Report No. 1985
August 2011
The New Zealand King Salmon
Company Limited: Assessment of
Environmental Effects – Water
Column
The New Zealand King Salmon
Company Limited: Assessment of
Environmental Effects – Water
Column
Paul Gillespie
Ben Knight
Lincoln MacKenzie
Prepared for
New Zealand King Salmon Ltd
Cawthron Institute
98 Halifax Street East, Private Bag 2
Nelson, New Zealand
Ph. +64 3 548 2319
Fax. + 64 3 546 9464
www.cawthron.org.nz
Reviewed by:
Approved for release by:
Chris Cornelisen
Rowan Strickland
Issue Date: 22 September 2011
Recommended citation:
Gillespie P, Knight BR, MacKenzie L 2011. The New Zealand King Salmon Company Limited: Assessment of Environmental
Effects – Water Column. Prepared for The New Zealand King Salmon Company Ltd. Cawthron Report No. 1985. 79 p.
© Copyright: Apart from any fair dealing for the purpose of study, research, criticism, or review, as permitted under the Copyright Act, this publication must
not be reproduced in whole or in part without the written permission of the Copyright Holder, who, unless other authorship is cited in the text or
acknowledgements, is the commissioner of the report.
EXECUTIVE SUMMARY
This report details the range of possible effects to water column ecology that may result from eight
proposed salmon farms in The New Zealand King Salmon Company Ltd (NZ King Salmon) Plan
Change for the Marlborough Sounds. The report focuses on effects associated with (1) farm structures
and surface water conditions, (2) depletion of dissolved oxygen (DO) from high levels of fish
respiration, and (3) nutrient loading associated with the addition of feed and production of fish wastes.
Of these three issues, the effects associated with nutrient loading are the most extensive and likely to
extend beyond the area of the proposed farms. Consequently the bulk of the report, and efforts around
our assessments, were heavily weighted toward this issue. The approach to assessing effects included
referencing published literature and the application of models for predicting effects of nutrient loading
on the water column environment.
Based on our assessment, the physical effects of farm structures on currents, waves, shading and water
column stratification are expected to be very small and highly localised. These physical effects could
potentially be important in areas where flows are low and waves are important (e.g. Papatua);
however, we note that the structure footprints are relatively small and therefore these effects are
unlikely to have a measurable influence on the ecology of the water column environment.
The effects of large numbers of salmon on depletion of dissolved oxygen (DO) is also expected to be
very small and limited to the vicinity of the farms. Currently, DO is measured as part of routine farm
management to ensure suitable water quality conditions for farmed salmon. It is possible that depleted
DO levels that do not harm the fish may harm other organisms in the water column (e.g. larvae);
however, these effects would be very small, highly localised and difficult to measure through
monitoring. The placement of farms in high-flow environments will mitigate effects of the fish on DO
levels beyond the farms.
The addition of salmon farms represent a new nutrient load to the Marlborough Sounds, with nitrogen
(N) being the most critical nutrient with regard to water column enrichment effects. An assessment
using a mass-balance modelling approach suggests that the existing systems are well within
experimentally derived ‘critical limits’ for nutrient loading. This is further supported by simple tidal
flushing models, which show the additional N load would result in very small increases to the total
nitrogen concentrations in the water column for both Sounds (0.65% in Pelorus Sound and 1.35% in
Queen Charlotte Sound). Increases in water column nutrients in turn have the potential to increase
Sound-wide phytoplankton biomass (measured as chlorophyll a (chl a) concentrations). However,
potential increases are expected to be small (~7.4% in Pelorus Sound and ~12% in Queen Charlotte
Sound).
More sophisticated 3D modelling highlights potential changes in dissolved inorganic nitrogen (DIN)
concentrations close to the proposed sites. The majority of the proposed sites are ‘high-flow’ sites
(>10 cm/s depth averaged currents) where DIN is rapidly diluted, so the modelled changes are
generally small outside of the proposed sites, but with localised ‘peaks’ where DIN plumes may
overlap. Given the biological uptake of DIN is likely greatest during spring to autumn seasons, when
light is less limiting, the best period to detect any DIN changes at regions identified in the model
would be in deeper waters during winter.
Report No. 1985
August 2011
iii
The models also indicate the potential for measurable increases in chl a, but we note that our simple N
to chl a scaling approach does not incorporate the dampening effect of the ecosystem (including
shellfish aquaculture) or time lags in growth. Consequently, the model estimates of chl a increases
may be overestimated. Indeed, chl a sampling undertaken before the existing salmon farms were
operating (1985) in Pelorus Sound and new unpublished measurements from a period when existing
farms were in place (2007 to 2009), do not appear to show any discernable differences in mean annual
concentrations in the inner or outer Sound regions. Similarly, analysis of recent (2003 to 2005)
unpublished chl a data from inner Queen Charlotte Sound and Tory Channel shows that it appears to
have concentrations typical of mesotrophic waters. The lack of discernible gradients in chl a
concentrations has also been noted in overseas studies aimed at detecting water column effects from
salmon farms. Nevertheless, we note our spatial models do highlight areas where the possible
magnitude of increases could be detected under appropriate conditions.
It is important to place the effects associated with the NZ King Salmon Plan Change sites into the
context of the existing environment; we have also considered whether they would be ecologically
damaging by shifting the regions from an existing mesotrophic state to a eutrophic state. A shift to a
eutrophic or ‘overly-enriched’ state is generally considered to be undesirable due to associated
increases in harmful algal blooms and wider ecosystem impacts. By considering the potential changes
to chl a concentrations predicted by our models, which indicate potential enrichment of the regions,
we note that the proposed changes would not be expected to lead to a shift from the present
mesotrophic state of the regions.
Nevertheless, additional nutrients have the potential to affect phytoplankton biomass and community
composition. This may have positive effects to components of the ecosystem through the provision of
additional resources for growth (e.g. mussels and fisheries); but there is also the potential for negative
impacts. In particular we raise the possibility that harmful algal blooms (HABs) that occur
occasionally, due to natural causes, may increase in intensity and/or spatial extent as a result of these
increased nutrients. To date there appears to be no spatial correlation between existing salmon farm
operations and HAB formation, but we acknowledge the potential for such effects. Reduction of feed
levels may lead to some mitigation of any observed stimulation in the growth of toxic species of
phytoplankton; however, we note that dinoflagellate cyst formation may lead to multi-year events even
with cessation of new nutrient additions.
Due to the complex nature and inherent variability in water column processes in the marine
environment, the assessment of effects associated with nutrient loading required the application of a
modelling approach. Our model estimates of maximum nutrient and phytoplankton changes likely to
occur as a result of the proposed farms are conservative. Predictions indicate nutrient loadings from
the proposed farms lie within system-wide limits and do not suggest their development would result in
significant changes to water column conditions (i.e. a shift to a eutrophic state). However, because
these predictions are based primarily on models, there remains some uncertainty with regard to the
effects that will actually occur following the addition of salmon farms in the Sounds. We therefore
recommend that any expansion of the salmon industry in the Marlborough Sounds proceed in a
precautionary staged manner, with appropriate monitoring and adaptive management measures in
place. We recommend monitoring of water column effects that addresses the local environment
around salmon farms and the wider ecosystem.
iv
Report No. 1985
August 2011
TABLE OF CONTENTS
EXECUTIVE SUMMARY......................................................................................................... III 1. INTRODUCTION .............................................................................................................. 1 Report scope and structure ....................................................................................................................... 1 1.2. Assessment approach ............................................................................................................................... 4 1.3. Issues and potential water column effects................................................................................................. 4 1.1. 2. EXISTING ENVIRONMENT ............................................................................................. 6 2.1. Overview of the Marlborough Sounds water column environment ............................................................ 6 2.1.1. Pelorus Sound ........................................................................................................................................... 7 2.1.2. Queen Charlotte Sound............................................................................................................................. 8 2.1.3. Port Gore................................................................................................................................................... 8 2.2. Physical characteristics ............................................................................................................................. 9 2.2.1. Residence times ...................................................................................................................................... 11 2.3. Dissolved oxygen .................................................................................................................................... 12 2.4. Nutrients and biological characteristics ................................................................................................... 12 2.4.1. Nutrients .................................................................................................................................................. 13 2.4.2. Sources and sinks of nitrogen in the Sounds, a mass-balance analysis ................................................. 15 2.4.3. Nutrient loading in relation to potential ecological limits .......................................................................... 18 2.4.4. Phytoplankton Biomass ........................................................................................................................... 19 2.4.5. Harmful Algal Blooms (HAB) ................................................................................................................... 22 3. 3.4. ASSESSEMENT OF PHYSICAL EFFECTS .................................................................. 23 Currents .................................................................................................................................................. 23 Waves ..................................................................................................................................................... 24 Temperature, salinity and stratification .................................................................................................... 24 Light attenuation ...................................................................................................................................... 25 4. ASSESSMENT OF DISSOLVED OXYGEN EFFECTS .................................................. 26 3.1. 3.2. 3.3. 5. ASSESSMENT OF NUTRIENT LOADING EFFECTS ................................................... 28 Nutrient toxicity ........................................................................................................................................ 28 5.2. Phytoplankton composition and HABs .................................................................................................... 28 5.3. Nutrient Mass-Balance and Critical Ecological Limits Assessment ......................................................... 32 5.3.1. Nitrogen loading rates in the Marlborough Sounds ................................................................................. 32 5.4. System-wide Effects on Phytoplankton Biomass and Nutrient Concentration ......................................... 33 5.5. Spatially explicit cumulative effects modelling ......................................................................................... 35 5.5.1. Spatial Modelling Methodology and Parameterisation............................................................................. 35 5.5.2. Spatial modelling results - Pelorus Sound ............................................................................................... 40 5.5.3. Spatial modelling results – Queen Charlotte Sound ................................................................................ 47 5.6. Wider ecosystem effects ......................................................................................................................... 52 5.1. 6. SUMMARY OF WATER COLUMN EFFECTS ............................................................... 53 7. MONITORING RECOMMENDATIONS .......................................................................... 60 8. REFERENCES ............................................................................................................... 64 9. APPENDICES ................................................................................................................ 72 Report No. 1985
August 2011
v
LIST OF FIGURES
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
vi
Maps showing the 8 salmon farm sites proposed in the current plan change application,
existing NZ King Salmon farm sites and two NZ King Salmon farm sites currently under
appeal ................................................................................................................................. 3
Simulated mean surface currents in Pelorus Sound and Queen Charlotte Sound over a
month long period. .......................................................................................................... 10
Graduated circle plots of % incidence of ‘high’ and ‘very high’ HAB risk at MSQP
monitoring sites in the Marlborough Sounds .................................................................... 31
Median (DIN and chlorophyll concentrations from the proposed salmon farms under
recommended initial limits over an 30 day period for the surfaceand bottom model layers
in Pelorus Sound for the period 25 June to 25 July 2008. ............................................... 41
Mean potential DIN and chlorophyll concentration changes from proposed salmon farms
under recommended initial limits over an 30 day period for the surface and bottom (lower)
model layers in Pelorus Sound for the period 25 June to 25 July 2008. ....................... 43
95th percentile values DIN and chlorophyll concentrations from the proposed salmon
farms under recommended initial limits over an 30 day period for the surface model
layers in Pelorus Sound for the period 25 June to 25 July 2008. ..................................... 44
Median and mean cumulative DIN and chlorophyll concentration changes from all
proposed, pending and existing salmon farms under recommended initial limits over an
30 day period for the surface and bottom model layers in Pelorus Sound for the period 25
June to 25 July 2008. ...................................................................................................... 46
Median potential DIN and chlorophyll concentration changes from proposed salmon
farms under recommended initial limits over an 30 day period for the surface and bottom
model layers in Queen Charlotte Sound. .......................................................................... 48
Mean potential DIN and chlorophyll concentration changes from proposed salmon farms
under recommended initial limits over an 30 day period for the surface and bottom model
layers in Queen Charlotte Sound for the period 28 August to 27 September 2008. ...... 49
95th percentile potential DIN and chlorophyll concentration changes from proposed
salmon farms under recommended initial limits over an 30 day period for the surface and
bottom model layers in Queen Charlotte Sound for the period 28 August to 27 September
2008. ................................................................................................................................. 50
Median and mean cumulative DIN and chlorophyll concentration changes from all
proposed and existing salmon farms under recommended initial limits over an 30 day
period for the surface and bottom model layers in Queen Charlotte Sound for the period
28 August (model day 95) to 27 September 2008.. .......................................................... 51
Surface plots of potential surface water concentration changes to DIN and Chlorophyll
from the proposed salmon farms. ................................................................................... 63
Report No. 1985
August 2011
LIST OF TABLES
Table 1.
Table 2
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14
Table 15.
Table 16.
Issues and potential water column effects and the their scale ........................................... 5
Water flow conditions and approximate depth beneath proposed farm sites. Current
speeds are depth-averaged values calculated from data collected during 30 day
deployments of Acoustic Doppler Current Profilers ............................................................ 9
Relevant properties of each Sound used to estimate tidal residence times and critical
nutrient loading limits. ..................................................................................................... 11
Typical water column characteristics for different trophic states, as summarized by Smith
et al. (1999) based on the review by Håkanson (1994). T ................................................ 12
Summary of existing knowledge relating to water column effects within the vicinity of the
six existing NZKS farms in the Marlborough Sounds. ...................................................... 14
Mean (Min-Max) dissolved and total nutrients measured over the period April 1984 to
April 1985 from inner Pelorus Sound sites (Mills Bay/Schnapper Point) to outer sites
(Richmond Bay), data from Gibbs et al. (1992), and unpublished monthly Cawthron
nutrient data (*) at inner QC Sound (Wedge Point) for the years 1997 to 1999. .............. 15
Relative magnitudes of nitrogen sources (finfish, riverine and oceanic) and sinks (mussel
harvests and denitrification) for the Pelorus Sound region. ............................................ 16
The relative magnitudes of nitrogen sources (finfish, riverine and oceanic) and sinks
(mussel harvests and denitrification) for the Queen Charlotte Sound region. ................ 17
Yearly ‘natural’, and existing net aquaculture (Salmon additions – shellfish removals)
nitrogen inputs for Pelorus Sound and Queen Charlotte (QC) Sound. .......................... 19
Mean (Min-Max) suspended and particulate properties of the water column measured
over the period April 1984 to April 1985 from inner Pelorus Sound sites (Mills
Bay/Schnapper Point) to outer sites (Richmond Bay), from Gibbs et al. (1992), and
unpublished weekly NIWA chlorophyll data (*) for the years 2003 to 2005. ................... 20
Change in estimated long-term steady-state nitrogen concentrations (above ambient)
within Pelorus and Queen Charlotte Sounds with existing salmon farm feeding levels and
mussel farms operating assuming complete mixing and exchange. ................................ 21
Yearly ‘natural’ and all possible (existing, pending and proposed) salmon farming nitrogen
inputs for Port Gore, Pelorus Sound and Queen Charlotte (QC) Sound. ....................... 33
Change in estimated long-term steady-state nitrogen and chl a concentrations from
background and existing conditions within Pelorus and Queen Charlotte Sounds under
fully developed proposed initial feeding scenarios with existing and pending salmon farms
in place, assuming complete mixing and tidal exchange (see Appendix 2). .................... 34
Summary of existing and proposed feed levels used in the cumulative effects model,
depth and flow conditions at the proposed sites.. ............................................................ 38
Summary of assessed effects of proposed salmon farm site development on water
column properties. ............................................................................................................ 56
Summary of site specific assessment of water column effects ........................................ 58
LIST OF APPENDICES
Appendix 1. Background information on nitrogen mass balance calculations in Pelorus and Queen
Charlotte Sounds. ............................................................................................................. 72
Appendix 2. Simple ‘open box’ modelling methodology ........................................................................ 75
Appendix 3. Site suitability for finfish farms in the Marlborough Sounds .............................................. 76
Appendix 4. Unpublished data from CTD surveys ................................................................................ 78
Report No. 1985
August 2011
vii
1.
INTRODUCTION
This report considers the effects of additional salmon farms on the water column environment,
and forms one part of a wider assessment of ecological effects that has been conducted to
inform a proposed Plan Change and resource consent process for eight new salmon farms to be
established within the Marlborough Sounds by The New Zealand King Salmon Company Ltd
(NZ King Salmon) (Figure 1). Details pertaining to other issues such as the specific nature of
the application, visual effects, landscape effects and other ecological effects (e.g. effects on the
seabed, effects on fish, effects on marine mammals etc.) are provided in separate reports.
1.1. Report scope and structure
Potential environmental effects associated with three primary water column issues are
assessed, including:
1.
Physical effects (e.g. on currents, waves) associated with the addition of threedimensional artificial structures (net pens) that extend from the water’s surface down
through the water column;
2.
Effects of dissolved oxygen depletion associated with respiration by large numbers of
fish within a relatively small volume of water; and
3.
Effects of nutrient loading associated with the addition of feed and subsequent fish
waste production.
The report is structured according to the effects associated with the above three water column
issues. The existing water column environment within the context of the above issues and
effects are first described for the Marlborough Sounds. The ‘Existing environment’ section
also provides background on the current sources and sinks of nutrients in the Sounds and
introduces concepts relating to nutrient levels and phytoplankton production that are later
referred to in the assessment of effects. Following the description of the existing water column
environment, we summarise the water column effects that could potentially occur from the
proposed NZ King Salmon Plan Change and subsequent addition of salmon farms in the
Sounds. Effects are categorised by issue and according to those that are likely confined to the
vicinity of a salmon farm and those that may also affect the wider Marlborough Sounds
ecosystem (e.g. Bay to Sound-wide scales).
The potential effects on the water column associated with the three main issues are then
assessed. Of the three issues, the effects associated with nutrient loading are the most
extensive and challenging to quantify. Consequently the bulk of the report, and efforts around
our assessments, are heavily weighted toward this issue. This is because the effects from
addition of nutrients, such as increases in phytoplankton, would not only be influenced by
point-source nutrient loading from salmon farms, but also a number of other factors such as
contributions from other nutrient sources (e.g. oceanic sources, runoff), the levels of mixing
and flushing in the Sounds, and light levels.
Report No. 1985
August 2011
1
The availability of nutrients directly influences the biomass of phytoplankton, which forms the
base of the food web; hence nutrient loading also has the potential to indirectly affect a range
of wider ecosystem processes. Some phytoplankton produce toxins and with sufficient light
and nutrients can form harmful algal blooms (HABs). The effects of nutrient loading from
salmon farms are therefore important to consider within the context of HABs in the
Marlborough Sounds. Through the use of models, our assessment also addresses the potential
effects of nutrient loading associated with multiple farms and assesses cumulative inputs at a
Sound-wide scale. Nitrogen is considered to be the most important nutrient limiting primary
production in the Marlborough sounds; hence our assessments on the effects of nutrient
loading focus on dissolved inorganic forms of nitrogen.
Due to the complex nature and inherent variability in water column processes in the marine
environment, the assessment of effects associated with nutrient loading requires the application
of models. Consequently, there remains some uncertainty with regard to the effects that will
actually occur following the addition of salmon farms in the Sounds. Recommendations are
made toward a conservative approach to initial development aligned with monitoring of effects
that addresses the local water column environment around salmon farms and the wider
ecosystem.
2
Report No. 1985
August 2011
D'
Ur
vil
le
Is.
TASMAN
BAY
TASMAN SEA
Expanded
area
PACIFIC
OCEAN
ok
Co
Kaitira
Waitata
St
it
ra
Tapipi
Richmond
Papatua
Port Gore
Pelorus Sound
p
Kene
eru S
ou nd
Kaitapeha
Qu e e
arlo
n Ch
o
tte S
und
Ngamahau
Tory Ch annel
Ruaomoko
TASMAN
BAY
2.5
5
10
Kms
D'
Ur
vi
lle
Is.
0
k
oo
C
St
Waihinau Bay
it
ra
Re
ac
h
White Horse Rock
W
ait
a
ta
Forsyth Bay
Port Gore
Melville Cove
Pelorus Soun
d
Crail Bay
Otanerau Bay
p
Kene
eru S
Ruakaka Bay
o und
Qu e
Figure 1.
o
tte S
harlo
en C
und
Clay Point
Tory Ch annel
Te Pangu Bay
PACIFIC
OCEAN
Maps showing the eight salmon farm sites proposed in the current plan change application (black
circles – top map), existing NZ King Salmon farm sites (red circles – bottom map) and two NZ
King Salmon farm sites currently under appeal (Melville Cove and White Horse Rock – green
triangles – bottom map)
Report No. 1985
August 2011
3
1.2. Assessment approach
To a large extent, the assessment of effects of salmon farms on the water column environment
is based on published literature and draws on knowledge from over 15 years of institutional
experience monitoring the environmental effects of aquaculture in the Marlborough Sounds.
Assessment of the physical effects from farm structures is based on previous research and
observations made in relation to similar artificial structures (e.g. mussel farms) in the marine
environment. The effect of farmed salmon on dissolved oxygen (DO) depletion is assessed
using data and information from the literature and the monitoring of DO within existing farms.
The assessment of the effects of nutrient loading on the water column was more involved and
included the application of the following three modelling techniques:
1.
Mass balance approach – A simple ‘closed box model’ based on available information on
sources and sinks of nitrogen in the Sounds is used to place levels of additional nutrient
loading within the context of ‘critical nitrogen loading rates’.
2.
Aspatial model – A basic ‘open’ version of the mass-balance approach above is used to
estimate long-term ‘steady state’ concentrations of nutrients that assumes complete tidal
mixing and exchange of water within the Sounds.
3.
Spatially explicit model (realistic model) – A numerical 3D hydrodynamic model is used
to generate finer-spatial resolution estimates of likely changes to DIN and chlorophyll a
(chl a) concentrations resulting from the proposed salmon farms. This approach reduces
uncertainty from the more simple modelling approaches above and allows for the
cumulative effects of multiple farms to be visualised at a Sound-wide scale.
Collectively, the above approaches provide greater confidence in the assessment and assist in
gauging the likelihood and magnitude of water column effects that are likely to occur as a
result of the proposed NZ King Salmon Plan Change and addition of salmon farms to the
Marlborough Sounds.
1.3. Issues and potential water column effects
As caged fish farming expands globally, water column issues are receiving increasing
attention (Crawford 2003; Read & Fernandes 2003; Buschmann et al. 2009). Overseas studies
show that finfish farms in areas with inadequate flushing and high stocking densities have the
greatest potential for adverse water column effects (Wu et al. 1994; La Rosa et al. 2002;
Buschmann et al. 2009). Water column effects have also been considered in relation to
salmon farming in New Zealand. Specific regions investigated in New Zealand include the
Firth of Thames (Zeldis 2008), Hauraki Gulf (Zeldis 2010), Golden Bay and Tasman Bay
(Zeldis et al. 2011), the Marlborough Sounds (e.g. Forrest et al. 2007, Figure 1) and Stewart
Island (Roper et al. 1988). Two potential issues to emerge from these studies are of particular
relevance to the expansion of salmon farming in the Marlborough Sounds. These are: (1)
4
Report No. 1985
August 2011
depletion of dissolved oxygen (DO) in the water column, and (2) nutrient enrichment of the
water column with related implications for primary production, plankton communities and
their consumers (e.g. mussels, fish etc.). A third issue relating to the effects of farm structures
on the physical environment is considered to be less significant. These issues and the likely
magnitude of associated effects are summarised in Table 9. The aim of this report is to assess
these issues for the eight proposed salmon farm sites (Figure 1). Where sufficient information
is available through previously published studies or existing data to estimate potential impacts,
we have used this information.
Table 1.
Issues and potential water column effects and the their scale (local versus wide, e.g. bay or Sound).
Issue
Potential effects
Physical water column
effects - Farm structures
occupy a three-dimensional
space at and below the water
column
Attenuation of currents
Dissolved oxygen depletion
- Presence of large numbers
of fish within a small
volume of water results in
high rates of respiration
(oxygen consumption)
Nutrient loading - Salmon
farming involves the
addition of feed and
therefore results in fish
waste production and new
inputs of nutrients into the
water column
Report No. 1985
August 2011
Local
Scale
Wide
Reduced concentration of dissolved oxygen
√
√
√
√
√
Oxygen depleted to levels adverse to biological
processes
√
Increased concentrations of dissolved nutrients
(ammonium toxicity)
√
Changes in phytoplankton community composition
(including HAB species)
√
√
Increased phytoplankton production (including
HAB species if present)
√
√
Reduction in wave action/energy
Effects on salinity and/or temperature stratification
Attenuation of incoming solar radiation
Increased zooplankton and higher trophic levels in
response to increased primary production
√
Cumulative inputs from multiple farms resulting in
system-wide changes in ecological integrity.
√
5
2.
EXISTING ENVIRONMENT
2.1. Overview of the Marlborough Sounds water column environment
The Marlborough Sounds with their numerous sheltered inlets and bays, broad open reaches
and proximity to the deep turbulent waters of Cook Strait provide a diversity of physical and
chemical water column conditions that shape the species composition, successional patterns
and biomass of the phytoplankton. In general terms the productivity of the Sounds would be
considered to be low to moderate with a high degree of seasonal, spatial and inter-annual
variability. Although phytoplankton communities are highly dynamic, there are consistent
seasonal patterns in phytoplankton biomass and species succession that occur in the Sounds
and throughout the wider region (MacKenzie & Gillespie 1986; Gibbs & Vant, 1997;
MacKenzie 2004) and are typical of temperate latitudes elsewhere. There are also consistent
spatial differences due to the hydrodynamic properties of specific environments that control
the residence time of phytoplankton populations and access to optimum light and nutrient
conditions.
Light limitation in late autumn/early winter generally leads to a slowdown in phytoplankton
growth and nutrient demand with the consequence that the concentrations of oxidised forms of
nitrogen (nitrate and nitrite) can accumulate and reach their annual maxima. This phenomenon
is also facilitated by the re-mineralisation of organic nitrogen in the sediments and water
column. Concurrently during this period, water column stratification that has been maintained
throughout the summer and autumn can break down due to increased wind mixing and a
cooling of surface waters. Diatoms respond very rapidly to water column mixing, increases in
nitrate (Carter 2004; Carter et al. 2005) and light, which usually leads to diatom blooms in late
winter to early spring – the period of the annual productivity maximum. Throughout the
spring a succession of diatom blooms may take place until early summer, when warming
surface waters stabilise the water column, preventing mixing, and favouring phytoplankton
communities dominated by flagellates. These are highly mobile and can take advantage of
vertical light and nutrient gradients. At these times the upper water column may become
largely depleted of inorganic nutrients and flagellate populations become established at the
density interface (pycnocline) where access to nutrients and light is optimal. Often there is a
secondary productivity maximum in late summer/autumn when zooplankton grazing pressure
that has built up over the spring and summer is relaxed.
Superimposed on this general seasonal pattern are nutrient enrichment and water column
mixing episodes brought on by floods, storms and upwelling events and complex biological
interactions (competition for nutrients, grazing etc.) that also play important roles in
structuring phytoplankton communities. Although there is very limited information describing
water column DO concentrations in the Sounds, we are not aware of any reports of related
impacts to pelagic marine life.
Pelorus and Queen Charlotte Sounds differ most markedly in the influence that freshwater
runoff has on the water column which is a function of the relative freshwater catchment area of
each Sound. Pelorus and Queen Charlotte Sounds have sea-surface areas of 385 km2 and
6
Report No. 1985
August 2011
305 km2 and freshwater catchment areas of ~1,725 km2 and 640 km2, respectively (Heath
1974; pers. estimate). Consequently the ratio of catchment to sea surface areas is much greater
in Pelorus Sound than Queen Charlotte Sound. Because of its importance to the mussel
farming industry most research has been focused on the Pelorus Sound system and there are
numerous published papers that deal with various aspects of the Sound’s hydrology and
plankton ecology. There has been relatively little equivalent research on Queen Charlotte
Sound and much of the existing information is contained in unpublished reports and datasets.
2.1.1. Pelorus Sound
The Pelorus River dominates the temperature, salinity, nutrient and turbidity fields of inner
Pelorus and Kenepuru Sounds and during high-flow periods the river’s influence can extend
throughout the Sound (Gibbs 1993; Gibbs et al. 1991, 1992). However, riverine inputs to
outer Pelorus Sound are small relative to the large volume of water exchanged with Cook
Strait through tidal wind-driven and estuarine processes (Gibbs et al. 1992; Dupra 2000).
Water movement in inner Pelorus Sound is driven by the lunar tide and an estuarine circulation
pattern induced by the seaward outflow of lower salinity surface water. This results in the
counter-flow of nutrient-enriched bottom waters into the inner Sounds with an intensity that
changes depending upon wind speed and direction and variations in the flow of the Pelorus
River (Gibbs 1993). The longer water-residence time and higher water column stability of
embayments off the main channels results in these regions frequently supporting
dinoflagellate-dominated communities (MacKenzie unpubl. data).
Seawater temperatures in inner Pelorus Sound are alternatively warmer in summer and cooler
in winter than outer Sound waters reflecting the shallow, low salinity conditions in the inner
Sound and the moderating influence of Cook Strait in the outer Sound. Gibbs et al. (1992)
showed that spatial variability in nutrients and phytoplankton biomass in the inner Sound was
associated with variations in river flows whereas in the outer Sounds productivity was
controlled by oceanic exchange and recycled nutrients from sediment re-mineralisation.
Following storms, phytoplankton may be flushed out of the Sound and low nitrogen and
phytoplankton biomass in summer coincides with low rainfall and low concentrations in Cook
Strait. Gibbs (1993) identified the important role that Kenepuru Sound plays in reducing the
flushing rate and providing a reservoir where enhanced phytoplankton production (MacKenzie
et al. 1986) can take place after nutrient enriching flood events in the inner Sound.
In situ nutrient supplementation experiments have shown substantial increases in
phytoplankton growth rates as the result of inorganic nitrogen (nitrate and ammonium)
additions but no response from inorganic phosphorus additions (Gibbs & Vant 1997).
Although dissolved reactive silicate or DRSi (a required nutrient for diatoms) additions were
not tested, the limited available data for the Sounds indicates that it is generally present in
excess of requirements in Pelorus Sound (Mackenzie unpublished) as well as the surrounding
regions including Tasman Bay (Mackenzie 2004). These results indicate that nitrogen is the
primary limiting nutrient for phytoplankton production in the Sounds.
Report No. 1985
August 2011
7
Inter-annual variations in river flows and weather patterns, including larger scale climate
perturbations such as the El Niño southern oscillation (ENSO) phenomenon impact on interannual variability of phytoplankton production and species composition (Carter 2004; Zeldis et
al. 2008b). There is evidence that persistent NNW winds in summer during an El Niño phase
results in upwelling at the Pelorus Sound entrance leading to higher nitrate availability and a
higher than normal phytoplankton biomass dominated by diatoms (e.g. Zeldis et al. 2008).
2.1.2. Queen Charlotte Sound
From a water column perspective there are several distinct biogeographical zones in Queen
Charlotte Sound. These include the inner Sound and bays southwest of Tory Channel
terminating in the Grove Arm, Tory Channel itself and the various bays which extend off it
(e.g. Onapua Bay, Oyster Bay) and the large north-eastern region of the Sound opening to
Cook Strait. Within this latter region, East Bay and Endeavour Inlet can be regarded as
discrete units. From the limited amount of physical and biological data that is available it is
clear that the physical properties, nutrient chemistry and hence the phytoplankton ecology
varies among these regions. The hydrodynamics of Queen Charlotte Sound are complicated
by having two entrances that differ in tidal phase.
Most of the water column research that has taken place has been in the Grove Arm since this
area has a history of frequent toxic micro-algal blooms (MacKenzie et al. 1998, 2004). High
oceanic salinities of surface waters within the inland reaches of the Grove Arm are common
and the area usually supports a high phytoplankton biomass. Inorganic nutrient concentrations
generally follow a predictable seasonal pattern although bottom waters usually contain high
levels of nitrate throughout the year and nutrient enrichment episodes associated with
intrusions of oceanic water have been identified. The mechanism of these intrusions is not
completely understood, however it may involve the onset of estuarine-like circulation during
heavy rainfall periods and tidally driven jets of deep bottom water from Tory Channel.
In contrast to the inner Sound, Tory channel is a highly turbulent and dynamic environment
and this is reflected in the biomass of the phytoplankton which (in the channel proper) is
usually relatively low with contrasting species composition.
Less is known about the water column and plankton ecology of the northern part of Queen
Charlotte Sound, except that it is characterised by a less stable water column with deeper
mixing than the inner Sound and the phytoplankton composition probably more closely
reflects that of Tory Channel. It is expected that East Bay and Endeavour Inlet will have
unique characteristics of their own.
2.1.3. Port Gore
One of the proposed salmon farm sites (Papatua) lies in Port Gore. Port Gore is a smaller
embayment bordering Cook Strait between Pelorus and Queen Charlotte Sound. Although
8
Report No. 1985
August 2011
there is very little available information describing water column nutrient and phytoplankton
characteristics in the region, they would be expected to be similar to the outer Sounds with
flushing from the Strait the primary controlling factor.
2.2. Physical characteristics
The Marlborough Sounds are temperate with water column temperatures generally ranging
between 10 and 20°C depending on the time of year and location (see Appendix 4). Salinity
varies as a function of rainfall and river flows. Surface salinity within the inner region of
Pelorus Sound (Schnapper Point) ranges between 31 and 33 psu (practical salinity units)
however further salinity reduction can occur after major rainfall events. This site is in closest
proximity to the Pelorus River. Salinity at sites in outer Pelorus and within Queen Charlotte
Sound and Port Gore are more saline and generally fall between 33 and 35 psu (Appendix 4).
Based on outputs from the SELFE hydrodynamic model (see Knight & Beasley, in prep),
surface currents are stronger than those near the bottom, and generally range up to 1 m s-1,
depending on conditions (wind, tide stage) and location. Currents along the main channels and
nearest the entrance to Cook Strait tend to be highest (Figure 2). Net transport of surface
waters is in a seaward direction, whereas bottom currents have a net inward flow. This is
likely a function of prevailing winds and estuarine circulation driven by freshwater inputs.
Simulated currents and general circulation patterns in Pelorus Sound are similar to those
observed by Gibbs et al. (1991). The proposed farms in Pelorus and Queen Charlotte Sounds
are situated in high-flow areas. The farm in Port Gore is situated in low-flow environment,
however it is in close proximity to Cook Strait (see Figure 1; Table 2).
Table 2.
Water flow conditions and approximate depth beneath proposed farm sites. Current speeds are
depth-averaged values calculated from data collected during 30 day deployments of Acoustic
Doppler Current Profilers (ADCPs). HF = High Flow, LF = Low Flow.
Flow
Depth averaged
current speed (cm s-1)
Depth (m)
Pelorus Sound
Kaitira (KAI)
Richmond Bay (RIC)
Taipipi (TAP)
Waitata Reach (WAT)
HF
HF
HF
HF
19.5
12.7
14.5
19.5
60
32 - 40
62
63
Queen Charlotte Sound
Ngamahau (NGA)
Ruaomoko (RUO)
Kaitapeha (KAP)
HF
HF
HF
22.3
29.1
10.4
23-35
50
60
Port Gore
Papatua (PAP)
LF
3.7
35
Site
Report No. 1985
August 2011
9
Figure 2.
10
Simulated mean surface currents in Pelorus Sound (top panel) and Queen Charlotte Sound (bottom
panel) over a month long period. Background colours refer to mean current speeds (m s-1)
(independent of direction), whilst arrows show net transport of water over the period.
Report No. 1985
August 2011
2.2.1. Residence times
Relative to the large volumes of water exchanged with Cook Strait through tidal, wind-driven
and estuarine processes, riverine inputs to outer Pelorus Sound are relatively small (e.g. Gibbs
et al. 1992; Dupra 2000). Using updated analyses of the volumes and surface areas of the
regions and the methods of Heath (1976), we estimate an average residence time (mean of
spring and neap) for water in Pelorus Sound as a whole of 14 days and for Queen Charlotte
Sound a residence time of about 36 days (Table 3). We note that our tidal estimate for Pelorus
Sound is shorter than the salt balance estimate of about 21 days by Dupra (2000) and more
detailed calculations of flushing in the Sound by Heath (1976), hence it appears tidal exchange
may overestimate the rate of flushing in the region in some years.
The flushing rate in Queen Charlotte Sound is complicated by having two entrances that differ
in tidal phase (R Heath, pers. comm.). As a consequence, the residence time of the outer
region of Queen Charlotte Sound (north and east of Ruakaka Bay where Tory Channel meets
the main channel of the Sound) is likely to be overestimated using the method of Heath (1976).
Table 3.
Relevant properties of each Sound used to estimate tidal residence times (= 2 x Tidal
Volume/Volume of the region at low water spring (LWS); Heath 1976) and critical nutrient
loading limits. Values shown are from Heath (1976; marked with *) and calculated independently
for this study.
Region
Pelorus Sound1
Inner QC Sound2
All QC Sound3
Surf.
Area
Tidal Range*
(m)
Tidal Volume.
(106 m3)
(km2)
385
68
305
Spring
2.37
1.4
1.4
Spring
912
95
427
Neap
1.46
0.5
0.5
Neap
562
34
152
Volume of
the region
at LWS4
Euphotic
Volume5
Tidal Residence
Time (days)
(106 m3)
9200
1747
9600
(106 m3)
5462
1045
4864
Spring
10.44
19.03
<23.27
Neap
16.94
53.18
<65.37
1
For the purposes of this analysis Pelorus Sound is considered to be the region south of Paparoa and Culdaff Point, excluding the
region east of Allen Strait.
2
For the purposes of this analysis Inner Queen Charlotte Sound is considered to be the region east of West Head and Dieffenbach
Point, excluding the region east of Allen Strait.
3
Due to the two entrances of the outer region of Queen Charlotte (QC) Sound, the estimated tidal residence time is likely to be
overestimated.
4
Volume has been calculated using charted data depth interpolated to an unstructured triangular mesh for all regions.
5
Euphotic volume is used for comparison to a critical nutrient loading rate (CNLR, see Section 5.3.1) and has been calculated
using the lower of the depth to the seabed or a seasonally averaged euphotic depth (19 metres from Beatrix Bay, Pelorus Sound,
Gibbs & Vant 1997).
The flushing rates provide a guide for estimating the amount of time any new nutrients may
spend in the Sounds, and are important when considering the effects of the proposed sites.
Although the estimates presented here are relatively simple, they show that Pelorus Sound is
probably flushed faster than Queen Charlotte Sound.
Report No. 1985
August 2011
11
2.3. Dissolved oxygen
Gibbs et al. (1991) reports surface and bottom water DO concentrations at six sites in Pelorus
Sound extending from Richmond Bay (mid Sound) to Schnapper Point (Kenepuru Sound) on
seven occasions from April 1984 to April 1985. These data demonstrated well-oxygenated
conditions encompassing all seasons throughout the study area. Surface water concentrations
ranged from 7.6 to 12.2 g/m3 with moderate reductions of <1 to around 2 mg/m3 in bottom
waters, probably due to the circulation of high salinity oceanic water into the Sound from
Cook Strait and/or oxygen consumption from the seabed.
Equivalent DO data are not available for Queen Charlotte Sound, however well-oxygenated
conditions would be expected to prevail there to a similar degree. New Zealand King Salmon
monitoring data for existing farm sites in both Sounds is discussed in Section 4.
2.4. Nutrients and biological characteristics
A key component of our water column assessment of the proposed plan change is to determine
the existing state of the system and the degree of potential modification from additional
nitrogen wastes generated by salmon. Water column nutrient and phytoplankton
concentrations can be used to define the degree of enrichment of a body of water – referred to
as the ‘trophic state’. Waters receiving low inputs of nutrients are defined as oligotrophic and
are characterised by low nutrient and phytoplankton concentrations, whilst eutrophic states are
characterised by high concentrations. The mesotrophic state refers to a balanced state whereby
additional nutrients contribute to increased primary production (the production of
phytoplankton and other autotrophs) and efficient transfer of this production through the food
web. In an eutrophic state this relationship starts to break down and increasing nutrient inputs
can lead to conditions (e.g. reduced DO levels) not suitable for some species. At extreme
levels of nutrient inputs, anoxia and azoic conditions can occur periodically, this trophic state
is termed hypertrophic or dystrophic (Smith et al. 1999; Table 4).
We follow the interpretation of Wild-Allen et al. (2010), who define the various trophic states
according to the mean annual water column properties detailed in Table 4. This interpretation
is important, as periodic high concentrations of chl a or nutrients would not necessarily
indicate a shift in trophic state.
Table 4.
Typical water column characteristics for different trophic states, as summarized by Smith et al.
(1999) and based on the review by Håkanson (1994). TN= total nitrogen, TP= total phosphorous,
chl= chlorophyll, SD= Secchi disc depth (a measure of water clarity).
Trophic
state
Oligotrophic
Mesotrophic
Eutrophic
Hypertrophic
12
TN
(mg/m3)
<260
260-350
350-400
>400
TP
(mg/m3)
<10
10-30
30-40
>40
chl
(mg/m3)
<1
1-3
3-5
>5
SD (m)
>6
3-6
1.5-3
<1.5
Report No. 1985
August 2011
In order to undertake assessment of the existing environment, we searched for any available
datasets (published and unpublished) that would be relevant. We accessed information from a
number of surveys that were undertaken in Pelorus Sound. The most comprehensive of these
were by Bradford et al. (1987) and Gibbs et al. (1992) who assessed nutrient and plankton
variability at sites associated with mussel farming. Both of these surveys were undertaken
before salmon farming commenced in Pelorus Sound. We were also provided with
unpublished chl a data for weekly monitoring sites in the inner and outer Pelorus Sound for a
period after existing salmon farms were operating (2007 to 2010).
The same level of background data was not available for Queen Charlotte Sound, but some
outer Queen Charlotte Sound sites were included in the study of Bradford Grieve et al. (1987)
and weekly water column monitoring of chl a from 2003 to 2010 in East Bay, Wedge Point
and Tory Channel. We were unable to access all of the chl a data for our assessment, but were
able to obtain some data for the period 2003 to 2005 for Wedge Point and Tory Channel when
most of the existing salmon farms were operating (excluding Clay Point).
2.4.1. Nutrients
There is general consensus that fish farms cause localised nutrient enrichment, however the
specific effects on wider-scale phytoplankton communities (e.g. species composition and
biomass) are not well understood for coastal waters (Frid & Mercer 1989; Wu et al. 1994,
1999; La Rosa et al. 2002). Based on water column monitoring of existing salmon farming
sites in the Marlborough Sounds, only slight nutrient enrichment has been observed within
close proximity to the farms (Table 5; Hopkins et al. 2004; Forrest et al. 2007).
Report No. 1985
August 2011
13
Table 5.
Summary of existing knowledge relating to water column effects within the vicinity of four
existing New Zealand King Salmon farms in the Marlborough Sounds where water column
nutrients have been measured. Data was collected as part of industry-funded annual monitoring
and from internally funded Cawthron research.
Farm Site
Nutrient sampling and results
Te Pangu
Nutrients were measured in 2004 at three water depths within the cages, 50 m from the farm and
at a reference site. These data indicated localised slight enrichment of the water column that
poses minimal risk to the environment.
Ruakaka
Nutrients were measured in 2002 at three water depths within the cages, 50 m from the farm and
at a reference site. These data indicated localised slight enrichment that poses minimal risk
to the environment.
Nutrients were measured again in 2010 at 50 m down-current and control sites. No significant
differences were found in ammoniacal-N, dissolved reactive phosphorous, nitrate-N, nitrite-N or
chl-a concentrations between the stations.
Otanerau
Nutrients were measured in 2003 at three water depths within the cages, 50 m from the farm and
at a reference site. These data indicated slight localised enrichment that poses minimal risk to
the environment.
Clay Point
WC nutrients were measured in 2008 at 50 m up-current of the farm and at 50 and 100 m downcurrent. These data indicated a slight, localised enrichment that poses minimal risk to the
environment.
In 2009 and 2010 WC measurements continued to show very slight localised enrichment in
nitrate-N near the cages, although the differences between near cage and control station samples
are not considered biologically significant given spatial and temporal variability.
On a larger spatial scale, dissolved nutrients from the study of Gibbs et al. (1992) show an
increasing NH4-N gradient and a decreasing NO3-N gradient from the inner to the outer Sound
(Table 6). This study also investigated other inorganic and organic nutrients, namely urea,
dissolved organic nitrogen (DON), dissolved reactive phosphorus (DRP), dissolved organic
phosphorus (DOP) and total phosphorus and nitrogen (TP and TN) concentrations as presented
in Table 6. The study highlights the large seasonal variability in the Sound, with low dissolved
inorganic nitrogen (DIN) concentrations in the summer (January-March) with higher DIN
concentrations recorded in the winter months. As mentioned previously, nitrogen is
considered the major limiting nutrient in the region and hence is the focus of our water column
assessment. By consulting the classification of trophic state provided by Smith et al. (1999;
Table 4) we can see that all mean TN and most maximum TN concentrations are less than the
mesotrophic limit of 260 mg TN/m3. TP concentrations are associated with levels typically
associated with a mesotrophic state (Table 4).
14
Report No. 1985
August 2011
Table 6.
Mean (Min-Max) dissolved and total nutrients measured over the period April 1984 to April 1985
from inner Pelorus Sound sites (Mills Bay/Schnapper Point) to outer sites (Richmond Bay), data
from Gibbs et al. (1992), and unpublished monthly Cawthron nutrient data (*) at inner QC Sound
(Wedge Point) for the years 1997 to 1999. Units are in mg/m3.
Station
Mills Bay
Schnapper Point
Four Fathom Bay
Crail Bay
Hallam Cove
Richmond Bay
Wedge Point*
NO3-N
13.1 (0.5-39)
25.6 (0.5-71)
32.1 (3.4-78)
18.5 (1.1-109)
23.6 (2.9-85)
30.8 (3.3-77)
22.3 (0-79)
NH4-N
19.5 (0.3-59.3)
17.6 (0.5-88)
14.1 (0.3-85)
15 (0.3-63)
12.3 (0.3-62.1)
11.9 (0.3-44.1)
36.6 (3.6-36.5)
Urea
52.0 (3-102)
50.4 (12-93)
48.8 (2-105)
52.4 (9-94)
48.3 (3-79)
51.8 (3-94)
DRP
8.4 (3-15.7)
8.8 (2-17.0)
7.9 (2-20.1)
8 (3-30.8)
8.3 (2-25.2)
8.3 (2-17.0)
15.5 (6.6-24.7)
Station
Mills Bay
Schnapper Point
Four Fathom Bay
Crail Bay
Hallam Cove
Richmond Bay
DON
52.3 (3-141)
34.1 (3-221)
39.3 (3-170)
37.5 (4-187)
27.7 (4-113)
25.8 (2-72)
DOP
4.2 (0.5-14.5)
3.6 (0.5-15.0)
3.7 (0.5-13.5)
3.6 (0.5-13.6)
3.2 (0.5-12.5)
3.3 (0.5-8.2)
TP
19.0 (5.9-41.7)
16.6 (4.7-29.1)
16.6 (4.3-44.1)
14.3 (4.9-39.9)
14.4 (4.7-36.4)
13.7 (7.1-26.6)
TN
167.4 (118-238)
156 (87-227)
159.3 (109-302)
146.9 (96-264)
138.5 (94-248)
136.4 (90-197)
DIN1
32.6
43.2
46.2
33.5
35.9
42.7
40.0
1. mean DIN values calculated based on the sum of mean nitrate N (NO3-N) and ammonical N (NH4-N) data.
A comprehensive dataset for the period 1997 to 1999 of monthly dissolved nitrogen and
phosphorous concentrations for the inner Queen Charlotte Sound (Wedge Point) was available
(Cawthron unpublished data). Given the outer reaches of both Sounds share a common body
of water (Cook Strait), it seems likely that the outer reaches of Queen Charlotte Sound (where
the proposed sites are situated) are probably better represented by the nutrient concentrations
in outer Pelorus than the Wedge Point data. Wedge Point DRP and ammonium (NH4-N)
concentrations were higher than those of inner Pelorus Sound, but DIN levels were similar.
The elevated DRP and ammonium levels may be associated with the Picton wastewater outfall,
given its proximity to Wedge Point. Assuming DIN:TN and DRP:TP ratios mirror those
observed in Pelorus Sound (DIN:TN ≈ 1:4, DRP:TP ≈ 1:2) then the TN concentration
(~160 mg TN/m3) would be typical of oligotrophic water, whilst the TP concentration
(~31 mg TP/m3) would be considered meso/eutrophic.
Bradford Grieve et al. (1987) also noted a relationship between winter (June 1981) dissolved
nutrients with salinity in both Sounds. Low salinity (~16 PSU) was associated with notably
higher levels of dissolved reactive silicate (DRSi – an important nutrient for diatom growth),
nitrate and NH4-N, while high (oceanic salinities) were generally associated with lower winter
nutrient concentrations.
2.4.2. Sources and sinks of nitrogen in the Sounds, a mass-balance analysis
The overall contribution of nitrogen from finfish farms in the Marlborough Sounds can be
placed in a wider context by comparing with other point and non-point sources and sinks in the
Report No. 1985
August 2011
15
region. Following the approach of MacKenzie (1998) and Zeldis (2008a), we considered the
existing imports of nitrogen to the Pelorus and Queen Charlotte Sounds from riverine, oceanic
and anthropogenic sources (e.g. existing salmon farming operations) and exports through
benthic denitrification, oceanic flushing and shellfish aquaculture (Table 7 and Table 8). A
discussion of the background calculation and sources of data underlying these tables is
provided in Appendix 1.
Table 7.
Relative magnitudes of nitrogen sources (finfish, riverine and oceanic) and sinks (mussel harvests
and denitrification) for the Pelorus Sound region. Note that loss of nitrogen through burial or
organic export is unknown. Q relates to the quantity or rate, with the units expressed in the
respective rows of the table.
Inputs
Waihinau Bay
(currently fallowed)
Forsyth Bay
Crail Bay (combined)
Pelorus/Rai Rivers
Kaituna River
Manaroa
Tuna Bay
Crail Bay
Waitaria
kg N per Q
Total
Nitrogen1
(Tonnes
N/yr)
References
3 kt Feed/yr
56
+ 168
Gowen & Bradbury 1987
3 kt Feed/yr
3 kt Feed/yr
56
56
+ 168
+ 168
+ 477
+ 83
+ 9.0
+ 6.3
+ 2.3
+ 2.5
Gowen & Bradbury 1987
Gowen & Bradbury 1987
WRENZ 2010
WRENZ 2010
WRENZ 2010
WRENZ 2010
WRENZ 2010
WRENZ 2010
Dupra 2000;
updated analysis of NIWA
data using approach of
Gibbs et al. 1992
Quantity or
Feeding
Rate (Q)
Net Oceanic exchange
(DIN)
Losses/Removals
Mussel Farming N
removal
Denitrification
+ 200 to
+ 4200
45 kT/yr
5.9
- 266
Zeldis 2008a; MFA 2010
386 km2
1204.50
- 465
Kaspar et al. 1985;
Christensen et al. 2003
Nitrogen Burial
1
16
-?
(small)
Note that oceanic exchange estimates refer to DIN rather than total N.
Report No. 1985
August 2011
Table 8.
The relative magnitudes of nitrogen sources (finfish, riverine and oceanic) and sinks (mussel
harvests and denitrification) for the Queen Charlotte Sound region. Note that several nitrogen
inputs and exports, including major oceanic fluxes, are unknown for this region.
Quantity or
Feeding Rate
(Q)
5 kt Feed/yr
kg N
per
Q
56
Total
Nitrogen
(Tonnes N/yr)
+ 280
Gowen & Bradbury 1987
Otanerau Bay
3 kt Feed/yr
56
+ 196
Gowen & Bradbury 1987
Ruakaka Bay
3 kt Feed/yr
56
+ 196
Gowen & Bradbury 1987
3.5 kt Feed/yr
56
+ 196
Gowen & Bradbury 1987
Inputs
Te Pangu Bay*
Clay Point
Picton
Wastewater
+9
Terrestrial Inputs
+ 16.6
Oceanic exchange
(DIN)
+ ? (large)
Losses/Removals
Oceanic exchange
(DIN)
353.2
Nitrogen Burial
Mussel Farming
N removal
Denitrification
Reference
Pers. estimate
Pers. estimate based on
freshwater inputs from
Heath 1976
Pers. estimate, assuming
natural N balance
- ? (small)
~2000 GWT
harvested
5.9
- 11.80
305 km2
1204
- 367
Zeldis 2008a; MFA 2010
Kaspar et al. 1985;
Christensen et al. 2003
* A consented staged increase of up to 6000 tonnes has been granted to the Te Pangu Bay site.
The present level of net aquaculture nitrogen inputs in Pelorus Sound (present consented
finfish additions minus shellfish removals) are about 41% and 6% of the estimated riverine
inputs and oceanic inputs1 respectively.
Mussel farming activities are limited in Queen Charlotte Sound (estimated at ~2000 green
weight tonne per year in this study; Table 8), so there is very little anthropogenic removal of
nitrogen from the region; consequently the contribution of new salmon farm nitrogen to the
system is likely to be greater in comparison to terrestrial and oceanic inputs than occurs in
Pelorus Sound. Insufficient data is available to accurately assess the existing salmon farm
inputs to oceanic and riverine inputs for Queen Charlotte Sound. Mean freshwater inputs are
measured at ~20% of Pelorus Sound (Heath, 1976), so assuming the same mean riverine N
concentrations as the Pelorus River, this would mean the salmon farm inputs would be about
1
Based on our updated analysis of unpublished NIWA data and applying the tidal flushing assumptions of Gibbs et al.
(1992). We note that farm inputs may represent up to 308% of ocean inputs if the lower estimate of Dupra (2000) are used,
hence we are uncertain as to the actual contribution of ocean inputs.
Report No. 1985
August 2011
17
50 times the freshwater inputs in Queen Charlotte Sound. Given the ocean inputs must at least
support the estimated level of denitrification (e.g. 367 tonne N/year) in Queen Charlotte
Sound, salmon farm inputs may presently represent up to 227% of the ocean inputs. At a
system-wide scale this suggests that Pelorus Sound nutrient budget is impacted by a relatively
small amount, and the Queen Charlotte Sound budget is already altered by salmon farm
operations.
This broad system-wide nutrient budget analysis does not consider spatial aspects of the inputs
or the level of ecosystem changes associated with changes to nutrient budgets. Without
detailed hydrodynamic analysis it is not possible to more precisely estimate these fluxes from
different areas of the Sounds. However, proximity of finfish farms to Cook Strait will clearly
be an important factor, with regions located in the outer Sounds having a greater degree of
interaction with Cook Strait and therefore a greater degree of flushing of inorganic and organic
wastes from the Sounds. In the case of Pelorus and Queen Charlotte Sounds where existing
farms are generally located near the entrance of the Sounds, the retained nutrients are likely to
be overestimated by a simple mass-balance analysis that does not precisely define their
location. These effects are accounted for in the spatially explicit modelling covered in Section
5.5 of this report.
2.4.3. Nutrient loading in relation to potential ecological limits
Nutrients are not an issue on their own, but they may cause problems if they influence
phytoplankton biomass to a point that disrupts ecological processes. Net nutrient additions to
the Sounds can be compared to experimental critical nutrient loading rates (CNLR) in euphotic
(well-lit) surface waters. CNLR is defined as a
“… nutrient loading rate which cannot be exceeded without loss of ecosystem integrity”(Olsen
et al. 2008).
This definition has been refined by Y Olsen (pers. comm. 9 November 2010) as:
“The upper nutrient loading rate that can still secure full ecosystem integrity in euphotic
planktonic ecosystems”
“Characteristics below the CNLR are efficient trophic transfers, linearity in the responses in
plankton biomass and flows of materials with nutrient loading rate, and a moderate
sedimentation rate to aphotic waters and the sea floor”
In general terms, exceeding the CNLR could potentially lead to large increases in
phytoplankton production and biomass, which in turn leads to a degradation of the trophic
status of the system (e.g. change towards a more enriched ecosystem). CNLR estimates from
18
Report No. 1985
August 2011
mesocosm experiments2 in Norway fell in the range of 3-20 mg N m-3 day-1 (Olsen et al. 2006,
2008). These estimates are based on relatively short experiments (18 to 21 days) and did not
allow for exchange of water and so are only applicable at the scale of systems where nutrients
will be conserved in this timeframe (e.g. the Sound-wide scale). Port Gore represents a
relatively small system with a low residence time, so we have not included this region in our
analysis. The CNLR estimate for a more realistic scenario in a well-flushed lagoon (residence
time ~5 days) with natural inputs of about 4 mg N/m3/day was approximately 8 mg N/m3/day
(Y Olsen pers. comm., unpublished data). From this research, a conservative value for the
Marlborough Sounds (a tidally flushed system) has been estimated to be 6 mg N/m3/day (Y
Olsen, pers. comm.).
This analysis highlights that the present net nutrient inputs from existing natural sources and
aquaculture operations (i.e. Table 7 and Table 8) are below the suggested conservative limit.
In Pelorus Sound the existing system is about 38% of the CNLR. Accurate estimates for
oceanic inputs were not available for Queen Charlotte Sound, but assuming a net zero ‘natural’
input to Pelorus Sound, then the existing inputs would be about 35% of the CNLR. Based on
this assessment, it appears the existing environments are unlikely to be near any critical
nutrient loading limits, beyond which could compromise the ecological integrity of the water
column environment.
Table 9.
Yearly ‘natural’, and existing net aquaculture (Salmon additions – shellfish removals) nitrogen
inputs for Pelorus Sound and Queen Charlotte (QC) Sound. Nutrient loading rates (NLRs) are
calculated for Pelorus Sound and QC Sound and are expressed as a percentage of a 6 mg N/m3/day
loading rate.
Location
Pelorus Sound*
Queen Charlotte
Sound
Euphotic
Volume
(106 m3)
5462
Salmon
TN
(t/year)1
504
Salmon
DIN
(t/year)2
410
Net
‘Natural’
N3
4049
1045
812
661
0
Total
N2
NLR
(mg N/day)
% of
CNLR
4553
2.28
38%
812
2.13
35%
* ‘Existing’ assumes all farms operating at 2010 discharge consent limits, in practice Waihinau Bay site was not operational and
operates in tandem with Forsyth Bay (i.e. only one of the farms operates at a time).
1.
Ratio of 56 kg TN/tonne of feed (Gowen & Bradbury 1987)
2R-atio of 45.6 kg DIN/tonne of feed (Gowen & Bradbury 1987)
3.
All other sources and sinks of nitrogen, excluding salmon farm inputs.
2.4.4. Phytoplankton biomass
Suspended and particulate properties of the water column were investigated by Gibbs et al.
(1992; Table 10). Higher mean concentrations of chl a (a proxy for phytoplankton biomass)
were measured in the inner Pelorus Sound (1.97 mg chl a /m3 in Mills Bay, Keneperu Sound
than the outer Sound (1.05 mg chl a/m3 in Richmond Bay). Considerable inter-annual
2
Mesocosms used by Olsen et al. (2006) were large transparent impermeable cylinders of volume 30-50 m3 lowered to
depths of 12-14 m.
Report No. 1985
August 2011
19
variability in chl a concentration was also recorded with autumn phytoplankton blooms
notable at all sites and spring phytoplankton blooms at inner Sound sites.
Based on the mean annual chl a concentrations, the system would be classified as mesotrophic
(Smith et al. 1999; Table 4). In the region of the proposed sites (Richmond Bay in outer
Pelorus Sound) the region prior to salmon farming is more accurately described as
oligotrophic/low mesotrophic due to the lower chl a concentrations recorded in this region.
Less data was available for Queen Charlotte Sound, but unpublished weekly water column
survey data undertaken by NIWA in Tory Channel and Wedge Point over the years 2003 to
2005 (Table 10) show mesotrophic chl a concentrations similar to those observed in inner
Pelorus Sound by Gibbs et al. (1992). The data collected in Queen Charlotte Sound are for a
period when most of the existing salmon farms were in operation (excluding Clay Point) and
show that the system in its present state could be classified as mesotrophic (Table 4).
Table 10.
Mean (Min-Max) suspended and particulate properties of the water column measured over the
period April 1984 to April 1985 from inner Pelorus Sound sites (Mills Bay/Schnapper Point) to
outer sites (Richmond Bay), from Gibbs et al. (1992), and unpublished weekly NIWA chlorophyll
data (*) for the years 2003 to 2005. Units are in mg/m3.
1.97 (0.6-3.9)
Particulate
Carbon
380 (50-1234)
Particulate
Nitrogen
37.8 (14.4-71.4)
Particulate
Phosphorus
6.4 (1.4-19.7)
914 (372-2900)
1.64 (0.4-6.0)
273 (46-1472)
28.3 (15.7-55.1)
4.2 (1.8-11.5)
1228 (388-6320)
1.47 (0.16-4.4)
244 (67-600)
25.1 (4.5-62.7)
5 (0.8-28.1)
776 (196-1500)
787 (129-1530)
1.3 (0.48-2.9)
1.57 (0.43-4.7)
250 (88-534)
239 (43-465)
23.4 ( 8.5-79.2)
26.8 (10.5-72.5)
2.7 (1.1-10.9)
3 (1.5-7.3)
765 (179-2310)
1.05 (0.13-2.8)
187 (32-529)
16 ( 6.7-31.2)
2 (1.1-8.2)
-
1.44 (0.14-4.26)
-
-
-
-
1.95 (0.8 – 5.7)
-
-
-
Station
Suspended Solids
Chlorophyll a
Mills Bay
Schnapper
Point
Four Fathom
Bay
Crail Bay
Hallam Cove
Richmond
Bay
Tory
Channel*
Wedge
Point*
1364 (397-3630)
Potential changes to phytoplankton biomass from existing salmon farms
Datasets from the studies of Gibbs et al. (1992) and Bradford Grieve et al. (1987) were
established prior to salmon farming commencing in Pelorus Sound (Waihinau Bay farm
opened in 1989 and Forsyth Bay in 1994). Since then, MSQP and NIWA water column
surveys enable identification of any major changes that have occurred in the region.
Unpublished NIWA data for outer Pelorus Sound3 (not Richmond Bay), collected after
existing farms were in operation, show low - but slightly increased, chl a concentrations with a
mean of 1.21 mg chl/m3 over a 2-year period (27 February 2007 to 24 February 2009).
3
NZ map grid (NZMG) location (East,North): 2591990, 6026010
20
Report No. 1985
August 2011
However, a 2-year mean for the inner Pelorus Sound (Schnapper Point4) of 1.46 mg chl/m3
over the same period, does not show evidence of increased chl a concentrations (i.e. the 2-year
mean is lower than the mean of Gibbs et al. 1992). These data suggest that the existing salmon
farms have had little effect on chl a concentrations in Pelorus Sound.
Analysis using a simple open-box model (see Appendix 2 for methods) show that long-term
increases in nitrogen from existing aquaculture (finfish additions and shellfish removal) are
about 0.49 and 3.92 mg TN/m3 above ambient concentrations in Pelorus and Queen Charlotte
Sound, respectively. The associated potential increase in chl a concentrations (a proxy for
phytoplankton biomass) associated with aquaculture inputs is 0.05 and 0.45 mg chl a/m3 in
Pelorus and Queen Charlotte Sound, respectively. Compared to background levels the total
nitrogen change is small (<5%) for both Sounds (Table 11). Pelorus Sound chl a changes are
estimated to be small (3.5%; Table 11) compared to measured mean background chl a
concentrations from throughout the Sound (Gibbs 1992; Table 8). The potential chl a change
due to existing salmon farms in Queen Charlotte Sound, based on this simple model, shows the
existing farms have the potential to increase chl a concentrations by a moderate amount
(26.3%; Table 11). The magnitude of the potential change in Queen Charlotte Sound
(0.45 mg chl/m3; Table 11) is small, and unpublished monitoring data suggests that the system
was mesotrophic with most of the existing sites in place (Table 10), so although the relative
change is large for the Queen Charlotte region, it does not appear to be near eutrophic limits
(as shown Table 4).
Table 11.
Change in estimated long-term steady-state nitrogen concentrations (above ambient) within
Pelorus and Queen Charlotte Sounds with existing salmon farm feeding levels and mussel farms
operating assuming complete mixing and exchange (see Appendix 2).
Description
Net Aquaculture N Load (tonnes/yr)
Net Aquaculture N load (tonnes/tide)
Mean Tidal Volume (106 m3)
TN Conc. Change (mg N/m3)
Percent Change in TN1
N to Chl a ratio
Potential Chl a Conc. Change (mg Chl/m3)
Potential Percent Change in Chl a2
Pelorus
238
0.338
737
0.458
0.31%
0.114
0.052
3.47%
QC
800.2
1.135
289.5
3.922
2.45%
0.114
0.445
26.28%
1. Assuming a mean annual Sound-wide TN concentration before salmon farming from Pelorus Sound of 150 mg TN/m3 (Gibbs et
al. 1992); a mean of 160 mg TN/m3 is assumed for QC Sound based on recorded DIN concentrations at Wedge Point and
assuming a 4:1 TN:DIN ratio (Table 4).
2. Assuming a mean annual Sound-wide chlorophyll concentration before salmon farming from Pelorus Sound of 1.5 mg Chl/m3
(Gibbs et al. 1992); a background of 1.7 mg Chl/m3 is assumed for QC Sound based on two years of collected data from Wedge
Point and Tory Channel collected while most existing farms were operating (Table 8).
4
NZ map grid (NZMG) location (East,North): 2589325, 6000725.
Report No. 1985
August 2011
21
2.4.5. Harmful Algal Blooms (HAB)
Pelorus Sound
Toxic and noxious phytoplankton blooms have fortunately been rare in Pelorus Sound.
Occasionally low levels of domoic acid (produced by planktonic diatoms in the genus
Pseudonitzchia) are identified, predominately in the inner Sounds, but no shellfish harvesting
closures have been necessary since a bloom of the dinoflagellate Alexandrium minutum in
Anakoha Bay in 1994. A bloom of the potentially ichthyotoxic flagellate, Pseudochattonella
verruculosa, occurred in Kenepuru Sound (inner Pelorus Sound) during the last week in July
2011, however there were no reports of associated fish deaths. This is probably because there
are no farms in the region. Previous experience of ichthyotoxic blooms in the vicinity of
salmon farms in New Zealand (MacKenzie et al. 2011a; MacKenzie 1991) suggest that caged
fish are more susceptible to impact than wild fish that can often avoid high concentrations of
the alga.
Queen Charlotte Sound
During summer a dinoflagellate-dominated community usually prevails in Grove Arm (inner
Queen Charlotte Sound) for long periods, and toxic blooms have occurred on a number of
occasions in the past. The area may function as an incubator and/or reservoir for harmful algal
species that can then be dispersed to other areas. There is evidence (MacKenzie et al. 2011a)
that a flagellate bloom responsible for killing fish at the Ruakaka farm in June 2010 originated
in Grove Arm under the influence of a bottom water intrusion event and spread from there
throughout the inner Sound.
Similar to the Grove Arm situation, the longer retention time, water column stability and high
fertility of the various side embayments extending off Tory channel may provide conditions
where flagellate-dominated communities can flourish and act as localised sources of spread of
harmful species to other regions of the Sound. The most recent example of this was a bloom
of the toxic dinoflagellate Alexandrium catenella (MacKenzie et al. 2011b) that began and
persisted for >2 months (March-May 2011) within the southern Tory Channel bays. Like the
dispersal of blooms from the Grove Arm, there is also good evidence that these bays acted as
incubators from which the bloom was dispersed through the Sound leading to widespread
shellfish biotoxin contamination and prolonged harvesting closures.
22
Report No. 1985
August 2011
3.
ASSESSEMENT OF PHYSICAL EFFECTS
Changes in the physical environment of the water column refers to changes that may occur to
properties, such as currents, waves, temperature, salinity, density structure or light attenuation.
Although cumulative changes in these physical water column properties are possible, they are
unlikely to be relevant at a system-wide (i.e. bay or Sound) scale due to the relatively small
area of the regions that will be occupied by the proposed structures.
We were not able to find definitive references which consider the effects of salmon farm
cage/net structures on the physical environment, but parallels exist with literature available for
other suspended aquaculture and natural structures, such as mussel farms (e.g. Plew et al.
2005; Plew 2009, 2011), suspended scallop culture (e.g. Grant & Bacher 2001) and kelp
forests (e.g. Jackson & Winant 1983; Elwany et al. 1995; Jackson 1997).
We note that the relative area of the proposed cage footprints (8 x 1.5 ha cage areas) is a small
proportion of the total Sound areas (0.01% for Pelorus and 0.02% for QC Sound),so we
consider it unlikely the structures would lead to large-scale alterations of Sound- or bay-wide
biophysical processes. Nevertheless local and cumulative wider-scale effects are possible, so
we describe the possible scale of changes that may occur based available information.
3.1. Currents
The effect of structures on currents in the water column is well documented (e.g. Grant &
Bacher 2001; Plew et al. 2005; Plew 2009, 2011), with all studies noting a reduction in
currents within the structures and localised attenuation from associated losses of kinetic energy
to turbulent wake (Plew et al. 2005). Recent research by Plew (2011) in Port Ligar, Pelorus
Sound, where mussel farms take up about 10% of the area of the bay, shows that mean current
speeds over the whole bay are attenuated by up to 7%, and changes of up to 100% are possible
within specific regions of the bay.
Additional losses of kinetic energy are likely to cause local modifications of currents close to
the proposed farms due to the addition of new structures. The relative area of the proposed
cage footprints as a proportion of the Sounds is small (0.01% for Pelorus and 0.02% for Queen
Charlotte), so we consider it unlikely that this would have a significant impact on mean current
speeds or flushing dynamics at a Sound-wide scale. The proposed sites may, however, have
local effects that are measurable. NIWA are currently in the process of recording currents
within net structures and so may be able to offer greater insights into the effects from net
structures on water column currents in future (Plew, pers. comm.). Based on observed and
modelled effects for mussel farm structures, however, it does not appear that noticeable effects
to mean currents would eventuate beyond the local scale of the proposed sites.
Report No. 1985
August 2011
23
3.2. Waves
Wave energy may be attenuated by salmon farm cage structures in a similar fashion to other
structures, such as floating breakwaters or mussel farms (Plew et al. 2005). We recognise that
the proposed sites would add cumulatively to effects from existing structures (e.g. mussel
farms in Pelorus Sound), but given the relatively small size of the proposed farms compared to
size of the bays or Sounds surrounding them, the wave attenuation effect would only be
observable close to the farm structures.
Measurements by Plew et al. (2005) on mussel farms show that attenuation of waves varies
with wave period. Wave attenuation of 5% - 20% was measured for shallow water (short
period) and transitional waves (moderate period) around mussel farms. The dampening effect
of the net structures associated with a salmon farm are likely to be greater than that of a mussel
farm; however it is difficult to speculate as to what the magnitude of this effect, or its
ecological consequences, might be. We speculate that this may have ecological implications in
environments that are dependent on wave energy for important ecosystem services, such as
flushing or transport of sediments (e.g. areas with low mean current speeds). Given the high
energy of the environments in which most of the proposed sites are located, we note that any
ecological implications would probably be small.
We also recognise that the proposed structures would add cumulatively to effects from existing
structures (e.g. mussel farms in Pelorus Sound), but given that the size of proposed farms is
relatively small compared to size of the Sounds or the bays surrounding them, in our opinion
the effect of wave attenuation would be minor at a Sounds- or bay-wide scale.
3.3. Temperature, salinity and stratification
It is possible that small changes in temperature could occur due to energy losses associated
with the metabolic heat loss of large numbers of fish kept in the cages, frictional losses from
current/structure interactions or electrical/mechanical energy inputs from equipment used at
the site. Salinity and temperature changes associated with structures are unlikely and have not
been documented in the literature we have reviewed. It is possible that small changes could
occur; however in our opinion these effects would probably be negligible at the proposed sites
under normal hydrodynamic conditions.
Stratification changes are theoretically possible and have been documented around mussel
farm structures where such effects may occur due to increased vertical mixing; however the
evidence for this effect is not clear (Plew et al. 2005). If effects did occur they would be
relatively localised and in our opinion would have minimal effect on the water column
environment and associated ecology.
24
Report No. 1985
August 2011
3.4. Light attenuation
Light attenuation is directly affected by shading from the farm structures, but we note that
these effects will be highly localised and only influence water passing through the shadow of
the farm. Similar small effects on the benthic environment are also noted in the Benthic
Report (Keeley & Taylor 2011).
It is possible that larger-scale light attenuation effects may also occur beyond the immediate
area of the farm from high turbidity plumes carried by currents and induced by fish faeces,
periodic maintenance (e.g. in-water cleaning of nets) or dissolved nutrients which may
stimulate phytoplankton to change the colour and clarity of the surrounding water; however,
these wider effects would likely be very small and difficult to measure.
Report No. 1985
August 2011
25
4.
ASSESSMENT OF DISSOLVED OXYGEN EFFECTS
Depletion of DO can occur within and around finfish farms due to the respiratory activities of
the farmed fish and microbial degradation of waste materials in seabed sediments. This issue
is of most significance to the farmed finfish stock, although it may also be of ecological
importance if the zone of DO depletion extends beyond the stock enclosures. Significant
depletion of water column DO concentrations at salmon farms overseas has only been
observed when cages are too heavily stocked, or where they are located in shallow sites with
weak flushing (La Rosa et al. 2002). These observations would also be expected under similar
conditions at proposed sites in the Marlborough Sounds.
Although water column DO concentrations will be reduced within farms due to fish
respiration, any reduction will be monitored at low-flow sites as a routine farm management
practice, and will not be allowed to fall below levels detrimental to the fish themselves.
Effects to potentially more sensitive organisms (e.g. zooplankton, including larval forms of a
variety of species) would be of minor consequence due to the small areas affected.
The stimulation of phytoplankton may also lead to some fluctuation in water column DO
levels, due to increased oxygen production during the day and increased uptake at night.
However, given the levels of change estimated, this is unlikely to cause significant DO
reduction at adequately flushed sites. For example, Roper (1988) recommends maintaining a
DO level of 79% saturation within salmon cages in Big Glory Bay, Stewart Island. To put this
into context, Wild-Allen et al. (2011) estimate, based on validated biogeochemical models,
that fish farm effects in south-eastern Tasmania of an order of 15-30% enhancement of chl a
would only cause a relatively insignificant 1-2% saturation reduction in DO.
In the Marlborough Sounds, annual monitoring data from existing salmon aquaculture
operations suggests that near-bottom water DO concentrations beneath the cages generally do
not become significantly depleted compared to sites away from the cages. On one occasion
(October 2007), however, particularly low DO concentrations between 3.1 and 5.3 mg/l were
recorded in the vicinity of the Otanerau Bay farm in Queen Charlotte Sound. These
concentrations can be detrimental to marine life. This farm is located in a particularly lowcurrent environment, and reduced DO concentrations observed there were also observed at
control locations outside the farm’s influence. Since maintenance of adequate DO levels is
critical to the survival of the farmed salmon stock, NZ King Salmon monitors concentrations at
their existing farms daily at a depth of ~5 m within the net pens. With few exceptions these
data also indicate that flushing rates were sufficient to maintain healthy growing conditions for
the stocks. Once again one notable exception occurred during October 2007 when
concentrations between 0.4 and 2.1 mg/l were recorded over a 4-day period. Concentrations
within this range would be deleterious to the salmon as well as most naturally occurring
pelagic fauna.
In relation to future development in the Marlborough Sounds, DO depletion is an issue that
may need to be considered if, for example, multiple farms in close proximity are proposed. In
26
Report No. 1985
August 2011
such instances there could be a potential for DO to become increasingly depleted as water
currents pass through sequential farms (Roper et al. 1998). It is generally considered that the
greatest potential for adverse effects in the water column will occur in areas subject to poor
flushing and a high stocking density (Wu et al. 1994; La Rosa et al. 2002). The risk of DO
depletion can therefore be avoided by allowing appropriate spacing between sites and/or
locating farms in areas that are sufficiently deep and well flushed by currents.
Although interactive effects would be possible at some of the proposed sites due to their close
proximity (i.e. Richmond/Taipipi, Ruaomoko/Kaitapiha, Waitata Reach/Waitata Reach
Extension), these are all high-flow sites. The strong mixing characteristics within these site
pairings would be expected to mitigate any cumulative interactive effects on DO depletion.
The proposed Papatua farm site, with average near-bottom current speeds of 3.4 cm/s, is
classed as a low-flow site. In view of this, there is a potential for measurable DO reduction to
occur there both within and beyond farm boundaries. As discussed earlier, previous DO
monitoring of existing low-flow farm sites suggests that potentially adverse DO concentrations
would occur only rarely (or not at all) as long as appropriate feed application levels are
maintained. Mitigation of any adverse reduction in DO could therefore be achieved through
monitoring as the site is developed.
Report No. 1985
August 2011
27
5.
ASSESSMENT OF NUTRIENT LOADING EFFECTS
5.1. Nutrient toxicity
The major DIN species excreted by fish is ammonium (NH4+) which is in equilibrium with unionised ammonia (NH3) and can be toxic at elevated concentrations in the marine environment.
The USEPA (1989) has an unacceptable biological effects threshold for combined NH3 + NH4+
concentrations of 3480 mg N/m3 at pH 6.5 and 250 mg N/m3 at pH 9.0 (Gray et al. 2002).
Because there is a potential for ammonium-N, released due to fish respiration within the
enclosures, to build up to toxic levels, it is important to consider the associated risks as they
relate to the hydrodynamic characteristics of the proposed sites. With the exception of the
Papatua site in Port Gore, all of the proposed farms are located at moderate to deep high-flow
sites. The flushing characteristics at these sites would be sufficient to prevent the within-farm
build-up of ammonium-N concentrations to potentially toxic or even near-toxic levels. Higher
concentrations of ammonium-N would be expected at the proposed low-flow Papatua site in
Port Gore, however toxic conditions would still be extremely unlikely to occur. We would
expect DO monitoring would occur at all the proposed sites, and any farm flushing problems
would be detected in a DO reduction. This would be likely to occur in advance of ammoniumN concentrations becoming problematic to the farmed fish and the surrounding environment.
As this issue has not been a problem at other similarly low-flow sites, we do not believe it is
important to monitor ammonium concentrations for toxicity reasons, although it may be useful
for quantifying the degree of new nutrient load to the region.
5.2. Phytoplankton composition and HABs
A concern with regard to water column nutrient enrichment is the potential for stimulation of
the growth of noxious or toxin-producing species of phytoplankton, thereby increasing the
frequency or magnitude of HABs (Anderson et al. 2002; Yap et al. 2004). Such events include
blooms of species that can be toxic to fish, and others that can accumulate in shellfish and
affect consumers. Changes in the relative proportion of macro-nutrients in the water column
could also alter the composition of the phytoplankton community by favouring particular
species or groups of species over others. This would be an issue if the proportional
composition of the nutrient loading source does not reflect that of the receiving water
environment.
Relatively consistent seasonal patterns occur in phytoplankton biomass and species
composition. Superimposed on these patterns, are the effects of episodes such as floods and
upwelling events with underpinning complex biological interactions amongst different
elements of the plankton. Diatoms are a major component of the phytoplankton community of
the Marlborough Sounds, particularly during the winter/spring and autumn bloom periods.
They are an example of a bloom-forming species that may be affected by changes in water
column nutrient conditions (e.g. Heisler et al. 2008). Diatoms require silica (Si) at a minimum
28
Report No. 1985
August 2011
Si:N:P ratio of 15:16:1 (Redfield 1934) in order to preclude Si-limitation for growth. Salmon
farming waste nutrient discharges, containing proportionally less Si would favour other
components of the phytoplankton community, such as micro flagellates and/or dinoflagellates,
over diatoms. If the nutrient wastes were sufficient to significantly reduce the existing nutrient
ratio in the surrounding environment below that required by diatoms, then it is possible that
other species could dominate over the major bloom periods.
The potential for discharges from salmon farms to induce Si-limitation of diatoms in the
receiving water would be remote, particularly in Pelorus Sound and inner Queen Charlotte
Sound where concentrations of Si are generally surplus to diatom requirements (see Section
2.4.1). Although Si concentrations can be lower in high-salinity oceanic waters (Bradford
1987), the inflow and mixing of freshwater would likely transport Si to all areas of the Sounds,
mitigating any differential effects on the phytoplankton community composition. The only
exception to this situation is Papatua, which is removed from large terrestrial sources of Si.
Phytoplankton blooms that occur periodically throughout the Sounds occasionally involve
potentially harmful species that can form HABs. These events appear to be regional
phenomena driven by larger-scale oceanic processes that are unrelated to salmon farming
activities (MacKenzie et al. 2011 a,b). Furthermore, there is no evidence to indicate that
localised enrichment from existing salmon farms in the Marlborough Sounds has resulted in an
increased incidence of HABs (Forrest et al. 2007; Keeley et al. 2009). Toxic algal blooms also
occur in overseas aquaculture areas that are far more developed than New Zealand (e.g. Chile),
however strong correlations between the occurrence of HABs and intensity of salmon farming
have not been established (Buschmann et al. 2006). Tett & Edwards (2002) concluded that in
Scotland there was no confirmed connection between HABs and salmon farming, and
suggested that nutrient enrichment by fish farms would be insignificant unless the farm was
located in an enclosed basin where water exchange was poor.
It is also important to recognise that toxic algal blooms are natural phenomena that occur nearannually in many regions of New Zealand that do not have established fish farms e.g. Bay of
Plenty and Hawke Bay (Keeley et al. 2005), Port Underwood (MacKenzie 2002).
Nonetheless, any nutrient discharge into a nutrient-limited environment will result in an
increase in phytoplankton biomass during periods of nutrient limitation. Where this enhanced
production occurs over a wide area, is rapidly diluted, or mitigated by other forms of
aquaculture (e.g. shellfish farming), it is unlikely to alter phytoplankton community structure.
Based on the above information on finfish farming in relation to HABs, nutrient discharges
from the proposed farms in the Marlborough Sounds would not be expected to result in the
initiation of new HAB events. However, incremental increases in nutrient concentrations from
salmon farms (i.e. in addition to those from other sources) would be expected to affect the
magnitude and/or duration of natural bloom events that may be limited by the availability of
nutrients.
Report No. 1985
August 2011
29
Staged development of salmon farms, in conjunction with detailed monitoring of water column
properties, including phytoplankton biomass and community composition, could be an
effective means of managing HAB risks (see Section 7). This is because enrichment effects
are largely reversible if the causative nutrient sources are removed (Heisler et al. 2008;
Okaichi 1997). It must be recognised, however, that after an initial seeding event that some
HABs can recur during successive years due to the production and deposition of resting stages
or cysts that can germinate when appropriate conditions prevail.
Phytoplankton monitoring of HABs is presently carried out by the Marlborough Shellfish
Quality Programme (MSQP) at 30 sites situated throughout the Marlborough Sounds. An
appraisal of this data, collected 2000-2008, revealed very low incidences of elevated HAB risk
(Figure 3). There were no obvious spatial patterns consistent with the distribution of either
salmon farms or mussel farms within the Sounds region. Risk specifically from phytoplankton
species that can be toxic to humans consuming shellfish were assessed to be ‘High’ and ‘Very
High’ on only 3% and <1% of occasions, respectively, during the 8-year period evaluated.
Incidences of elevated risk from ichthyotoxic species were even less common, with <1% of all
samples scoring a ‘>/=High’ ranking (see Keeley et al. 2009). Nevertheless any increase in
the abundance of these naturally occurring species would represent an increased risk. Included
amongst the high-risk species observed in the Sounds were amnesic shellfish poisoning (ASP)producing Pseudo-nitzschia spp., as well as neurotoxic shellfish poisoning (NSP)-producing
Karenia cf mikimotoi and Heterosigma akashiwo which can be toxic to fish.
As noted in the Section 2.4.1, there have been two notable HAB events in Queen Charlotte
Sound since 2008. A bloom of the ichthyotoxic (toxic to fish) flagellate, Pseudochattonella
verruculosa, occurred in the vicinity of the salmon farm in Ruakaka Bay in June 2010, and a
bloom of the dinoflagellate, Alexandrium catenella ,occurred in Tory Channel that persisted
from early March until mid to late April 2011. The Tory Channel bloom resulted in the
interruption of recreational and commercial shellfish harvesting. An additional but lower
intensity bloom of P verruculosa, also occurred during July 2011 in Kenepuru Sound (inner
Pelorus Sound), however there have been no reports of fish deaths. This is not unusual
because there are no fish farms in the vicinity of the bloom; wild fish are generally able to
avoid localised areas of high concentrations of the alga whereas caged fish are not. In spite of
these recent incidences, the frequency of HABs in Queen Charlotte Sound remains low.
Because we cannot predict the development of HABs within the regions of the proposed new
sites, it will be important to monitor phytoplankton species composition throughout both
Sounds. Spatial model predictions of changes in DIN and chl a concentration due to the
proposed new farms can be used to identify appropriate monitoring locations, however
additional attention should be paid to nearby poorly flushed embayments that may act as
sources of inocula for toxic species.
30
Report No. 1985
August 2011
Figure 3.
Graduated circle plots of % incidence of ‘high’ (left) and ‘very high’ (right) HAB risk at MSQP
monitoring sites in the Marlborough Sounds (based on 2001-2008 data). A & B. Phytoplankton
biomass, C & D. ichthyotoxic species, and E & F. phytoplankton toxic in shellfish.
Report No. 1985
August 2011
31
5.3. Nutrient mass-balance and critical ecological limits assessment
Simple mass-balance models based on available information (Table 7, Table 8) show that new
finfish aquaculture would add cumulatively to existing anthropogenic and natural inputs in
both Sounds. In the case of Pelorus Sound, where considerable mussel farming activities take
place, these inputs would be partially mitigated by exports when shellfish are harvested (Table
7). We have updated our existing CNLR analysis (Section 2.4.3) to incorporate the alteration
of the nutrient loading rate from the proposed farms.
5.3.1. Nitrogen loading rates in the Marlborough Sounds
We have recalculated the nutrient loading rate (NLR) based on the volume of the euphotic
zone, where light is sufficient to support phytoplankton production, and compared it to the
CNLR (6 mg N m-3 day-1). Initial new nitrogen inputs (see following Table 14), equating to
about 420 and 364 tonnes per year in Pelorus Sound in Queen Charlotte Sound respectively,
would result in total net nitrogen additions that are about 42% and 51% of a conservative
CNLR estimate of 6 mg N/m3/day, respectively (Table 12).
The proposed expansion of finfish aquaculture is planned to be implemented in a staged
manner, whereby recommended initial feed loadings are much less than the long-term
development scenarios. The flushing characteristics of the farm locations will ensure that only
a proportion of the nutrients released will remain in the systems, thus reducing the effective
nutrient loading. Therefore we believe it is unlikely that any system-wide limits will be
exceeded by the proposed developments.
32
Report No. 1985
August 2011
Table 12.
Status
Existing
Pending
Proposed
Total
Possible
Yearly ‘natural’ and all possible (existing, pending and proposed) salmon farming nitrogen inputs
for Port Gore, Pelorus Sound and Queen Charlotte (QC) Sound. Nutrient loading rates are
calculated for Pelorus Sound and Queen Charlotte (QC) Sound and are expressed as a percentage
of a 6 mg N/m3/day loading rate.
Location
Pelorus Sound
QC Sound
Pelorus Sound
Port Gore
Pelorus Sound
QC Sound
Port Gore
Pelorus Sound
QC Sound
Port Gore
1.
Euphotic
Volume
(106 m3)
5462
Salmon TN1
(Tonne/yr)
1045
5462
1045
Net
‘Natural’
N3
4049
Total N4
(Tonne/yr)
NLR
(mg N/m3/day)
% of
CNLR
504
Salmon
DIN2
(Tonne/yr)
410
4553
2.28
38%
812
84
56
420
364
168
1008
1176
224
661
68
45
342
296
136
820.8
957.6
182.4
0
812
2.13
35%
4049
0
5057
1176
2.54
3.08
42%
51%
Total N calculated at rate of 56 kg N/tonne feed (Gowan & Bradbury 1985).
DIN calculated at a rate of 45.6 kg DIN/tonne feed (Gowan & Bradbury 1985).
3.
‘Natural’ inputs is the net TN inputs from riverine and ocean sources less any denitrification or aquaculture removals (from
Table 7 and Table 8). Pelorus Sound inputs estimated using the highest estimate of net DIN ocean inputs. Queen Charlotte Sound
nitrogen balance set at zero, assuming net oceanic and other inputs approximately match denitrification and aquaculture removal
rates.
4.
Total N is the sum of salmon and net ‘natural’ inputs.
2.
5.4. System-wide effects on phytoplankton biomass and nutrient
concentration
A simple approach to account for the effect of tidal flushing on nitrogen concentrations in the
Sounds is to estimate long-term steady state concentration changes above ambient
concentrations assuming complete mixing and exchange, as was undertaken to estimate
existing changes from present levels of aquaculture (Section 2.4.4).
Tidal flushing assumptions were used to assess long-term steady state estimates of the
magnitude of change to DIN concentrations (see Appendix 2 for detailed methods). Chl a
changes were estimated using a standard molar ratio for nitrogen to carbon (Redfield 1934)
and a carbon:chl a weight ratio of 50:1. The results show potential long-term increases in
nitrogen from pre-aquaculture conditions of 1.42 and 5.7 mg TN/m3 in Pelorus and Queen
Charlotte Sound respectively (Table 11). Similarly, increases in chl a concentrations of 0.16
and 0.65 mg chl a/m3 in Pelorus and Queen Charlotte Sound, respectively, are possible.
Compared to background levels the total nitrogen change is small (<5%) for both Sounds, and
when the relative change from initial feeding levels at the pending and proposed sites is
considered, we see the change from the existing environment is smaller (0.65% in Pelorus and
1.35% in Queen Charlotte Sound).
The potential change in chl a concentrations in Pelorus Sound from existing, pending and
proposed salmon farms is estimated to be relatively small (8.8%) compared to measured mean
Report No. 1985
August 2011
33
background concentrations from throughout the Sound (Gibbs, 1992; Table 10). The potential
change in chl a concentrations from existing and proposed salmon farms in Queen Charlotte
Sound is relatively high (38%). Water column measurements taken at Wedge Point and Tory
Channel during years when most of the existing salmon farms were in operation (2003 to
2005) show that the region is presently mesotrophic (mean annual chl a concentration
<3 mg/m3 (Table 10). Therefore it is important to consider the relative change attributable to
the proposed farm sites. The associated relative potential chl a increases from the initial
feeding levels at the pending consent and proposed plan change sites are about 7.4% in Pelorus
Sound and about 12% in Queen Charlotte Sound. The magnitude of the potential increases in
chl a are not large enough to increase the mean annual chl a concentration to a eutrophic state
in either Pelorus or QC Sound.
Table 13.
Change in estimated long-term steady-state nitrogen and chl a concentrations from existing
background conditions within Pelorus and Queen Charlotte Sounds under proposed fully
developed initial feeding scenarios with existing and pending salmon farms in place and assuming
complete mixing and tidal exchange (see Appendix 2).
Description
Net Aquaculture N Load (tonnes/yr)
Net Aquaculture N load (tonnes/tide)
Mean Tidal Volume (106 m3)
TN Conc. Change (mg N/m3)
Percent change from background TN1
Potential increase from existing TN
N to chl a ratio
Potential chl a conc. change (mg/m3)
Potential change from background chl a2
Potential increase from existing chl a conc.
Pelorus
742
1.053
737
1.429
0.95%
0.65%
0.114
0.162
10.82%
7.35%
QC
1164.2
1.652
289.5
5.706
3.80%
1.35%
0.114
0.648
38.23%
11.95%
1
. Assuming a mean annual sound-wide TN concentration before salmon farming from Pelorus Sound of 150 mg/m3 (Gibbs et al.,
1992) and a mean of 160 mg TN/m3 for QC Sound based on recorded DIN concentrations at Wedge Point and assuming a 4:1
TN:DIN ratio (Table 6).
2
. Assuming a mean annual sound-wide chl a concentrations before salmon farming from Pelorus Sound of 1.5 mg/m3 (Gibbs et
al., 1992); a background of 1.7 mg chl a/m3 is assumed for QC Sound based on two years of data from Wedge Point and Tory
Channel collected while most existing farms were operating (Table 10).
Although useful for assessing possible long-term changes at a Sound-wide scale, the modelling
approach has the following limitations:
34
1.
It does not account for the spatial location of the source of the nutrients and hence has
the potential to over or under estimate the magnitude of the changes at the system or
finer-scales.
2.
It assumes the only mechanism for exchange is tidal flushing. However other flushing
mechanisms such as wind or density driven vertical currents may also be important at
particular times and regions. Therefore there is some uncertainty in these system-wide
estimates. Queen Charlotte Sound has two entrances, so it may be too simplistic to
consider this region a tidally flushed system.
Report No. 1985
August 2011
A more complex spatially explicit approach has also been employed in this assessment to
provide improved estimates of likely changes to DIN and chl a concentrations resulting from
the proposed salmon operations. This approach removes much of the uncertainty from the
simple tidally-flushed approach, but due to the resources involved in running the complex
models they cannot provide us with the long-term steady-state response of Sound-wide
changes. Hence although simplistic, our open-box models provide us with useful information
on the potential far-field changes that are possible in the Sounds, while our spatial models are
useful in helping to assess the near and intermediate field changes.
5.5. Spatially explicit cumulative effects modelling
As an extension to the relatively simple box models detailed above, we have also calibrated
spatially explicit hydrodynamic models for Pelorus and Queen Charlotte Sounds according to
available acoustic doppler current profiling (ADCP) and astronomic tidal elevation data. As
with any model, the hydrodynamic performance of our models is not perfect, but we are
satisfied with the simulation of current speeds and phase, and general circulation (Knight &
Beamsley, in prep). We therefore believe our model is suitable for assessing the potential
distribution and dilution of salmon farm waste streams, although we recommend monitoring is
undertaken to validate our model estimates if the proposed sites are developed.
5.5.1. Spatial modelling methodology and parameterisation
In assessing the cumulative effects of nutrients from the proposed farms, we simulated the
release of a constant source of passive tracers at the locations of proposed and existing sites.
The tracers were released at varying internal time intervals between 1 and 60 seconds
(determined by the internal time step, with 60 sec equal to the time step of the model) within
an approximated volume of the water column. This approximate volume was designed to
reproduce the horizontal and vertical footprint of each farm site (approximately 1.5 ha at the
surface and 20 metres deep = 300,000 m3).
The release volume for each cage site is approximate as it depends on the element geometry of
the model, which is generally defined as triangles in the horizontal plane with edges of about
20 metre length at the farm locations (area is ~200 m2). The vertical resolution also varies, but
is generally 3 to 5 metres at the surface and the 20 metre depth is approximated to the lowest
cell where the depth from the surface to the cell is greater than 20 m. In the case of round
polar cirkelTM cages, the footprint is based on a minimum bounding rectangle around the
circles. We recognise that our assumptions will lead to an underestimation of near-field tracer
concentrations (e.g. up to ~1 km) from the proposed sites due to numerical dilution, but that
our dilutions are generally much lower than other similar studies e.g. Zeldis et al.(2011) which
uses 1 km2 horizontal resolution, so would be about 50 times larger. Resolving intermediate
scale mixing and dilution is important, so we consider our approach suitable for this purpose.
Report No. 1985
August 2011
35
The tracer outputs from the model are scaled so that the model tracer loads match the
estimated constant yearly DIN loads expected to be released under given feeding regimes
(Table 14)5. The feeding rates are converted to DIN loads assuming a ratio of
45.6 kg DIN/tonne of feed (Gowen & Bradbury, 1987). This approach differs from the
previous box models which considered TN with a conversion rate of 56 kg DIN/tonne of feed.
The reason for our different approach was that the complex models were run for shorter
periods. These shorter periods may not have been sufficient to accommodate the time lags for
conversion of dissolved and particulate organic N in the salmon wastes to forms available for
phytoplankton. Our models will therefore underestimate the long-term organic contribution to
the nutrient pool. Given the fraction of organic N produced by the farms is much smaller than
the DIN contribution, we do not believe this would have a large influence on the results of our
spatial models. The outputs of each farm model (i.e. a plume of tracers) were added to other
farm models for every 30 minute period to generate a cumulative effects layer of estimated
DIN concentrations; from this, the distribution median and other percentile statistics were
generated.
Modelling of DIN does not simulate DIN uptake by phytoplankton or other aquatic autotrophs
(e.g. macroalgae). Although this is an unnatural scenario when nitrogen is limiting, it is
representative of winter conditions in the Sounds when light availability is the dominant
controlling factor for phytoplankton production and DIN concentrations are seen to rise in the
region (e.g. Gibbs et al. 1992). In order to simulate possible changes to phytoplankton during
high production periods limited only by nitrogen, we used the same approach that has been
applied to our simple mixing models. This approach assumes the entire increase in DIN is
converted to phytoplankton biomass with stoichiometric nutrient ratios (106:16 for C:N,
Redfield 1934) and commonly observed carbon to chlorophyll weight ratios for phytoplankton
(50:1 for C:chl a ratio). Chl a concentration estimates are used to allow comparison to
measured chl a concentrations provided in the literature and other monitoring data. This
modelling approach aims to provide extreme scenarios of the cumulative effects from the
proposed and existing farms to estimate possible relative changes with respect to observed
background data.
In the case of chl a, we recognise that our model does not account for time lags associated
with the growth of phytoplankton that typically double over 2-4 days (Eppley 1972).
Therefore our near to intermediate field (<10 km from discharge) predictions are likely to
overestimated. Similarly, additional primary production is generally associated with an
increase in secondary production (zooplankton and other grazers) which, although not
considered in our model, would act to dampen phytoplankton growth (e.g. Olsen et al. 2007).
Our choice of a 50:1 weight ratio for carbon:chl a is also conservative, as under well-lighted
conditions many species will put less effort into pigment production and may have
carbon:chl a ratios of up to 200:1 (e.g. Taylor et al. 2007); therefore estimated chl a
concentration increases would be lower for a given increase in DIN. The consequence of
5
Note that our spatial modelling considers ‘recommended initial feed loads’ (RIFL) for the proposed and pending sites and
‘predicted sustainable feed loads’ (PSFL) for existing sites. The PSFL values used for modelling the existing sites differ
from present maximum feeding scenarios used in the box models, hence PSFL values may be lower than current operational
feeding levels at some sites.
36
Report No. 1985
August 2011
these layers of conservatism means the model results for chl a should be considered as
maximum possible increases from additional DIN, rather than a long-term steady increase.
Report No. 1985
August 2011
37
Table 14.
Summary of existing and proposed feed levels used in the cumulative effects model, depth and
flow conditions (LF= low flow, HF = high flow) at the proposed sites. RIFL = recommended
initial feed level, PSFL = predicted sustainable feed level, MCFL = maximum conceivable feed
level (= maximum consented feed levels for existing sites). Feeding rates are converted to DIN
assuming a ratio of 45.6 kg DIN/tonne of feed.
Site
Existing
Clay Point
(CLA)
Te Pangu Bay
(TEP)
Otanerau Bay
(OTA)
Ruakaka Bay
(RUA)
Forsyth Bay
(FOR)
Waihinau Bay
(WAI)
Crail Bay
(CRA1)
Crail Bay
(CRA2)
Proposed
Kaitira (KAI)
Richmond Bay
(RIC)
Taipipi (TAP)
Waitata Reach
(WAT)
Ngamahau
(NGA)
Ruaomoko
(RUO)
Kaitpeha
(KAP)
Papatua
(PAP, 10 Cage
Fallowed)
Pending
Waitata Reach
Extension
(WHR)
Melville Cove
(MEL)
Flow
type
Site
Depth
RIFL
PSFL
MCFL
m
kt /yr
kt/yr
kt/yr
HF
30-40
-
~4
4
HF
27-31
-
~4
4
LF
37-39
-
~2
4
LF
34-35
-
~2
4
LF
30-32
-
2
4
LF
28-30
-
2.5
3
LF
1
1
LF
1
1
HF
~60
3
4↓
6*
HF
~35
1.5
2
4
HF
~62
3
4↓
5
HF
~63
3
4↓
6†
HF
~35
1.5
3↑
4
HF
~50
3
4↓
7*
HF
~60
2
3.5
4
LF
~35
3
1.5
2
HF
22-28
1.5
2
3
LF
~20
1
1.5
2
↓ Adjusted down from capacity predicted by modelling in order to limit size of footprint (exceeds 20 ha total or max.
distance of 500 m) as a conservative measure based on experience with comparable high-flow sites.
*
Possible capacity suggested by least conservative DEPOMOD model validation regression; involves extrapolation
beyond conditions experienced to date and may be unrealistic.
As the models assume nitrogen limitation, excess photosynthetically available radiation (PAR)
would have to be available to realise chl a changes. Therefore the maximum chl a changes
predicted by the model could only occur when such conditions exist (e.g. at times primarily
38
Report No. 1985
August 2011
over the spring to autumn period). Gibbs (1992) and unpublished Cawthron data show that N
limitation only really occurs in mid-summer (January and February, ~17% of the year), but for
the purpose of conservatism we consider it possible that maximum predicted model estimates
could occur for ~50% of the year. We estimate the potential change to the annual mean
concentrations of chl a from the model using a 50% scaling factor; hence we consider a
median change of 1 mg chl/m3 predicted by the model would change the mean annual
concentration by 0.5 mg chl/m3 for the purposes of assessing possible trophic state changes.
A primary aim of this model is to guide monitoring to areas potentially most impacted by the
proposed operations rather than to try to improve on the Sound-wide assessment to critical
limits that have been derived from in situ experimental observations (e.g. the approach of
Olsen et al. 2008) and possible long-term trophic state changes estimated by our simple openbox model. The model also provides information on likely changes to DIN concentrations
around the sites during winter (May-July) a period when chl a would not be expected to
change due to light limitation. Over the spring to autumn period (August to April) the model
results show the maximum potential changes to chl a and DIN concentrations. We highlight
that the model chl a results represent maximum potential increases because of the conservative
modelling approach (either full uptake or no uptake by phytoplankton, no grazing and a low
chl a:C ratio).
Assumptions and limitations of our modelling approach
We have applied a relatively simple mass-conservative model to estimate effects, but we
recognise that additional complexity in the ecological modelling within the water column
ecosystem would add to our state of knowledge and provide more realistic estimates of the
magnitude of effects from the proposed developments (e.g. Anderson & Mitra 2010). More
complex models have been undertaken around New Zealand (e.g. Zeldis et al. 2010; Zeldis et
al. 2011); however these models require a considerably greater investment of time and data
collection to gain confidence in their outcomes. We also recognise that with any model there
will always be uncertainties outside of observed data, and even with increased complexity,
potential effects can be missed. We therefore present the worst-case scenarios here, whereby
the effects of any increases in DIN concentration on chl a are approximated by simple, yet
easily described relationships.
In recognising our simplification of the water column ecology, we also realise that other
aspects, such as the models performance with regard to mixing and dilution of the DIN plumes
from the farms have not been directly verified and may present additional sources of
uncertainty in the estimates. Nevertheless, the SELFE model has been applied to a number of
coastal environments around the world (e.g. Baptista et al. 2005; Myers 2007; Rodrigues et al.
2009 a,b, Zhang et al. 2004)6. We therefore believe the model results provide a suitably
realistic simulation of the Sound environments and possible changes from any newly imported
DIN to the Sounds. The model information will enable identification of monitoring locations
appropriate for detecting environmental changes due to the proposed farm operations. The
6
See http://www.stccmop.org/CORIE/modeling/elcirc/elcircjour.html for a larger list of publications
Report No. 1985
August 2011
39
finer spatial-scale model used here is more appropriate for this purpose than the Sound-wide
box models.
Further details of the modelling methods and parameterisation used in this investigation are
included in Knight & Beamsley,(in prep) and details on the SELFE model are available in
Zhang & Baptista (2008).
5.5.2. Spatial modelling results - Pelorus Sound
Cumulative 60-day model runs were undertaken for Pelorus Sound. The outputs represent
steady-state concentration results for the near and intermediate fields around the farms (i.e. up
to 10 km), but not necessarily the long-term, far-field changes predicted in our simple ‘open
box’ model. Nevertheless, the model achieves a major objective, which was to identify
locations that may be altered by a measurable amount and may be targeted for monitoring to
detect environmental changes from the proposed farm operations and test model predictions.
Despite the relatively short period modelled, median DIN concentrations show the potential for
increases close to the proposed sites in Pelorus Sound due to interacting effects of multiple
DIN plumes (Figure 4). The most affected areas are Ketu Bay, Richmond Bay, Waihinau Bay
and Papatua (Port Gore) which all represent potentially important locations for monitoring.
The median surface DIN concentration increases predicted after 30 days are highest in Ketu
Bay (up to 5 mg DIN/m3) which is located close to three of the proposed sites (Kaitira, Taipipi
Point and Richmond Bay) with a combined initial feed loading of 7.5 kT. The modelled
increases are relatively small when compared to measured long-term (2007 to 2010)
background concentrations of between 30 and 79 mg DIN/m3 in winter7 with an annual mean
of ~42.7 mg DIN/m3. Modelled increases therefore represent about 6 to 16% of winter
background levels in the region and ~12% of the mean annual concentrations. We note that
the proposed initial feed loadings for the sites close to Ketu Bay (~7.5 kT) are of a similar
order to the combined existing feed levels from the existing Clay Point and Te Pangu sites in
Queen Charlotte Sound (~8 kT). Although nutrient data was limited for the Queen Charlotte
Sound sites, gradients in dissolved nutrients have been detected between background and near
farm concentrations at overseas salmon farm areas (e.g. Navarro et al. 2008). Therefore it is
possible that the magnitude of DIN changes predicted by the model (i.e. 12% above mean
annual DIN) could be detected, particularly during winter or in deeper water where
phytoplankton uptake would be lower due to light limitation.
7
5th and 95th percentile values from unpublished data for outer Pelorus Sound, winter defined as period between 1 May and 1
August, 2007 to 2011. Range is similar to winter values presented in Gibbs et al. 1992 for Richmond Bay
40
Report No. 1985
August 2011
Figure 4.
Median (50th percentile) DIN and chl a concentrations from the proposed salmon farms under
recommended initial limits (n=1440) for the surface (upper) and bottom (lower) model layers in
Pelorus Sound during the 30-day period 25 June (model day 30) to 25 July 2008. Note the largest
values on the scale represent about 16% and 53% of the mean annual DIN and chl a concentrations
respectively.
Report No. 1985
August 2011
41
The mean annual chl a concentrations are about 1.5 mg chl a/m3 (Gibbs et al. 1992; Table 10),
therefore the potential increase in the median chl a concentration of about 0.5 mg/m3 shown in
the model for Pelorus Sound represents about a 30% increase from mean annual background
values. Assuming our 2-month model results represent 50% of ‘steady-state’ mean annual
changes, the potential concentration change in chl a (<0.4 mg chl a/m3) would not, however,
be sufficient to cause a change in trophic state (mean annual chl a > 3 mg chl a/m3).
In the case of Papatua, where a low level of flushing is observed, DIN and chl a changes are
higher (up to 15% and 45% of Pelorus DIN and chl a concentrations over a large proportion of
Port Gore). Thus the predicted potential concentration change in chl a would not be sufficient
to cause a change in trophic state. Nevertheless, we consider that, if development of this site
proceeds, it should be coordinated with water column monitoring to confirm that mean annual
chl a concentrations were not increased to eutrophic levels. Monitoring would be particularly
important for this region if the pending Melville Cove consent is also granted, as modelling
shows the potential for cumulative effects in the region.
Phytoplankton require time to assimilate and grow, as they typically have doubling rates of 1
to 4 days (e.g. Eppley 1972), and the DIN increases located close to the proposed sites are
likely to be relatively new DIN (1 to 2 days old after being released into the water column);
therefore our simple scaling of DIN to chl a is likely to overestimate the phytoplankton
biomass increase in areas close to the salmon farms as it assumes instant assimilation and no
mortality (e.g. through zooplankton/mussel grazing). Full ecosystems models, such as applied
in Tasman Bay (Zeldis et al. 2011) and the Firth of Thames (Zeldis et al. 2010) note that
modelled chl a changes generally occur many kilometres away from the farm sites. An in situ
water column study (Navarro et al. 2008) also failed to establish a clear relationship between
salmon farm inputs and chl a gradients around the farm even though significant increases in
ammonium and dissolved organic nitrogen (DON) were detected.
Figure 4 shows median concentration changes that are not as large as the mean concentration
changes shown in Figure 5. This indicates that the distribution of changes in each model cell
is skewed towards the lower end of the distribution (i.e. a ‘long-tailed’ distribution). This also
indicates the model runs may not quite have reached ‘steady-state’ conditions, or the regions
are subject to dynamic conditions (e.g. wind/river influences). There are only slight
differences between the mean and the median around the sites which suggests the distributions
are only slightly skewed. At some of the sites the differences are larger (e.g. Papatua), this
suggests periodic flushing events may occur and the modelled period may have an influence
on our results. In order to be clear in our reporting of results, we show both mean, median and
95th percentile results, but note that the median presents the best representation of the central
tendency of the distribution and magnitude of changes (i.e. 50% of the time the effects will be
greater than the median). However the mean may be more representative of the level of
change over a longer time period.
42
Report No. 1985
August 2011
Figure 5.
Mean potential DIN and chl a concentration changes from proposed salmon farms under
recommended initial limits (n=1440) for the surface (upper) and bottom (lower) model layers in
Pelorus Sound during the 30-day period 25 June (model day 30) to 25 July 2008. Note the largest
values on the scale represent about 16% and 53% of the mean annual DIN and chl a concentrations
respectively.
Hydrodynamic studies of the Pelorus Sound (e.g. Sutton & Hadfield 1997; Proctor & Hadfield
1998) note that estuarine circulation can be a prominent feature in the region, particularly
following high-flow events in the Pelorus River. This circulation pattern results in low salinity
(and density) surface water flowing out of the Sound (e.g.Figure 2) and this is balanced by a
return flow of higher salinity (more dense) water flowing into the Sound from Cook Strait.
Report No. 1985
August 2011
43
The effect of this circulation on dissolved nutrients is evident in Figure 4 and Figure 5, where
the deeper water column DIN concentrations can be seen to move further into the Sound. This
will have implications for the amount of time salmon farm DIN stays in the Sound, with the
deeper water column DIN remaining for longer periods than wastes released at the surface. If
the model was run for a longer time we may have seen the influence of the lower water column
DIN extend further towards the entrance of the Pelorus River/Havelock and increase beyond
the levels shown in Figure 4. Potential chl a results are also shown on the map for the bottom
layer of the model. The assimilation of DIN where light is low will be lower; therefore chl a
estimates are likely to be overestimated. Recorded data from the inner Pelorus Sound
(Schnapper Point; Table 10), collected before and after existing outer Sound salmon farms
were developed, shows no increase in mean annual chl a concentrations (Section 2.4.4).
We have presented median and mean results to show the magnitude of changes likely to be
detected in the region, but periodically, changes greater (or less) than these can occur in the
region. In order to see how large these changes could be, we also investigated the 95th
percentile values modelled over the period (Figure 6). These results showed that greater
increases in DIN or chl a concentrations were possible at times (i.e. up to 1 day in 20) and a
larger area could be affected. The increase in area is particularly evident at the Papatua site in
Port Gore and highlights the episodic flushing of the region. Despite this increase in area the
maximum increases in DIN are small (<16%), although the potential exists for larger relative
changes in chl a (up to 53%).
Figure 6.
44
95th percentile values DIN and chl a concentrations from the proposed salmon farms under
recommended initial limits (n=1440) for the surface model layers in Pelorus Sound during the 30day period 25 June (model day 30) to 25 July 2008. Note the largest values on the scale represent
about 16% and 53% of the mean annual DIN and chl a concentrations respectively.
Report No. 1985
August 2011
The increase in concentrations, due to development of the proposed new sites (Figure 4 to
Figure 6), do not show the effect of changes from background due to the existing and newly
proposed sites in the region. We revisited our analysis to investigate cumulative changes from
an increase in the number of known nutrient sources in the region (all proposed, in process and
existing sites).
Figure 7 shows the estimated changes from existing and proposed salmon farm operations and
highlights the areas that may be changed the most from their pre-salmon farming state.
Waihinau Bay and Port Ligar in particular are highlighted by this analysis and we can see that
the area of largest change associated with the proposed sites (Ketu Bay) is relatively small
when compared to existing regions (e.g. Crail or Waihinau Bay). Given the proposed plan
change sites are generally removed from the influence of existing sites, the cumulative effects
of proposed and existing sites do not appear to be much larger than the existing effects of
presently consented salmon farms.
Despite the uncertainties inherent in the model, it shows that measurable nutrient changes may
occur within some localised areas when compared to background concentrations and that the
effects decrease with increasing distance from salmon farms. Although phytoplankton
biomass increases are also possible, it is unlikely any clear gradients will be observed around
the farms due to time lags and food web grazing effects on phytoplankton. Measured chl a
data in the region collected after existing farms were operating in the region provides some
evidence that this will be the likely result. Similarly, a focused study of water column
(Navarro et al. 2008) was unable to detect chl a gradients around a salmon farm.
Report No. 1985
August 2011
45
Figure 7.
46
Median (upper) and mean (lower) cumulative DIN and chl a concentration changes from all
proposed, pending and existing salmon farms under recommended initial limits (n=1440) for the
surface (upper) and bottom (lower) model layers in Pelorus Sound during the 30-day period 25
June (model day 30) to 25 July 2008. Note that the scale differs from that in Figure 4. Changes
from existing low flow sites (e.g. Crail Bay and Waihinau) are most evident in this analysis. Note
the largest values on the scale represent about 20% and 227% of the mean annual DIN and chl a
concentrations respectively.
Report No. 1985
August 2011
5.5.3. Spatial modelling results – Queen Charlotte Sound
Queen Charlotte Sound model runs were undertaken for a longer period than those for the
Pelorus Sound model (125 days or ~ 4 months). In order to analyse a long enough period to
detect a range of conditions, but allowing sufficient time to generate ‘steady state’ conditions
within the Sound, we analysed the cumulative effects over the last 30 days of the model run
(model day 95 to 125).
Queen Charlotte Sound cumulative nutrient results (Figure 8) show the potential for localised
water column enrichment close to the proposed sites. The largest median changes in DIN were
~2.5 mg/m3 in bays near the proposed Kaitepeha and Ruaomoko sites. This change is
relatively small (~5%) when compared to mean annual Wedge Point DIN concentrations
(40 mg/m3). Although TN concentrations were not available in the region, it is unlikely this
level of DIN increase would result in an associated change in TN concentrations to conditions
typical of eutrophic waters (Table 4). Similarly, potential chl a increases are also of a level
that do not suggest a change in trophic state (<0.3 mg chl a/m3), assuming potential increases
shown in Figure 8 represent steady-state changes.
Unlike Pelorus Sound, mean concentration changes (Figure 9) are comparable with median
concentration changes (Figure 8). This implies that the distributions of change are ‘balanced’
(i.e. not skewed). It also suggests that the nutrient plumes in the upper and lower water
column follow a relatively stable path and were not influenced by wind or rain to a large extent
over the modelled period (28 August to 27 September 2008). Some variation in the vertical
distribution of mixed DIN is evident from models (Figure 8 and Figure 9), but despite rainfall
events during the period modelled, the same degree of estuarine circulation seen in Pelorus
Sound is not evident in Queen Charlotte Sound.
Report No. 1985
August 2011
47
Figure 8.
48
Median (50th percentile) potential DIN and chl a concentration changes from proposed salmon
farms under recommended initial limits (n=1440) for the surface (upper) and bottom (lower)
model layers in Queen Charlotte Sound during the 30-day period 28 August (model day 95) to 27
September 2008. Note the largest values on the scale represent about 18% and 47% of the mean
annual DIN and chl a concentrations respectively.
Report No. 1985
August 2011
Figure 9.
Mean potential DIN and chl a concentration changes from proposed salmon farms under
recommended initial limits (n=1440) for the surface (upper) and bottom (lower) model layers in
Queen Charlotte Sound during the 30-day period 28 August (model day 95) to 27 September 2008.
Note mean concentrations are similar to the median, suggesting a ‘balanced’ distribution through
time for the near and intermediate-field locations, suggesting ‘steady state’ conditions are probably
realised over the period. Note the largest values on the scale represent about 18% and 47% of the
mean annual DIN and chl a concentrations respectively.
Report No. 1985
August 2011
49
Figure 10 shows that, at times, (5% of the time or 1 day in 20), the cumulative effects may be
larger than the median and mean, up to 3 to 4 mg DIN/m3 (or 0.35 to 0.45 mg chl a/m3). This
result is lower than the predicted median changes close to the proposed Pelorus sites after 26
days, so even the largest changes seem to be relatively small in the Queen Charlotte Sound.
Figure 10.
95th percentile potential DIN and chl a concentration changes from proposed salmon farms under
recommended initial limits (n=1440) for the surface (upper) and bottom (lower) model layers in
Queen Charlotte Sound during the 30-day period 28 August (model day 95) to 27 September 2008.
Note the largest values on the scale represent about 18% and 47% of the mean annual DIN and chl
a concentrations respectively.
The suitability of the proposed site selection is reinforced by a comparison to low-flow sites
with existing consents (Figure 11). These show modelled increases that are much larger from
existing consented sites that are less well flushed (e.g. Ruakaka and Otanerau). These sites, in
combination with the proposed site effects, are seen to potentially appreciably increase
ambient nutrient and/or chl a concentrations in their local regions. High-flow sites, such as
those located in Tory Channel and the proposed sites can be seen to be rapidly diluted. When
the results of all sites (existing and proposed) are compared to mean annual background
concentrations, we can see that large regions of the Queen Charlotte Sound may have potential
DIN increases of ~10% and ~100% in chl a. This result is consistent with the studies of WildAllen et al. (2009) who also estimate increasing areas of higher chl a with increased farmed
salmon production. However, chl a data taken after existing sites were operating in the region
suggests that although, at times, high chl a concentrations are possible (maximum of depth
averaged concentration of 4.26 mg chl a/m3 recorded in Tory Channel), mean annual chl a
concentrations are similar to Pelorus Sound (Table 10).
50
Report No. 1985
August 2011
Figure 11.
Median (upper) and mean (lower) cumulative DIN and chlorophyll concentration changes from all
proposed and existing salmon farms under recommended initial limits (n=1440) for the surface
(upper) and bottom (lower) model layers in Queen Charlotte Sound during the 30-day period 28
August (model day 95) to 27 September 2008. The largest values on the scale represent about
75% and 201% of the mean annual DIN and chl a concentrations respectively. Note that the scale
differs between these maps and the ‘proposed site only’ analysis (Figure 8). Changes from
existing low-flow sites (e.g. Ruakaka and Otanerau) are particularly evident in this analysis.
Report No. 1985
August 2011
51
There are also potentially greater changes close to the existing low-flow sites; although as
mentioned previously, chl a increases predicted by our model are not likely to be achieved
close to the farms. DIN changes are likely particularly close to the proposed farm sites and
during winter when phytoplankton uptake will be lower. These results highlight the potential
for large cumulative changes from pre-salmon farming conditions in the region; but existing
data, undertaken while the Ruakaka and Otanerau farms were operating, shows these changes
to be short-lived and not associated with a shift to harmful species (Section 2.4.4). Therefore
the changes from the additional proposed sites should not be problematic to the ecosystem or
proposed salmon operations. Given the potential for phytoplankton changes to occur, we
recommend water column monitoring of chl a and HAB species is undertaken in regions
located away from the proposed sites (e.g. existing Tory Channel and Wedge Point monitoring
sites). If significant departures from existing HAB occurrence or chl a concentrations were
observed, then appropriate management actions could be undertaken to ensure that ongoing
detrimental cumulative nutrient effects do not occur.
5.6. Wider ecosystem effects
Stimulation of phytoplankton growth would be expected to have the follow-on effect of also
stimulating phytoplankton consumers such as micro- and meso-zooplankton, and a variety of
suspension feeding animals (e.g. mussels, scallops etc.), thus providing at least partial
mitigation with respect to bloom development. Pelorus Sound, for example, contains a
particularly high biomass of farmed GreenshellTM mussels that would likely have a dampening
effect on phytoplankton enhancement. In other words, the food web acts like a buffer that,
within limits, can mitigate phytoplankton responses to excess nutrients (Olsen et al. 2007).
However, such ecosystem effects are complex and are very difficult to predict (Rosenzweig
1971). In view of the low levels of phytoplankton enhancement predicted to occur as a result
of the new proposed farms (see following modelling results), no adverse food web
perturbations would be expected. A more likely result would be a slight increase in the rate of
production of farmed mussels and natural phytoplankton grazers in the regions predicted to
experience the largest increase in chl a concentrations.
The stimulation of phytoplankton production through nutrient enrichment can have significant
effects on the coastal ecosystem. For example, phytoplankton blooms resulting in chl a
concentrations in excess of about 5 mg/m3 may produce visible discolouration of the water
column (Eppley et al. 1977), significantly reduced light availability to bottom waters and the
seabed, and enhanced sedimentation rates. Such conditions occur naturally in the
Marlborough Sounds periodically; however excessive nutrient enrichment could increase
bloom frequency, duration and intensity. In extreme cases of enrichment, follow-on ecosystem
effects could occur. These might include dissolved oxygen depletion, severe light limitation
for macroalgal growth, depositional impacts to seabed life and changes in phytoplankton
species composition (Forrest et al. 2007). Modelled predictions of the increases in
phytoplankton biomass expected to result from the proposed new farm developments (see
Sections 5.4 and 5.5) would not be sufficient to cause such follow-on effects. However the
potential for cumulative effects in some regions (Section 5.5) highlights the importance of
staged development and monitoring as an adaptive management approach.
52
Report No. 1985
August 2011
6.
SUMMARY OF WATER COLUMN EFFECTS
Our assessment considered the effects of the NZ King Salmon proposed Plan Change and
addition of eight new salmon farms on the water column environment in the Marlborough
Sounds. Overall, our assessment suggests that the effects of: farms structures on physical
characteristics of the water column, fish respiration on levels of dissolved oxygen (DO), and
nutrient loading on the surrounding water environment, will be small at a Sound-wide scale
(Table 15). However, we have considered a range of possible effects, and note there may be
fine temporal or spatial-scale changes that have the potential to adversely affect the ecosystem
or the farming operations themselves (e.g. as in the case of harmful algal blooms). We also
summarise more site-specific considerations (see Table 16).
Physical effects associated with the farm structures are expected to be very small and highly
localised. Although these effects could potentially be important in areas where flows are low
and waves are important (e.g. Papatua), we note that the structure footprints are relatively
small and therefore these effects are unlikely to have a measurable influence on the ecology of
the water column environment (see Table 15).
The effects of large numbers of salmon on depletion of DO is also expected to be very small
and limited to the vicinity of the farms. Currently, DO is measured as part of routine farm
management to ensure suitable water quality conditions for farmed salmon. It is possible that
depleted DO levels that do not harm the fish may harm other organisms in the water column
(e.g. larvae); however these effects would be very small, highly localised and difficult to
measure through monitoring. The placement of farms in high-flow environments will mitigate
effects of the fish on DO levels beyond the farms.
In order to assess effects associated with nutrient loading, we have applied a range of
modelling and mass-balance estimates in combination with existing datasets and other studies
to assess potential changes in the regions around the proposed sites. A review of the literature
and chl a data from the Sounds (undertaken before and after existing sites were in place)
suggests the effects of nutrient loading on the water column environment (e.g. increases in
phytoplankton biomass) will be small. However, outputs from conservative models indicate
there is the potential for measurable water-column changes in the Sounds (e.g. increases in
nutrient concentrations and phytoplankton biomass).
In our simplest modelling approach we consider the Sounds (excluding Port Gore) as simple
closed box systems, and compare the estimated net nitrogen loading rate for both Sounds to a
critical nutrient loading rate (CNLR). The CNLR is based on experimental changes in
phytoplankton production in response to increased nutrient loading and is the level where
increases in phytoplankton biomass will result in adverse effects are observed. At a Soundwide scale, the nitrogen loading appears to be sufficiently under a CNLR considered
appropriate for the Sounds (42% and 51% of the CNLR for Pelorus and Queen Charlotte
Sounds respectively). This gives us confidence that nutrient loading from the combined farms
(existing and proposed) will not reach critical levels that could compromise the ecological
integrity of the systems. Nevertheless, new additional nutrients have the potential to affect
Report No. 1985
August 2011
53
phytoplankton and the wider water column communities. Therefore, we also assessed the
relative change from the proposed sites, and the potential for a change of trophic state (e.g.
shift from mesotrophic to eutrophic conditions) in the Sounds by comparing the potential
changes from background to typical water column properties for different trophic states (Table
4).
The box modelling approach was then extended to include the effects of tidal flushing (i.e. an
‘open-box’) within Sound-wide estimates of nitrogen concentration and phytoplankton
biomass. The results of the simple models show the potential for small, long-term increases in
total nitrogen concentrations in both Pelorus and Queen Charlotte Sound (Table 13).
Phytoplankton biomass estimates (using chl a as a proxy) show that Pelorus and Queen
Charlotte increases associated with the proposed farms should also be small (7.35% and
11.95% increases above existing chl a changes; Table 13). However, modelling of all existing,
pending and proposed sites shows the cumulative change could be as high as an 11% and 38%
increase above ambient environmental chl a levels for Pelorus and Queen Charlotte Sound
respectively.
More advanced, spatially explicit modelling (e.g. Figure 4 and Figure 8) also highlights the
potential for overlapping nutrient plumes and the potential for locally increased DIN
concentrations that may fuel increased phytoplankton biomass. The degree of dilution and
flushing from the proposed sites can also be observed in the model results, with proposed highflow sites showing increases that are over relatively small areas compared to existing farms
that are located in low-flow environments. The regions that appear most likely to be affected
by increased nitrogen loading are Ketu and Richmond Bay in Pelorus Sound, Papatua in Port
Gore and Kaitepha Bay in Queen Charlotte Sound (Table 16), although the magnitude of
change in these areas does not suggest a change in trophic state.
At the Papatua site, where a low level of flushing is observed, DIN and chl a changes are
higher (up to 15% and 45% of Pelorus DIN and chl a concentrations over a large proportion of
Port Gore). Assuming the results based on a 2-month model simulation represent ‘steadystate’ changes, the potential concentration change in chl a (<0.8 mg chl a/m3) would not be
sufficient to cause a change in trophic state (defined as an increase in mean annual chl a to
>3 mg/m3).
Model outputs indicate that nutrient loading effects are greater in some regions of the Sounds
when the cumulative inputs from existing and proposed farms are considered. General regions
where effects may be highest include Crail Bay, Waihinau Bay in Pelorus Sound, and the
vicinity of Ruakaka and Otanerau Bay in Queen Charlotte Sound. These areas are where
effects are most likely to be measurable; hence they should be included as sampling locations
within a water quality monitoring programme (see Section 8) and for validating model
estimates of effects.
The modelling approaches used in this assessment are conservative and in reality the effects
are likely to be smaller than those predicted. For example, in Queen Charlotte Sound, where
predicted changes are estimated to be the largest, the mean annual chl a concentrations in Tory
54
Report No. 1985
August 2011
Channel, when many of the existing salmon farms were operating (Table 10), do not appear to
be higher than the mean of all of Pelorus Sound sites surveyed prior to salmon farming. This
result highlights the conservatism inherent in our modelling approach, which forecasts
potential effects and does not account for ecosystem processes such as food web dampening or
regeneration times for phytoplankton. Nevertheless, high chl a concentrations and HABs
have, at times, been observed in the Sounds; so there is a clear need to gradually increase
salmon production while confirming (through monitoring) that nutrient loading effects are in
fact small and less than those predicted
An important consideration with regard to our assessment is that other activities in the coastal
zone contribute nutrients to the Sounds. In Pelorus Sound, this may be particularly important
as there is the potential for increases in land-derived nutrient loading to occur as a function of
changing land use and increased pastoral farming in the Rai and Pelorus River Catchments.
Similarly increased urban development and associated nutrient wastes in Queen Charlotte
Sound may also contribute to nutrient loading. Changes in these additional nutrient sources
are important to consider alongside future development of finfish aquaculture in the Sounds.
Sound-wide monitoring of the water column environment (described below) will assist in
understanding cumulative effects of multiple sources of nutrients on the health of the wider
ecosystem.
Report No. 1985
August 2011
55
Table 15.
Summary of assessed effects of proposed salmon farm site development on water column properties.
Issue
Potential effects
Nature and magnitude of assessed effects
Physical water column
effects - Farm structures
occupy a three-dimensional
space at and below the water
column
Attenuation of currents
Based on observations and model simulations for mussel aquaculture structures, only minor effects on
currents within close proximity to the proposed farms are expected.
Reduction in wave
action/energy
The farms structures will attenuate waves within the vicinity of the farm. The proposed farms will lie
in high energy environments and represent a very small area of the Sounds; hence the effects on waves
will be minor.
Effects on salinity and/or
temperature stratification
The effect of structures on currents and waves may have a small effect on the stratification (mixing) of
the water column; however, this effect will likely be highly localised and would be of little ecological
importance in terms of the wider Sounds environment.
Attenuation of incoming
solar radiation
The farm structures will shade incoming solar radiation and will reduce the amount of light that is able
to penetrate the water column and reach the underlying seabed. Effects will be highly localised and
therefore minor with regard to the wider Sounds marine environment.
Reduced concentration of
dissolved oxygen (DO)
Most farms will be situated in deep and highly flushed waters and therefore will likely lead to only
minor localised effects on DO levels in the water column.
Oxygen depletion to levels
that affect biological
processes
Levels of DO in the water column that become detrimental to marine life are unlikely to occur at the
proposed farms. Adequate flushing and maintenance of DO levels are required for successful farming
of salmon. Hence, the effects of low levels of DO on the surrounding water column environment are
likely to be minor.
Dissolved oxygen depletion Presence of large numbers of
fish within a small volume of
water results in high rates of
respiration (oxygen
consumption)
Report No. 1985
August 2011
56
Table 15 (continued). .Summary of assessed effects of proposed salmon farm site development on water column properties.
Nutrient loading - Salmon
farming involves the addition
of feed and therefore results in
fish waste production and new
inputs of nutrients into the
water column
Report No. 1985
August 2011
Increased concentrations of
dissolved nutrients
(ammonium toxicity)
The production of fish waste will result in an increase in dissolved nutrients within the water column
around the farms and within the surrounding water column. The effect on concentrations will be
greatest near the farms and will decrease with distance as a function of mixing and dilution. Increased
concentrations of ammonium can become toxic to sea life; however, levels of ammonium above cited
thresholds for adverse effects are unlikely to occur, particularly beyond close proximity of the farms.
Increased phytoplankton
production (including HAB
species if present)
When conditions are suitable, increased concentrations of nutrients (particularly nitrogen) can enhance
the growth of phytoplankton. The extent to which the added nutrients from salmon farms could
enhance growth, leading to changes in phytoplankton biomass over and beyond the existing levels, will
be limited in time and space. Assessment of net nitrogen inputs (including proposed new inputs) is
below critical loading rates based on experimentally derived assessments of conservative critical limits;
nutrient loading from the proposed sites is unlikely to compromise the integrity of planktonic
ecosystems in the region. Forecasted changes in nutrient concentrations, both at the local scale of
individual farms and at the Sound scale, provide an indication of the potential for phytoplankton
biomass increases in the intermediate and far fields. These are relatively small at a Sound-wide scale
(up to 7.4% and 12% increase from existing chl a concentrations in Pelorus and QC Sound
respectively), but may be measurable at an intermediate scale.
Increased zooplankton and
higher trophic levels in
response to increased
primary production
An increase in nutrient concentrations and subsequent increases in phytoplankton biomass could
potentially lead to increased secondary production in farmed mussels and zooplankton. Such a food
web response would have a dampening effect on the development of adverse levels of phytoplankton
biomass (i.e. algal blooms).
Cumulative inputs from
multiple farms could result
in sound-wide changes in
ecological integrity.
A critical loading assessment shows the sounds environments will remain below critical nutrient
loading rates which can “still secure full ecosystem integrity in euphotic planktonic ecosystems” (Olsen
pers. com.) and incorporate wider characteristics, which include: “…efficient trophic transfers, linearity
in the responses in plankton biomass and flows of materials with nutrient loading rate, and a moderate
sedimentation rate to aphotic waters and the sea floor” (Olsen, pers. comm.). Sound-wide modelling
also shows mean annual chl a concentrations will remain below concentrations that are associated with
a higher trophic (i.e.‘eutrophic’) state.
57
Table 16.
Summary of site-specific assessment of water column effects
Issue
Physical Water
Column Effects Farm structures
occupy a threedimensional space at
and below the water
column
Dissolved oxygen
depletion - Presence
of large numbers of
fish within a small
volume of water
results in high rates of
respiration (oxygen
consumption)
58
Site
High flow sites:
Kaitira, Richmond
Bay, Taipipi,
Waitata, Ruamoko,
Kaitpeha,
Ngamahau.
Site Specific Effects
Physical effects may be difficult to detect around high flow
sites due to their dynamic environments. Mixing effects
may be more likely to be detected around the structures at
these sites due to frictional turbulence effects increasing
non-linearly with current speeds.
Low-flow site:
Papatua
Physical effects at this site will be comparable to existing
low-flow sites (e.g. Waihinau, Otanerau, Ruakaka). As
with existing sites attenuation of currents will reduce
already low currents in the region close to cages. This site
differs from existing sites because it is located close to
Cook Strait, and hence may periodically be subject to large
wave/swell events. We would expect these events to
partially mitigate the effects of flow reductions from cages
(e.g. decreased transport of enriched sediments under the
nets) and note that proposed periodic fallowing would
ensure currents are not attenuated for long periods of time.
High-flow sites:
Kaitira, Richmond
Bay, Taipipi,
Waitata, Ruamoko,
Kaitpeha,
Ngamahau.
Slight to moderate localised depletion of DO would be
expected at all high flow sites. This degree of reduction
would not represent a significant risk to marine life and
would not be expected to extend beyond farm boundaries.
Low flow site:
Papatua
Significant DO depletion may occur periodically; but can
be monitored and mitigated through temporary feed
reduction if necessary. Farmed salmon would be most at
risk.
Report No. 1985
August 2011
Table 16 (continued).
Nutrient loading Salmon farming
involves the addition
of feed and therefore
results in fish waste
production and new
inputs of nutrients
into the water column
Summary of site-specific assessment of water column effects
Kaitira, Richmond
Bay, Tapipi
Waitata Reach
Ruamoko, Kaitpeha
Ngamahau
Papatua
Report No. 1985
August 2011
Modelling shows that a large proportion of the dissolved
nutrient released is flushed from the Sound at these outer
Sound sites (particularly in the surface waters). Modelling
shows the potential for overlapping effects of dissolve
nutrient plumes in the region of Ketu and Richmond Bays
for these sites; however, the magnitude of the effects is
relatively minor compared to median winter background
concentrations. Although there is potential for associated
increases in phytoplankton biomass, we note that our
modelling shows small increases in chl a that would likely
be difficult to measure in the context of natural variation.
Modelling of this highly flushed site shows the potential
for overlapping effects with an existing site in Waihinau
Bay and the pending consent for the Waitata Reach
extension site. Although the Waihinau Bay site is
predicted to have measurable influence on DIN
concentrations in that region, the additional effect on DIN
from the newly proposed site is small. There is also the
potential for associated small increase in phytoplankton
biomass.
Modelling of these closely-spaced, but well flushed sites
shows the potential for overlapping effects from the
nutrient plumes in the region of Mid Queen Charlotte
Sound and Tory Channel. There is also the potential for an
associated small increase in phytoplankton biomass in the
region.
Due to the high currents and flushing at this site detectable
changes are not apparent in our models. The dispersive
nature of this site means it will contribute to a slight
increase in the background nutrient concentrations in the
region, but it would be difficult to measure nutrient or
phytoplankton biomass changes in the context of natural
variation.
At this comparatively low-flow site, the magnitude of local
DIN changes is expected to be greater than the other
proposed sites. The spatial modelling used in our
assessment also shows Papatua to be removed from the
influence of existing sites, although it may interact with the
pending Melville Cove application. The modelled DIN
increases are, however, relatively small and the proximity
to Cook Strait means a large proportion of the nutrients
will be flushed from the region. Similarly the
phytoplankton biomass changes are also predicted to be
small and given the conservatism inherent in our approach
the maximum potential changes shown are unlikely to be
realised.
59
7.
MONITORING RECOMMENDATIONS
Physical effects associated with the farm structures are expected to be very small and highly
localised. Omission of guidance for thresholds for physical effects in new World Wildlife
Fund (WWF) draft aquaculture standards (WWF 2011) highlights the perceived low relative
importance of physical effects; however we do recognise that cumulative effects of increasing
numbers of marine structures can add to region-wide changes in flushing characteristics.
Physical effects from the proposed structures are unlikely to have a measurable influence on
the ecology of the water column environment because of the relatively small footprint of the
structures (<0.02%); hence we not believe any monitoring of the physical effects of farm
structures would be necessary.
The effects of large numbers of salmon on depletion of dissolved oxygen is also expected to be
very small and limited to the vicinity of the farms. Currently, DO is measured as part of
routine farm management to ensure suitable water quality conditions for farmed salmon. It is
possible that depleted DO levels that do not harm the fish may harm other organisms in the
water column (e.g. larvae); however, these effects would be very small and highly localised.
The placement of farms in high-flow environments will mitigate effects of the fish on DO
levels beyond the farms. For these reasons it would not be essential to monitor DO
concentrations within the vicinity of the proposed high-flow farms, however all low-flow
farms should be monitored routinely within net pens to provide feedback for adaptive
management with respect to appropriate stocking densities. We also recommend the inclusion
of DO as a water quality indicator when monitoring the effects of nutrient loading on the water
column (see Table 1 below). Some guidance for appropriate DO thresholds may also be
available through international standards (e.g. WWF 2011), which highlight the importance of
DO for monitoring for salmon health and wild species surrounding a farm.
In order to minimise environmental effects, considerable effort has been made to determine the
most suitable sites for the proposed salmon farms. Most of the sites are located in deep, highly
flushed waters and near the entrances of the Sounds, which will allow for a higher level of tidal
exchange with Cook Strait. Although placed in areas that will minimise effects on the water
column, potential effects of the proposed farms in relation to nutrient loading will need to be
monitored over time.
The prediction of nutrient loading effects on the water column assumed recommended initial
feed levels for all of the eight proposed farms as part of NZ King Salmon’s proposed Plan
Change for the Marlborough Sounds. In order to assess the cumulative effects of an initial
development scenario, models used for predicting effects of nutrient loading included all
existing and proposed farms. Our assessment therefore represents the largest potential effects
that could be expected to occur under an initial feeding scenario with all farms in place.
Consequently the levels of effects predicted in the assessment are greater than those that would
occur during early stages of development (see Benthic Report - Keeley et al. 2011).
In reality, the farms will be developed over time, which will allow for monitoring of the water
column environment as the farms are developed. Monitoring as development progresses will
60
Report No. 1985
August 2011
in turn assist in validating model estimates of the effects of the complete development and will
further increase the understanding of the effects of the salmon farms on water column
processes in the Sounds. A similar MOM (Modelling - On-growing fish farms - Monitoring)
approach has been used in Norway to inform management strategies around the development
of salmon farming (Ervick et al. 1997; Hansen et al. 2001).
The effects of nutrient loading from salmon farms, while estimated to be small in terms of the
wider Sounds environment, are important to monitor and understand due to the potential
effects on phytoplankton production and possible enhancement of HABs. However, it is
important to consider that salmon farming is one of many human activities within the coastal
zone that potentially affect water quality and the health of the Sounds marine ecosystem. Land
uses in coastal catchments (e.g. pastoral farming, coastal development, forestry, sewage
outfalls) can also have significant impacts on downstream coastal waters (Cornelisen et al. in
press; Gillespie et al. in press) and occur closer to the head of the Sounds so may be retained
for longer periods. Mussel farming also impacts water column conditions through the removal
of plankton from the water column and conversion of water column biomass into faeces that
are deposited on the seabed. Complicating matters is that climate-related processes (season,
weather, cycles such as El Niño; Zeldis et al. 2008) also affect water column conditions and
influence the relative contributions of land-derived and oceanic sources of nutrients within the
water column over time.
For the above reasons, we would recommend two components to monitoring water column
effects associated with the proposed salmon farms:
1.
Short-term (1-2 year) monitoring at the ‘farm scale’ that involves targeted surveys for the
purpose of validating models and quantifying the effect of individual farms on
surrounding water quality.
2.
Contributions toward a longer-term (>10 year) programme that involves multiple
stakeholders and is established to collect robust Sound-wide datasets for the purpose of
monitoring the ‘health’ of the Sounds environment over time.
The purpose of farm-scale monitoring is primarily to validate model estimates and measure
effects of salmon farms on nutrient concentrations within the surrounding water column.
Dissolved nutrient concentrations are highly variable both spatially and temporally due to
numerous physical and biological processes. To increase the likelihood of measuring farm
effects, we recommend a series of fine-scale surveys be carried out at a subset of farms (and
reference areas) that represent the range of environmental conditions where the farms are
situated. These surveys would involve collecting discrete water samples for measuring
nutrient concentrations and phytoplankton composition and biomass (e.g. chl a) along transects
that move away from the farm and span potential nutrient gradients. During the surveys,
standard water quality parameters would also be collected using towed sensors (for measuring
salinity, temperature, chl a, turbidity, DO). Similar surveys are conducted to evaluate the
effects of mussel farms on the depletion of phytoplankton from surrounding waters (e.g.
Keeley et al. 2009). It is recommended that one round of surveys be conducted during two
different seasons (winter and spring/summer) to account for trends in phytoplankton biomass
Report No. 1985
August 2011
61
and nutrient concentrations. Results from initial surveys would then be reviewed to inform
whether additional surveys over time would be required.
It is recommended that long-term monitoring focus on the second component and address
potential far-reaching effects of multiple farms on the wider ecosystem. Such monitoring is
required since the effects of multiple farms on water column processes (e.g. phytoplankton
production) may occur over time scales (days) and spatial scales (kilometres downstream of
farms) that lie outside the scope of farm-scale monitoring programmes (see Olsen 2007).
Possible components of long-term monitoring include contributions toward: (1) a Sound-wide
field sampling programme (e.g. expansion of the existing Marlborough Shellfish Quality
monitoring Programme, MSQP), and (2) establishment of permanent monitoring platforms
with high frequency sampling capabilities.
Potential water column indicators to be measured as part of a Sound-wide field sampling
programme include phytoplankton biomass (and proxies e.g. chl a) and composition and the
concentration of DO and DIN (see Volkmann et al. 2009). Outputs from the SELFE model
used in this assessment would assist in identifying areas to focus monitoring efforts in relation
to salmon farms (Figure 12). Data collected as part of the field sampling programme would
cover spatial and coarse temporal variability. The data could then be interpreted alongside
time-series data collected at established platforms, which are spatially confined (e.g. platforms
at inner and outer regions of each Sound) but provide temporally high-resolution data on key
water quality variables.
Permanently established platforms such as moored sensor arrays would enable the collection of
robust, time-series data for monitoring water quality for multiple purposes, including State of
the Environment (SoE) monitoring (by Council and Ministry for the Environment), MSQP
monitoring of water quality and phytoplankton blooms, validation of models, and research.
Long-term deployment would also enable changes in the environment associated with
development of aquaculture to be assessed within the context of natural variability and climaterelated changes. Similar monitoring platforms have been established within the vicinity of
Aquaculture Management Areas in Tasman Bay (Cawthron’s TASCAM buoy) and in the Firth
of Thames (Turner & Felsing 2005; Zeldis et al. 2005).
Sensor technology has rapidly improved and variables such as salinity, temperature, chl a,
turbidity, dissolved nitrogen (nitrate), and oxygen can be reliably measured remotely, and if
required, transmitted in near real-time. The monitoring platforms should include instruments
for measuring weather variables and currents, both of which are important for interpreting
results and understanding the physical dynamics of the Sounds. We would recommend that
interpretation of data from long-term monitoring programmes be carried out at yearly intervals
and independently reviewed. Over time, as data and knowledge increases, water column
indicators can be integrated within a wider adaptive management framework for managing
future aquaculture development in the Sounds.
62
Report No. 1985
August 2011
Figure 12.
Plots of potential surface water concentration changes to DIN and Chl a from the proposed salmon
farms. Orange circles represent areas within the ‘intermediate’ field of effects, which modelling
indicates could be affected by a measurable amount and may present suitable areas for monitoring.
White circles represent areas removed from the influence of the proposed sites and present
potential control sites.
Report No. 1985
August 2011
63
8.
REFERENCES
Abo K, Yokoyama H 2007. Assimilative Capacity of Fish Farm Environments as Determined
by Benthic Oxygen Uptake Rate: Studies Using a Numerical Model. Bull. Fish. Res.
Agen. No 19: 79-87.
Anderson DM, Burkholder JM, Cochlan WP, Glibert PM, Gobler CJ, Heil CA, Kudela RM,
Parsons ML, Rensel J, Townsend DW, Trainer VL, Vargo GA 2008. Harmful algal
blooms and eutrophication: Examining linkages from selected coastal regions of the
United States. Harmful Algae 8: 39-53.
Anderson DM, Glibert PM, Burkholder JM 2002. Harmful algal blooms and eutrophication:
nutrient sources, composition and consequences. Estuaries 25: 704-726.
Anderson TR, Pondaven P 2003. Non-Redfield carbon and nitrogen cycling in the Sargasso
Sea: pelagic imbalances and export flux. Deep-Sea Research I, 50: 573-591.
Anderson TR, Mitra A. Dysfunctionality in ecosystem models: An underrated pitfall? Progress
in Oceanography 84 (1-2): 66-68.
ANZECC 2000. Australian and New Zealand guidelines for fresh and marine water quality
2000 Volume 1. National Water Quality Management Strategy Paper No. 4. Australian
and New Zealand Environment and Conservation Council and Agriculture and
Resource Management Council of Australia and New Zealand, Canberra.
Baird ME, Suthers I 2007. A size-resolved pelagic ecosystem model. Ecological Modelling
203: 185-203.
Baird ME, Walker S, Wallace B, Webster I, Parslow J 2003. The use of mechanistic
descriptions of algal growth and zooplankton grazing in an estuarine eutrophication
model. Estuarine, Coastal and Shelf Science 56: 685-695.
Baptista AM, Zhang Y-L, Chawla A, Zulauf M, Seaton C, Myers EP, Kindle J, Wilkin M,
Burla M, Turner PJ 2005. A cross-scale model for 3D baroclinic circulation in estuaryplume-shelf systems: II. Application to the Columbia River. Continental Shelf
Research, 25:935-972
Barter P, Forrest BM 2002. Monitoring receiving environment effects. In: Ray DE (ed) New
Zealand Municipal Wastewater Monitoring Guidelines, Chapter 11. New Zealand
Water Environment Research Federation, Wellington.
Bacher C, Duarte P, Ferreira J, Heral M, Raillard O 1998. Assessment and comparison of the
Marennes-Oleron Bay (France) and Carlingford Lough (Ireland) carrying capacity with
ecosystem models. Aquatic Ecology, 31:379-394.
Bradford JM, Chang FH, Baldwin R, Chapman B, Downes M, Woods P 1987. Hydrology,
plankton, and nutrients in Pelorus Sound, New Zealand, July 1981 and May 1982. New
Zealand Journal of Marine and Freshwater Research 21 (2): 223-233.
Buschmann AH, Riquelme VA, Hernandez-Gonzalez MC, Varela D, Jimenez JE, Henriquez
LA, Vergara PA, Guinez R, Filun L 2006. A review of the impacts of salmonid
farming on marine coastal ecosystems in the southeast Pacific. ICES Journal of Marine
Science 63 (7): 1338-1345
Buschmann AH, Cabello F, Young K, Carvajal J, Varela DA, Henríquez L 2009. Salmon
aquaculture and coastal ecosystem health in Chile: Analysis of regulations,
environmental impacts and bioremediation systems. Ocean & Coastal Management 52
(5): 243-249.
64
Report No. 1985
August 2011
Carter CM 2004. Spatial and temporal dynamics of phytoplankton communities in a coastal
ecosystem. A thesis in partial fulfilment of the requirements for the degree of Doctor of
Philosophy in Zoology, University of Canterbury, Christchurch, New Zealand. 177 p.
Carter CM, Ross AH, Schiel DR, Howard-Williams C, Hayden B 2005. In situ microcosm
experiments on the influence of nitrate and light on phytoplankton community
composition. Journal of experimental Marine Biology and Ecology 326: 1-13.
Carver CEA, Mallet AL 1990. Estimated carrying capacity of a coastal inlet for mussel culture.
Aquaculture 88: 39-53.
Christensen PB, Glud RN, Dalsgaard T, Gillespie P 2003. Impacts of longline mussel farming
on oxygen and nitrogen dynamics and biological communities of coastal sediments.
Aquaculture 218 (1-4): 567-588
Cloern JE 2001. Our evolving conceptual model of the coastal eutrophication problem. Marine
Ecology Progress Series 210: 223-253.
Crawford C 2003. Environmental management of marine aquaculture in Tasmania, Australia.
Aquaculture 226: 129-138.
Carver CEA, Mallet AL 1990. Estimating carrying capacity of a coastal inlet for mussel
culture. Aquaculture 88: 39-53.
Degobbis D 1989. Increased eutrophication of the northern Adriatic Sea: second act. Marine
Pollution Bulletin 20: 452–457.
Duarte CM, Agusti S, Agawin NSR 2000. Response of a Mediterranean phytoplankton
community to increased nutrient inputs: a mesocosm experiment. Marine Ecology
Progress Series 195: 61-70.
Dupra V 2000. Pelorus Sound New Zealand N and P budgets. LOICZ Biogeochemical
Modelling Node, http://nest.su.se/mnode/New_Zealand/PelorusSound/Pelorusbud.htm.
Elwany MHS, O'Reilly WC, Guza RT, Flick RE 1995. Effects of Southern California kelp
beds on waves. Journal of waterway, port, coastal and ocean engineering 121 (2): 143150.
Emeis KC, Struck U, Leipe T, Pollehne F, Kunzendorf H, Christiansen C 2000. Changes in the
C, N, P burial rates in some Baltic Sea sediments over the last 150 years--relevance to
P regeneration rates and the phosphorus cycle. Marine Geology 167 (1-2): 43-59.
Eppley RW, Rogers JN, McCarthy JJ 1969. Half-saturation constants for uptake of nitrate and
ammonium by marine phytoplankton. Limnology and Oceanography 14: 912-920.
Eppley RW 1972. Temperature and phytoplankton growth in the sea. Fish. Bull 70 (4): 10631085.
Eppley RW, Harrison WG, Chisholm SW, Stewart E 1977. Particulate organic matter in
surface waters of southern California and its relationship to phytoplankton. Journal of
Marine Research 25: 671-696.
Ervik A, Hansen PK, Aure J, Stigebrandt A, Johannessen P, Jahnsen T 1997. Regulating the
local environmental impact of intensive marine fish farming I. The concept of the
MOM system (Modelling-Ongrowing fish farms-Monitoring). Aquaculture 158 (1-2):
85-94.
Forrest B, Keeley N, Gillespie P, Hopkins G, Knight B, Govier D 2007. Review of the
ecological effects of marine finfish aquaculture: final report. Prepared for Ministry of
Fisheries. Cawthron Report No. 1285. 71 p.
Report No. 1985
August 2011
65
Frid CLJ, Mercer TS 1989. Environmental monitoring of caged fish farming in macrotidal
environments. Marine Pollution Bulletin 20: 379-383.
Gibbs MT 2007. Sustainability performance indicators for suspended bivalve aquaculture
activities. Ecological indicators 7: 94-107.
Gibbs MM, James MR, Pickmere SE, Woods PH. 1991. Hydrodynamic and water column
properties at six stations associated with mussel farming in Pelorus Sound, 1984-85.
New Zealand Journal of Marine and Freshwater Research 25: 239-254.
Gibbs MM, Pickmere SE, Woods PH, Payne GW, James MR, Hickman RW, Illingworth J
1992. Nutrient and chlorophyll a variability at six stations associated with mussel
farming in Pelorus Sound, 1984–85. New Zealand Journal of Marine and Freshwater
Research 26: 197-211.
Gibbs MM. 1993. Morphometrically induced estuarine phytoplankton patchiness in Pelorus
Sound, New Zealand. New Zealand Journal of Marine and Freshwater Research 27:
191-199.
Gibbs MM, Vant WN 1997. Seasonal changes in factors controlling phytoplankton growth in
Beatrix bay, New Zealand. New Zealand Journal of Marine and Freshwater Research
31: 237-248.
Gibbs M, Ross A, Downes M 2002. Nutrient cycling and fluxes in Beatrix Bay, Pelorus Sound,
New Zealand. New Zealand Journal of Marine and Freshwater Research 36: 675-697.
Gillespie P, Asher R, Doyle M 2001. Impact of Nelson (Bell Island) regional sewerage
discharge on Waimea Inlet – Part II. Nutrient enrichment potential of receiving waters,
Cawthron Report No. 680, 27 p. plus appendices.
Gillespie P, Forrest R, Knight B, Cornelisen C, Young R 2011. Variation in Nutrient Loading
from the Motueka River into Tasman Bay, 2008: Implications for the river plume
ecosystem. New Zealand Journal of Marine and Freshwater Research 45.
Gillibrand PA, Turrell WR 1997. The use of simple models in the regulation of the impact of
fish farms on water quality in Scottish Sea Lochs. Aquaculture 159: 33-46.
Giovanardi F, Vollenweider RA 2004. Trophic conditions of marine coastal waters: experience
in applying the Trophic Index TRIX to two areas of the Adriatic and Tyrrhenian seas.
Journal of Limnology 63 (2): 199-218.
Gowen RJ, Bradbury NB 1987. The ecological impact of salmonid farming in coastal waters: a
review. Oceanography and Marine Biology Annual Review 25: 563-575.
Grant J, Bacher C 2001. A numerical model of flow modification induced by suspended
aquaculture in a Chinese bay. Canadian Journal of Fisheries and Aquatic Sciences 58
(5): 1003-1011.
Gray JS, Wu RS, Or YY 2002. Effects of hypoxia and organic enrichment on the coastal
marine environment. Marine Ecology Progress Series 238: 249-279.
Hall POJ, Holby O, Kollberg S, Samuelsson M 1992. Chemical fluxes and mass balances in a
marine fish cage farm IV, nitrogen. Marine Ecology Progress Series 89: 81-91.
Hakanson L 1994. A review of effect-dose-sensitivity models for aquatic ecosystems.
Internationale Revue der Gesamten Hydro-biologie 79, 621-667.
Hansen PK, Ervik A, Schaanning M, Johannessen P, Aure J, Jahnsen T, Stigebrandt A 2001.
Regulating the local environmental impact of intensive, marine fish farming:: II. The
monitoring programme of the MOM system (Modelling-Ongrowing fish farmsMonitoring). Aquaculture 194 (1-2): 75-92.
66
Report No. 1985
August 2011
Hawkins AJS, James MR, Hickman RW, Hatton S, Weatherhead M 1999. Modelling of
suspension-feeding and growth in the green-lipped mussel Perna canaliculus exposed
to natural and experimental variations in seston availability in the Marlborough
Sounds, New Zealand. Mar. Ecol. Prog. Ser. 191, 217-232.
Heath RA 1976. Broad classification of New Zealand inlets with emphasis on residence times.
New Zealand Journal of Marine and Freshwater Research 10 (3): 429–444.
Heisler J, Glibert PM, Burkholder JM, Anderson DM, Cochlan W, Dennison WC, Dortch Q,
Gobler CJ, Heil CA, Humphries,E . Lewitus A, Magnien R, Marshall HG, Sellner K,
Stockwell DA, Stoecker DK Suddleson M. 2008. Eutrophication and harmful algal
blooms: A scientific consensus. Harmful Algae 8: 3-13.
Hevrøy EM, Sandnes K, Hemre GI 2004. Growth, feed utilisation, appetite and health in
Atlantic salmon (Salmo salar L.) fed a new type of high lipid fish meal, Sea Grain®,
processed from various pelagic marine fish species. Aquaculture, 235(1-4). Pp. 371392.
Hood RR, Kohler K, McCreary J 2003. A four dimensional validation of a coupled physicalbiological model of the Arabian Sea. Deep-Sea Research II 50: 2917-2945.
Hopkins GA, Forrest BM 2002. Environmental impacts of the Ruakaka Bay salmon farm.
Cawthron Report No. 763. 34 p. plus appendices.
Hopkins GA 2004. Seabed impacts of Marlborough Sounds salmon farms: Te Pangu Bay
monitoring 2003. Cawthron Report No. 847b. 25 p. plus appendices.
Hopkins GA, Forrest BM, Clarke M 2004a. Environmental impacts of the Otanerau Bay
salmon farm, Marlborough Sounds. Cawthron Report No. 824. 57 p. plus appendices.
Howarth RW, Marino R 2006. Nitrogen as the limiting nutrient for eutrophication in coastal
marine ecosystems: Evolving views over three decades. Limnology and Oceanography
51 (1): 364-376.
Inglis GJ, Hayden BJ, Ross AH 2000. An overview of factors affecting the carrying capacity
of coastal embayments for mussel culture. Report for Ministry for the Environment No.
MFE00505.
Jackson GA, Winant CD 1983. Effect of a kelp forest on coastal currents. Continental Shelf
Research 2 (1): 75-80.
Jackson GA 1997. Currents in the high drag environment of a coastal kelp stand off California.
Continental Shelf Research 17 (15): 1913-1928.
Jiang WM, Gibbs MT 2005. Predicting the carrying capacity of bivalve shellfish culture using
a steady, linear food web model. Aquaculture 244: 171–185.
Kaspar HF, Gillespie PA, Boyer IC, MacKenzie AL 1985. Effects of mussel aquaculture on
the nitrogen cycle and benthic communities in Kenepuru Sound, Marlborough Sounds,
New Zealand. Marine Biology 85 (2): 127-136.
Kaspar HF, Hall GH, Holland AJ 1988. Effects of sea cage salmon farming on sediment
nitrification and dissimilatory nitrate reductions. Aquaculture 70 (4): 333-344.
Keeley N, Hatton S, Heasman K, Divett T, Gibbs M 2005. Open Ocean Aquaculture: Annual
report. Cawthron Report No. 1069.
Report No. 1985
August 2011
67
Keeley N, Forrest B, Hopkins G, Gillespie P, Clement D, Webb S, Knight B, Gardner J 2009.
Review of the Ecological Effects of Farming Shellfish and Other Non-finfish Species
in New Zealand. Prepared for the Ministry of Fisheries. Cawthron Report No. 1476.
150 p. plus appendices.
Keeley N, Taylor D 2011. The New Zealand King Salmon Company Limited: Assessment of
Environmental Effects - Benthic. Prepared for The New Zealand King Salmon
Company Ltd. Cawthron Report No. 1983.
Knight B, Goodwin E, Jiang W, Carbines G 2010. Development of settlement model for
Marlborough Sounds blue cod (Parapercis colias). Prepared for Ministry of Fisheries.
Cawthron Report No. 1707. 34 p.
Knight B, Beamsley B 2011 in prep. Calibration and methodology report for Marlborough
Sounds.
La Rosa T, Mirto S, Favaloro E, Savona B, Sarą G, Danovaro R, Mazzola A 2002. Impact on
the water column biogeochemistry of a Mediterranean mussel and fish farm. Water
Research 36: 713-721.
Lee JHW, Choi K, Arega F 2003. Environmental Management of marine fish culture in Hong
Kong. Marine Pollution Bulletin 47: 202-210.
MacKenzie L 1991. Toxic and noxious phytoplankton in Big Glory Bay, Stewart Island, New
Zealand. Journal of Applied Phycology 3: 19-34.
MacKenzie L 1998. Blowing the budget? Nutrient resources and the Marlborough mussel crop.
Seafood New Zealand March 1998: 41-44.
MacKenzie L 2004. River inputs, re-mineralisation and the spatial and temporal distribution of
inorganic nutrients in Tasman Bay, New Zealand. New Zealand Journal of Marine and
Freshwater Research 38: 681-704.
MacKenzie L 2002. An evaluation of the risk to consumers of Pectenotoxin 2 seco acid
(PTX2-SA) contamination of GreenshellTM mussels. A report for the Marlborough
Shellfish Quality Programme (MSQP). Cawthron Report No. 750.
MacKenzie AL, Gillespie PA 1986. Plankton ecology and productivity, nutrient chemistry and
hydrography of Tasman Bay, New Zealand, 1982-1984. New Zealand Journal of
Marine and Freshwater Research 20: 365-395.
MacKenzie AL, Kaspar HF, Gillespie PA 1986. Some observations on phytoplankton species
composition, biomass and productivity in Kenepuru Sound, New Zealand, 1982-1983.
New Zealand Journal of Marine and Freshwater Research 20: 397-405.
MacKenzie L, Truman P, Satake M, Yasumoto T, Adamson J, Mountfort D, White D 1998.
Dinoflagellate blooms and associated DSP-toxicity in shellfish in New Zealand. In
Reguera B. Blanco J, Fernandezand ML, Wyatt T (Eds), Harmful Algae. Xunta de
Galicia and Intergovernmental Oceanographic Commission of UNESCO. Pp. 74-77.
MacKenzie L, Adamson J 2004. Water column stratification and the spatial and temporal
distribution of phytoplankton biomass in Tasman Bay, New Zealand. New Zealand
Journal of Marine and Freshwater Research 38: 705-728.
MacKenzie L, Beuzenberg V. Holland P, McNabb, P, Selwood A 2004. Solid phase adsorption
toxin tracking (SPATT): A new monitoring tool that simulates the biotoxin
contamination of filter feeding bivalves. Toxicon 44: 901-918.
MacKenzie AL, Smith KF, Rhodes LL, Brown A, Viliami Langi V, Edgar M, Lovell G,
Preece, M 2011a. Mortalities of sea-cage salmon (Oncorhynchus tshawytscha) due to a
68
Report No. 1985
August 2011
bloom of Pseudochattonella verruculosa (Dictyochophyceae) in Queen Charlotte
Sound, New Zealand. Harmful Algae (in press).
MacKenzie AL, Harwood T, McNabb P, Boundy M 2011b. Paralytic shellfish poisoning event,
Marlborough Sounds, 2011. A report for the New Zealand Food Safety Authority, June
2011. Cawthron report No. 1945.
Myers EP 2007. Evaluation of the SELFE/ELCIRC Models in the Delaware Bay Model
Evaluation Environment. ASCE Conference Proceedings 324. Newport, Rhode Island,
USA. Pp. 42-42.
Navarro N, Leakey RJG, Black KD 2008. Effect of salmon cage aquaculture on the pelagic
environment of temperate coastal waters: seasonal changes in nutrients and microbial
community. Marine Ecology Progress Series 361: 47-58.
Ogilvie SC, Ross AH, James MR, Schiel DR 2003. In situ enclosure experiments on the
influence of cultured mussels (Perna canaliculus) on phytoplankton at times of high
and low ambient nitrogen. Journal of Experimental Marine Biology and Ecology 295
(1): 23-39.
Olsen Y, Agustí S, Andersen T, Duarte CM, Gasol JM, Gismervik I, Heiskanen AS, Hoell E,
Kuuppo P, Lignell R 2006. A comparative study of responses in planktonic food web
structure and function in contrasting European coastal waters exposed to experimental
nutrient addition. Limnology and Oceanography 51 (1): 488-503.
Olsen LM, Holmer M, Olsen Y 2008. Perspectives of nutrient emission from fish aquaculture
in coastal waters: Literature review with evaluated state of knowledge. Final report for
The Fishery and Aquaculture Industry Research Fund. 87 p.
Olsen Y, Andersen T, Gismervik I, Vadstein O 2007. Protozoan and metazoan zooplanktonmediated carbon flows in nutrient-enriched coastal planktonic communities. Marine
Ecology Progress Series 331: 67.
Olsen Y, Olsen LM 2008. Environmental impact of aquaculture on coastal planktonic
ecosystems. In: Tsukamoto K, Kawamura T, Takeuchi T, Beard TD, Kaiser MJ ed.
Fisheries for Global Welfare and Environment. TERRAPUB. Pp. 181-196.
Papatryphon E, Petit J, Van Der Werf H, Sadasivam K, Claver K 2005. Nutrient-balance
modelling as a tool for environmental management in aquaculture: the case of trout
farming in France. Environmental Management 35: 161-174.
Piña-Ochoa E, Álvarez-Cobelas M 2006. Denitrification in Aquatic Environments: A Crosssystem Analysis. Biogeochemistry 81 (1): 111-130.
Plew DR, Stevens CL, Spigel RH, Hartstein ND 2005. Hydrodynamic implications of large
offshore mussel farms. Oceanic Engineering, IEEE Journal of 30 (1): 95-108.
Plew DR 2009. Changes in currents caused by ribbon marine farms in an embayment. In
Australasian Coasts and Ports Conference 2009. New Zealand Coastal Society,
Wellington. Pp 6.
Read P, Fernandes T 2003. Management of environmental impacts of marine aquaculture in
Europe. Aquaculture 226: 139-163.
Redfield AC 1934. On the proportions of organic derivations in sea water and their relation to
the composition of plankton. In University Press of Liverpool. James Johnstone
Memorial Volume. (ed. R.J. Daniel): 177-192.
Ren JS, Ross AH, Hadfield MG, Hayden BJ 2010. An ecosystem model for estimating
potential shellfish culture production in sheltered coastal waters. Ecological Modelling
221 (3): 527-539
Report No. 1985
August 2011
69
Rodrigues M, Oliveira A, Costa M, Fortunato AB, Zhang Y. 2009a Sensitivity Analysis of an
Ecological Model applied to the Ria de Aveiro, Journal of Coastal Research, 56:448452.
Rodrigues M, Oliveira A, Queiroga H, Fortunato AB, Zhang YJ 2009b. Three-dimensional
modeling of the lower trophic levels in the Ria de Aveiro (Portugal). Ecological
Modelling, 220(9-10):1274-1290.
Roper DS, Rutherford JC, Pridmore RD 1988. Estimation of sustainable salmon production in
Big Glory Bay, Stewart Island. Consultancy report T7074/1 July 1988. Water Quality
Centre, DSIR. Hamilton, New Zealand.
Rosenzweig M 1971. Paradox of enrichment: destabilization of exploitation ecosystems in
ecological time. Science 171: 385-387.
Sarą G, Scilipoti D, Mazzola A, Modica A 2004. Effects of fish farming waste to sedimentary
and particulate organic matter in a southern Mediterranean area (Gulf of
Castellammare, Sicily): a multiple stable isotope study (δ13C and δ15N). Aquaculture,
234(1): 199-213.
Schartau M, Oschlies A 2003. Simultaneous data-based optimization of a 1D-ecosystem model
at three locations in the North Atlantic, Part II – standing stocks and nitrogen fluxes.
Journal of Marine Research 61: 795-821.
SEPA 2000. Policy on regulation and expansion of caged fish farming of salmon in Scotland.
Policy No 40, Scottish Environmental Protection Agency.
Smith V, Tilman G, Nekola J 1999. Eutrophication: impacts of excess nutrient inputs on
freshwater, marine, and terrestrial ecosystems. Environmental pollution 100 (1-3): 179196.
Soto D, Norambuena F 2004. Evaluation of salmon farming effects on marine systems in the
inner seas of southern Chile: a large-scale mensurative experiment. J. Appl. Ichthyol.
20, 493-501.
Sutton PJH, Hadfield MG 1997. Aspects of the hydrodynamics of Beatrix bay and Pelorus
Sound, New Zealand. New Zealand Journal of Marine and Freshwater Research 31:
271-279.
Taylor A, Geider RJ, Gilbert F 1997. Seasonal and latitudinal dependencies of phytoplankton
carbon-to-chlorophyll a ratios: results of a modelling study. Marine Ecology Progress
Series. 152: 51-66.
Tett P, Edwards V 2002. Review of harmful algal blooms in Scottish coastal waters. School of
Life Sciences, Napier University, Edinburgh. 120 p.
USEPA (United States Environmental Protection Agency) 1989. Ambient water quality criteria
for ammonia (saltwater). Misc Rep Ser, USEPA, Washington, DC.
Vincent WF, Howard-Williams H, Downes M, Dryden SJ 1989. Underwater light and
photosynthesis at three sites in Pelorus Sound, New Zealand. New Zealand Journal of
Marine and Freshwater Research 23: 79-91.
Wild-Allen K, Herzfeld M, Thompson PA, Rosebrock U, Parslow J, Volkman JK 2009.
Applied coastal biogeochemical modelling to quantify the environmental impact of fish
farm nutrients and inform managers. Journal of Marine Systems 81 (1-2): 134-147.
WRENZ 2010. NIWA Water Resource Explorer New Zealand (WRENZ), web-based tool:
http://wrenz.niwa.co.nz/webmodel/
70
Report No. 1985
August 2011
Wu RSS, Lam KS, MacKay DW, Lau TC, Yam V 1994. Impact of marine fish farming on
water quality and bottom sediment: a case study in the sub-tropical environment.
Marine Environmental Research 38: 115-145.
Wu RSS, Shin PKS, MacKay DW, Mollowney M, Johnson D 1999. Management of marine
fish farming in the sub-tropical environment: a modelling approach. Aquaculture 174:
279-298.
WWF 2011. Salmon Aquaculture Dialogue: Second draft standards for responsible salmon
aquaculture. WWF Draft Report, 88p. Downloaded 2011 from:
http://www.worldwildlife.org/what/globalmarkets/aquaculture/WWFBinaryitem21275.
pdf
Yap LG, Azanza RV, Talaue-McManus L 2004. The community composition and production
of phytoplankton in fish pens of Cape Bolinao, Pangasinan: a field study. Marine
Pollution Bulletin 49: 819-832.
Yokoyama H, Inoue M, Abo K 2004. Estimation of the assimilative capacity of fish-farm
environments based on the current velocity measured by plaster balls. Aquaculture 240
(1-4): 233-247.
Yokoyama H, Inoue M, Abo K 2007. Macrobenthos, current velocity and topographic factors
as indicators to assess the assimilative capacity of fish farms: Proposal of two indices.
Bulletin of Fisheries Research Agency (Japan).
Zeldis J 2008 (a). Exploring the carrying capacity of the Firth of Thames for finfish farming: a
nitrogen mass-balance approach. NIWA Client Report: CHC2008-02. 28 p.
Zeldis J 2008 (b). Origin and processing of nutrients in Golden and Tasman Bays. Tasman
District Council Envirolink Advice Grant and Client Report May 2008 CHC 2008 052
(Client Tasman District Council). http://www.tasman.govt.nz/pdfs/chc2008_052.pdf
Zeldis JR, Howard-Williams C, Carter CM, Schiel DR 2008. ENSO and riverine control of
nutrient loading, phytoplankton biomass and mussel aquaculture yield in Pelorus
Sound, New Zealand. Marine Ecology Progress Series 371: 131-142.
Zeldis J, Broekhuizen N, Forsyth A, Morrisey D, Stenten-Dozey J 2010. Waikato marine
finfish farming; production and ecological guidance. NIWA Client Report CHC2010147. Prepared for Ministry of Fisheries Aquaculture Unit. 113 p.
Zeldis JR, Hadfield M, Morrisey D, Broekhuizen, Stenton-Dozey J 2011. Tasman aquaculture:
guidance on farming additive species – Stage 2. NIWA Client Report CHC2011-029
prepared for Ministry of Fisheries Aquaculture Unit. 71 p.
Zhang Y-L, Baptista AM, Myers EP 2004. A cross-scale model for 3D baroclinic circulation in
estuary-plume-shelf systems: I. Formulation and skill assessment. Continental Shelf
Research, 24: 2187-2214
Zhang Y-L, Baptista AM 2008. SELFE: A semi-implicit Eulerian-Lagrangian finite-element
model for cross-scale ocean circulation. Ocean Modelling 21 (3-4): 71-96.
Report No. 1985
August 2011
71
9.
APPENDICES
Appendix 1. Background information on nitrogen mass balance calculations in
Pelorus and Queen Charlotte Sounds.
Salmon farm nitrogen sources
Existing finfish inputs were assessed based on current operational feed rates, which may be
lower than the consented maximum feed rate (e.g. 5000 tonnes feed/yr versus a consented limit
of 6000 at Te Pangu Bay). These operational feed rates represent derived environmental limits
based on years of operational experience of existing farms rather than the legal limits imposed
by consent conditions.
The nutrient waste analysis assumes an economic food conversion ratio (EFCR, produced live
weight fish to dry weight feed ratio from operational farms) of 1:1.7, which is in the range of
EFCRs for Marlborough Sound salmon farms (1.67 for high flow sites and 1.83 for low-flow
sites; NZ King Salmon, unpublished data). The DIN contribution to the environment per tonne
of fish produced each year is estimated to be 77.5 kg, and TN is discharged at approximately
95.2 kg based on recalculation from Gowen & Bradbury 1987. The total nitrogen load (i.e.
inorganic and organic nitrogen) will be available for biological assimilation; however it is
likely that in the real system a proportion of the solid waste will be buried in sediments.
Riverine and oceanic nitrogen sources
Gibbs et al. (1992) estimated the oceanic inputs to be about 12,000 tonnes DIN per year for the
whole Sound assuming complete tidal exchange of Cook Strait water (Gibbs pers. comm.8).
Revisiting the estimate of Gibbs et al.(1992) using new unpublished weekly data provided by
NIWA (Figure 1.1) show high week to week variation in natural inputs from Cook Strait to the
region. DIN concentrations are higher in Pelorus Sound than Cook Strait in approximately
25% of the samples9 over the period February 2007 to July 2010 (Figure 1.1). During these
periods, Cook Strait may be a sink for DIN.
Analysis of new upublished NIWA data suggests that, on average, Pelorus Sound imports DIN
from Cook Strait, with a mean difference between the Strait and inner Pelorus Sound
concentrations of +11.15 mg DIN/m3 (standard error ±1.70 mg DIN/m3). This suggests the
natural net DIN supply from Cook Strait may be as high as 4200 ±640 tonnes DIN per year
based on the assumption that tidal water is fully exchanged in the Sound.
8
Gibbs et al. (1992) assumed complete tidal exchange of oceanic water using the mean of spring and neap tidal volume
estimates (535 x 106 m3 - Heath 1976) (M. Gibbs pers. comm.). This approach ignores estuarine circulation during Pelorus
River flood events, but represents the majority of the year. An estimated mean DIN concentration of 30 mg DIN/m3 for Cook
Strait water yields an average mass load into the sound of 11,724 tonnes of DIN per year (M. Gibbs, pers. comm.).
9
Cook Strait water was assumed to be 40 metres deep in the “Outer Pelorus Sound” site. Samples that were not made on the
same day were interpolated linearly between weekly measurements to match inner Sound samples. Inner Sound water was
assumed to be the Schnapper Point sampling location, located at the entrance of Kenepuru Sound.
72
Report No. 1985
August 2011
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
-80
-60
-40
-20
0
20
40
60
80
3
Concentration Difference (Outer - Inner, mgDIN/m )
Figure 1.1.
Distribution of weekly DIN concentration differences between Cook Strait (Outer) and inner
Pelorus Sound2 sorted by month for the period February 2007 to July 2010 (data provided by M.
Gibbs, NIWA; n = 146). Positive concentrations indicate Cook Strait is generally importing DIN
into the Sound, but during winter (May to August) it appears DIN is sometimes exported to the
Strait. Blue boxes shown in this figure mark the interquartile range, with the red vertical line
representing the median of the data, blue lines extend out to mark the shorter of 1.5 times the
interquartile range or minima/maxima. Red dots are ‘outliers’ – points that lie outside of 1.5 times
the interquartile range (blue lines).
Riverine inputs of N to the inner Pelorus Sound were estimated as ~300 tonnes per year by
Dupra (2000) (note however, a discrepancy with more recent estimates made using WRENZ:
Table 2). Recent analysis of the Motueka River (Gillespie et al., 2011) suggests differing river
flows can deliver varying amounts on nutrients, so a single estimate should only be used as a
guide for average inputs to the region. This is consistent with the findings of Zeldis et al.
(2008) who noted that although riverine and ocean nitrogen supplies sustain year-round mussel
production, there appears to be considerable inter-annual variation associated with El Nino/La
Nina cycles affecting riverine and oceanic nutrient inputs. Re-analysis of new data confirms
that there can be a high degree of variability in oceanic DIN inputs (Figure 1.1).
In the case of Queen Charlotte Sound, only a small riverine (mean river flow of about
7 cumecs, WRENZ 2010), although Heath (1976) reports that fresh water inputs are ~20% of
Pelorus Sound; a wastewater input at Picton also exists.
Natural and aquaculture nitrogen sinks
Benthic denitrification represented the largest quantified net N sink in both Sounds. We
estimate this at 465 tonnes N/yr denitrified from the Pelorus region and 367 tonnes N/yr from
the Queen Charlotte region, assuming denitrification rates measured in Pelorus Sound (Kaspar
et al. 1985; Christensen et al. 2003) are similar to Queen Charlotte Sound. We note that the
values recorded in Pelorus are low compared to a global review of rates (Piña-Ochoa &
Álvarez-Cobelas 2006) and those measured in Tasman Bay (Christensen et al. 2003). The
Report No. 1985
August 2011
73
reasons for the relatively low denitrification measurements in the Marlborough region are
currently unknown.
The next most important sink of nitrogen in the Sounds was estimated to be the removal of
mussel protein through shellfish harvests (Mackenzie 1998; Figure 1.2). At a Sound-wide
scale, the application of additional nitrogen to the ecosystem (such as may occur through feedadded fish farming) may be partially offset by nitrogen removed yearly through mussel
harvests. MacKenzie (1998) noted in his “back of the envelope” calculations that at the time
of the study approximately 600 tonne TN/yr was removed by mussel harvesting in the region.
Updating the calculations of MacKenzie (1998) using a more conservative value for the
nitrogen removal rate10, results in an estimate of 265 tonnes of N removed per year for Pelorus
Sound and 11.8 tonnes per year for Queen Charlotte Sound.
Figure 1.2.
Mussel farms in Waihinau Bay can be seen as straight white lines in the image. Mussel farms are
present throughout the Marlborough Sounds and are one source of nitrogen removal in the region.
(Image Source: Google Earth 2010).
It is also likely that a proportion of the nutrients entering the region will be buried in the
sediments. The small difference between measured denitrification rates (Kaspar et al. 1985;
Christensen et al. 2003) and the N loss estimate of Dupra (2000) provide some evidence that a
small amount of N burial may occur in the region. Although N burial has not been measured
directly in the region we note that globally burial rates have been measured at rates similar to
denitrification rates (e.g. ~1 to 5 g N/m2/yr in the Baltic Sea, Emeis et al. 2000). No allowance
has been made for burial in the calculations due to a lack of data for the Marlborough Sounds,
but it is recognised that this may represent an additional sink of nitrogen in the region.
10
5.9 kg N per GWT of mussels harvested (Zeldis 2008a) rather than the 14 kg N per GWT value used by MacKenzie (1998).
74
Report No. 1985
August 2011
Appendix 2. Simple ‘open box’ modelling methodology
The tidal flushing time information can be useful for estimating the degree to which nutrients
are retained within the Sounds. A simple approach to account for the effect of tidal flushing on
N concentrations in the Sounds is to estimate long-term steady state concentration changes
above ambient concentrations assuming complete mixing and exchange, as defined by Roper et
al. (1988):
ΔC = I
Q
(1)
Where, ΔC is the change in nutrient concentration relative to an ambient (oceanic)
concentration, I is the nutrient load per tide and Q is the net exchange volume between a Sound
and Cook Strait (i.e. mean spring and neap tidal exchange).
We use this approach to assess how water column nutrient changes may relate to changes in
phytoplankton biomass assuming that nitrogen is the only limitation on phytoplankton growth
(i.e. light, standing stock or grazing are not limiting). Using this assumptions they calculated
that the carbon fixed by phytoplankton was equal to the nutrient stoichiometry described by
Redfield (1934) where carbon (C) is fixed at a ratio of approximately 106 mol C to every
16 mol N. The molar mass of N and C is 14 g/mol and 12 g/mol respectively and an
approximate conversion to the commonly measured phytoplankton pigment chlorophyll a is
approximately 50 grams of C to every gram of Chlorophyll a (Chl a).
Report No. 1985
August 2011
75
Appendix 3. Site suitability for finfish farms in the Marlborough Sounds
As can be seen in the spatial model predictions for the Pelorus (e.g. Figure 7) and Queen
Charlotte Sounds (e.g. Figure 11), the physical characteristics of a site is not only important for
determining benthic effects, but also the degree of water column modification. It is
acknowledged that the benthic suitability of a site for finfish aquaculture will largely depend
on water depth, current speed and proximity to the entrance of the Sounds (see Forrest et al.
2007).
A relatively simple approach to assess the benthic suitability of a site has been developed and
tested by Yokoyama et al. (e.g. 2004, 2007) using two basic indices: embayment degree (ED)
and index of suitable location (ISL). It is recognised by Olsen et al. (2008) that this model
may also be useful for assessing water column suitability. Checking the performance of this
model to monitored benthic performance (Table 4.1) and application of this model to results
from our hydrodynamic model (Figure 4.1) clearly identifies the Sounds entrances and main
channels as the best regions for finfish farming. Hence the proposed sites identified (Figure 1)
were flagged in the planning stages as suitable locations within the Sounds and are less likely
to experience increased nutrient or phytoplankton bloom problems.
Table 3.1.
Table showing measured depths, current speeds, calculated index of suitable location (ISL),
present feed and estimated fish production levels for six sites in the Marlborough Sounds. A
subjective Cawthron classification is also given based on a qualitative knowledge of the long-term
historical benthic response to feed loadings of these sites, it may not reflect current benthic
performance under higher loads
Site
1
76
Clay Point
Te Pangu Bay
Waihinau Bay
Otanerau Bay
Ruakaka Bay
Forsyth Bay
Crail Bay
Crail Bay
Depthaveraged
currents
(m/s)
Depth
(m)
ISL
Present Feed
Levels
(tonnes N/yr)
Present Salmon
Production1
(tonnes fish/yr)
Cawthron
Classification
0.20
0.15
0.08
0.06
0.04
0.04
0.03
0.03
35
30
28
35
35
35
30
27
1.40
0.68
0.20
0.13
0.05
0.06
0.03
0.02
3,500
5,000
3,000
3,500
3,500
3,000
1,600
1,400
2,059
2,941
1,765
2,059
2,059
1765
941
824
Excellent
Excellent
Good
Good
Poor
Poor
Poor
Poor
fish production is estimated using an eFCR ratio of 1.7:1.
Report No. 1985
August 2011
Figure 3.2.
Index of suitable location (ISL) data for the outer and entire (inset) Pelorus Sound (top figure) and
Queen Charlotte Sound (bottom figure) regions based on modelled mean current speed and depth
for the region for a 1-month period from 27 September to 26 October 2004. Red regions represent
poor site characteristics and green indicate the best regions for finfish aquaculture based on
modelled current speeds and water depth. Distance from the Sound entrance will also be an
important variable to consider in designating areas suitable for finfish aquaculture.
Report No. 1985
August 2011
77
Appendix 4. Unpublished data from CTD surveys
20
Temperature (°C)
Schnapper Point
West Beatrix
Waitata
15
10
20
Port Gore
Temperature (°C)
Wedge Point
Tory Channel
East Bay
15
10
Jan
Feb
Apr
May
Jul
Sep
Oct
Dec
Month
Figure 4.1.
78
Mean monthly depth-averaged column temperatures at MSQP monitoring sites in Pelorus Sound
(upper), Port Gore and Queen Charlotte Sound (lower) for the period .
Report No. 1985
August 2011
Salinity (PSU)
35
33
Schnapper Point
West Beatrix
Waitata
31
Salinity (PSU)
35
34
Port Gore
Wedge Point
Tory Channel
East Bay
33
Jan
Feb
Apr
May
Jul
Sep
Oct
Dec
Month
Figure 4.2.
Depth-averaged mean monthly water column salinites at MSQP monitoring sites in Pelorus
(upper), Port Gore and Queen Charlotte (lower) Sound . PSU= practical salt units.
Report No. 1985
August 2011
79