Land links to water - based business
The Landcare Research-led Integrated Catchment Management Programme at Motueka is helping to create a better understanding of how activities in area affect one another, as this 2008 case study for the Crown Company Monitoring Advisory Unit (CCMAU) explains.
Wangapeka River
Aquaculture has been described by Minister Jim Anderton as having “almost limitless potential” (New Zealand Aquaculture Council 2006). New Zealand's aquaculture industry is fast growing and aiming for sales of $1 billion per year by 2025.
However, runoff from land - including sediments and nutrients - is recognised as “one of the greatest threats to near-shore fisheries” (Ministry of Fisheries 2006). Landcare Research's Integrated Catchment Management (ICM) research has identified land-based physical factors and human activities in the Motueka region that have potential impacts on Tasman Bay's coastal marine environment—and on its marine-based businesses.
Considerable expansion of aquaculture is planned in Tasman Bay, which currently supports over $20 million1 of annual earnings from New Zealand's greenshell mussel industries. Tasman District Council has designated approximately 4200 hectares (with potential returns of over $32m per year2) as aquaculture management areas (AMAs) for longline culture of greenshell mussels, and collection of both mussel and scallop spat. However, considerable uncertainty exists over the future of the Bay's scallop industry (Murdoch 2008, Reich 2008) and the productive potential of the AMAs (Gillespie & Rhodes 2006, Gillespie 2007a).
An, as yet unidentified, cause has resulted in a recent decline in scallop production, causing annual losses of up to $17 million3. Scallop harvesting in the Bay is now closed to commercial fishermen, whereas 7 years ago scallops provided up to 70% of the boats' income.
New management approaches
Landcare Research began ICM research in the Motueka River catchment in 2000 to identify management approaches that enable sustainable use of the region's land, rivers and the near-coastal marine environment, for multiple, interacting and potentially conflicting uses.
Riverine plume
Recent research has identified a riverine (freshwater) plume that results in a land-sourced ‘footprint' over approximately 70-90 km2 of seabed off the Motueka River mouth (Forrest et al 2007) in ‘normal' conditions. Floods can periodically expand the plume's area of impact to 300-400 km2.
Research on the river plume suggests that land-based activities pose a high risk to economic returns from the Bay's aquaculture industry. The plume either entirely encompasses or partially impinges on the designated AMAs in western Tasman Bay. Land-sourced influences in marine areas affected by the plume include suspended fine sediment, associated elevated nickel and chromium levels and, periodically enhanced plant nutrient (N, P and Si) concentrations (Gillespie 2007b).
The amount of sediment transported from the land into Tasman Bay has been estimated at 311,000 tonnes per year (Basher pers. comm.; Wild et al. 2006) using data from a monitoring station set up near the Motueka River mouth in 2001 to determine the magnitude and frequency of sediment yields to the Bay.
Sediment impact
While more data are needed to quantify the impact of sediment on scallop quality and yield, available data show that fine sediment discharged from the Motueka catchment into Tasman Bay may persist for months in the near-sea-floor feeding environment of scallops at concentrations sufficient to inhibit scallop feeding (and consequently reduce growth), and kill shellfish spat (Gillespie & Rhodes 2006).
Significant differences in scallop growth are observed between areas within and outside the boundaries of the plume. The Challenger Scallop Enhancement Company estimates that, in three years alone, it has lost over $16 million (wholesale value) from unsuccessful seeding of spat in soft sediments near the Motueka River mouth4.
In addition, sediment-borne contaminants have the potential to affect yields from longline culture of scallops and mussels. Research has identified elevated sediment-derived nickel and chromium levels, and fluctuating levels of contaminants such as bacteria, in the Bay. Accumulation of these in shellfish can reduce their quality and saleability.
However, there are also potential benefits from river plume, for example, increased (though not excessive) availability of nitrogen to support growth of phytoplankton—a food source for shellfish. Modeling tools are being developed by the Cawthron Institute to quantify the inter-relationships and impacts of these influences on the marine environment and its productivity.
Linking the information
Linking the Motueka catchment's land-based information to the marine characteristics in Tasman Bay will help marine businesses plan and manage for optimal returns. It may also help explain the currently unexplained production variability. For example, knowledge of sediment changes in the Bay (in space and over time) allows seeding of spat to be timed and positioned to minimise sediment effects, enables appropriate scallop rotation scheduling to be planned, and suggests that long-line or basket culture could reduce sediment impacts. Sources of fine sediment have been identified to enable the Tasman District Council to assess mitigation options for land-owners to use in their long-term development plans and sustainable co-existence of the region's sector-based industries.
Funding and technology transfer
Landcare Research's ICM programme has received funding from the Foundation for Research, Science and Technology of (on average) $1.9 million per year over the past 8 years. This funding supports five research themes focused on the catchment's land, freshwater, coastal and marine environments, human dimensions in resource management, and integration of biophysical, economic and social information and approaches to catchment management.
These are researched in a collaborative, participatory partnership which combines expertise in terrestrial, marine and freshwater science (Landcare Research, NIWA, the Cawthron Institute, Scion, GNS and University of Otago) with knowledge from industry and other stakeholders (such as the Tasman District Council, and Maori).
End-users are active programme participants in both setting goals for the research and in developing solutions. Additional annual support from stakeholders ($900,000 in 2007/08) is an indication of the value stakeholders place on the research.
Visualising the future
The ICM programme's IDEAS model can simulate how change in one enterprise affects others in the Motueka region. For example, intensification of land use (conversion of forestry to sheep/beef/dairy farming) is predicted to double sediment yields, and increase nitrogen (N) in rivers by over 500 tonnes per year—an annual loss of over $0.5 million at today's N fertiliser (urea) prices. For the marine-based industries, future ICM research will improve models that link interactions between natural physical processes and human behaviour in the region with “downstream” environmental effects. This will also allow improved quantification of potential economic impacts.
Ongoing collection of long-term in situ data on the characteristics of the Motueka river and its out-welling plume will enable better understanding of climatic events and land-use changes on coastal ecosystems, and the quantification of relationships between river flow, sediment and nutrient loads, coastal water quality and the sustainability of fish and shell fish resources. This will provide Tasman Bay's commercial fishing and aquaculture industries with indicators necessary to gauge risks and predict production (and economic) outcomes within the context of extreme variability that has, to date, been a major hindrance to long-term planning and economic forecasting.
References
Forrest BM, Gillespie PA, Cornelisen CD, Rogers KM. 2007. Multiple indicators reveal river plume influence on sediments and benthos in a New Zealand coastal embayment. New Zealand Journal of Marine and Freshwater Research, 2007, 41: 13—24.
Gillespie, P, Rhodes L. 2006. Cawthron Institute Report Number 1114. The quantity and quality of suspended particulate material of near-bottom waters in the Motueka River plume, Tasman Bay.
Gillespie, P 2007a. River Outwelling Plumes: good or bad places to farm mussels? Motueka Integrated Catchment Management (Motueka ICM) Programme Coastal Report Series.
Gillespie, P 2007b. Nutrient Loading from the Motueka River into Tasman Bay, 2007. Ibid.
MfE, 2007. Aquaculture Risk Management Options. Appendix 1: The New Zealand aquaculture industry. http://www.mfe.govt.nz/publications/oceans/aquaculture-risk-management/html/page9.html
Ministry of Fisheries, 2006. The State of our Fisheries.
Murdoch, H. Tasman Bay scallop-bed decimation a mystery. The Press. 12 August 2008.
Reich, J. What's killing Tasman Bay's scallops? Nelson Mail. 31 August 2008.
Statistics New Zealand 2007. Fish monetary stock account: 1996-2007.
http://www.stats.govt.nz/analytical-reports/fish-monetary-stock-account-1996-2007.htm
Wild M, Hicks M, Merrilees R 2006. Suspended sediment monitoring in the Motueka catchment: data report to 1 May 2006. NIWA Client Report CHC2006-087, National Institute of Water and Atmospheric Research, Christchurch.
Acknowledgements
Thanks to Mitch Campbell, Challenger Scallop Enhancement Company and Paul Gillespie, Cawthron Research Institute (ICM collaborator), for information and helpful comment.
Footnotes
1Tasman and Golden Bays together produce 20% of spat for the greenshell mussel industry. 2007 value >$200m - $175m export; $38m domestic, 75% production from Nelson/Marlborough (NZ Marine Farming Association); assuming 50/50 split.
2Figure based on greenshell mussels only: Annual return from greenshell mussel farming currently estimated at $43,000 per hectare http://www.mfe.govt.nz/publications/oceans/aquaculture-risk-management/html/page9.html
Of designated AMA area by Tasman District Council, areas authorised by MFish to date: 749ha for mussel farming and mussel spat catching; 2000 ha for scallop spat catching (but only 500 ha can be used at once); 269 ha for mussel spat catching (MFish - D Turnbull pers. comm.)
3 Tasman Bay normally produces a third of the upper South Island's scallop harvest. Annual values of between $0.5 and $17 million are a result of natural variability in yields.
4Based on seeding of 50 million spat per year, 40% survival, average weight of 13.5g per scallop, and wholesale price of $20 per kg (Mitch Campbell, pers. comm.)