on a regular basis. Gauging Station 912105a (Gregory River at
Riversleigh) is especially notable as it has been equipped for continuous logging of in situ water quality
data over the past several years. The three continually logged parameters are conductivity, pH and
temperature. While water quality samples at some NRM gauging station sites have been regularly
collected over several decades, the dataset has as yet not been analyzed or reported to any great degree.
The targeted parameters in this sampling program have tended to be the major ions (chloride, sulphate,
carbonate, sodium etc.), pH and turbidity. Although nutrient analysis has received more emphasis in
NRM environmental monitoring assessments in recent years, this particular aspect of water quality
assessment is lacking.
Table 2 provides a list of NRM gauging stations with some of the more substantial datasets available, as
well as a broad subset of water quality parameters of general interest. Data is presented from two
intermittent systems (the Seymour & Nicholson Rivers) as well as four sites on the perennial
groundwater-fed systems in the Gregory-Lawn Hill Creek catchment. The substantial effects of
groundwater influence on ambient water quality at the perennial sites is immediately apparent. Median
conductivity values were high at all four sites, ranging between 500 and 600 µS/cm. While data is limited
for the intermittent sites, median values were relatively low (ca. 50 µS/cm), indicative of wet season
surface runoff that may have little interaction with soil. The median turbidity values at all sites were low,
but especially so in the spring-fed systems (all less than 5 ntu), demonstrating the characteristic water
clarity evident in the Gregory-Lawn Hill Creek system.
Australian Centre for Tropical Freshwater Research
Page 21
Table 2: Summary Water
Quality Parameters at NRM
Gauging Stations.
Stream Discharge (m³/s)
Conductivity@ 25°C (µS/cm)
Turbidity (ntu) (upper reporting
limit of 100)
pH (pH units): Field
Total Alkalinity as CaCO3
Hardness as CaCO3
Total Suspended Solids
Nitrate as NO3 (mg/L)
Total Nitrogen (mg/L)
Total Phosphorus as P
Copper as Cu soluble (mg/L)
Iron as Fe soluble (mg/L)
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
912112a Seymour
R. @ Main Road
(1970-1988)
11
0.017
0/3.55
13
54
32/90
8
-
912108a O'Shannassy
R. @ 17.7km (19681988)
52
0.433
0.15/9.25
52
590
160/835
21
5
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
No. of results
Median
Min/Max
4/100
13
14
9/21
13
12
7/21
10
24
10/140
6
0.4/3
1
0.01/0.01
9
0.1/1.8
1/100
51
322
58/500
53
320
49/447
38
9.5
1/459
10
0.5
0.4/2.6
23
0.04
0.02/1.4
Gauging
Station
Australian Centre for Tropical Freshwater Research
912105a Gregory R. @
Riversleigh (1969-2002)
71
3.701
1.69/181
98
549.4
132/653
44
2.05
0.3/100
23
7.9
7.3/9.0
96
306.41
58/374
58
305.5
58/372
65
9
0/1280
41
0.21
0/9.0
14
0.1073
0.047/0.217
22
0.00895
0.0029/0.0976
31
0.01
0/0.06
51
0.02
0/0.68
Page 22
912101a Gregory R.@
912103a Lawn Hill
Gregory Downs (1968- Ck.@ Lawn Hill (19682002)
1998)
77
49
3.33
0.567
na/13.45
0/6.46
45
52
500
545
165/610
178/640
31
23
2
3.9
0.8/100
28
8.3
7.8/8.5
69
281
89/435
70
278.48
85/351
53
5
0/425
19
0.5
0/10.5
7
0.051/0.15
7
0.005/0.009
15
0.01
0/0.06
29
0.03
0/0.42
1/21
2
7.9/7.9
51
300
106/431
52
297
103/371
35
10
2/316
19
0.5
0/2.2
2
0.0812/0.106
2
.0115/0.0121
5
0/0.01
25
0.03
0/1.6
912107a Nicholson R.
@ Connolly's Hole
(1968-1988)
18
0.2125
0/933.89
20
57
33/100
12
17
3/100
19
15
8.0/34
19
13
7.0/36
16
10
5.0/45
8
0.4/2.4
1
0.01/0.01
13
0.48
0.04/1.3
As would be expected for spring-fed systems draining a soluble limestone/dolomite karst environment,
values for pH, alkalinity, hardness and nitrate were much higher in the perennial systems relative to
values obtained from rainfall run-off dependent streams. The relative closeness of the median to
maximum values for a number of parameters such as conductivity, alkalinity and hardness at perennial
sites are indicative of relative constancy in a number of aspects of water chemistry. Again, this is not
surprising considering the consistent base-flow conditions typifying these spring-fed sites. Description of
background metals levels would be a useful exercise given the mining industry interests in the region,
however relevant data are sparse. The levels of the few metals species with some amount of data
available (i.e. iron and copper) are within the range of what would be expected for a heavily mineralised
region.
As is evident from the median and minimum/maximum values for stream discharges associated with
water sample collection at sites, the vast majority of samples have been collected during what would be
considered baseflow or low flow conditions. This reflects the situation that water samples at NRM
gauging sites are usually collected three to four times a year and due to wet season access constraints at
many locations, most samples are collected during the dry season. While available data may provide
some utility in establishing ambient baseflow or low flow water quality conditions it has some
limitations. There has been considerable recent interest in the effects of land use on contaminants
discharged to marine environments. Given that most contaminant transport occurs during major flood
events, flow weighted sampling (i.e. samples collected during flood events) is needed to gauge useful
estimates of sediment/contaminant load discharged to coastal environments during these events (Brodie,
2002). While median total suspended solids (TSS) values at all sites are quite low (<25), the high
maximum TSS values at a number of sites, presumably some of the few collected during high flow flood
events suggests substantial sediment loads during rainfall run-off events.
Australian Centre for Tropical Freshwater Research
Page 23
7.0
FRESHWATER FISH COMMUNITIES
The distinct lack of scientific knowledge regarding the northern monsoonal rivers and the fish
communities they support has been noted for some time (Bishop & Forbes, 1991). However, despite the
current uncertainty over the exact distributions, taxonomy and biology of many fish species, the
freshwater fishes across the northern Australian tropics do represent one of the better studied elements of
the aquatic fauna. In terms of the broad scale regional fish community, the riverine catchments
discharging into the Gulf of Carpentaria form a transitional zone between the Timor Sea Division
(Western Australia and the Northern Territory) and the Cape York Peninsula drainage division. With the
exception of the western portion of Cape York Peninsula, the fish diversity of Gulf catchments is
generally regarded as impoverished in relation to other areas of northern Australia (Allen et al., 2002).
The piscifauna of the Nicholson catchment, particularly the Lawn Hill Creek and Gregory River systems
possibly represent an exception to this generalization. Dames & Moore (1994) described these systems as
regionally significant due to ‘a remarkable diversity of fishes comparable to the major coastal streams of
Cape York Peninsula and Arnhem Land’, areas whose stream systems support some of the richest fish
species diversities by Australian standards. Whether this is an entirely deserved description remains to be
seen and is yet to be rigorously tested, but the statement does highlight the somewhat unique character of
the Nicholson-Gregory’s fish community.
A number of locations within the Nicholson-Gregory catchment have through time been subject to
periodic fish surveys of varying spatial extent and duration. As part of the Century Zinc project
Environmental Impact Assessment, Dames & Moore (1994) documented 29 fish species from the
permanent and intermittent stream systems in close proximity to the Century Zinc mine site (i.e. Page,
Archie, Coglan, Mitton, Lawn Hill and Louie Creek systems). The Musselbrook Reserve Scientific Study
subsequently recorded 15 fish species from the intermittent systems of the nearby Musselbrook Resource
Reserve such as Musselbrook, Stockyard and Colless Creeks (Leggett & Byron, 1998). In more recent
times, the state-wide Long-Term Monitoring Program for freshwater fishes, carried out by the
Queensland Department of Primary Industries (QDPI) has surveyed seven sites along the NicholsonGregory system on a yearly basis since 2000. Sites include six locations on the Gregory River between
Riversleigh and the Gregory’s confluence with the Nicholson River, as well as one site on the lower
reaches of the Nicholson River. Although the primary survey emphasis of this particular program is
aimed at commercially or recreationally important species such as barramundi, catfish and grunter,
information on all fish species collected during surveys is recorded. This program has thus far collected
approximately 27 species in the Nicholson-Gregory system since its inception (Jebreen et al., 2002,
QDPI, unpublished data), although the taxonomy of a number of species recorded is currently somewhat
uncertain.
The QDPI have also recently completed a rapid assessment of fish biodiversity across a number of
southern Gulf of Carpentaria river systems, including 11 sites across the Nicholson-Gregory catchment
(Hogan & Valance, 2005). This study tentatively identified 30 species from these sites. Other results of
this survey including the possible discovery of several new fish species from southern Gulf catchments
(yet to be verified) as well as substantial range extensions for several species previously only recorded
from the Northern Territory highlights the very formative current state of freshwater fish ecology existing
for Gulf of Carpentaria catchments.
7.1
Fish Survey Methodology
As part of the ACTFR catchment assessment, the freshwater fish assemblages at a range of sites within
the Nicholson-Gregory catchment were sampled once during July 2004. Given that the Gregory River
and parts of the Nicholson River are subject to regular yearly surveys as part of the QDPI Long-Term
Fish Habitat Monitoring Program, sites on the main Gregory River channel were largely avoided to
prevent unnecessary redundancy in sampling effort. In order to encompass a broad array of habitats,
including those often overlooked in typical surveys the 2004 ACTFR survey program instead
concentrated effort primarily upon smaller tributary systems and off-channel water-bodies throughout the
Gregory-Lawn Hill catchment. Sampling was non-destructive and predominantly involved use of either
single pass boat mounted (Smith-Root 2.5 GPP) or backpack (Smith Root Model 12-B) electro-fishing
techniques. Boat sampling was undertaken for approximately two hours at each site. Backpack sampling
Australian Centre for Tropical Freshwater Research
Page 24
entailed one series of 5 x 10m transects being surveyed in each sample reach. More detailed data
pertaining to sampling duration and catch per unit effort were retained but not included in this report.
Most captured fish were identified, measured and released immediately, except in the case of a small
number of specimens requiring more detailed identification, which were accordingly retained and
preserved. Observations of the apparent level of habitat disturbance at sample sites at the time of
sampling were also noted. This included any impacts by feral and domestic animals (both riparian and
instream), the presence of exotic weeds and fauna as well as fishing or camping activities.
7.2
Fish Survey Results
Time, access and aquatic habitat availability constraints meant some desired target sites across the
catchment were unable to be sampled. Nevertheless, a broad cross-section of the aquatic habitat types
occurring throughout the Gregory-Lawn Hill catchment were surveyed. 18 sites in total were sampled
over the July survey period including perennial streams as well as permanent and intermittent off-channel
lagoons (see Map 1 below). Site coordinates are listed in Table 3.
Table 3
2004 ACTFR Fish Survey Sites
Site Number
Site Name
Site Coordinates (Lat./Long.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Louie Ck. near Adel’s Grove
Lawn Hill Ck. @ Rocky Lagoon
Lawn Hill Ck. d/s Rocky Lagoon
Lawn Hill Ck. 5km d/s Adel’s Grove
Lawn Hill Ck. @ Lawn Hill Station
Lawn Hill Ck. @ Doomadgee X-ing
Lawn Hill Ck. @ Blue Hole
Lawn Hill Ck. @ Blue Hole ford
Corinda Lakes
Atlas Waterhole
Lawn Hill Ck. (North Branch)
Lawn Hill Ck. (Middle Branch)
Lawn Hill Ck. (South Branch)
Pelican Waterhole
Gregory R. d/s Punjaub Station
1-Mile Creek X-ing
Beames Brook @ Brinawa Station
Beames Brook @ Black Gully
18˚ 41’ 45.0”S, 138˚ 32’ 0.0”E
18˚ 40’ 55.6”S, 138˚ 32’ 21.3”E
18˚ 40’ 27.1”S, 138˚ 32’ 49.6”E
18˚ 38’ 0.0”S, 138˚ 33’ 45.0”E
18˚ 34’ 5.0”S, 138˚ 35’ 5.2”E
18˚ 34’ 6.9”S, 138˚ 35’ 5.2”E
18˚ 4’ 18.4”S, 138˚ 55’ 10.0”E
18˚ 4’ 18.4”S, 138˚ 54’ 11.8”E
18˚ 6’ 21.1”S, 139˚ 4’ 40.7”E
18˚ 3’ 18.3”S, 138˚ 55’ 2.8”E
18˚ 5’ 20.0”S, 139˚ 4’ 20.8”E
18˚ 5’ 21.2”S, 139˚ 4’ 20.5”E
18˚ 5’ 22.1”S, 139˚ 4’ 20.0”E
18˚ 7’ 23.6”S, 139˚ 1’ 24.0”E
18˚ 9’ 3.2”S, 139˚ 8’ 30.0”E
18˚ 10’ 30.0”S, 139˚ 12’ 30.0”E
18˚ 09’ 55.1”S, 139˚ 14’ 24.2”E
18˚ 08’ 1.1”S, 139˚ 14’ 26.2”E
Australian Centre for Tropical Freshwater Research
Survey
Method
Backpack
Boat
Backpack
Boat
Boat
Backpack
Boat
Backpack
Boat
Boat
Backpack
Backpack
Backpack
Boat
Boat
Boat
Backpack
Boat
Page 25
Map 1 2004 ACTFR Fish Survey Sites
The 2004 ACTFR fish surveys returned a total of 28 species of fish (16 families) over the course of the
18 sites sampled. The total list of species recorded, along with common names is outlined in table 4.
Species lists and abundances obtained at each individual site are provided in Table 5.
Australian Centre for Tropical Freshwater Research
Page 26
Table 4
2004 Fish Survey: Total Species list (with common names).
Species
Melanotaenidae (Rainbowfishes)
Melanotaenia splendida inornata
Atherinidae (Hardyheads)
Craterocephalus. stramineus
Craterocephalus. stercusmuscarum
Gobiidae (Gobies)
Glossogobius giurus
Eleotridae (Gudgeons)
Oxyeleotris lineolatus
Oxyeleotris selheimi
Ambassidae (Glassfish)
Ambassis agrammus
Ambassis macleayi
Apogonidae (Cardinalfishes)
Glossamia aprion
Toxotidae (Archerfishes)
Toxotes chatareus
Terapontidae (Grunters)
Amniataba percoides
Scortum oglbyi
Hephaestus carbo
Hephaestus fuliginosus
Leiopotherapon unicolor
Plotosidae (Eel-tailed catfish)
Neosilurus ater
Neosilurus hyrtlii
Porochilus rendahli
Ariidae (Fork-tailed catfish)
Arius graeffei
Arius midgleyi
Arius berneyi
Arius leptaspis
Belonidae (Longtoms)
Strongylura krefftii
Soleidae (Soles)
Brachiurus salinarum
Centropomidae (Giant perches)
Lates calcarifer
Clupeidae (Herrings)
Nematalosa erebi
Osteoglossidae (Bony tongues)
Scleropages jardinii
Engraulidae (Anchovies)
Thryssa scratchlyi
Australian Centre for Tropical Freshwater Research
Common Names.
Eastern (chequered) rainbowfish
Strawman, Blackmast.
Fly-specked hardyhead
Flathead goby
Sleepy cod
Striped sleepy cod, Giant gudgeon
Sailfin glassfish, Sailfin perchlet
Macleay’s glassfish
Mouth almighty
Seven-spot archerfish
Barred grunter, Banded grunter
Gulf grunter
Coal grunter
Sooty grunter, Black bream
Spangled perch
Black catfish, Butter Jew, Narrow-fronted tandan
Hyrtl’s tandan
Rendahl’s catfish
Lesser Salmon catfish, Blue catfish
Shovel-nosed catfish, Silver cobbler
Berney’s catfish
Salmon catfish, Triangular shield catfish
Freshwater longtom
Saltpan sole
Barramundi
Bony bream, Bony herring
Saratoga, Silver barramundi
Freshwater anchovy
Page 27
Table 5
2004 ACTFR Fish survey results: Nicholson-Gregory Catchment
Site Number
7
8
9 10 11
Species
1
Melanotaenidae (Rainbowfishes)
2
3
4
5
6
12 13
14
15 16
17
18
Melanotaenia splendida inornata 6
Atherinidae (Hardyheads)
9
10
2
9
10 10
2
20
4
-
2
16
28
4
2
4
79
Craterocephalus. stramineus
C. stercusmuscarum
Gobiidae (Gobies)
-
1
1
1
8
5
1
3
2
-
6
16
-
-
-
4
2
-
1
-
2
Glossogobius giurus
Eleotridae (Gudgeons)
2
5
-
1
-
-
3
8
2
-
1
-
-
-
-
-
-
-
Oxyeleotris lineolatus
O. selheimi
6
6
3
2
4
-
7
8
8
3
3
2
12
15
6
1
2
5
3
6
2
-
1
-
2
-
1
3
4
1
4
1
2
Ambassis agrammus
A. macleayi
Apogonidae (Cardinalfishes)
1
-
-
1
18
-
-
42
11
-
7
24
-
-
1
-
-
86 210 1
-
8
Glossamia aprion
Toxotidae (Archerfishes)
4
-
-
9
9
1
1
1
-
8
5
1
-
5
70 14
7
1
Toxotes chatareus
Terapontidae (Grunters)
6
1
-
2
-
2
5
-
5
-
-
1
8
-
41
1
1
22
Amniataba percoides
Scortum oglbyi
Hephaestus carbo
H. fuliginosus
Leiopotherapon unicolor
Plotosidae (Eel-tailed catfish)
1
1
2
-
3
5
8
21
1
2
-
68
2
2
-
5
3
5
3
3
1
1
7
1
3
2
1
3
3
2
2
2
4
87
2
1
8
2
1
5
1
-
-
Neosilurus ater
N. hyrtlii
Porochilus rendahli
Ariidae (Fork-tailed catfish)
-
-
-
1
-
1
-
1
-
1
1
-
-
-
-
-
-
4
-
2
1
-
3
3
-
1
-
Arius graeffei
A. midgleyi
A. berneyi
A. leptaspis
Belonidae (Longtoms)
-
-
-
-
-
-
1
-
-
1
1
-
-
-
-
-
-
1
-
1
1
5
2
1
-
2
-
Strongylura krefftii
Soleidae (Soles)
3
-
-
-
-
-
2
-
5
1
-
-
-
2
-
1
-
1
Brachiurus salinarum
Centropomidae (Giant perches)
-
-
-
2
-
-
-
-
-
-
-
-
-
-
3
8
1
1
-
-
1
-
4
8
-
25
1
-
-
-
-
7
3
-
1
5
Nematalosa erebi
Osteoglossidae (Bony tongues)
-
-
50
-
2 259
-
20
4
-
-
1
2
4
2
-
-
-
-
-
1
-
-
-
-
-
-
-
-
-
-
-
-
-
14
9
5
17
8
6
8
7
9
10
12
Ambassidae (Glassfish)
Lates calcarifer
Clupeidae (Herrings)
Scleropages jardinii
Engraulidae (Anchovies)
Thryssa scratchlyi
Total Site diversity
- 14
2
1
1
13 -
-
12 16
10
2
15 13
14 20
Species such as Macleay’s glassfish (Ambassis macleayi) and bony bream (Nematalosa erebi) were the
most numerically abundant fish in terms of total specimens collected over the course of the survey,
Australian Centre for Tropical Freshwater Research
Page 28
although this result was largely due to the exceptional abundance of these species at a limited number of
sites. The rainbowfish Melanotaenia splendida inornata was the most common species in terms of it’s
overall ubiquity, being found at all sites bar one (and likely present there as well). Other species such as
sleepy cod Oxyeleotris lineolatus, giant gudgeon Oxyeleotris sellheimi, mouth almighty Glossamia
aprion, barred grunter Amniataba percoides and spangled perch Leiopotherapon unicolor were also
widespread, being recorded at the vast majority of survey sites. In contrast, several species such as the
saratoga Scleropages jardinii, freshwater anchovy Thryssa scratchleyi and a number of the various
catfish species were not numerically abundant and only documented at a small number of locations,
possibly indicative of patchy spatial distribution throughout the catchment. The collection of freshwater
anchovy from Atlas Waterhole is notable, as the distribution of this species is not particularly well
known. Freshwater anchovy have also been occasionally collected from the Gregory River during the
course of the DPI Long-Term monitoring program (Jebreen et al., 2002). The capture of a juvenile
freshwater anchovy (25mm SL) was particularly interesting considering the reproductive biology of this
species is also currently poorly understood (Allen et al., 2002). This small juvenile recorded from a
typically isolated off-stream lagoon is suggestive of the capacity for freshwater breeding.
One of the more notable sites surveyed was 1-Mile Creek, a location which produced an impressive 20
species from the sample reach. This site was characterised by a variety of flow habitats and a structurally
complex environment including highly abundant aquatic macrophyte communities. Corinda Lakes was
another site of some note, yielding a very high density of the recreationally and commercially significant
barramundi. These fish were primarily in the 500mm-750mm (Standard Length) size range, equating
approximately to a three to six year age bracket, a stage at which these fish (generally mature males) will
usually begin migration from upstream freshwater habitats to downstream estuarine spawning grounds.
This site is somewhat unusual in being a permanent lagoon, fed by apparently constant stream-flow from
Lawn Hill Creek into and out of the far ‘downstream’ end of the waterbody, essentially making the site a
massive backwater. Substantial macrophyte communities (primarily Vallisneria spp.) had established on
the sloping littoral margins of this waterhole. Pronounced movement is a striking feature of the
barramundi life cycle, particularly in the biology of juvenile barramundi in the 1+ year age class (ca. 250350mm SL). At this point juvenile barramundi tend to migrate from estuaries and tidal habitats into the
freshwater environments of rivers including billabongs, floodplain lagoons and wetlands before moving
back into estuarine reaches upon maturity (Pusey et al., 2004). This presumably facilitates rapid growth
in the relative absence of large predators to a point they can successfully compete and survive in estuarine
environments. Corinda Lakes may not be a barramundi ‘nursery’ environment in the strict sense of the
term, the relatively large sizes and probable cannibalistic predilections of the resident barramundi
population would likely make life difficult for small, young juveniles. However, the site perhaps
represents an important, productive and sheltered environment where larger juveniles (2+years) can
‘grow out’ to maturity. Hogan & Valance (2005) also noted the high habitat values of this particular site.
While not comparatively quantified, many of the reaches of local perennial stream systems that undergo
significant braiding and anastomosis into shallower multiple flow paths on the low gradient Gulf plains
(i.e. the Gregory River and Lawn Hill Creek) appear to be quite productive aquatic environments. Many
of these sites were characterised by substantial aquatic macrophyte communities primarily composed of
Vallisneria spp., Potamogeton crispus and Ottelia alismoides. These macrophyte communities did not
appear as abundant throughout many of the higher catchment reaches surveyed for fish. It is interesting
to note that few young juvenile barramundi (i.e. 1+ year age group: 250-350mm SL) were recorded
during this survey, with the vast majority in the 3+ year and older size category. Those few 1+
barramundi collected were all recorded from these smaller, shallower, braided stretches of perennial
streams on the alluvial plains, rather than larger instream or off-channel lagoons. As well as important
migration and dispersal conduits for certain species between upstream freshwater environments and the
downstream estuaries, sections of these shallower middle stream reaches could also possibly represent
important ‘nursery’ habitats for some aquatic fauna (an issue obviously yet to be investigated in any great
depth).
The community composition of the fish fauna for the most part coincides with the results of other surveys
carried out in the area (Dames & Moore, 1994; Leggett & Byron, 1998; Jebreen et al., 2002, QDPI
Australian Centre for Tropical Freshwater Research
Page 29
unpublished data). This study did document range extensions for a number of fish species (cf. Allen et
al., 2002), a not particularly surprising outcome considering the generally limited survey effort the region
as whole receives. Expansions to the often discontinuous distributions that presently appear for many fish
species in the published literature will no doubt continue to occur as areas across northern Australia
become better surveyed.
The apparent relative diversity of the fish fauna of the Nicholson-Gregory catchment is an issue worth
addressing in more detail. Some degree of caution should always be applied when comparing fish
diversity results from a particular project to those obtained from other studies. Issues such as relative
sampling techniques and survey effort, catchment size, survey site catchment position and diversity
enhancement via estuarine vagrants are just some of the factors potentially confounding comparisons.
Nevertheless, the diversity of the Nicholson-Gregory catchment appears quite high, especially
considering the minimal contribution made by estuarine vagrants to overall species richness in this and
other surveys (the actual relevance of rigid designations for many northern Australian fish species as
either solely freshwater or estuarine in their habits is perhaps open to conjecture). To provide some frame
of reference, the Murray-Darling basin, Australia’s largest drainage division with a catchment area of
over 1,000,000 km² has around 33 resident ‘freshwater’ fish species (although this example is regarded as
an anomalous outlier to most species diversity/catchment area relationships). The 28 species obtained in
this study alone equates quite favourably in simple species richness terms to the results of similar shortterm surveys in other areas across northern Australia generally regarded a highly speciose by Australian
standards. Herbert et al. (1995) collected between 24-36 species for most of the larger riverine
catchments of western Cape York Peninsula (although the Wenlock River yielded an impressive 45
species). Pusey et al. (1995) collected 36 and 25 species respectively from the Mulgrave and South
Johnstone Rivers, two relatively small drainages in Queensland’s Wet Tropics. At least 52 species have
been documented in the Alligator Rivers region of the Northern Territory (Bishop et al., 1990, Bishop,
2001) bearing in mind this is probably by far the most thoroughly surveyed aquatic environment in
northern Australia, with years of cumulated research effort available.
It should also be borne in mind the results of this particular 2004 study are almost certainly a
considerable underestimate of actual fish diversity. Single surveying techniques, even electro-fishing
(which is one of the more effective fish sampling methodologies) are invariably subject to a degree of
sampling bias. The effectiveness of electro-fishing for example varies over different species, with some
taxa inherently more susceptible to galvanotaxis (stunning) than others. Environmental variables such as
the time of day, season, water depth, temperature, conductivity and visibility are all additional factors that
can substantially affect results. The patchy spatial occurrence of a number of species recorded in this
survey also underlines the often ‘hit and miss’ nature of one-off, broad scale fauna surveys. Fish species
composition at particular locales can also often vary considerably on a seasonal basis (Bishop & Forbes,
1991) with results from a single survey basically giving a brief ‘snapshot’ of the species present at one
moment in time. Sampling during or immediately after the wet season for example could yield a
substantially different suite of species at many of these sites sampled in 2004.
When the results of collective fish survey effort carried out in the Nicholson-Gregory catchment are
collated, a significant number of additional species emerge that have been recorded in other aquatic
surveys. The recent and very thorough review of north-eastern Australian fish survey effort carried out by
Pusey et al., (2004) documents reliable records of at least 35 fish species in the freshwater reaches of the
Nicholson-Gregory catchment (see Table 6). Moreover, a number of records exist from various studies
identifying further fish species possibly occurring within the catchment that are yet to be conclusively
verified (see Table 7). While efforts have been taken during this review to avoid any glaring errors in
aggregated fish records, it should be recognised that any collective appraisal of fish survey effort in a
catchment is susceptible to inclusion of occasional misidentifications. Accurate field identification to
species for many northern Australian fish groups such as the catfish, terapontid grunters, glassfish,
gudgeons and gobies can be challenging for even experienced field personnel. A number of past
identifications were possibly based upon classification schemes that have since been reviewed with
consequent changes to taxonomy. Similarly, the systematics of some pertinent fish groups remains
somewhat confused. All of these issues collude to cast at least some degree of doubt over several
identifications outlined in table 7 that have not yet been validated by a specialist fish taxonomist.
However, a number of the species outlined in table 7 such as the giant glassfish and toothless catfish
Australian Centre for Tropical Freshwater Research
Page 30
possess distinguishing morphological features that makes misidentification very unlikely (these particular
species have also been documented over several different studies through time). Similarly, anecdotal
accounts by local residents of distinctive species such sawfish (Pristidae) and stingray (Dasyatidae)
occurring in the freshwater reaches of the Gregory River-Lawn Hill Creek catchment should be viewed as
accordingly reliable.
With respect to the overall fish diversity of the focus drainage it should also be noted that the lower
reaches of the Nicholson-Gregory catchment in particular have not as yet been comprehensively
surveyed. Therefore a number of additional widespread species that tend to commonly associate with the
freshwater/estuarine interface such as tarpon (Megalops cyprinoides) and empire gudgeon (Hypseleotris
compressa) are almost certain to also occasionally occur in the freshwater reaches of the system. When
these factors and all species reliably documented from collective survey efforts are taken into account,
the actual fish diversity of the catchment probably easily exceeds 40 species and in the unlikely event of
mass misidentifications could be even considerably higher.
Table 6
Additional reliably identified fish species formally recorded from the NicholsonGregory catchment in Pusey et al., 2004.
Species
Common Name
Atherinidae (Hardyheads)
Hardyhead
Craterocephalus munroi
Ambassidae (Glassfish)
Elongate glassfish
Ambassis elongatus
Ambassis spp. (formerly A. muelleri) Northwest glassfish
Vachelli’s glassfish
Ambassis vachellii
Gobiidae (Gobies)
Golden goby
Glossogobius aureus
Glossogobius spp. 2
Munro's goby
Eleotridae (Gudgeons)
Barred gudgeon
Bostrichthys zonatus
Purple-spotted gudgeon
Mogurnda mogurnda
Table 7.
Unconfirmed records of fish species possibly resident in the Nicholson-Gregory
catchment. Sources: Wager (1993), Dames & Moore, (1994), QDPI (unpublished data),
Pusey et al., (2004), Hogan & Valance (2005).
Additional Species
Plotosidae (Eel-tailed catfish)
Anodontiglanis dahli
Ariidae (Fork-tailed catfish)
Arius paucus
Atherinidae (Hardyheads)
Craterocephalus marjoriae
Ambassidae (Glassfish)
Parambassis gulliveri
Denariusa bandata
Terapontidae (Grunter’s)
Scortum neili
Eleotridae (Gudgeons)
Eleotris melanosoma
Soleidae (Soles)
Brachirus selheimi
Australian Centre for Tropical Freshwater Research
Common Name
Toothless catfish
Carpentaria catfish
Marjorie’s hardyhead
Giant glassfish
Pennyfish
Neil’s grunter
Ebony gudgeon
Freshwater sole
Page 31
The exact factors responsible for the high diversity of the Nicholson-Gregory catchment in relation to the
purportedly depauperate Southern Gulf catchments can only be speculated upon given the limited scope
of this survey. Possible mechanisms may include the somewhat interrelated processes of enhanced habitat
diversity and flow constancy potentially operating in the Gregory River sub-catchment. When
commenting upon the high fish diversity of Wet-Tropics streams in relation to other drainages in northern
Queensland, Pusey & Kennard (1996) suggested the reliable flows tending toward constancy and a
diverse and readily available array of lotic habitats as the major reasons for the exceptionally high fish
diversity occurring in the Wet Tropics. The reliable and constant spring fed base-flows throughout many
streams in the Gregory River-Lawn Hill Creek catchment may similarly provide for a predictable and
constant array of habitats being continually available to a diverse range of species with consequent
‘species packing’.
While not comparatively quantified during this survey, the substantial habitat diversity provided by the
catchment as a whole, but particularly the perennial systems of the Gregory-Lawn Hill catchment could
also be a major contributing factor to the high relative fish diversity. The Nicholson River proper has a
very different flow regime and hydrochemistry to that of the Gregory sub-catchment, with the Nicholson
more typical of a northern monsoonal river. How different a fish fauna the Nicholson River supports and
whether this affects overall catchment fish diversity is yet to be examined. Significant relationships
between fish diversity and the habitat complexity of waterbodies have been demonstrated in some
northern Australian freshwater ecosystems (Bishop & Forbes, 1991). The high diversity of aquatic
habitats available in the perennial systems of the Gregory catchment is noteworthy, including a spectrum
of flow environments such as fast flowing cascades, riffles and runs in shallow sections extending
through to deeper, essentially lacustrine waterbodies in some of the larger channels. Instream cover can
also be highly complex and abundant with well developed undercut banks, often profuse macrophyte
communities and substantial quantities of large woody debris. Collectively, these environmental features
could promote maintenance and persistence of a relatively diverse fish fauna in comparison to the
harsher, more episodic and unpredictable flow conditions and habitat availability that perhaps typify
other Southern Gulf catchments.
Because of time and habitat availability constraints, the ephemeral and semi-permanent aquatic habitats
of the catchment could not be assessed to any great degree in 2004. These environments have received
considerable attention in some of the previous survey work occurring in the catchment. The smaller,
temporary streams of the catchment do maintain an unusual aquatic ecology in that they are annually
colonized by a small suite of extremely hardy fish which breed in large numbers in the absence of large
predators while water is present, but typically die off as the dry season progresses (Dames & Moore,
1994). The limited habitat availability and harsh physicochemical conditions that typify these ephemeral
or semi-permanent water bodies for substantial periods means the more abundant species tend to be
generalist feeders such as rainbow fish (Melanotaenia splendida) and spangled grunter (Leiopotherapon
unicolor), species that can capitalize on variable food sources (Leggett & Byron, 1998). More specialised
fauna such as carnivorous predators like the freshwater longtom (Strongylura kreftii) and saratoga
(Scleropages jardinii) require reasonable water quality and a reliable food supply and are therefore
apparently most abundant in permanent stream habitats (Dames & Moore, 1994). The fish fauna of these
perennial creeks and any permanent refuge pools in intermittent systems (e.g. Archie Creek) likely play a
critical role as source populations and linkages in ecosystem dynamics at a landscape scale (Dames &
Moore, 1994).
7.3
Significant Fish Species of the Nicholson-Gregory Catchment
The fish fauna of the Nicholson-Gregory catchment, while speciose, doesn’t exhibit any apparent level of
endemism (i.e. fish species whose distribution is limited solely to a particular catchment). The vast
majority of fish species collected during this and other surveys in the Nicholson-Gregory catchment have
a widespread distribution across much of northern Australia, although some notable exceptions do occur.
The Gregory River-Lawn Hill Creek catchment was for some time thought to support the only known
Queensland population of the ‘strawman’ or ‘blackmast’ (Craterocephalus stramineus). Hogan &
Valance (2005) have however recently reported this species from waterholes in the adjoining Leichhardt
River catchment. This fish species’ Queensland population is geographically isolated from the only other
Australian Centre for Tropical Freshwater Research
Page 32
known sub-populations in north-western Australia (Allen et al., 2002). C. stramineus was recorded at
three locations in the 2004 ACTFR surveys and was quite abundant at one site in Lawn Hill Creek.
Comparing the genetic status of this Gregory-Leichhardt River sub-population for any incipient
speciation in relation to the only other known populations in the Ord River (WA) and some of the
western drainages of the Northern Territory (i.e. the Victoria, Daly, Finniss and Katherine Rivers) would
be an interesting proposition.
The coal grunter (Hephaestus carbo) and saratoga (Scleropages jardinii) are two other notable species
with sporadic distributions across northern Australia and which are probably restricted to the Lawn Hill
Creek-Gregory River system in the Southern Gulf catchments. Coal grunter were recorded at several sites
during 2004 surveys and also regularly appear in QDPI survey results from the main Gregory River
system. Only one saratoga (a small specimen ca. 30cm TL) observed in Lawn Hill Creek was
documented during this 2004 ACTFR survey. A number of local landholders and residents report this
species has never been highly abundant in many reaches of the catchment, although specimens are still
apparently observed occasionally in Lawn Hill Creek inside the National Park boundary as well as
possibly some locations along the Beame’s Brook system. This species is perhaps surprisingly yet to be
recorded in any fish surveys from the main Gregory River channel. The natural rarity of this fish coupled
with often cryptic habits based upon ambush predation from the cover of fringing riparian vegetation may
not make this species particularly conducive to being recorded in electrofishing surveys. However,
considering the unique phylogenetic status of this species (it is one of the few ‘primary’ Australian
freshwater fish of Gondwanan origin), a more accurate appraisal of it’s current distribution and
population status within the catchment could be warranted.
Numerous researchers have noted the disjunct distributions of these three afore mentioned species across
northern Australia, although the exact mechanisms behind these distributional anomalies are yet to be
fully explained. A possible contributing factor for some species could be the biogeographic consequences
of the formation of a substantial brackish-freshwater inland sea (Lake Carpentaria) in a depression in the
present day Gulf of Carpentaria some 70,000-100,000 years BP (Torgensen et al., 1985). Subsequent sea
level changes and physiographic events appear to support at least to some extent the current distribution
of some fish species such as the saratoga in the Fly River (PNG) and some Gulf of Carpentaria drainages
(Herbert et al., 1995). Hogan & Vallance (2005) recently documented the presence of Neil’s Grunter
(Scortum neili) from the Nicholson-Gregory catchment, although this record is yet to be conclusively
confirmed. The possible presence of this uncommon species, previously known only from the Victoria
River system in the Northern Territory would also be a significant discovery if verified.
A recent, definitive overview of the conservation status of freshwater fish in Queensland is unfortunately
lacking. According to Wager (1993) most species in the Nicholson-Gregory system have common/secure
status, with little conservation concern. A number of species were given indeterminate, uncertain or
restricted status, but many of these designations may be more a reflection of distributional uncertainties
at the time of that publication, rather than any genuine conservation significance. Given there still exists
considerable uncertainty over the taxonomy and systematics of many fish taxa (i.e. the terapontid
grunters) as well as substantial gaps in many species’ distributional data, a revision of the conservation
status of fish species across northern Australia may occur at some point in the future (or would certainly
be desirable). On the basis of current data at least, most species thus far recorded from the catchment
would probably elicit minimal conservation attention.
One species of some note that has remained unrecorded in fish surveys within the catchment is the
freshwater sawfish (Pristis microdon), the largest freshwater ‘fish’ in Australia and a species listed as
Vulnerable under the Commonwealth EPBC Act and Endangered under the 2000 IUCN Red List of
threatened species. Pogonoski et al. (2002) has recently suggested this species should be ascribed
Critically Endangered conservation status on an Australia-wide basis. While at least 5 species of sawfish
(including the freshwater sawfish) are known in from northern Australian waters (all with conservation
concern), the majority have primarily marine or estuarine habitat preferences, although they may
occasionally enter freshwaters. Pristis microdon however appears to be the most freshwater adapted of
the Australian sawfish species and can apparently breed in freshwater environments (Pogonski et al.,
2002). The species appears confined to upper reaches of estuaries and freshwater drainages and has been
recorded up to 500km upstream of marine environments in some northern Australian rivers (Allen et al.,
Australian Centre for Tropical Freshwater Research
Page 33
2002; Pogonoski et al., 2002). This species is under threat from a number of activities including habitat
degradation through water pollution and habitat loss, but particularly through commercial and
recreational fishing practices where this species is taken as bycatch (Pogonoski et al., 2002). This species
is highly susceptible to entanglement in fishing and trawling nets. A study on the Embley estuary on the
eastern Gulf of Carpentaria revealed Pristis microdon made up ca. 10% of gill net bycatch in the middle
estuary region (Pogonoski et al. 2002). With their large size and unwieldy saw-shaped rostrum, any
instream barrier (including small weirs, dams, road culverts) may impede their movement through
watercourses and limit distributions (Burrows, 2004). Due to their large size and slow reproductive
capacity, these species are particularly susceptible to population declines in the face of this array of
pressures. Freshwater and estuarine habitats of northern Australia appear crucial to the continued survival
of this species (Pogonoski et al. 2002).
While no formal records of sawfish exist from this catchment, numerous reliable anecdotal reports exist
of large specimens of sawfish species occurring well into the freshwater reaches of the NicholsonGregory catchment, including sites such as Lawn Hill Creek at Blue Hole (J. Tait, pers. comm.). The fact
that sawfish species have not yet been recorded in any of the recent fish survey series carried out in the
Nicholson-Gregory catchment is certainly not indicative of localized population decline. The species
while widespread, is naturally uncommon, so its absence from sporadic fish surveys is not necessarily an
issue of great concern. However, given the precarious nature of it’s population status an accurate
assessment of current (or historic) distribution in the catchment would certainly be valuable for
management and conservation planning purposes.
In a similar situation to the freshwater sawfish, a number of additional, poorly known species of
conservation concern such as the giant freshwater whipray (Himantura chaophraya) and various whaler
sharks (i.e. Glyphis sp. A and Glyphis sp. C) could very possibly inhabit the brackish-freshwater reaches
of the Nicholson-Gregory catchment. The freshwater whipray is a bottom-dweller whose abundance and
distribution is unclear. It has been recorded from estuaries and freshwater reaches of a number of large
rivers in northern Australia (Allen et al. 2002) and also occurs throughout south-east Asian waters. This
species is vulnerable to fishing as both prey and bycatch, drought and movement barriers. It has been
listed as Vulnerable under the 2000 IUCN Red List of threatened species (Critically Endangered in
Thailand). The various Glyphis species (river whaler sharks) are piscivores adapted to hunting in cloudy
estuarine and river waters. These species can be easily confused with the more common Bull Shark,
Carcharinus leucas, which occurs in the same habitat and possibly occupy similar ranges during certain
life cycle stages. These species are threatened by recreational line fishing, gill netting and habitat
degradation (DEH, 2004). Glyphis sp. A is listed as Critically Endangered under the Commonwealth
EPBC Act 1999 and has also been nominated for listing as Endangered under the Qld. Nature
Conservation Act. Glyphis sp. C is currently listed as Endangered under the EPBC Act.
7.4
Habitat Condition
There were a number of disturbances associated with the condition of riparian zones on watercourses
throughout the region, these however will be discussed in more detail in the riparian vegetation section of
this report (Section 8). The importance of the integrity of riparian vegetation to freshwater fish
communities (and aquatic ecosystems as a whole) should not be under-estimated (see Pusey &
Arthington, 2004). One of the more significant disturbances noted as relevant to actual instream aquatic
habitats in the Nicholson-Gregory fish survey sites were associated with feral pigs and cattle access to
waterholes. These effects tended to be far greater in the shallower, seasonal wetlands, where broad-scale
cattle and pig access to littoral margins greatly increases turbidity, and likely also causes substantial
nutrient enrichment. The effects of stock access on adjacent bank erosion and instream turbidity in the
more seasonal and semi-permanent wetlands in the catchment have been noted on other occasions
(Leggett & Byron, 1998). The nutrient enrichment associated with increased turbidity and cattle and pig
defecation also has implications for algal blooms and their associated effects on water quality. The
propensity of feral pigs to root and forage for bulbs and rhizomes of aquatic macrophtyes and possibly
freshwater mussels is another concerning impact for many local wetlands. Evidence of feral pigs
methodically rooting up the margins of lagoons as waters receded with progression of the dry season was
readily apparent at several sites including several not surveyed for fish (Pelican Waterhole, Bluebush
Swamp, Pandanus Waterhole etc.). The depth of water in which pigs were actually observed foraging at
Australian Centre for Tropical Freshwater Research
Page 34
some sites can be quite significant (see Figures 1 & 2). Impacts on aquatic macrophtye communities and
increased turbidity could be expected to have considerable repercussions for local fish communities.
Figures 1 & 2
Feral boar (Sus scrofa), foraging on instream macrophyte communities at
Pandanus Waterhole
Along the perennial systems such as Lawn Hill Creek and the Gregory River, in-stream habitats appeared
for the most part to be virtually un-impacted and in near pristine condition. Disturbances caused by pig
foraging and cattle access was occasionally observed in littoral margins of these perennial watercourses
where access permitted and some of the shallower sections of braided stream reaches. The periodic
division of flows producing shallower, multiple flow paths that occurs in some perennial systems upon
the Gulf plains may possibly increase potential for impacts from stock access and feral pig activity
compared to that experienced on the larger single channels of these systems in higher reaches. However,
pig and cattle associated impacts generally seemed to be greater in the riparian zone on higher levees
rather than within aquatic habitats themselves. The typical morphometry of these perennial stream
Australian Centre for Tropical Freshwater Research
Page 35
channels may play a part in the relative levels of disturbance received. The wetted stream width of
considerable lengths of Lawn Hill Creek and the Gregory River is characterised by steeply incised, ‘Ushaped’ channels which often descend quite abruptly into deep water. This cross sectional profile, the
relatively constant water levels as well as quite substantial riparian vegetation on the water’s edge (i.e.
stands of Pandanus aquaticus) may inhibit broad scale instream access by both cattle and pigs to the
same extent seen in the shallower, more seasonal wetland environments.
Other minor disturbances included some road crossings which were observed to result in increased
downstream turbidity and sedimentation after vehicle passage. A number of camping areas near crossings
are heavily patronised by tourists and associated practices such as the use of soaps and detergents and
cleaning of vehicles within streams could have some impacts, particularly during peak visitation periods,
but effects would be expected to be localised.
Hydrologic connectivity in the sense of the capacity for fish movement both longitudinally (up and
downstream) and laterally (from the river channel to floodplains) throughout a catchment is one of the
most important determinants of fish community structure and an important indicator of fish community
health (as well as ecosystem health in general). The local stream systems in the Nicholson-Gregory
catchment would certainly provide vital life-cycle linkages for aquatic fauna such as barramundi (Lates
calcarifer) and the giant freshwater prawn or cherabin (Macrobrachium rosenbergii), both species whose
lifecycle and recruitment involves pronounced movement from marine to freshwater conditions. Many
solely freshwater fish also undergo considerable movements within a catchment on a seasonal basis and
at different stages of their life history (Bishop & Forbes, 1991).
The flat topography of much of the Nicholson-Gregory catchment means substantial natural barriers to
fish movement are few and migratory species such as barramundi can penetrate inland freshwaters for a
considerable distance (well over 200km in the case of the Gregory River). Significant man-made barriers
are also presently rare, but the size and location rather than the sheer numbers of barriers can have far
reaching repercussions for fish fauna. The Doomadgee Weir on the Nicholson River and the Escott Weir
on the Gregory River represent the two impoundment barriers within the catchment which likely have the
greatest potential for greatest negative impacts upon fish movement. Hogan & Vallance (2005) note these
particular structures have not apparently prevented upstream movement of species such as barramundi.
While available data supports the notion that barramundi can certainly still move up through these
systems to some degree (and this may well depend on certain specific flow conditions now being met),
the specific ecological effects of these structures remain largely unknown. The exact magnitude of
impacts, if any, across a broader suite of species is also difficult to gauge on the basis of currently sparse
information. A number of the rare studies of fish movement in northern Australia have revealed different
species migrate under different flow conditions and low-flow migration or movement by many species
should not be discounted when considering this issue. It is also worth noting that numerous small road
crossings and culverts are also scattered throughout the catchment. While seemingly innocuous, these
smaller structures may also impede fish passage at low flows, although most are drowned out during
reasonable flood events. Impacts on fish populations due to these smaller movement barriers are also
uncertain, but would seem relatively minimal for the most part.
7.4.1
Introduced Fish Species
The Southern Gulf catchments in general have thus far apparently avoided any notable broad-scale exotic
fish incursions. None of the fish surveys conducted within the Nicholson-Gregory catchment that were
accessed during compilation of this report have as yet recorded the presence of any of the common
introduced pest fish species such as the mosquitofish (Gambusia holbrooki) or the various cichlids such
as tilapia (Oreochromis mossambicus, Tilapia mariae etc.) that are prominent and successful invaders of
many of northern Australia’s river systems (see Arthington, 1991). However two recent publications
(Allen et al., 2002 and Pusey et al., 2004) have both reported the mosquitofish (Gambusia holbrooki) as
occurring within the Nicholson catchment. Communication with relevant authors however failed to reveal
any relevant context as to the actual origin (e.g. where, when and who made the initial discovery) which
does cast some degree of doubt over the resultant veracity of this record. Whether this record represents
genuine documentation of a successful feral establishment within the catchment or is simply one of the
periodic mistakes that occasionally crop up (and consequently often perpetuate) in fish distribution
Australian Centre for Tropical Freshwater Research
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records is presently unknown. Gambusia are a small, often very cryptic species that can be easily
overlooked for example in typical electro-fishing surveys. It’s absence from recent fish survey work is
therefore unfortunately not necessarily indicative of actual absence from the catchment and information
of current distribution and abundance, if any, is completely lacking. The fact that a noxious fish could
possibly have established in a catchment far outside the primary distribution of the species (i.e. eastern
Queensland and much of NSW and Victoria) highlights the ease of spread and the very real threats posed
to Gulf catchments by non-native species. If in fact the species does occur, it was quite probably the well
intentioned, but ultimately misguided efforts of local people who deliberately or accidentally facilitated
spread of this noxious fish species.
Passive and active anthropogenic translocations, inter-basin water transfers for irrigation purposes and
flood linkage of watersheds all represent potential avenues for exotic fish (as well as native Australian
species not indigenous to Gulf catchments) incursions into the Southern Gulf. The recent furore
associated with the discovery of a tilapia introduction into the massive Burdekin River catchment in
northern Queensland underscores the need for continual vigilance regarding this threat (see Courier Mail
19th Feb. 2005, Burrows, 2005). The possible consequences of this pest species’ occurrence in Burdekin
River tributaries are yet to be realized but could be collectively massive from both environmental and
economic perspectives. A notable feature of the Gulf of Carpentaria drainage division as a whole is it’s
relatively flat topography and the resultant inter-mingling of floodwaters from many of the larger
catchment systems during wet season flood events. Such drainage linkage has been identified as an
efficient mechanism for the potential rapid dispersal of exotic species such as tilapia across the drainages
of northern Australia (Russell et al., 2003). Wet season catchment linkage and the fact that introduced
pest species such as tilapia are naturally tolerant of relatively brackish water quality conditions may see
inevitable dispersal of some exotic species via ‘creek hopping’ during floods should they ever become
established in any Southern Gulf drainages.
The cross-catchment dispersal of exotic fish species via inter-basin irrigation water transfers from east
coast, Wet-Tropics catchments to the drainages of the Gulf of Carpentaria has in particular been
identified as a management issue of particular relevance to Southern Gulf drainages. Irrigation water
transfers from the Barron River catchment to the Upper Walsh River have been implicated in the
presence of guppy (Poecilia reticulata) in some northern Gulf drainages and concerns exist tilapia and
other pest species could spread via the same mechanism (Ryan et al., 2002; Russell et al., 2003). It has
also been suggested low-lying land between the headwaters of the upper Mitchell and the Barron Rivers
are subject to inundation during floods, a process providing occasional catchment linkage. Available data
on fish distributions however does not suggest this is actually a major fish movement pathway.
Public education regarding dangers associated with transferring fish between catchments may be an issue
paramount in minimizing the risks of invasion of Southern Gulf catchments. Non-native fishes escaping
or being released from home aquaria or being actively stocked into farms dams are not uncommon
practices that can facilitate dispersal of exotic species into previously pest-free catchments. Anecdotal
reports also exist regarding the concerning habit of recreational fishers transporting pest species such as
tilapia from Wet-Tropics drainages for use as live bait when fishing for barramundi in Gulf catchments.
Escapees from such practices could quite possibly allow pest species to establish a foothold for
subsequent dispersal throughout the Southern Gulf.
The likely ecological impact of exotic fish establishment should it occur in the Nicholson-Gregory
catchment is difficult to predict. Successful establishment of self-sustaining feral populations of nonnative fishes varies widely between regions and is usually dependent on factors such as existing fish
diversity, levels of resource competition and the degree of anthropogenic disturbance in the environment
(Russell et al., 2003). Resource competition (perhaps mediated by interference and aggression),
predation on the eggs and fry of native fish and to a lesser extent introduction of parasites and pathogens
represent just some of the possible impacts of exotic fishes on native ecosystems (Arthington, 1991). The
decline of indigenous fishes in association with introduction of exotic fish species has most often
occurred in polluted environments or habitats experiencing significant disturbances such as hydrologic
alteration (Arthington, 1991; Bunn & Arthington, 2002). These habitat disturbances are thought to
enhance the competitive ability of introduced species whose typical ecological traits such as habitat
generalism and trophic plasticity makes them better able to exploit such altered environments.
Australian Centre for Tropical Freshwater Research
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7.4.2
Recreational Fishing
Bishop & Forbes (1991) noted that the effective management of biological resources requires a sound
knowledge of the factors which influence the population dynamics of species in question. As has been
continually reiterated throughout this report, knowledge of what species actually occur in various
northern Australian riverine catchments, let alone the factors driving population dynamics and resultant
abundance cycles remains patchy at best. For these (and other) reasons, the effects of recreational fishing
on freshwater fish stocks in Australia remain virtually unknown. The ease of capture of many of the
commonly targeted recreational fish species in northern freshwater systems (sooty grunter, catfish etc.) is
notable, in turn making these fish species vulnerable to localized overexploitation. Notable resident
species of the Gregory-Lawn Hill catchment such as saratoga may also be vulnerable to over-fishing in
localized stretches of rivers due to their slow breeding habits and susceptibility to lures (see Herbert et
al., 1995; Allen et al., 2002).
While a poorly studied issue, concerns over the effects of recreational fishing in northern Australian
freshwater ecosystems have been raised on several occasions. Improved vehicular access to escarpment
dry season refuge habitats in the Northern Territory has been noted as introducing a vulnerability factor
to aquatic ecosystems through over-fishing of pre-spawning refuge populations (Bishop & Forbes, 1991).
Long-term monitoring by Pusey (2004) in the upper Burdekin catchment noted changes in the population
structure of the popular recreationally targeted species the sooty grunter (H. fuliginosus) at certain
localities, including decreased numbers of both adult and juvenile fish. It was suggested the low numbers
of mature adults in the area may have resulted in failed juvenile recruitment, in spite of apparently
favorable recent breeding conditions. The area is a popular camping and recreation destination which
receives significant levels of tourist visitation at certain times. Although not rigorously explored,
anecdotal evidence of quite intense fishing pressure from recreational anglers in some locations was
proposed as a plausible contributing factor.
While the recreational fishing scenario may be slightly different for the perennial systems of the
Nicholson-Gregory catchment, an analogous situation could conceivably develop. The vastly improving
road networks throughout the region, rising tourist visitation rates and concomitant fishing pressure
increases raise some concerns from this perspective. While fishing pressure could be anticipated to be
localised around certain points and significant areas of the catchment are inaccessible for several reasons,
substantial stretches of Lawn Hill Creek and the Gregory River are nonetheless readily accessible to
tourists and locals alike. Evidence of illegal use of gill nets in the freshwater systems of the catchment
was also observed several sites during the 2004 fish surveys (see Figure 3). A number of local
landholders voiced concerns over the apparent frequency of illegal netting, a practice which obviously
has considerable ramifications for the long-term integrity of aquatic ecosystems.
Another point particularly relevant to fisheries/aquatic ecosystem health is the need for whole of
catchment approaches to resource management, especially when dealing with migratory fish species such
as barramundi. The status of freshwater populations is inextricably linked to ‘wet season’ spawning
populations in downstream estuaries and coastal environments (and vice versa). The cumulative effects of
fishing effort, both in upstream and downstream reaches of the catchment, movement barriers and other
impacts is not to be discounted and could place populations under some duress.
Australian Centre for Tropical Freshwater Research
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Figure 3
7.4.3
Gill-net on creek bank, Lawn Hill Creek catchment
Fish Kills
Fish kills are a frequent occurrence in the wetland environments of northern Australia. While fish kills in
the perennial watercourses of the Nicholson-Gregory catchment are an apparently rare event, they are not
unheard of. McIlwaine (2002) reported a fish kill occurring in Lawn Hill Creek in August 2002.
Documentation of this event was prompted by reports from local residents of fish populations being
observed ‘gulping’ air at the water surface, with a number of fish deaths reported, including barramundi
(Lates calcarifer) and catfish species (Arius leptaspis). Autopsy of a single barramundi specimen
collected at the site apparently suggested starvation or inappropriate diet as the likely cause of mortality.
McIlwaine (2002) proposed the poor preceding wet season may have resulted in depleted food resources
for fish populations in the subsequent dry season, thereby attributing to fish deaths.
The spatial and temporal unpredictability and remoteness of fish kills in northern Australia has largely
limited their detailed investigation. While occurring in billabongs and riverine environments throughout
the year in the wet-dry tropics, fish kills are most common during the transition period from dry to wet
season, usually between October and January (Townsend et al., 1992). It is at this time fish tend to be
most stressed by from deteriorating environmental conditions and when they are most exposed to
terrestrial toxicants associated with first flush flows of early wet season rainfall. A range of factors have
been proposed for these natural events including low dissolved oxygen resulting from the high oxygen
demand of organically loaded inflows (Townsend et al., 1992). Elevated aquatic biotoxins (i.e.
aluminium) associated with natural acid water runoff has also been proposed as a major contributor to
some fish kills (Bishop & Forbes, 1991). The leaching of soluble ichthyocidal compounds (natural fish
poisons) such as saponins from vegetation surrounding watercourses during the first wet-season rains is
yet another factor proposed to induce fish kills (Bishop & Forbes, 1991). Interestingly, these authors
noted nearly 70 species of plants have been used as ichthyocides in the subsistence hunting of Aboriginal
people in northern Australia. No universal explanation exists for fish kills and a complex array of
interactive factors may play a role.
With regard to the Lawn Hill Creek fish kill episode, while poor recruitment of fodder fish resulting from
a failed preceding wet season may have placed some stress on local fish populations and been a
contributing factor to the event, whether poor diet was the sole cause is debatable. The acute nature of the
Australian Centre for Tropical Freshwater Research
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event, the multiple species effected and reports of fish ‘gulping air’ at the water’s surface suggest low
dissolved oxygen may also have played a substantial if not dominant role. Given the anecdotal reports of
a ‘cold snap’ in the weather leading up to this event, a thermocline inversion of a deep, instream
waterbody bringing anoxic water to the surface (or some similar oxygen depleting process) could also be
another possibility.
7.5
Conclusions
The information outlined in this report provides baseline data as to the basic characteristics of the
Nicholson-Gregory fish fauna as a whole, as well as data relating to fish assemblage structure at specific
sites within the Gregory River-Lawn Hill Creek catchment. As previously touched upon however, a rapid
assessment such as this employing a single sampling occasion (and a single sampling technique) has an
array of associated shortcomings. While this study has touched upon some issues, carefully designed
surveys with specific aims are needed to provide insight into critical issues relevant to management such
as species distribution patterns throughout the catchment or identification of vital habitats at a landscape
scale such as refuges or nurseries. These results should therefore be regarded as representing a starting
point for the assessment and monitoring of the catchment’s fish fauna. Repeated sampling at a range of
judiciously selected locations and at different times of the year would be required to gain a more robust
dataset regarding fish community structure throughout the catchment.
It also worth noting that information based solely on species presence and distribution alone may not be
adequate to usefully assess the potential effects of any proposed future developments in the region on the
resident fish fauna. Background information on the environmental requirements, trophic ecology, life
histories and general biology of fish, information usually conspicuously absent across northern Australia,
is required for this purpose (sensu Bishop, 2001). Research into ecology at this level similarly requires
long-term study at carefully selected sampling sites.
Given the typically sporadic survey attention the catchment currently receives, landholders and other
local residents can often supply informative qualitative data regarding the resident aquatic fauna. Local
knowledge can therefore yield valuable additional information on what is still essentially a poorly known
fish assemblage. During the course of this 2004 survey, local knowledge, particularly from indigenous
residents (who often have long standing familiarity with fish fauna at some sites) was very useful in
accurately suggesting areas where some of the less common species such as freshwater anchovy Thryssa
scratchleyi could be found. Local knowledge also identified fish species which while not collected during
2004 ACTFR surveys, were subsequently found to have been recorded when collective survey effort in
the catchment was collated (i.e. the giant glassfish Parambassis gulliveri). With regard to the utility of
anecdotal evidence, local information for example could be useful in describing past and current
distributions of poorly known species of conservation concern such as the freshwater sawfish. Given that
the distinctive physical morphology of sawfish species makes even non-specialist misidentification
unlikely, a study collating anecdotal information from local residents regarding sawfish distribution
within the catchment could be a worthwhile endeavor.
Australian Centre for Tropical Freshwater Research
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8.0
RIPARIAN VEGETATION (John Dowe)
8.1
Introduction
Riparian zones are well recognized as keystone areas of biological, physical and chemical interaction
between terrestrial and aquatic ecosystems, and have a high biodiversity in relation to surrounding
landscapes. The linear riparian vegetation systems associated with major creeks and rivers of the Gregory
catchment provide important habitats and movement corridors for many plant and animal species in what
is essentially an arid and sparsely vegetated country (Dames & Moore 1994; Environment North 1999).
Many locally occurring species are essentially restricted to riparian areas, including birds such as the
Purple Crowned Fairy Wren and Crimson Finch. Seasonal migrants such as the Dollarbird, Torresian
Imperial Pigeon and Common Koel may also depend upon these riparian systems as a dispersal conduit
into the interior (Dames & Moore, 1994). The riparian fringes and permanent waters also represent a
refuge for terrestrial fauna during both the dry season, and also during flood events when they may be the
highest feature not inundated on a floodplain.
The riparian zone is important to the functioning and integrity of instream aquatic environments.
Mediation occurs through the function of terrestrial inputs, light and thermal regulation, nutrient
interception and release, maintenance of bank stability and provision of a variety of habitat types and
refugium (Naiman & Decamps 1997). As a simple example of the value of riparian zones to aquatic
ecosystems, the direct consumption of terrestrial materials by aquatic organisms has been documented for
many of the species inhabiting the Gregory catchment. Local fish species such as the sooty grunter
(Hephaestus fuliginosus) are well known for their propensity for congregating and feeding below fruiting
cluster figs (Ficus racemosa) and Leichhardt trees (Nauclea orientalis). This consumption of fruit by
many Australian freshwater fish is apparently common (see Pusey & Arthington, 2004).
Food of terrestrial origin such as leaves and fruit has also been documented as a significant dietary
component for many of northern Australia’s freshwater turtle species (Kennett & Tory 1996; White
1999). The flowers, fruit leaves and bark of streamside plants such as Melaleuca spp. (Paperbark),
Pandanus spp. and Ficus spp. (Figs) all may be dietary resources of turtle species throughout the Gregory
catchment (White 1999). Figs may be such an important dietary component for the highly frugivorous
Gulf Snapping Turtle (Elseya lavarackorum), that the presence of riparian fig trees has in fact been
suggested as a potential limiting factor in the distribution of this species in the Gregory catchment (White
1999). While not proven, associated dispersal of riparian seeds by frugivorous aquatic species has been
suggested as a related ecosystem function, and may be a plausible mechanism for upstream dispersal of
riparian plants (Kennett & Tory 1996). The linkages between the riparian and instream habitats provide
maintenance of fundamental and long-term function and composition of these ecosystems.
The vegetation within the Gregory River catchment is predominantly eucalypt woodland and open
forests, with areas of grasslands, gidgee scrubs, and freshwater and estuarine wetlands (Blackman et
al.1996). Vegetation surveys have been provided for the Lawn Hill Creek area within the Lawn Hill
National Park (Bean 1992), and for pasture lands (Tothill and Gillies 1992). Plant identification books for
north-west Queensland that are relevant to the Gregory River catchment are available (Milson 2000a,
2000b). The condition of the vegetation of the catchment, for the most part, was summarised as
‘unchanged since settlement’ except for the replacement of Tussock Grassland by Open Tussock
Grassland of Astrebla [Mitchell Grass] (Department of Primary Industries 1993). A brief account of
riverine vegetation was provided on the Australian Heritage Database (2004), which also listed at least
two species for the bioregion that are rare in Queensland, Cycas brunnea (Cycadaceae) and Brachychiton
collinus (Sterculiaceae), but neither of these species are associated with the riparian zone.
The aim of this survey was to provide baseline data on the floristic composition, structure, and
reproductive regime of the riparian vegetation for selected water courses within the Gregory River
catchment, downstream from Adels Grove on Lawn Hill Creek, downstream of The Knob on Gregory
Australian Centre for Tropical Freshwater Research
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River, and to as far downstream on tributaries to the confluence of Albert River and Beames Brook. As
the survey was conducted during August, the results reflect the dry season condition of the riparian zone.
8.2
Methods
The sites surveyed and GPS readings are listed in Table 8 and indicated on Figure 4. Surveys were
conducted between 10-16 August 2004, which is the dry season in that area. Data collection utilised the
Tropical Rapid Assessment of Riparian Condition (TRARC) pro formae. The TRARC method records
data on stream morphology; status of fencing; cattle and/or feral animal activities; the dominant trees and
deleterious weeds and their population structures; the presence of additional weeds; dominant grasses;
species within the understorey; percentage covers of standing dead vegetation, canopy, understorey,
debris, and bare ground. Surveys were based on a 100 m x 5-20 m transect at each site, placed parallel to
the stream edge, with the ultimate width of the transect being dependent on the width of the riparian zone
[not less than 5 m, and not greater than 20 m]. GPS readings were taken at the centre [50 m point] of the
transect. The TRARC method allows the ecological characteristics of a site to be scored and comparative
scores between sites to be determined. The higher the score the greater the ecological health of a site.
Although the TRARC method was used in data collection, scores are provided only as a guide, on the
rational that these surveys are intended to provide base data and not an appraisal of the ‘ecological health’
of the sites per se: the TRARC scores are therefore listed but will not be discussed further in this report.
However, data from the TRARC method can also be used to analyse species distribution, abundances and
population structure, which was the object of this study.
Table 8. Study site names and GPS readings of riparian vegetation survey sites in the Gregory River
catchment, conducted 10-16 August 2004.
watercourse
Gregory River
Beames Brook
Lawn Hill Creek
Running Creek
One Mile Creek
Elizabeth Creek
location
The Knob
Six Mile
Gregory Downs
Gregory Downs (Planet Downs)
Tirranna
Brinawa crossing
downstream of Black Gully jnt
Brookdale
upstream of Albert River jnt
Big Lagoon
Lawn Hill Station
Bluewater Waterhole crossing
road to Almora
Brinawa/Punjaub road
Punjaub road crossing
Australian Centre for Tropical Freshwater Research
GPS
S18° 54’ 22.1”, E138° 58’ 58.5”
S18° 43’ 19.6”, E139° 11’ 19.8”
S18° 38’ 39.3”, E139° 15’ 07.7”
S18° 29’ 52.6”, E139° 17’ 17.1”
S17° 53’ 39.0”, E139° 17’ 07.5”
S18° 09’ 56.6”, E139° 14’ 22.0”
S18° 09’ 08.3”, E139° 14’ 56.2”
S18° 03’ 50.2”, E139° 15’ 47.4”
S17° 52’ 47.8”, E139° 20’ 28.4”
S18° 41’ 01.5”, E138° 32’ 19.5”
S18° 34’ 24.5”, E138° 34’ 58.7”
S18° 04’ 18.1”, E138° 54’ 13.4”
S18° 19’ 27.6”, E139° 15’ 51.5”
S18° 09’ 42.1”, E139° 13’ 35.8”
S18° 03’ 55.5”, E138° 54’ 22.8”
Page 42
Figure 4: Study sites of riparian vegetation surveys in the Gregory River catchment, conducted 10-16
August 2004.
8.3
Results
Altitude readings, and channel and riparian zone widths are presented in Table 9. Sixteen species of trees
and shrubs were recorded as being a part of the dominant component of vegetation in the riparian zone
(Table 10). The six most common tree species, each present at 40% or more of sites were, in order of
decreasing occurrence, Melaleuca leucadendra, Nauclea orientalis, Pandanus spiralis, Ficus racemosa,
Livistona rigida and Terminalia canescens (Figure 5). Distribution maps of these species are presented in
Figure 6. A further four species were present in 13-27% of sites whilst seven species were present in only
one site each. A summary of the abundance, percentage cover, size and degree of regeneration of
Melaleuca leucadendra, the most dominant tree species, is provided in Table 11, and a summary of
population structure is presented in Table 12.
Table 9. Study site names, altitude readings*, channel widths and riparian zone widths at the Gregory
River catchment sites, 10-16 Aug. 2004.
*altitude readings taken with GPS may have ± 50 m variation from true height above sea-level, and must
be used with caution.
1
median ratio of channel width: riparian zone width is 0.7 for the 15 sites.
watercourse
Gregory River
Beames Brook
location
The Knob
Six Mile
Gregory Downs
Gregory Downs Station
Tirranna
Brinawa crossing
Australian Centre for Tropical Freshwater Research
altitude
97 m
68 m
72 m
54 m
17 m
48 m
channel
width1
10 m
15 m
8m
10 m
3m
3m
riparian
width1
15 m
20 m
20 m
15 m
8m
10 m
Page 43
Lawn Hill Creek
Running Creek
One Mile Creek
Elizabeth Creek
downstream of Black Gully jnt
Brookdale
upstream of Albert River jnt
Big Lagoon
Lawn Hill Station
Bluewater Waterhole crossing
road to Almora
Brinawa/Punjaub road
Punjaub road crossing
46 m
32 m
14 m
119 m
75 m
9m
54 m
52 m
46 m
3m
7m
4m
12 m
15 m
4m
4m
5m
5m
8m
7m
8m
7m
10 m
7m
7m
8m
7m
Table 10: Dominant tree and shrub species in the riparian zone of 15 study sites in the Gregory River
catchment, recorded in 100 m x 5-20 m transects, parallel to stream edge, 10-16 August 2004.
species
# sites [n=15]
%cover
status
where species
at all
was present
sites
14
41.3
dominant
Melaleuca leucadendra
9
7
rare-occasional
Nauclea orientalis
7
16.3
frequent-dominant
Pandanus spiralis
6
7
rare-occasional
Ficus racemosa
6
4.7
rare-frequent
Livistona rigida
4
2.4
rare-occasional
Terminalia canescens
4
<2
frequent-dominant
Excoecaria parvifolia
2
<2
rare-frequent
Casuarina
cunninghamiana
2
<2
dominant
Vitex acuminata
1
<2
rare
Melaleuca bracteata
1
<2
occasional
Lysiphyllum
cunninghamii
1
<2
occasional
Corymbia bella
Corymbia sp.
1
<2
occasional
1
<2
frequent
Acacia torulosa
1
<2
dominant
Lophostemon
grandiflorus
1
3.3
dominant
Melaleuca argentea
Australian Centre for Tropical Freshwater Research
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4.7
Livistona rigida
2.4
Terminalia canescens
7
Ficus racemosa
Nauclea orientalis
7
Melaleuca leucadendra
41.3
Pandanus spiralis
16.3
Figure 5: The six most dominant tree species and their total percent cover in the riparian zone of 15
study sites in the Gregory River catchment, recorded in 100 m x 5-20 m transects, parallel to stream edge,
10-16 August 2004.
Australian Centre for Tropical Freshwater Research
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Figure 6. Distribution maps of the six most dominant tree species in the Gregory River catchment
riparian study. Top left: Melaleuca leucadendra. Top right: Pandanus spiralis. Centre left: Nauclea
orientalis. Centre right: Ficus racemosa. Bottom left: Livistona rigida. Bottow right: Terminalia
canescens.
Australian Centre for Tropical Freshwater Research
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Table 11. Abundance of large Melaleuca spp. in 15 study sites in the riparian zone of Gregory River
catchment, presented in decreasing number of mature individuals, recorded in 100 m x 5-20 m transects,
parallel to stream edge, 10-16 August 2004. Degree of regeneration was estimated by the presence of
class sizes in addition to mature individuals: 0 class sizes = absent; 1 class size = occasional; 2 class sizes
= frequent; 3 class sizes = abundant.
* = Melaleuca argentea; all others Melaleuca leucadendra.
study site
Beames Brook,
upstream of Albert
R jnt
Gregory R, The
Knob
Gregory R, Six
Mile
Lawn Hill Ck,
Lawn Hill Stn
Gregory R, Gregory
Downs
Beames Brook,
downstream of
Black Gully jnt
Gregory R, Planet
Downs
Running Ck
Beames Brook,
Brinawa crossing
Beames Brook,
Brookdale
*Elizabeth Ck
Gregory R,
Tirranna
One Mile Ck
Lawn Hill Ck, Big
Lagoon
Bluewater
Waterhole crossing
#individuals
42
%cover
70
size range
8-10 m
34
60
14-16 m
30
70
22
55
14-15 m
frequent
18
40
9-12 m
frequent
18
60
7-10 m
occasional
15
40
10-14 m
occasional
12
12
40
40
10-11 m
8-10 m
absent
occasional
12
30
10-11 m
absent
11
11
50
20
4-7 m
10-12 m
frequent
occasional
8
8
30
20
5-7 m
10-11 m
absent
occasional
5
25
7-8 m
occasional
Australian Centre for Tropical Freshwater Research
degree of regeneration
absent
occasional
frequent
Page 47
Table 12: Population structure of large Melaleuca spp. [M. leucadendra and *M. argentea] in the
Gregory River catchment, in the riparian zone of 15 study sites in the Gregory River catchment, recorded
in 100 m x 5-20 m transects, parallel to stream edge, 10-16 August 2004, arranged in descending order of
degree of regeneration based on the total number of individuals in class sizes.
location
*Elizabeth Ck
Gregory R, Six Mile
Lawn Hill Ck, Lawn Hill Stn
Gregory R, Gregory Downs
Gregory R, The Knob
Beames Brook, downstream of
Black Gully jnt
Gregory R, Planet Downs
Beames Brook, Brinawa
crossing
Gregory R, Tirranna
Lawn Hill Ck, Big Lagoon
Bluewater Waterhole crossing
Beames Brook, upstream
Albert R jnt
Beames Brook, Brookdale
Running Ck
One Mile Ck
# mature
11
30
22
18
34
18
# subadults
18
14
4
2
20
1
# saplings
30
6
18
4
0
0
# seedlings
0
0
0
0
0
0
15
12
4
0
0
2
0
0
11
8
5
42
1
0
0
0
0
35
100
0
0
0
0
0
12
12
8
0
0
0
0
0
0
0
0
0
Of the primary deleterious weeds associated with the riparian zones in rivers within the wet/dry tropics of
northern Queensland, only Cryptostegia grandiflora (rubber vine) was present, and only at six sites three on Beames Brook and in close proximity to each other; two sites on the Gregory River; and the
Running Creek site. A summary of the presence, the abundance, and number of host trees is presented in
Table 13, and a distribution map is presented in Figure 7.
Table 13: Presence and abundance of Cryptostegia grandiflora (rubber vine) in the Gregory River
catchment riparian vegetation study sites, presented in decreasing number of mature individuals recorded
in the riparian zone of 15 study sites in the Gregory River catchment, recorded in 100 m x 5-20 m
transects, parallel to stream edge, 10-16 August 2004.
study site
Beames Brook,
Brinawa crossing
Gregory R, Six Mile
Beames Brook,
Brookdale
Running Ck
Beames Brook,
downstream of Black
Gully jnt
Gregory R, Gregory
Downs
# mature individuals
40
% cover
5
# host trees
10
14
4
5
5
6
4
4
1
1
1
0
0
1
1
0
Australian Centre for Tropical Freshwater Research
Page 48
Figure 7: Distribution map of Cryptostegia grandiflora, Rubber vine, in the Gregory River catchment,
recorded 10-16 August 2004.
A list of non-deleterious weeds is presented in Table 14, and a list of all species recorded in the riparian
zone is presented in Appendix 2.
Table 14: Non-deleterious weed species in the riparian zone of 15 study sites in the Gregory River
catchment, recorded in 100 m x 5-20 m transects, parallel to stream edge, 10-16 August 2004.
species
Achyranthes aspera
Calytropis procera
Cardiospermum halicacabum
Xanthium occidentale
Australian Centre for Tropical Freshwater Research
sites present
Gregory R, camping site at Gregory Downs
(n=1)
Gregory R, Six Mile; Gregory R, Gregory Downs Station
(n=2)
Gregory R, Gregory Downs Station
(n=1)
Gregory R, The Knob; Gregory R, Six Mile; Gregory Rr,
camping site at Gregory Downs; Gregory R, Gregory
Downs Station; Gregory R near Tirranna Roadhouse;
Beames Brook, Brookdale; Beames Brook, upstream of
Albert R junction; Lawn Hill Ck, Lawn Hill Station;
Running Ck, Almora Station; One Mile Ck, Punjaub;
Elizabeth Ck, Lawn Hill Station
(n=11)
Page 49
8.4
Summary of Survey Sites
8.4.1
Gregory River - The Knob
Access: Situated about 3 km off the Camooweal-Burketown road, 38 km south of Gregory Downs, where
a well-formed track lead to the river with the site at the end of the track, on the eastern side of the river.
GPS: S18° 54’ 22.1”, E138° 58’ 58.5”; Altitude: 97 m
Geophysical setting: Channel width was 10 m with a perennial flow, the riparian width 15 m, and with a
2 m vertical rise from the water to the transect position. Slumping occurred in 20% of the transect, and
gullying in 5% with two 1 m wide gullies. The stream bed was rocky and the banks were sandy. There
were no fences or waterpoints, and the site had cattle tracks both parallel and perpendicular to the stream
edge.
Transect: Transect was 100 m long by 15 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 34 mature individuals,
14-16 m tall, 20 subadults 6-10 m tall, and cover of 60%. Other significant species included Ficus
racemosa with 10% cover, and Acacia torulosa and Livistona rigida each with 5% cover. Fine woody
debris accounted for 10-29 % of cover and course woody debris for 1-20% of cover. There were no
deleterious weed species. TRARC score was 70.6, a rating of good condition.
Species recorded:
Acacia torulosa
Chrysopogon elongatus
Clerodendrum floribundum
Erythrophleum chlorostachys
Ficus racemosa
8.4.2
Livistona rigida
Melaleuca leucadendra
Vitex acuminata
Xanthium occidentale
Gregory River - Six Mile
Access: Situated about 8 km off the Camooweal-Burketown road 18 km south of Gregory Downs, where
a well-formed track lead to the river where the site was at the end of the track, on the eastern side of the
river. GPS: S18° 43’ 19.6”, E139° 11’ 19.8”; Altitude: 68 m
Geophysical setting: Channel width was 20 m with a perennial flow, the riparian width 35 m, and with a
2 m vertical rise from the water to the transect position. Slumping or gullying did not occur in the
transect. The stream bed was rocky and the banks sandy. There were no fences or waterpoints, and the
site had no identifiable cattle tracks.
Transect: Transect was 100 m long by 20 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 30 mature individuals,
10-12 m tall, 14 subadults 2-3 m tall, 6 saplings 1-1.5 m tall, and cover of 70%. Other significant species
included Pandanus spiralis with 50% cover along the stream edge, and Ficus racemosa, Livistona rigida
and Nauclea orientalis each with 10% cover. Fine woody debris accounted for 30-49% of cover and
course woody debris for 1-20% of cover. The only deleterious weed species was Cryptostegia
grandiflora (rubber vine) with 14 mature individuals of which six were climbing host trees, with 5%
cover. TRARC score was 60.6, a rating of average condition.
Species recorded:
Acacia torulosa
Calytropis procera
Chrysopogon elongatus
Cryptostegia grandiflora
Ficus racemosa
Flueggea virosa subsp. melanthesoides
Australian Centre for Tropical Freshwater Research
Livistona rigida
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Xanthium occidentale
Page 50
8.4.3
Gregory River - Gregory Downs Public Camping Area
Access: Situated on the Gregory River downstream about 500 m from the Gregory Downs/Adels Grove
road bridge crossing, where a well-formed track leads to the river downstream, and the site was near the
end of the track, on the eastern side of the river. GPS: S18° 38’ 39.3”, E139° 15’ 07.7”; Altitude: 72 m
Geophysical setting: Channel width was 20 m with a perennial flow, the riparian width 12 m, and with a
3 m vertical rise from the water to the transect position. Slumping or gullying did not occur in the
transect. The stream bed was rocky and the banks sandy. There were no fences or waterpoints, and the
site had random cattle tracks, although camping sites and human debris were present.
Transect: Transect was 100 m long by 12 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 18 mature individuals,
9-12 m tall, 2 subadults 7-9 m tall, 4 saplings 3-4 m tall, and cover of 40%. Other significant species
included Ficus racemosa also with 40% cover, Pandanus spiralis with 80% cover along the stream edge,
and Nauclea orientalis with 15% cover. Fine woody debris accounted for 10-29 % of cover and course
woody debris for 1-20% of cover. The only deleterious weed species was Cryptostegia grandiflora
(rubber vine) with one mature individual, with 1% cover. TRARC score was 65.3, a rating of average
condition.
Species recorded:
Acacia torulosa
Achyranthes aspera
Calytropis procera
Cryptostegia grandiflora
Ficus racemosa
8.4.4
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Vitex acuminata
Xanthium occidentale
Gregory River - Gregory Downs Station (Planet Downs)
Access: Situated about 1 km downstream from the Gregory Downs Station, where a well-formed track
leads to the river where the site is at the end of the track, on the eastern side of the river downstream of a
water pumping station. GPS: S18° 29’ 52.6”, E139° 17’ 17.1”; Altitude: 54 m
Geophysical setting: Channel width was 10 m with a perennial flow, the riparian width 15 m, and with a
4 m vertical rise from the water to the transect position. Slumping occurred in 10% of the transect, and
there was no gullying. The stream bed was rocky and the banks sandy. There was a fence 100 upstream,
and a pumping station 50 m upstream, that supplied the house, and cattle tracks were parallel to the
stream edge.
Transect: Transect was 100 m long by 15 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra, with 15 mature individuals,
10-14 m tall, 4 subadults 8 m tall, and cover of 40%. Other significant species included Pandanus spiralis
with 40% cover along the stream edge, Ficus racemosa with 15% cover, Livistona rigida with 10% cover
and Nauclea orientalis with 5% cover. Fine woody debris accounted for 10-29 % of cover and course
woody debris for 1-20% of cover. There were no deleterious weed species. TRARC score was 65.6, a
rating of average condition.
Species recorded:
Cardiospermum halicacabum
Chrysopogon oblongatus
Ficus racemosa
Livistona rigida
Australian Centre for Tropical Freshwater Research
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Xanthium occidentale
Page 51
8.4.5
Gregory River – West of Tirranna Roadhouse
Access: Situated about 2 km west of the Tirranna Roadhouse on the Doomadgee/Burketown road, 200 m
upstream of the causeway, on the eastern side of the river. GPS: S17° 53’ 39.0”, E139° 17’ 07.5”;
Altitude: 17 m
Geophysical setting: Channel width was 3 m with a perennial flow, the riparian width 8 m, and with a 2
m vertical rise from the water to the transect position. Slumping occurred in 10% of the transect, and
there was no gullying. The stream bed was rocky and the banks sandy loam. There were no fences or
waterpoints, and cattle tracks ran parallel to the stream.
Transect: Transect was 100 m long by 8 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 11 mature individuals,
10-12 m tall, 1 subadult 7 m tall, and cover of 20%. Other significant species included Casuarina
cunninghamiana and Pandanus spiralis with 20 % cover each, the latter confined to the stream edge, and
Nauclea orientalis and Terminalia canescens each with 15 % cover. Fine woody debris accounted for 3049 % of cover and course woody debris for 1-20% of cover. There were no deleterious weed species.
TRARC score was 70.4, a rating of good condition.
Species recorded:
Atalaya hemiglauca
Casuarina cunninghamiana
Chrysopogon oblongatus
Crotalaria novae-hollandiae
Excoecaria parvifolia
Imperata cylindrica
Melaleuca leucadendra
8.4.6
Nauclea orientalis
Pandanus spiralis
Senna sp.
Terminalia canescens
Vitex acuminata
Xanthium occidentale
Beames Brook - Brinawa Crossing
Access: Situated about 0.6 km west of Brinawa homestead on the Brinawa/Punjaub road, 200 m
upstream from the crossing, on the eastern side of the stream.
GPS: S18° 09’ 56.6”, E139° 14’ 22.0”; Altitude: 48 m
Geophysical setting: Channel width was 3 m with a perennial flow, the riparian width 10 m, and with a 2
m vertical rise from the water to the transect position. Slumping or gullying did not occur in the transect.
The stream bed was loamy and the banks loamy. There were no fences or waterpoints, and cattle tracks
ran parallel to the stream.
Transect: Transect was 100 m long by 10 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 75-89%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra, with 12 mature individuals,
8-10 m tall, 2 saplings 2-3 m tall, and cover of 40%. Other significant species included Livistona rigida
and Nauclea orientalis each with 15 % cover. Fine woody debris accounted for 10-29 % of cover and
course woody debris for 1-20% of cover. The only deleterious weed species was Cryptostegia
grandiflora (rubber vine) with 40 mature individuals of which 10 were climbing host trees, with 5%
cover. TRARC score was 58, a rating of poor condition.
Species recorded:
Cryptostegia grandiflora
Excoecaria parvifolia
Flueggea virosa subsp. melanthesoides
Lysiphyllum cunninghamii
Livistona rigida
Australian Centre for Tropical Freshwater Research
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Terminalia canescens
Vitex acuminata
Page 52
8.4.7
Beames Brook - Downstream of Black Gully Junction
Access: Situated about 0.7 km downstream of the Beames Brook/Black Gully junction on the eastern
side of the stream, reached by a 2 km track that leaves the Gregory Downs/Burketown road 100 m north
of the Black Gully crossing.
GPS: S18° 09’ 08.3”, E139° 14’ 56.2”; Altitude: 46 m
Geophysical setting: Channel width was 3 m with a perennial flow, the riparian width 8 m, and with a 1
m vertical rise from the water to the transect position. Slumping did not occur in the transect, and
gullying in 10%, with four 1 m wide gullies. The stream bed was loamy and the banks loamy. There were
no fences or waterpoints, and cattle tracks ran mostly parallel to the stream, and some perpendicular.
Transect: Transect was 100 m long by 8 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 75-89 %, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 18 mature individuals,
and one subadult 4 m tall. Other significant species included Excoecaria parvifolia and Vitex acuminata
each with 30% cover. Fine woody debris accounted for <10 % of cover and course woody debris for 120% of cover. The only deleterious weed species was Cryptostegia grandiflora (rubber vine) with one
mature individual, one immature individual, with 1% cover. TRARC score was 52.1, a rating of poor
condition.
Species recorded:
Acacia bidwillii
Alternanthera nodiflora
Cryptostegia grandiflora
Excoecaria parvifolia
8.4.8
Goodenia strangfordii
Melaleuca leucadendra
Sporobolus sp.
Vitex acuminata
Beames Brook - Brookdale
Access: Situated about 2 km north of the Brookdale homestead, off the road on a 0.4 km long well
formed track that ends at the stream, with the site on the eastern side of the stream. GPS: S18° 03’ 50.2”,
E139° 15’ 47.4”; Altitude: 32 m
Geophysical setting: Channel width was 7 m with a perennial flow, the riparian width 7 m, and with a 2
m vertical rise from the water to the transect position. Slumping occurred in 60% of the transect, and
gullying in 10% with two 1-2 m wide gullies. The stream bed was loamy and the banks loamy. There
were no fences or waterpoints, and cattle tracks ran parallel to the stream edge.
Transect: Transect was 100 m long by 7 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 75-89%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 12 mature individuals,
10-11 m tall, and cover of 30%. Other significant species included Livistona rigida and Excoecaria
parvifolia each with 20% cover, Terminalia canescens with 15% cover and Nauclea orientalis with 5%
cover. Fine woody debris accounted for 10-29 % of cover and course woody debris for 1-20% of cover.
The only deleterious weed species was Cryptostegia grandiflora (rubber vine) with four mature
individuals all of which were climbing a host tree, and two immature individuals, with 5% cover.
TRARC score was 52.7, a rating of poor condition.
Species recorded:
Alternanthera nodiflora
Ceratophyllum demersum
Cryptostegia grandiflora
Excoecaria parvifolia
Ipomoea sp. (aquatic)
Livistona rigida
Melaleuca leucadendra
Nauclea orientalis
Australian Centre for Tropical Freshwater Research
Persicaria attenuata
Santalum lanceolatum
Schoenoplectus mucronatus
Sporobolus sp.
Terminalia canescens
Vitex acuminata
Xanthium occidentale
Page 53
8.4.9
Beames Brook - Upstream of Albert River Junction
Access: Situated about 8 km upstream of Beames Brook/Albert River junction, 200 upstream from
Burketown/Gregory Downs road crossing, on the eastern side of the stream. GPS: S17° 52’ 47.8”, E139°
20’ 28.4”; Altitude: 14 m
Geophysical setting: Channel width was 4 m with a perennial flow, the riparian width 8 m, and with a 2
m vertical rise from the water to the transect position. Slumping occurred in 30% of the transect, and
gullying in 10% with two 1-2 m wide gullies and one 5 m gully. The stream bed was rocky and the banks
sandy loam. There were no fences or waterpoints, and cattle tracks ran parallel to the stream.
Transect: Transect was 100 m long by 8 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 42 mature individuals,
8-10 m tall, and cover of 70%. Other significant species included Pandanus spiralis with 15 % cover
confined to the stream bank, and Casuarina cunninghamiana and Nauclea orientalis each with 10%
cover. Fine woody debris accounted for 30-49 % of cover and course woody debris for <1 % of cover.
There were no deleterious weed species. TRARC score was 64.9, a rating of average condition.
Species recorded:
Casuarina cunninghamiana
Chrysopogon oblongatus
Excoecaria parvifolia
Flueggea virosa subsp. melanthesoides
Gymnathera oblonga
Melaleuca leucadendra
8.4.10
Nauclea orientalis
Pandanus spiralis
Senna sp.
Sida acuta
Vitex acuminata
Xanthium occidentale
Lawn Hill Creek -Big Lagoon
Access: Situated about 1 km downstream of the Lawn Hill Creek/Louie Creek junction; travelling
towards Gregory Downs from Adels Grove, take track to left 1 km east of Louie Creek crossing, then
follow rough track for 600 m to site which is on the southern side of the creek. GPS: S18° 41’ 01.5”,
E138° 32’ 19.5”; Altitude: 119 m
Geophysical setting: Channel width was 12 m with a perennial flow, the riparian width 7 m, and with a 3
m vertical rise from the water to the transect position. Slumping did not occur in the transect, and
gullying in 5% with one < 1 m wide gully. The stream bed was rocky and the banks sandy. There were no
fences or waterpoints, and cattle tracks ran parallel to the stream.
Transect: Transect was 100 m long by 7 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Lophostemon grandiflorus with 42 mature
individuals, 10 saplings 2-3 m tall, with 50 % cover. Other significant species included Melaleuca
leucadendra with 20 % cover and Lysiphyllum cunninghamii with 15 % cover. Fine woody debris
accounted for 50-74% cover and course woody debris for 1-20% of cover. There were no deleterious
weed species. TRARC score was 69.3, a rating of average condition.
Species recorded:
Capparis lasiantha
Flueggea virosa subsp. melanthesoides
Lophostemon grandiflorus
Lysiphyllum cunninghamii
Melaleuca leucadendra
Vitex acuminata
8.4.11 Lawn Hill Creek - Lawn Hill Station
Access: Situated about 1 km downstream of Lawn Hill Station; travelling north on Adels
Grove/Doomadgee road, at 1.2 km past Lawn Hill Station, take track to left for 200 m to Lawn Hill
Creek, with the site on the eastern side of the creek.
GPS: S18° 34’ 24.5”, E138° 34’ 58.7”; Altitude: 75 m
Australian Centre for Tropical Freshwater Research
Page 54
Geophysical setting: Channel width was 15 m with a perennial flow, the riparian width 10 m, and with a
4 m vertical rise from the water to the transect position. Slumping and gullying did not occur at this site.
The stream bed was rocky and the banks sandy loam. There were no fences or waterpoints, and cattle
tracks ran parallel to the stream.
Transect: Transect was 100 m long by 10 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 22 mature individuals
14-15 m tall, four subadults 8-9 m tall, 18 saplings 2-3 m tall, and cover of 55%. Other significant species
included Pandanus spiralis with 30% cover restricted to the stream edge, and Ficus racemosa and
Nauclea orientalis each with 10% cover. Fine woody debris accounted for 30-49 % of cover and course
woody debris for 1-20% of cover. There were no deleterious weed species. TRARC score was 69.8, a
rating of average condition.
Species recorded:
Chrysopogon oblongatus
Clerodendrum floribundum
Ficus racemosa
Flueggea virosa subsp. melanthesoides
Gymnathera oblonga
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Xanthium occidentale
8.4.12 Lawn Hill Creek - Bluewater Waterhole Crossing
Access: Situated on Lawn Hill Creek, 200 m downstream of the Doomadgee/Punjaub road crossing,
about 18 km from Burketown/Doomadgee road.
GPS: S18° 04’ 18.1”, E138° 54’ 13.4”; Altitude: 9 m
Geophysical setting: Channel width was 4 m with a perennial flow, the riparian width 7 m, and with a 1
m vertical rise from the water to the transect position. Slumping occurred in 20% of the transect, and
gullying in 5% with two 1 m wide gullies. The stream bed was rocky and the banks sandy. There were no
fences or waterpoints, and cattle tracks ran parallel to the stream.
Transect: Transect was 100 m long by 7 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 75-89 %, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with five mature individuals,
7-8 m tall, 100+ saplings 1-2 m tall, and cover of 25%. Other significant species included Excoecaria
parvifolia with 10 % cover, and Melaleuca trichostachya, Terminalia canescens and Corymbia bella,
each with 5% cover. Fine woody debris accounted for 10-29 % of cover and course woody debris for 120% of cover. There were no deleterious weed species. TRARC score was 54.2, a rating of poor
condition.
Species recorded:
Corymbia bella
Cyperus sp.
Excoecaria parvifolia
Flemingia sp.
Imperata cylindrica
Lobelia dioeca
Melaleuca leucadendra
Melaleuca trichostachya
Sida sp.
Terminalia canescens
Vitex acuminata
8.4.13 Running Creek - Almora
Access: Situated about 0.3 km downstream of the Burketown/Gregory Downs road crossing; take road to
Almora which heads north-east about 100 m south of Running Creek, for 300 m, turn left toward creek
(no track), where site is on the southern side of the creek. GPS: S18° 19’ 27.6”, E139° 15’ 51.5”;
Altitude: 54 m
Australian Centre for Tropical Freshwater Research
Page 55
Geophysical setting: Channel width was 4 m with a perennial flow, the riparian width 7 m, and with a 2
m vertical rise from the water to the transect position. Slumping occurred in 40% of the transect, and
gullying in 20% with one < 1 m wide gully, and three 1-2 m wide gullies. The stream bed was muddy
with loamy banks. There were no fences or waterpoints, and cattle tracks ran mainly parallel to the
stream.
Transect: Transect was 100 m long by 7 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with 12 mature individuals,
10-11 m tall, and cover of 40%. Other significant species included Ficus racemosa and Nauclea
orientalis each with 20% cover, and Livistona rigida and Pandanus spiralis each with 10% cover. Fine
woody debris accounted for 30-49 % of cover and course woody debris for 1-20% of cover. The only
deleterious weed species was Cryptostegia grandiflora (rubber vine) with four mature individuals, with
1% cover. TRARC score was 63.7, a rating of average condition.
Species recorded:
Cayratia trifolia
Chrysopogon oblongatus
Cryptostegia gandiflora
Ficus racemosa
Flueggea virosa subsp. melanthesoides
Gymnathera oblonga
Livistona rigida
Melaleuca leucadendra
Nauclea orientalis
Pandanus spiralis
Persicaria attenuata
Vitex acuminata
Xanthium occidentale
8.4.14 One Mile Creek - Punjaub
Access: Situated about 6 km west of the Beames Brook crossing at Brinawa on the Brinawa/Punjaub
road, with the site 200 m upstream of the crossing over One Mile Creek, on the western side of the creek.
GPS: S18° 09’ 42.1”, E139° 13’ 35.8”;
Altitude: 52 m
Geophysical setting: Channel width was 5 m with a perennial flow, the riparian width 8 m, and with a 1
m vertical rise from the water to the transect position. Slumping occurred in 40% of the transect, and
gullying in 10% with two 1 m wide gullies. The stream bed was muddy and the banks loamy. There were
no fences or waterpoints, and cattle tracks ran parallel to the stream edge.
Transect: Transect was 100 m long by 8 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 75-89%, with 5-25% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca leucadendra with eight mature individuals,
5-7 m tall, and cover of 30%. Other significant species included the shrub Vitex acuminata with 60%
cover primarily beneath M. leucadendra, and Terminalia canescens with 1% cover. Fine woody debris
accounted for 10-29 % of cover and course woody debris for <1% of cover. There were no deleterious
weed species. TRARC score was 54.4, a rating of poor condition.
Species recorded:
Acacia bidwillii
Alternanthera nodiflora
Ceratophyllum demersum
Chrysopogon oblongatus
Goodenia strangfordii
Melaleuca leucadendra
Australian Centre for Tropical Freshwater Research
Ottelia alismoides
Sida acuta
Terminalia canescens
Vallisneria nana
Vitex acuminata
Xanthium occidentale
Page 56
8.4.15 Elizabeth Creek – Lawn Hill Station
Access:
Situated on the Doomadgee/Punjaub road, about 16 km south-east of the
Burketown/Doomadgee road junction, about 100 m upstream of the crossing on the northern side of the
creek. GPS: S18° 03’ 55.5”, E138° 54’ 22.8”; Altitude: 46 m
Geophysical setting: Channel width was 5 m with an annual flow, the riparian width 7 m, and with a 2 m
vertical rise from the water to the transect position. Slumping occurred in 10% of the transect, and
gullying in 5% with one 1 m wide gully. The stream bed was muddy and the banks loamy. There were no
fences or waterpoints, and cattle tracks ran parallel to the stream edge.
Transect: Transect was 100 m long by 7 m wide, placed contiguous and parallel to the stream edge.
Vegetation: Linear continuity of vegetation was 90-100%, with <5% standing dead vegetation, and with
no evidence of clearing. The dominant species was Melaleuca argentea with 11 mature individuals, 4-7
m tall, 18 subadults 2-3 m tall, 30 saplings 1-2 m tall, and cover of 50%. Other significant species
included Excoecaria parvifolia and Corymbia bella, each with 15% cover. Fine woody debris accounted
for 10-29 % of cover and course woody debris for 1-20% of cover. There were no deleterious weed
species. TRARC score was 64.3, a rating of average condition.
Species recorded:
Chrysopogon oblongatus
Digitaria sp.
Excoecaria parvifolia
Corymbia bella
8.5
Flueggea virosa subsp. melanthesoides
Melaleuca argentea
Xanthium occidentale
Summary
The median ratio of the width of the channel to the width of the riparian zone was 0.7; eleven sites had a
ratio of 0.7 or less, and four had a ratio greater than 0.7, i.e. making the riparian zone consistently
narrower than the width of the channel at the study sites, and indeed structurally representing a narrow
ribbon of vegetation along stream edges. This is the common condition of watercourses in areas of
monsoonal or strong seasonal rainfall in tropical Australia, and can be accounted for by water
requirements of riparian species in a seasonal rainfall environment, and not necessarily the geophysical
morphology of the streams and soil types and conditions. Within the Gregory River catchment where the
sites were located, there is considerable variation in soil conditions ranging from alluvial river sands to
dark clay loams, and there appears to be no direct relationship between riparian width and edaphic
conditions.
The most dominant riparian species recorded was Melaleuca leucadendra, occurring in 14 of the 15 sites
and with a total cover of 41.3%. The average number of mature individuals at each site where they
occurred was 18, which placed then at an average linear separation of 5.7 m. The estimated height range
of mature M. leucadendra was 5-16 m, with an average at all sites of 9.6 m. This range of estimated
heights may reflect soil types or degree of water saturation into the bank substrate. The site at Beames
Brook, upstream from the Albert River junction, had the greatest density with 42 mature individuals
recorded in the 100 m transect. The second most dominant species was Pandanus spiralis occurring at
seven sites, with a total cover of 16.3%. Other dominant species included Nauclea orientalis and Ficus
racemosa each with a cover of 7%, and Livistona rigida with a cover of 4.7%. The shrub Vitex
acuminata was very common as an understorey element at three sites, including Beames Brook at
Brookdale, Running Creek and One Mile Creek.
The only deleterious weed recorded was Cryptostegia grandiflora (rubber vine), at six of the 15 sites.
The number of mature individuals ranged from one [Beames Brook, Black Gully junction and Gregrory
River, Gregory Downs] to 40 at Beames Brook, Brinawa Crossing. Rubber vine was more or less
confined to a discrete area centred on three of the four Beames Brook sites, nearby Running Creek, and
two upstream sites on the Gregory River.
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The understorey vegetation was limited because of seasonal effects; there were no annuals present
[including both herbs and grasses] and all perennial grasses had browned-off or were reduced to
subterranean shoots. The effects of cattle browsing and/or trampling on the remaining understorey
species were evident in many sites.
The Tropical Rapid Appraisal of Riparian Condition method was applied to all sites. Based on the
TRARC scores, five sites were in the poor category, eight sites were in the average category and two sites
in the good category. Cattle were present at all sites, although no relationship between estimated stocking
rates and the TRARC score was evident.
8.6
Aquatic Weeds
Beyond those wetland-riparian weed species already known to be established in the Nicholson-Gregory
catchment, most prominent aquatic weed species such as salvinia and water hyacinth have yet to be
recorded within the catchment. However a small infestation of para grass (Brachiaria mutica) was
recorded at a reach on Beames Brook during the 2004 ACTFR survey period (Figure 8). This appears to
be one of the earliest (if not the first) records for this particular species in the Nicholson-Gregory
catchment. Para grass is an exotic, semi-aquatic grass species native to tropical South America or Africa
and now a pan-tropical weed (Smith, 2002). Introduced to Australia in the 1800’s as a pasture species it is
a highly invasive grass that spreads vigorously from stolon fragments. It is sometimes spread
intentionally as a pasture species but also by birds and floodwaters and can create dense monocultures in
wetland environments, choking out native species.
Figure 8 Para grass infestation at Beames Brook
Ponded pasture species have been a contentious and long-standing natural resource management issue in
northern Australia (Clarkson, 1995). For some time ponded pastures were being strongly promoted and
advocated by some government departments while at the same time being viewed with considerable
concern by others. While a number of the often enormously productive ponded pasture species can offer
economic benefit to the pastoral industry as dry-season cattle fodder, they exhibit many life history traits
Australian Centre for Tropical Freshwater Research
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predisposing them to developing into significant weeds which can spread quickly from pastoral lands to
adjacent areas and cause substantial environmental degradation.
Hymenachne amplexicaulus is another ponded pasture species that has been introduced to both
Queensland and the Northern Territory and has been named as one of Australia’s top 20 worst weeds on
the Weeds of National Significance list. It has been repeatedly stated this weed poses a particular concern
to the wetlands of the Southern Gulf (Environment North 1998; SGCI, 2000). Hymenachne has been
established and trialled in some Gulf catchments as a ponded pasture, though apparently with limited
success (Burrows, 2004). Hymenachne’s distribution in the Northern Territory is currently expanding
(particularly in the Adelaide and Mary River floodplains) with new infestations being continually located
(Smith, 2002). Hymenachne is currently in its early stages of spread and could potentially invade
substantially larger areas of northern Australia. Predictive ecoclimatic modeling of the potential
distribution of hymenachne suggests the species could form permanent populations across much of
coastal and sub-coastal northern Australia (Csurhes et al., 1999). While actual habitat under threat is
difficult to predict, the impact of hymenachne is expected to be greatest in seasonal freshwater wetlands
up to 2m deep in tropical areas, so it therefore has considerable relevance to Southern Gulf catchments.
With a propensity for occupying littoral margins of watercourses, hymenachne may potentially invade the
niche of native flora such as waterlilies and lotus (Sainty & Jacobs, 1994).
While species such as hymenachne and para grass can establish to some extent in a broad spectrum of
unpolluted tropical wetland habitats, the vast majority of problematic infestations do tend to occur in
seasonal and stillwater lowland environments where there is a high influx of nutrients and sediments,
often from upstream agricultural sources (Csurhes et al., 1999). Both hymenachne and para grass dislike
pronounced seasonal draw-down in water levels and can be controlled to some extent by cattle grazing
(Damien Burrows pers. comm.). Wetland areas or particular habitats within the catchment such as
sections of Bluebush Swamp, Atlas Waterhole and the shallower reaches of perennial streams could be
susceptible to infestation by ponded pasture species, particularly in light of current environmental
disturbances (i.e. nutrient enrichment and sedimentation) associated with cattle and feral pigs in some of
these environments.
9.0
MACROINVERTEBRATES
Aquatic invertebrates (animals lacking backbones) include an array of faunal groups such as insects,
crustaceans, worms and molluscs. Shifts in societal concerns toward recognizing the need for
maintenance of the ecological values of environments have led to recent emphasis on aquatic biota when
assessing water quality and aquatic habitat condition. Aquatic macroinvertebrates in particular have
quickly found favour as a biological monitoring tool for a number of reasons including their ubiquity,
cost-effectiveness and their keystone role in the trophic functioning and energy dynamics of aquatic
ecosystems. The ecological contribution made by aquatic invertebrates also extends beyond the aquatic
environment itself. Many aquatic insects emerge and disperse from the water as adults and studies in the
wet-dry tropical environments of Australia (Lynch et al., 2002) suggest aquatic insect emergence may be
an important contributor to riparian food webs along streams, particularly during the dry season.
Predation upon emerged aquatic insects is an avenue by which aquatic secondary production may
subsidize adjacent terrestrial food webs.
In a familiar situation a number of macroinvertebrate focused studies have been carried out across the
Nicholson-Gregory catchment, although spatial extent and temporal replication is far from
comprehensive. As part of the Century Mine Project EIS, Dames & Moore (1994) collected a total of 180
species/taxa from 11 sites potentially influenced by the mine proposal (i.e. Archie, Coglan, Mitton, Lawn
Hill, Louie Creeks etc.). Similarly, Thurgate (1998) documented 159 benthic macroinvertebrate ‘species’
from nine sites on both perennial and intermittent systems in the Musselbrook Creek-Lawn Hill Creek
area. Both of these studies are notable in that they involved invertebrate identifications to species/genus
level where possible. Research to this level of taxonomic resolution is rare in northern Australia, where
macroinvertebrate based studies (uncommon to begin with) typically only identify invertebrates to family
level and higher. Both of these studies were however limited in spatial extent and aimed to generate basic
taxonomic inventories rather than assessing ecological condition at sites.
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Rapid macroinvertebrate bio-assessment techniques (RMB) have been widely adopted in the monitoring
and evaluation of the ecological integrity of Australian rivers for some time (see Chessman, 1995, Choy
& Thompson, 1996). Six sites within the catchment (including Archie Creek, Lawn Hill Creek and the
Gregory River) have been subject to periodic RMB surveys as part of various AUSRIVAS (Australian
River Assessment Scheme) assessments of river health, a nation wide monitoring project overseen by the
Department of Natural Resources and Mines in Queensland. Spatial coverage is somewhat limited and
most sites have only been sampled in one year, which involves two sampling occasions, one in autumn
and one in spring. One site on the Gregory River at Gregory Downs has however been sampled over four
separate years and is perhaps approaching the level of replication required to attain a robust dataset. The
results of these assessments are unfortunately yet to be published.
9.1
Macroinvertebrate Assessment Methodology and Data Analysis
Rapid assessment techniques are most appropriate when a preliminary survey is required over a broad
area at a large number sites or when an initial assessment of the condition of a waterway is needed for
management purposes (Chessman, 1995). For these reasons a rapid macroinvertebrate bioassay is suitable
in establishing baseline information as to the integrity of waterways in the Nicholson-Gregory catchment.
In May 2004, the macroinvertebrate fauna at twelve sites was surveyed, with survey effort concentrated
in the Gregory-Lawn Hill Creek sub-catchment. Site locations are listed in Table 15.
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Table 15 Macroinvertebrate Survey Sites, 2004
Site
Gregory River @ The Knobbies
Gregory River @ 6-Mile
Gregory River @ Gregory Downs
Gregory River @ Old Planet Downs Stn.
Gregory River @ Punjaub Stn.
Running Creek @ Almora Stn.
Beame’s Brook @ Brinawa Stn.
Beame’s Brook @ Main Road X-ing
Gregory River near Tirranna R’house
Louie Creek near Adel’s Grove
Lawn Hill Creek 5km d/s Adel’s Grove
Lawn Hill Creek @ Doomadgee X-ing
Site Coordinates
18˚ 51’ 57.3” S, 139˚ 6’ 26.3”E
18˚ 43’ 44.5”S,139˚ 11” 16.4” E
18˚ 38’ 20” S, 139˚ 15’ 15.0”E
18˚ 30’ 24.0”S, 139˚ 16’ 45.2”E
18˚ 10’ 15.0” S, 139˚ 8’ 10.5”E
18˚ 18’ 20.1” S, 139˚ 16’ 2.9”E
18˚ 09’ 55.1”S, 139˚ 14’ 24.2”E
17˚ 54 ‘47.5”S, 139˚ 20’ 30.6”E
17˚ 53’ 30.0”S, 139˚ 17’ 15”E
18˚ 41’ 45”S, 138˚ 32’ 0.0”E
18˚ 38’ 0.0”S, 138˚ 33’ 45”E
18˚ 34’ 6.9”S, 138˚ 35’ 5.2”E
Invertebrate communities were sampled at each site using a standard dip net (triangular frame:
300mmx300mmx300mm, 650mm bag depth, mesh size 250 µm). Sampling was stratified across two
different habitat types (bank edges & riffle/runs) with 3 replicate samples of each habitat type collected
within a 50m reach at each site (each replicate covered approx. 2 – 2.5m of habitat). Each sample was
live picked on site for 15 minutes. Sampling of flowing riffle or run environments would usually not be
advisable for biological monitoring purposes throughout much of arid/semi-arid Australia. The typical
ephemeral nature of these habitat types in such climatic regimes coupled with questionable
representativeness on catchment scales would provide uncertain value as a sampling habitat. In this
particular case however, riffle/run habitats were sampled as the perennial nature of streamflow in the
major systems of this catchment makes such habitat types continually available. Many of the more
disturbance sensitive macroinvertebrate taxa additionally tend to associate more strongly with riffle/run
habitats. Collected taxa were subsequently identified to family level where possible, although some of the
more taxonomically challenging groups were only identified to higher levels.
Macroinvertebrate monitoring usually entails biological information being reduced to a much simpler
metric or biotic index, supposedly more easily interpreted by non-specialists. However, a bewildering
array of metrics addressing various aspects of community structure are now in existence. A small subset
of these metrics were utilized to assess the ecological condition of sites including standard metrics such
as site species richness, individual abundance, community evenness and the SIGNAL2 index. The
SIGNAL (Stream Invertebrate Grade Number Average Level) biotic index has been demonstrated as one
of the more sensitive metrics for discriminating anthropogenic impacts (Metzeling et al. 2003), although
the protocol has undergone several refinements. The SIGNAL index involves macroinvertebrate taxa
being assigned pollution sensitivity grade numbers from 1 (most tolerant) to 10 (most sensitive). The
overall SIGNAL score for a sampling site is calculated by averaging the pollution sensitivity grade
numbers of all macroinvertebrate families present in a sample (Chessman, 1995). The SIGNAL scores
utilised in this study were derived from the most recently published sensitivity grade number appropriate
to a particular taxon (i.e. Chessman, 2003). In the event a sensitivity grade rating was not available for a
particular faunal taxon, it was simply excluded from the subsequent analysis.
In order for biotic metrics or indices to be meaningful, the score from a particular site has to be judged
against a standard score from another site known to be in good ecological condition (i.e. a reference site).
In this survey a condition rating was generated for each sampling site based upon the standard reference
selection criteria developed for use in Queensland’s Department of Natural Resources, Mines and Energy
AusRivAS macroinvertebrate sampling program (relevant field sheets can be found at
http://ausrivas.canberra.edu.au/Bioassessment/Macroinvertebrates/Man/Sampling/Qld/Datasheets/Qld_sit
e_information_sheet_Sept_04.pdf). Ratings of 1 (severely degraded) to 5 (pristine or near pristine) were
applied to each of 10 criteria relating to various disturbance sources. The total aggregate score from these
10 criteria theoretically provides an overview of the levels of disturbance a particular site is subject to,
and hence some meaningful capacity to compare scores across various sites. A total score of 45 or higher
is generally regarded as the threshold for unimpaired reference status.
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9.2
Results
7083 individual animals from 56 taxa were collected throughout the course of the macroinvertebrate
surveys (See Appendix 3.0 for results in their entirety). Dipterans, particularly the chironomids (nonbiting midges, bloodworms) dominated the fauna at most sites. Baetid and caenid mayflies were also
present at all sites. The most common caddisflies were Cheumatopsyche spp. (Hydropsychidae), and
Chimarra spp. (Philopotamidae). While these taxa were occasionally highly abundant, they were
generally only present in genuine rocky riffle habitat and virtually absent from the unconsolidated silt
bottomed run environments of the floodplain. The leptophlebiid mayflies were one of the few taxa
addressed in greater taxonomic detail in this survey. Three genera/species were identified, including two
(Thraulus spp. and Jappa kutera) with widespread distributions across much of Northern Australia and
Australia respectively (Dean, 1999). The third genera collected, Leptophlebiidae Genus V (spp. AV1) is
the first record of this taxon in Queensland (Faye Christidis pers. comm.). Previous studies have only
documented this species from the Northern Territory and northern Western Australia. This is suggestive
of the macroinvertebrate communities of the Gregory catchment sharing at least some affinity with
Northern Territory fauna.
Most sites sampled satisfied ‘reference site’ criteria based upon the level of human impact these
particular reaches were subject to (i.e. reference criteria scores of 45 or higher). Those few sites that
failed to meet reference status were only regarded as mildly impaired. The impacts which consistently
affected ratings were streamside vegetation alteration (due to exotic weed infestations and stock access
issues) and levels of stream bank erosion (again typically due to stock access). These impacts were all
rated as either minor or moderate. The scores obtained at each from the various macroinvertebrate
metrics (SIGNAL Index, site taxonomic richness etc.) are therefore those that could be expected for sites
in near-pristine or only slightly impaired ecological condition.
Edge habitats had on average the higher taxon richness (Figure 9). The number of species and abundance
of individuals was typically less in run environments (silty substrate) than the riffle (rocky substrate)
habitat types. While riffles were prevalent in the higher gradient environments in the upper and middle
reaches of streams, these run environments became common once stream systems began traversing the
low gradient Gulf Plains region. The relatively unconsolidated and structurally monotonous substrate
occurring in these run environments is likely not naturally conducive to establishment of a diverse and
abundant macroinvertebrate fauna.
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Figure 9
Average number of taxa per habitat type, ACTFR 2004 Macroinvertebrate surveys
Average No. of taxa
30
25
20
15
10
5
0
Edge
Riffle
Run
Habitat type
SIGNAL scores for riffle/run environments ranged between 3.69 and 4.68, while edge habitat SIGNAL
ratings ranged 3.19 to 4.30 (Table 16). The lower diversity of run environments has possibly had some
level of effect on Evenness and SIGNAL indices, but it is difficult to analyse or elaborate upon given the
small number of available samples. The differences between riffle and run environments underlines the
need for careful selection of appropriate reference sites should RMB assessments be considered for future
monitoring within the catchment.
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Table 16. Summary Macroinvertebrate indices and stream reach Reference Condition Criteria
scores, May 2004
Site
Louie Ck. nr. Adel's
Grove
Lawn Hill Ck. 5km
d/s Adel's Grove
Lawn Hill Ck. @
Lawn Hill Stn.
Gregory R. @ The
Knobbies
Gregory R. @ 6-Mile
Gregory R. d/s
Camping area
Habitat No. Taxa Individuals Evenness (J) Signal2
Reach Condition
Score
Riffle
Edge
24
34
472
332
0.84
0.87
4.30
3.19
47
Riffle
Edge
22
23
264
272
0.77
0.81
4.68
3.86
46
Riffle
Edge
25
30
664
300
0.74
0.77
4.30
4.11
46
Riffle
Edge
Riffle
Edge
21
30
21
25
458
252
375
283
0.73
0.79
0.78
0.78
4.45
3.70
4.45
3.86
48
Riffle
Edge
20
20
306
278
0.80
0.63
4.32
4.00
45
20
23
240
295
0.83
0.75
4.24
3.95
46
21
27
123
210
0.76
0.87
3.90
3.60
47
16
22
136
303
0.58
0.83
3.69
3.76
44
11
22
76
222
0.60
0.79
4.36
3.45
46
23
22
318
272
0.69
0.78
4.32
4.00
47
29
27
342
301
0.75
0.76
3.89
4.30
47
Gregory R. @
Gregory Downs Stn. Riffle
Edge
Running Ck. @
Run
Almora Stn.
Edge
Gregory R. @
Run
Punjaub Stn.
Edge
Beames Brook @
Run
Brinawa Stn.
Edge
Beames Brook @
Riffle
Main Road X-ing
Edge
Gregory R. nr.
Riffle
Tirranna R'house
Edge
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Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Given the limited dataset of this survey and the fact the vast majority of sites fulfilled reference condition
criteria, comparative or predictive assessments regarding ecological conditions of sites were neither
feasible nor warranted. There are some notable aspects of the results that warrant additional attention,
particularly if further macroinvertebrate survey work was to be considered.
9.3
Discussion
Dames & Moore (1994) noted the river and creek systems of the Lawn Hill area contained aquatic
invertebrate communities of similar family/genus composition, species richness and community structure
to those typifying Northern Territory billabong ecosystems (i.e. the work of Marchant, 1982). Where the
macroinvertebrate diversity of the Gregory-Lawn Hill catchment stands in relation to other environments
in northern Australia is difficult to gauge given the taxonomic resolution used in this survey, but it would
be an interesting proposition given the apparent relative diversity of the fish fauna. On the basis of
comparison with studies such as Pearson et al. (1986) in Queensland’s rainforest streams, Thurgate
(1998) suggested the streams of the Musselbrook-Lawn Hill area may have a comparatively low species
richness. As is the case with previous discussion of the relative fish diversity of the catchment (Section 7
of this report), comparisons with other research is fraught with confounding effects such as relative
research effort, taxonomic resolution, habitat selection and sampling techniques.
The macroinvertebrate assemblages of the Gregory-Lawn Hill area would certainly be unlikely to
approach the levels of diversity displayed by the markedly speciose streams of Queensland’s Wet
Tropics, which rank among the world’s most diverse described faunas. A more relevant comparison
however would be to macroinvertebrate communities in other catchments of semi-arid or monsoonal
northern Australia, information for which is glaringly minimal. In an admittedly cursory comparative
context, the macroinvertebrate diversity of the Gregory-Lawn Hill catchment is at the least comparable to
that of other wet-dry tropical Australian ecosystems which are regarded as relatively diverse by
Australian standards (i.e. cf. Marchant, 1982, Outridge, 1987). This issue is obviously yet to be rigorously
explored and requires more comprehensive spatial and temporal replication to yield any robust insights
into comparative diversity.
The range of SIGNAL scores obtained at sites during this survey does merit some discussion in relation
to the typical SIGNAL scores documented from other research. Chessman et al. (1997) classified sites in
Hunter River catchment (NSW) into five categories of indicative environmental quality on the basis of
their overall SIGNAL values: >7, excellent (unimpaired and rich in sensitive taxa); 6-7, good
(unimpaired); 5-6, fair (mildly impaired); 4-5, poor; <4, very poor (severely degraded). Such indicative
ranges were not strictly developed for application over broad spatial scales. It does however underline the
need for recognition of the existence of simple biogeographical differences in taxa and natural faunal
shifts proceeding downstream in rivers and between habitat types. Bunn & Davies (2000) for example
demonstrated significantly depressed SIGNAL scores for pristine south-western Australia forest streams
in relation to pristine south-eastern Australian forest streams. This apparent anomaly was due in large
part to the natural absence or poor representation of particular groups of fauna in south-western forest
streams.
A similar situation may be evidenced in the SIGNAL scores emerging from stream reaches in the
Gregory-Lawn Hill catchment. Of the 52 taxa collected for which SIGNAL scores were available, 52%
were regarded as tolerant (i.e. a sensitivity rating of 1-3). Moderately and highly sensitive taxa
(sensitivity grades 4-7 & 8-10) made up 42% and just 6% respectively of the residual taxa (these sensitive
taxa may have some potential utility as ‘indicator’ taxa when assessing ecosystem health). The Gregory
catchment appears to be characterised by a quite tolerant macroinvertebrate fauna, with few taxa highly
sensitive to habitat degradation. Due to natural environmental variability and unpredictability, much of
semi-arid and monsoonal Australia is typified by a generalist macroinvertebrate fauna with inherently
broad environmental tolerances (although some notable exceptions do occur as discussed in section
9.3.2). While the substantial presence of these relatively tolerant taxa is not necessarily indicative of
aquatic degradation, their numerical dominance in samples may have the effect of overwhelming and
dragging down overall SIGNAL scores at many sites. It should also be noted in this case that the level of
taxonomic resolution dedicated to some taxa such as the chironomids and HUL complex (dragonfly
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Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
larvae) necessitated the use of the lower sensitivity grades derived for higher taxonomic classifications in
Chessman (2003). This analytical artefact could also have contributed to the low overall SIGNAL values
for sites, although the effects would probably have been relatively minimal. Given that many, if not all
sites sampled would be regarded as relatively pristine, the need for recalibration of SIGNAL water
quality ranges or individual scores for taxa may be necessary if continued monitoring is undertaken. As
already touched upon, a more detailed focus upon a suite of the more sensitive taxa (i.e. components of
the EPT complex: ephemeroptera, plecoptera, trichoptera etc.) may alleviate some of this effect of the
dominance of tolerant taxa.
While the macroinvertebrate data and reach condition assessments obtained from this survey may provide
some indicative baseline information on ecological integrity of instream habitats, expected taxa,
community organization and spatial variation in assemblage structure, considerable temporal replication
would be required to reliably `account for both the seasonal and annual variability often exhibited by
macroinvertebrate communities (see Marchant, 1982). Documenting any temporal variability is essential
to discriminate between natural variability and anthropogenic impacts (Marchant, 1982, Bunn & Davies,
2000). Therefore these results should be regarded as just a preliminary step in establishing a more
rigorous dataset relevant to long-term monitoring of aquatic environments in the Gregory River-Lawn
Hill catchment.
9.3.1
The Natural Values of Karst and Spring Environments
While some elements of the aquatic fauna of the Nicholson-Gregory catchment have received varying
levels of scientific scrutiny, the biological values of the karst environments and associated wetlands in the
Gregory-Lawn Hill region are one area which remains virtually unknown. Morgan (1999a) has already
noted an urgent need to determine the specific values and condition of individual springs in the area.
When surface expression of water occurs in karst environments, the normal range of wetland features is
produced. However an additional array of unique features, some with exclusive and specialized faunas,
may occur (Humphreys, 2000). This includes springs and spring brooks, mound springs and tufa
(travertine) deposits. Because these environments tend to be geographically isolated and any associated
specialised biota have such restricted distributions, speciation is common. Karst wetlands for example are
known to often support a wide range of stygofauna (usually invertebrates living exclusively in
subterranean habitats) that can be both highly diverse and endemic (Humphreys, 2000). The surface
wetlands associated with exsurgent springs also often house biota of considerable natural significance.
Admittedly patchy surveys of the spring complexes of the Great Artesian Basin have revealed a ‘treasure
trove’ of distinctive organisms including several endemic snail, crustacean and fish species as well as a
suite of vascular plants that are likely endemic to spring environments (Fensham & Fairfax, 2003).
The biological values of the limestone springs and similar habitats in the Gregory-Lawn Hill regions,
while known to be regionally significant refugia for remote and rare floral populations (Anon. 2004), are
currently largely undescribed from a botanical standpoint. As an example of the possible latent
biodiversity values of the Barkly karst, some largely opportunistic survey work has documented
Australia’s seventh and largest troglophilic (cave-dwelling) atyid shrimp species (Pycnisia bunyip) in
Forbes Inferno Cave at Boodjamulla National Park (Suzuki & Davie, 2003). Similarly, Eberhard (2003)
documented a new and likely endemic undescribed species of aquatic amphipod crustacean from the
nearby Nowranie Caves, an area of the Barkly karst near Cammooweal.
Fensham & Fairfax (2003) noted a variety of threats to the spring environments of Australia’s Great
Artesian Basin. A number of these including exotic plants and ponded pastures, rooting, trampling and
grazing by feral and pastoral animals as well as destructive fires are also potential threats to the integrity
of spring environments in the Gregory-Lawn Hill area. Concerns regarding the need for fire protection
and the threats posed by high grazing pressures and uncontrolled tourism have also been raised for the
spring ecosystems of the region (Morgan, 1999a).
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Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
10.0
OTHER AQUATIC FAUNA
10.1
Reptiles
While the Lawn Hill area is particularly noted for its terrestrial herpetofaunal diversity (Cogger &
Heatwole, 1981), there is also a significant reptile fauna associated with aquatic and riparian habitats of
the Nicholson-Gregory catchment. A number of aquatic or semi-aquatic snakes including the Arafura file
snake (Acrochordus arafurae), Macleay’s water snake (Enhydris polylepis) and keelback (Tropidonophis
mairii) are known from the area (White, 2004). Freshwater crocodiles (Crocodylus johnstoni) can be
abundant in some areas of the catchment with the occasional saltwater crocodile (Crocodylus porosus)
also occurring (primarily in lower reaches). Merten’s water monitor (Varanus mertensi) and Mitchell’s
water monitor (Varanus mitchelli) are two varanid (goanna) species also associated with aquatic-riparian
habitat throughout the region (White, 2003; Anon., 2004).
The wetlands of the Nicholson-Gregory catchment also contain a substantial suite of freshwater turtle
species. The distribution and taxonomy of Australian freshwater turtle species, particularly in northern
regions was for some time quite uncertain (and considerable shortcomings no doubt continue to exist). A
collective review of the available species lists and faunal surveys from the area would probably be
susceptible to this taxonomic confusion. Based upon the most recent work of White (2004), at least four
turtle species occur in the catchment including the northern snakeneck turtle (Chelodina canni), the
sawshell turtle (Elseya latisternum), Worrell’s turtle (Emydura worrelli) and the particularly noteworthy
and recently ‘rediscovered’ Gulf snapping turtle (Elseya lavarackorum). Elseya lavarackorum was for
some time known only from fossils found in the area and presumed extinct, until living specimens were
recently discovered in the catchment (see Thompson et al., 1997).
10.2
Cane Toads
While not specifically surveyed as part of this project, cane toads (Bufo marinus) were an ever-present
component of the aquatic-riparian fauna during the survey period, and were observed at most sites, often
in very high numbers. A native of central America introduced to Queensland in 1935, cane toads have
rapidly colonized the Southern Gulf region and are progressively dispersing across much of the
Australia’s ‘Top End’. The species first appeared in the Gregory-Lawn Hill catchment in the early-mid
1980’s and various faunal surveys have revealed this species has invaded most habitat types in the area,
but are a particularly abundant if not the dominant vertebrate species occurring in riverine/aquatic
environments (Dames & Moore, 1994, White, 2003).
For logistical reasons, most studies on the effects of cane toads on native aquatic fauna have focused
upon small, relatively common native organisms such as fish, frogs and aquatic invertebrates (see Alford
et al., 1995). While all stages of the toad life cycle are toxic, a surprising number of aquatic predators
apparently either ignore cane toad eggs and larvae or are capable of consuming some or all of the aquatic
life cycle stages of toads with no ill effects (Alford et al., 1995). While a wide variety of species may
cope with the presence of cane toads with no drastic effects, some species such as native frogs and
freshwater snails experience high rates of mortality when exposed to cane toad eggs or hatchings. Adult
toads may also have an indirect inhibiting effect on native faunal populations through competition with
native insectivorous taxa (Catling et al., 1999)
Actual quantitative studies of the impacts of toad invasions on the taxa intuitively most susceptible to
toad invasions (i.e. larger, terrestrial predators of frogs) have been minimal. Cane toads have however
been repeatedly implicated in the dramatic decline of native species which feed on amphibians (Catling et
al., 1999) and the situation has been repeated in the Gregory-Lawn Hill area. Within twelve months of
the arrival of cane toads, both Burnett (1997) and White (2004) reported an apparent drastic reduction in
the abundance of a number of large, previously common aquatic/riparian reptile species along Lawn Hill
Creek near Blue Hole Outstation and in Boodjamulla (Lawn Hill) National Park respectively (olive
pythons, Mitchell’s & Merton’s water monitors etc.). White (2004) also reported significant local
mortality in freshwater crocodiles apparently due to consumption of cane toads. While significant
declines in populations of some native species apparently occur upon the arrival of cane toads in an area,
there is often a subsequent recovery after a certain period as animals become more circumspect about
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eating toads, or avoid consuming toad poison glands. As an example, while there was such a dearth of
sightings of Merten’s water monitor for some time there were concerns it had disappeared entirely from
Boodjamulla National Park, a number of positive sightings have been made in recent times (Parsons et
al., 2003), possibly suggesting a population recovery.
11.0
CONCLUSIONS
Despite being attributed high natural values, the aquatic ecosystems of the Nicholson-Gregory catchment
are essentially poorly known, despite the best efforts of past research. This is however not an unusual
situation. Lake (1995) made the valid point that northern Australian wetlands as whole are being exposed
to an array of threats before there exists even an elementary understanding of their ecology.
As per the vast majority of natural resource surveys in northern Australia, this study was largely
taxonomic in nature or offered a brief snapshot of ecological condition at a select number of sites across
the catchment. It would however be remiss to judge the apparent ecological condition of aquatic
ecosystems on the basis of a small number of site visits. In seasonal environments especially, many of the
typical condition indicators such as species composition and the influence or impacts of pest animals and
plants can vary greatly through time. In order to assess the ecological integrity of wetlands, a
comprehensive inventory and database of spatial and temporal variability is required (Storrs & Finlayson,
1997). Baseline information on the ecological character and condition of wetlands at one point in time,
while useful, should be coupled with effective monitoring programs. Wetland monitoring needs to be
well-designed and able to answer discrete objectives within realistic timeframes (Storrs & Finlayson,
1997).
While occasional, sporadic surveys can add valuable knowledge to what is still a poorly known ecology,
such piecemeal approaches will provide minimal rigor in assessing the potential impacts of any future
developments within the Nicholson-Gregory catchment. Considerable spatial and temporal patchiness
characterizes most monsoonal environments. This characteristic necessitates the need for permanent,
long-term monitoring of ecological to better comprehend the vagaries of a variable environment and to
better discriminate between variation attributable to natural environmental fluctuations and impacts of
anthropogenic origin. Additionally, predictions of the possible anthropogenic impacts on native
ecosystems cannot be made without robust knowledge as to the underlying mechanisms effecting
ecosystem dynamics such as breeding and recruitment, trophic relationships, species distributions etc. As
noted by Bishop (2001), the risks of errors in such impact assessments are minimised if background
biological and ecological information is available. Such knowledge of ecological fundamentals also
requires consistent long-term study at carefully selected sites.
12.0
RECOMMENDATIONS
•
Development of a flow weighted water quality sampling program targeting sample collection at
various sites during wet season flood events would provide valuable insights into
sediment/contaminant loads discharged to Gulf of Carpentaria coastal waters. The dynamics and
effects of land-based runoff into Gulf marine environments are currently virtually unknown.
•
Establishment of annual or possibly even seasonal fish surveys on a regular basis at a selected
number of sites throughout the catchment. As well as a focus on species distribution and
abundance, surveys should endeavour to generate more detailed knowledge of the habitat, life
history and trophic requirements of local fish species.
•
Additional fisheries related attention could also be focused upon anecdotal surveys of local
residents to provide historic as well as possibly contemporary context to the distribution of
endangered species such as the freshwater sawfish Pristis microdon. Public education of local
residents (which would also require a broader whole of Gulf approach) regarding introduced fish
species could also conceivably be incorporated into such a program.
Australian Centre for Tropical Freshwater Research
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Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
•
A more thorough assessment of the degree of impact associated with fish movement barriers
throughout the catchment. This could entail opportunistic visits to relevant sites during wet
season flood events to gauge hydrologic conditions and consequent fish movement issues at
potential fish passage barriers.
•
This particular project was structured as an initial preliminary assessment particularly with regard
to riparian vegetation assessment, where only 13 sites covering a small proportion of total
catchment area were investigated. More comprehensive spatial and temporal replication of
riparian condition assessment would greatly enhance any future natural resource management
efforts over a broader scale, particularly in light of current weed control and riparian fencing
initiatives at some sites.
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Appendix 1.0 Potable Water Tests.
Gregory Downs.
Potable water quality samples at Gregory Downs were collected during a period when tourist visitation
rates are normally high (17th May). A sequence of four water samples were collected at a range of sites
both upstream and downstream of possible human influence near the Gregory Downs township. One
sample was taken 2km upstream of the township itself, one immediately upstream of the uppermost
extent of tourist camping access to the riverbed, one sample taken immediately downstream of the main
camping area, and one final sample taken 2km downstream of the township. All samples were tested for
specific general water quality parameters such as major ions and microbiological parameters (faecal
coliforms/100mL).
The samples tested from the Gregory Downs township area demonstrated very similar and consistent
water quality across all sites (results in their entirety are provided in Appendix 1.2). The range of faecal
coliform concentrations fell within the concentration range that might be expected for natural waters
within the region. Fluoride and nitrate concentrations conformed to NHRMC (1996) Australian Drinking
Water guidelines. It should be recognised however that one-off sampling reflects only a ‘snapshot’ of
water quality conditions at one moment in time. Tourist numbers present at the time of sampling were
apparently down on the numbers that typically at that time of year, and considerably higher densities of
campers are not uncommon. These particular samples were taken about two weeks after the Gregory
River Canoe race, an annual event that attracts high tourist numbers. The data did not demonstrate a
persistent influence from these activities. Opportune sampling for acute human impacts during a peak
tourist visitation period such as the Canoe Race may be warranted should the issue remain a local
concern.
Due to an array of environmental concerns arising from unregulated tourist utilisation of the Gregory
River and it’s immediate environs there has been significant recent developments to this situation. The
Burke Shire Council has recently indicated plans to fence off and restrict broad scale vehicular access to
the river reach at Gregory Downs currently receiving tourism pressure. While still in the early stages of
consultation and development the plan is to allow walking access for visitors to the river environment
with alternative facilities and amenities to be made available for tourists with regard to camping and
accommodation.
Doomadgee.
Figures 10-11 outlines the waste disposal issues at Doomadgee. After the site situation was reviewed, one
potable water sample was collected at the town water supply pumping station adjacent to the main
township. Parameters tested in this case were microbiological (faecal coliforms/100mL), total metals and
trace organics. On the basis of parameters tested at Doomadgee, there appeared to be no discernible effect
from any seepage from the dump directly on receiving water quality. Trace organics, particularly
petroleum hydrocarbons, BTEX and oil and grease were not detected. Trace metals and faecal coliforms
were within a concentration range that might be expected for natural waters within the region. This data
suggested that at the time of sampling no obvious influence of the dump could be determined in the
receiving water body. However, it is strongly recommended that use of this water as a raw drinking water
supply require it be treated prior to human consumption (as does occur in the town water treatment plant).
Australian Centre for Tropical Freshwater Research
76
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Figure 10 Old waste near Doomadgee Township (the gully in the background drains into the
Nicholson Weir impoundment, which is ca. 150-200m away
Figure 11. Old waste dump at Doomadgee
Australian Centre for Tropical Freshwater Research
77
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Similar to the Gregory Downs results, these are only relevant to the water quality in the Nicholson River
at the particular time sampling was carried out. The environmental conditions at the time of sampling can
obviously be a significant consideration for concerns of this type. If the issue of possible water supply
contamination remains a priority, sampling at a more targeted time when a more likely influence is to be
expected (such as during the wet season when substantial surface and sub-surface run-off occurs) would
be recommended. Rainfall events that cause overland flow from the ‘old dump’ area into the weir
impoundment while the Nicholson River itself is not flowing should be targeted.
Appendix 1.2. Potable Water Test Results.
ACTFR ANALYTICAL DATA REPORT 14J150 - A
Number of Samples:
Sample Arrival:
1
18.05.04
PARAMETER
Sample 1
Microbiological
Faecal Coliforms (/100mL)
PARAMETER
Sample 1
Total Metals
8 (7)*
Silver (µg/L)
Aluminium (µg/L)
Trace Organics Organics
Arsenic (µg/L)
< 0.05
101
<1
TRH C5 – C9 P&T (mg/L)
< 0.040
Barium (µg/L)
TRH C10 – C14 (mg/L)
< 0.10
Beryllium (µg/L)
< 0.1
TRH C15 – C28 (mg/L)
< 0.20
Cadmium (µg/L)
0.05
TRH C29 – C36 (mg/L)
< 0.20
Chromium (µg/L)
0.5
Benzene (mg/L)
< 0.001
Cobalt (µg/L)
0.7
Toluene (mg/L)
< 0.001
Copper (µg/L)
1
Ethylbenzene (mg/L)
< 0.001
Iron (µg/L)
Total Xylenes (mg/L)
< 0.003
Manganese (µg/L)
19
Oil and Grease (mg/L)
<1
Molybdenum (µg/L)
0.3
Nickel (µg/L)
Lead (µg/L)
26
859
< 0.1
2
Antimony (µg/L)
0.1
Selenium (µg/L)
<1
Thallium (µg/L)
< 0.05
Zinc (µg/L)
13
* - Replicate sample analysis result. Replicate sample collected in the field
Australian Centre for Tropical Freshwater Research
78
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
ACTFR ANALYTICAL DATA REPORT 14J150 - B
Number of Samples:
Sample Arrival:
4
18.05.04
PARAMETER
Sample 3
Sample 4
Sample 5
Sample 6
Microbiological
Faecal Coliforms (/ 100mL)
5 (12)*
13 (21)*
12 (22)*
20 (32)*
pH
8.36
8.28
8.33
8.34
Conductivity (µS/cm)
588
587
586
585
Total Dissolved Salts (mg/L)
284
285
303
302
Total Hardness (mg/L as
CaCO3)
312
321
332
329
Total Alkalinity (mg/L as
CaCO3)
291
291
313
316
1
1
1
1
2.4
1.9
3.5
1.9
Sodium (mg/L)
5
5
5
5
Potassium (mg/L)
2
2
2
2
Calcium (mg/L)
46
45
49
49
Magnesium (mg/L)
48
51
51
50
Sulphate (mg/L)
8
7
8
6
Chloride (mg/L)
7
7
7
7
Bicarbonate (mg/L)
348
348
347
370
Carbonate (mg/L)
2.4
<1
4.8
4.8
Fluoride (mg/L)
0.2
-
-
0.29
6
-
-
2
General Water Quality
True Colour (TCU)
Turbidity (NTU)
Major Ions
Nitrate + Nitrite (µg NOXN/L)
Australian Centre for Tropical Freshwater Research
79
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
ACTFR TECHNICAL REPORT 14J150 – A AND B
Number of Samples:
Sample Arrival:
5
18.05.04
14J150 – A
This sample was collected immediately downstream of a dump site that is located upstream of the
Doomadgee drinking water supply.
On the basis of the parameters tested, there appeared to be no discernible indication of any seepage
influence from the dump on the receiving water quality.
°
Trace organics, particularly petroleum hydrocarbons, BTEX and Oil and Grease, were not
detected,
°
Trace metals were within the concentration range that might be expected for natural waters
within the region, and
°
Faecal coliform concentrations were also within the concentration range that might be expected
for natural waters within the region. This suggests that the use of this water as a raw drinking
water supply requires that the water is treated (e.g. filtration and disinfection) prior to human
consumption.
Future monitoring that endeavours to test for any the influence the dump may have on receiving water
quality is suggested to be conducted in the post-wet season period. This timing represents the best
possible periodicity for subsurface down-gradient interactions between the dump site and the river as a
result of the regional wet season inundation.
14J150 – B
These samples were collected from the Gregory River near Gregory Downs. For the parameters tested,
the samples have very similar water quality, indicating a consistency in water quality between the sites.
The samples are characterised as having:
°
Medium level conductivities (e.g. 300 to 800µS/cm),
°
High hardness, due to the dominance of calcium, magnesium and bicarbonate (values of 200 to
500 mg CaCO3/L have shown a propensity to increased scaling problems and difficulties with
detergent lathering),
°
Faecal coliform concentrations that fall within a concentration range that might be expected for
natural waters within the region, but which exceed raw drinking water guidelines (<1/100mL as
per Australian Drinking Water Guidelines (NHMRC 1996), and
°
Fluoride and nitrate concentrations that conform to NHMRC (1996) Australian Drinking Water
Guidelines (i.e. <<1.5mg F/L and <<<11mg NOX-N/L).
Australian Centre for Tropical Freshwater Research
80
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Appendix 2: Taxonomic list of plant species in the riparian zone of 15 study sites in the Gregory River
catchment, recorded in 100 m x 5-20 m transects, parallel to stream edge, 10-16 August 2004.
Acacia stenophylla A.Cunn. ex Benth.
Acacia torulosa Benth.
Acacia farnesiana (L.) Willd.
Achyranthes aspera L
Alternanthera nodiflora R.Br.
Atalaya hemiglauca (F.Muell.) F.Muel.
ex Benth.
Lysiphyllum cunninghamii (Benth.) de
Wit
Calytropis procera (Aiton) W.T.Aiton
Capparis lasiantha RBr. ex DC
Cardiospermum halicacabum L.
Casuarina cunninghamiana Miq.
Cayratia trifolia (L.) Domin
Ceratophyllum demersum L.
Chrysopogon elongatus (R.Br.) Benth.
Clerodendrum floribundum R.Br.
Corymbia bella K.D.Hill &
L.A.S.Johnson
Corymbia sp.
Crotalaria sp.
Cryptostegia grandiflora R.Br.
Cyperus sp.
Digitaria sp.
Erythrophleum chlorostachys (F.Muell.)
Baill.
Eucalyptus microtheca F.Muell.
Excoecaria parvifolia F.Muell.
Ficus racemosa L.
Flemingia sp.
Flueggea virosa subsp. melanthesoides
(F.Muel.) G.L.Webster
Australian Centre for Tropical Freshwater Research
Goodenia strangfordii F.Muell.
Gymnathera oblonga (Burm.f.)
P.S.Green
Imperata cylindrica (L.) Raeusch.
Ipomoea sp (aquatica?)
Limnophila brownii Wannan
Livistona rigida Becc.
Lobelia dioeca R.Br.
Lophostemon grandiflorus (Benth.) Peter
G.Wilson & J.T.Waterh.
Ludwigia octovalvis (Jacq.) P.H.Raven
Melaleuca argentea W.Fitz.
Melaleuca bracteata F.Muell.
Melaleuca leucadendra (L.) L.
Nauclea orientalis (L.) L.
Nymphaea gigantea Hook.
Nymphoides crenata (F.Muell.) Kuntze
Ottelia alismoides (L.) Pers.
Pandanus spiralis R.Br.
Persicaria attenuata (R.Br.) Sojak
Santalum lanceolatum R.Br.
Schoenoplectus mucronatus (L.) Palla ex
J.Kern.
Senna sp.
Sida acuta Burm.f.
Sporobolus caroli Mez
Terminalia canescens (DC) Radlk. ex T.
Durand
Vallisneria nana R.Br.
Vitex acuminata R.Br.
Xanthium occidentale Bertol.
81
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Appendix 3. Macroinvertebrate Survey Results (biota totals from pooled replicates at each habitat type).
Order
Nematoda
Platyhelminthes
Collembola
Oligochaeta
Hirudinea
Cnidaria
Cladocera
Copepoda
Ostracoda
Decapoda
Gastropoda
Bivalvia
Acarina
Coleoptera
Diptera
Ephemeroptera
Hemiptera
Odonata
Taxa
Habitat
Nematoda
Turbellaria
Temnocephalidea
Collembola
Oligochaeta
Hirudinea
Hydridae
Cladocera
Copepoda
Ostracoda
Atyidae
Palaemonidae
Sundatelphusidae
Parastacidae
Lymnaeidae
Planorbidae
Corbiculiidae
Sphaeriidae
Hydracarina
Elmidae
Dytiscidae
Hydrophilidae
Gyrinidae
Noteridae
Scirtidae
Hydraenidae
Chironomidae
Ceratopogonidae
Simuliidae
Tabanidae
Culicidae
Athericidae
Empididae
Baetidae
Caenidae
Leptophlebiidae
Corixidae
Gerridae
Hydrometridae
Mesoveliidae
Nepidae
Notonectidae
Pleidae
Veliidae
Gomphidae
HUL
Protoneuridae
Louie Ck.nr Adel's
Riffle
Edge
0
0
2
0
0
0
0
0
9
4
0
0
0
1
0
0
0
1
6
1
0
10
17
1
0
0
0
0
0
6
0
4
4
4
0
0
9
13
51
5
0
46
4
12
1
0
0
3
0
0
0
0
88
44
3
4
49
0
20
8
0
4
0
0
0
0
28
14
29
10
11
0
0
22
0
9
0
1
0
3
0
0
0
6
0
23
1
13
26
7
58
16
0
13
Australian Centre for Tropical Freshwater Research
Gregory R. @ 6-mile
Riffle
Edge
0
0
0
1
0
0
0
0
6
2
0
0
0
0
0
0
0
1
0
0
0
16
4
18
0
0
0
0
3
0
0
1
6
0
0
3
15
18
5
5
2
24
0
4
0
0
0
0
0
0
0
3
117
78
13
0
43
0
8
1
0
0
0
0
3
0
10
8
28
16
4
0
0
0
0
1
0
0
0
2
0
0
0
0
0
18
0
0
11
3
10
38
0
4
Gregory R. @ Gregory
Downs Station
Riffle
Edge
0
0
0
2
0
0
0
0
8
0
0
0
0
0
0
0
0
1
0
0
1
9
1
34
0
0
0
0
4
2
0
0
6
27
2
2
18
8
26
10
0
1
0
3
0
0
0
0
0
0
0
0
43
91
4
0
1
0
1
0
0
0
0
0
0
0
10
33
50
9
0
0
0
1
0
0
0
0
0
1
0
0
0
0
0
0
0
0
3
1
11
26
0
1
Beames Brook @
Brinawa
Run
Edge
0
0
0
0
0
0
0
0
4
3
0
0
0
0
0
0
0
1
0
2
0
13
2
18
0
1
0
0
0
6
0
0
0
0
0
2
9
12
5
2
0
11
0
0
0
0
0
0
0
0
0
3
46
76
3
5
0
0
1
2
0
0
0
0
0
0
1
10
2
8
1
0
0
2
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
14
0
13
Gregory R. @ Punjaub
Run
Edge
4
0
0
0
0
0
0
0
5
0
0
0
0
0
0
0
2
6
2
2
0
35
0
16
0
0
0
0
0
0
0
0
0
1
0
1
10
35
1
4
0
8
0
0
0
0
0
0
0
0
0
0
83
41
8
3
0
0
0
0
1
0
0
0
0
0
8
37
2
49
0
0
5
20
0
0
2
0
1
0
0
0
0
0
0
5
0
1
0
0
1
11
0
16
Gregory R. @ The
Knobbies
Riffle
Edge
0
0
12
0
0
0
0
0
5
1
0
0
0
0
0
0
0
1
0
0
1
16
8
22
0
0
0
0
0
5
0
1
1
7
0
1
12
25
7
4
0
16
0
0
0
0
0
0
0
0
0
1
75
63
0
2
4
2
2
0
0
2
0
0
0
0
30
14
107
13
8
0
0
4
0
1
0
0
0
2
0
0
0
0
0
1
0
3
1
5
14
15
0
4
82
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Trichoptera
Lepidoptera
Coenagrionidae
Isostictidae
Leptoceridae
Ecnomidae
Philopotamidae
Hydropsychidae
Hydroptilidae
Calomatoceridae
Pyralidae
0
0
0
2
16
10
4
0
24
15
1
7
0
0
0
0
0
1
0
0
0
14
50
23
0
0
0
0
0
15
0
0
2
1
0
0
0
0
0
6
8
23
1
0
13
0
0
19
1
0
7
0
0
6
0
0
0
1
0
0
0
0
0
0
0
9
8
0
0
0
0
0
0
0
1
0
0
0
0
0
0
4
0
5
3
0
0
0
0
0
0
0
0
16
108
45
1
0
1
0
0
9
0
0
1
1
0
0
Appendix 3 (continued).
Class/Order
Nematoda
Platyhelminthes
Collembola
Oligochaeta
Hirudinea
Cnidaria
Cladocera
Copepoda
Ostracoda
Decapoda
Gastropoda
Bivalvia
Acarina
Coleoptera
Diptera
Ephemeroptera
Taxa
Habitat
Nematoda
Turbellaria
Temnocephalidea
Collembola
Oligochaeta
Hirudinea
Hydridae
Cladocera
Copepoda
Ostracoda
Atyidae
Palaemonidae
Sundatelphusidae
Parastacidae
Lymnaeidae
Planorbidae
Corbiculiidae
Sphaeriidae
Hydracarina
Elmidae
Dytiscidae
Hydrophilidae
Gyrinidae
Noteridae
Scirtidae
Hydraenidae
Chironomidae
Ceratopogonidae
Simuliidae
Tabanidae
Culicidae
Athericidae
Empididae
Baetidae
Caenidae
Gregory River d/s Greg.
Dwns. Campground
Riffle
Edge
0
0
0
0
0
0
0
0
11
2
0
0
0
0
0
0
0
0
0
0
0
29
4
19
0
0
0
0
1
0
0
0
0
0
0
0
12
27
39
2
0
2
0
0
0
0
0
0
0
0
0
0
87
133
6
1
11
1
7
0
0
0
0
0
1
0
23
30
17
9
Australian Centre for Tropical Freshwater Research
Gregory R. nr Tirranna
Roadhouse
Riffle
Edge
0
0
1
0
0
0
0
0
14
3
2
0
0
0
1
0
0
1
4
5
1
36
7
5
0
0
0
0
3
0
0
0
2
1
4
1
11
2
23
2
3
40
0
3
0
3
1
0
0
0
0
0
92
80
9
5
5
0
8
1
0
0
0
0
1
0
59
25
41
23
Beames
Brook
nr
Intersection
Riffle
Edge
1
0
4
0
0
0
0
0
3
2
0
0
0
0
0
0
0
1
0
0
0
33
3
16
0
0
0
1
2
18
0
0
0
3
1
0
1
3
67
10
9
14
0
1
0
0
0
0
0
0
0
0
57
42
2
0
20
1
1
1
0
0
1
0
0
0
78
71
6
12
Running Ck. @ Almora
Run
0
0
0
0
14
0
0
0
1
3
2
3
0
0
0
0
0
0
16
0
4
0
1
0
0
0
44
2
2
0
0
0
0
6
9
Edge
0
0
0
0
5
0
0
0
1
4
2
5
0
0
0
0
0
1
10
1
9
12
0
0
1
21
24
1
0
0
3
0
0
13
9
Lawn Hill Ck. d/s Adel's
Grove
Run
Edge
0
0
0
0
0
0
0
0
12
6
0
0
0
0
0
0
0
0
0
1
0
23
1
18
0
0
0
0
4
3
0
0
1
8
3
2
8
43
68
16
0
3
0
0
0
0
0
0
0
0
0
0
57
57
9
1
15
0
20
0
0
0
2
0
1
0
13
20
12
8
Lawn Hill Ck. @ Lawn
Hill Station
Riffle
Edge
0
0
2
0
1
0
0
0
17
1
3
0
0
0
0
0
0
0
0
1
0
6
9
30
0
0
0
0
0
0
0
0
13
5
12
1
1
27
62
7
2
4
2
5
0
0
0
0
0
0
0
1
81
83
5
2
19
2
50
2
0
0
4
1
3
0
37
8
42
4
83
Riparian Vegetation in the Gregory River Catchment, ACTFR Report 04/xx
Hemiptera
Odonata
Trichoptera
Lepidoptera
Leptophlebiidae
Corixidae
Gerridae
Hydrometridae
Mesoveliidae
Nepidae
Notonectidae
Pleidae
Veliidae
Gomphidae
HUL
Protoneuridae
Coenagrionidae
Isostictidae
Leptoceridae
Ecnomidae
Philopotamidae
Hydropsychidae
Hydroptilidae
Calomatoceridae
Pyralidae
0
0
0
0
0
0
0
0
0
2
9
0
0
0
0
1
46
20
3
0
6
0
1
0
0
0
0
0
0
0
1
11
1
0
0
2
2
0
3
2
0
0
Australian Centre for Tropical Freshwater Research
0
1
0
0
0
0
0
0
0
1
12
0
0
0
0
4
4
15
4
0
9
3
0
0
0
0
1
0
3
0
2
19
9
0
0
16
3
0
6
3
0
0
0
0
0
0
0
0
0
0
0
0
34
0
0
0
1
1
3
20
1
0
2
0
0
0
0
0
0
0
0
0
0
15
2
0
0
14
7
0
3
0
2
0
2
0
0
0
0
0
0
2
1
0
4
4
1
0
1
1
0
0
0
0
0
1
14
0
0
4
0
2
16
3
0
3
32
6
0
7
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
3
18
0
0
0
0
1
3
1
0
0
11
0
0
0
0
0
0
2
0
1
2
30
7
0
0
15
4
0
1
0
0
1
0
0
0
0
0
0
0
0
0
3
55
0
0
0
0
0
24
210
2
0
6
0
5
1
0
0
0
2
0
0
6
31
16
0
1
19
7
0
16
1
0
5
84