Derwent Estuary Rice Grass
Eradication Program
Review of distribution, survey areas, recent actions
& recommendations
(reporting period Dec 2008 - Dec 2009)
Jason Whitehead DECEMBER 2009
The Derwent Estuary Program (DEP) is a
regional partnership between local
governments, the Tasmanian State
Government, commercial and industrial
enterprises, and community-based groups
to restore and promote our estuary. The
DEP was established in 1999 and has been
nationally recognised for excellence in
coordinating initiatives to reduce water
pollution, conserve habitats and species,
monitor river health and promote greater
use and enjoyment of the foreshore. Our
major sponsors include: Brighton, Clarence,
Derwent Valley, Glenorchy, Hobart and
Kingborough councils, the Tasmanian State
Government, Southern Water, Tasmanian
Ports Corporation, Norske Skog Boyer,
Nyrstar Hobart and Hydro Tasmania
Derwent Estuary Rice Grass Eradication Program
Review of distribution, survey areas, recent actions & recommendations
REPORTING PERIOD December 2008 – December 2009
Preamble
Rice grass in the Derwent estuary has the potential to cause serious ecological
impacts. Infestations have the potential to dramatically alter the ecological and
natural heritage of the estuary. Invasion alters the distribution and habits of a range
of resident flora and fauna, including shore birds, fish, invertebrates, seagrasses and
saltmarsh. Infestations progressively invade the immediate and surrounding area of
intertidal zones altering estuarine sediment dynamics.
Rice grass was deliberately introduced into the Derwent estuary in the 1930’s and by
the 1990’2 had spread from those areas of initial introduction – covering ~ 1
hectare. Rice grass spreads via underground rhizomes and through seed dispersal.
The seed remains viable for several years and is water dispersed (thus influenced by
tides, currents and winds). Rice grass has the potential to invade 180 hectares of
intertidal habitat throughout the estuary.
Eradication is an achievable aim of rice grass management in the Derwent estuary.
Successful control had occurred through 1998-2002, but subsequent surveys were
not conducted until 2006 – when it appears that rice grass had endured in the
estuary due to propagation from the dispersed seed bank. Subsequent control
efforts have continued. The December 2009 survey is the first to not have located
rice grass plants in the Derwent estuary – however, it will be a minimum of several
years until eradication can be declared.
The Derwent Estuary Program is dedicated to continued survey efforts into the
future, which have and will in-part be support by an Australian Government
Coastcare Grant. It is important to also acknowledge that the success to date has
arisen from a high level of commitment from the Tasmanian Parks and Wildlife
Service and the State Department of Primary Industries, Parks Water, and
Environment and other funding support.
History of rice grass survey and treatment in the Derwent estuary
Rice grass was deliberately imported into Australia between 1927 and 1952, and
specifically to the Derwent estuary at Austins Ferry (1930) and Bridgewater (197477) by the then Department of Agriculture. Rice grass was thought to provide river
bank stabilisation, assist in land reclaimation and also provide fodder for livestock.
The underpinning reasons for its introduction to the Derwent estuary is unclear
(Boston 1981).
In the mid – 1990’s the Tasmanian Parks and Wildlife Service (TPWS) mapped and
treated rice grass infestations in the Derwent estuary (Megalos 1997). In 1997 a
mapping survey indicated that rice grass occupied ~1 hectares of intertidal habitat
(Figure 1). From 1998 until 2002, the former state Department of Primary
Industries, Water and Environment (DPIWE) conducted annual treatment (Fusilade)
and monitoring of rice grass, and by 2002 the extent had been reduced to 1m2
(which was subsequently treated). Recommendations on how to use Fusilade for
rice grass treatment can be found in the subsequent DPIWE (2002) report: Strategy
for the management of rice grass (Spartina anglica) in Tasmania, Australia (October
2002 – second edition).
Figure 1. Rice grass in the Derwent estuary in 1997 (DPIWE 2002).
A further Derwent estuary rice grass survey in 2006 by the former Department of
Primary Industries, Water (DPIW) and identified 8m2 of rice grass was in the estuary.
DPIW staff were supported through funding from Natural Heritage Trust (NHT) to
continue eradication efforts between 2006 and 2008. A Derwent estuary rice grass
management plan was created by DPIW, in partnership with the Derwent Estuary
Program, and annual surveys and treatment (Fusilade Forte) were carried out
(Appendix 1). Survey efforts have involved walking foreshores. Survey personnel
have been both car and boat based in order to reposition to different survey
locations around the coast. Prior to 2008 the rice grass surveys had only been
conducted within the middle stretches of the Derwent estuary, between the
Bridgewater causeway and Tasman Bridge. In 2008 the Derwent Estuary Program
surveyed an extensive area of the upper estuary via kayak (Appendix 2) and did not
locate any rice grass.
Rice grass seed remains viable for several years, and as a result continued
monitoring, and potential treatment, of rice grass in the Derwent estuary is of
critical importance. The Derwent Estuary Program was awarded Australian
Government Coastcare funding to continue this work through December 2008 –
December 2009. This report describes the survey and treatment efforts.
Recent rice grass survey and treatment (Dec 2008 –Dec 2009)
A summary of recent rice grass survey and treatment can be found in Table 1. In
December 2008-January 2009 only 4m2 of rice grass was found in the middle estuary
(Figure 2), which was subsequently treated. Areas of foreshore extensively surveyed
in December 2008 –January 2009 and December 2009 are mapped (Figures 3 and 4).
Figure 2. Rice grass in the Derwent estuary in December 2008 – January 2009. Sites
numbered (1-4) refer to sites listed in Table 1.
Future work
The survey conducted in December 2009 did not find any rice grass within the
survey region. Rice grass was last treated in the estuary in April 2009. As the seed
remains viable for several years, annual surveys will be continue within the middle
estuary (between the Bridgewater causeway and Tasman Bridge), with extra
attention given to those areas of known previous rice grass occurrence. As
opportunity allows the monitoring will also be undertaken on a less frequent basis
above the Bridgewater causeway. Tidal flat and wetland communities here are at
risk if rice grass persists within the estuary.
Figure 3. Foreshore area surveyed (December 2008 – January 2009).
Figure 4. Foreshore area surveyed (December 2009).
Acknowledgment
The Derwent Estuary Program were supported through an Australian Government
Coastcare Grant to undertake survey and treatment through December 2008 –
December 2009. The Derwent Estuary Program wish to acknowledge the on-ground
support from the following people: Alasdair Morton, Shane Hogue, Stephen
Pratten, Chris Rees (DPIPWE staff), Allison Coombe (Glenorchy City Council), Jill
Pearson (NRM –South).
References
Boston , K.G., (1981) The introduction of Spartina townsendii (s.l.) to Australia. Department of
Geography, Melbourne State College.
DPIWE (Department of Primary Industries, Water and Environment) 2002. Strategy for the
management of rice grass (Spartina anglica) in Tasmania, Australia (October 2002 – second edition).
Megalos, J., (1997) Report on Derwent River rice grass eradication : Spraying, February 1997. Parks
and Wildlife Service, Tasmania.
Appendix 1: Rice Grass Area-Based Management Plan Derwent
Estuary (2006-2008)
Location and Objectives of Plan
Location: Derwent Estuary
Objectives:
• To eradicate rice grass infestations in the Derwent Estuary region to create a rice grass free area
coordinated by community management:
Duration of Plan: 2006 to 2008
Funding: Regional Competitive Projects in Tasmania under the Natural Heritage Trust, 2006-2008.
Nature of Infestation
2
2
2
2
Size of pre-treated infestation: 4m (2008) 8m (2006) 1m (2002), 40m (2001) 1 ha (1997)
Rate of spread: annual surveys successful in controlling spread
Potential extent: Rice grass has the potential to invade 180ha of intertidal habitat in the Derwent
Estuary region. Rice grass currently inhabits <0.001% of its potential range in this region.
Impacts to Region
Ecology: Infestations have the potential to dramatically alter the ecological and natural heritage of the
estuary. Invasion alters the distribution and habits of a range of resident flora and fauna, including
shore birds, fish, invertebrates, seagrasses and saltmarsh.
Industry: Infestations progressively invade the immediate and surrounding area of intertidal zones
altering estuarine sediment dynamics, effecting navigation and tourism.
Recreation: Rice grass may inhibit coastal access and use, and detrimentally effect recreational fishing
and boating.
Regional Planning Considerations
Existing Plans and Strategies: This management plan is designed to compliment existing regional
plans and strategies that affect the estuary. The following regional plans and strategies have been
identified as having working associations with this plan:
• Derwent Estuary Environmental Management Plan (2001)
• Strategy for the Management of Rice Grass (Spartina anglica) in Tasmania. Second edition (2002);
• State Coastal Policy (1996);
• Weedplan (Tasmanian Weed Management Strategy) (1996).
•
•
•
Management Action
Integrated control Techniques: Physical removal and spraying with Fusilade Forte are being
used to make the Derwent River region a rice grass free area.
Timing of Control: Control efforts need to occur during the growth phase of the plant from
November to June. To successfully achieve eradication the DPIW recommend two surveys take
place each season (December and March). If only one survey is conducted this should occur in
March as the plant is very prominent with its seed head. All control efforts will occur on the
falling tide when rice grass infestations are fully exposed.
Chemical control methods will cease to allow a minimum of 3 hours drying time before tidal
submersion or when average wind speed exceeds safe operating conditions.
Management Responsibility:
Responsibility for planning and implementing control efforts and monitoring will be shared by
Derwent Estuary Program (DEP) and the community in accordance with this management plan. The
DEP Program Manager will coordinate the management of Rice Grass for this region. The DPIW is
willing to provide advice and authorise the use of Fusilade Forte under the supervision of a staff
member as required by the Australian Pesticides and Veterinary Medicines Authority (Permit Number
per 5096).
Expected Outcomes:
• Establish and maintain the estuary as a rice grass free area. Follow up treatment for regrowth to
be managed and monitored in agreement with this plan. This work to be completed with the
assistance of the Marine Environment Section DPIW (6233 3370).
• 2006 to 2008 complete two surveys per year (December and March) to treat all regrowth in
accordance with this management plan or one survey to be completed in March.
• It is anticipated with thorough bi-annual surveys, that by summer of 2009 no rice grass will be
found in the Derwent Estuary.
Review of Plan
Identified stakeholders will review this Area-Based Management Plan in 2008 to ensure eradication is
achieved.
Appendix 2: Upper estuary rice grass survey lines (April-May 2008).
No rice grass identified