Ross Sea ecosystem research
The Ross Sea lies 3500 km south of New Zealand next to Antarctica. It encompasses the main fishing grounds for Antarctic toothfish, a species NIWA scientists are studying so that it can be fished sustainably. In order to do this, we need a good understanding of the population dynamics of Antarctic toothfish and to learn more about the ecosystem of which the fish are a part.
Why choose to study this region? The Ross Sea interests scientists for a number of reasons:
1. It supports a diverse ecosystem
- as well as covering the main fishing grounds for Antarctic toothfish, the region sustains a variety of bird and sea-life, some in unusually high concentrations
- studying the interconnected food web that nourishes the local ecosystem will allow us to understand how to manage a more sustainable toothfish fishery.
2. It is ecologically significant
- the Ross Sea is home to the main nursery grounds for juvenile and sub-adult species of toothfish
- primary production (the conversion of solar energy into chemical compounds via photosynthesis) in the region has intense peaks, linked to changes in sea-ice (including Ross Sea polynya: openings in the ice)
- the Ross Sea ecosystem is one of the least human-impacted shelf sea ecosystem in the world
- it is similar to regions used in previous research, allowing us to draw on published information when other data is limited. McMurdo Sound, in the south-west of the Ross Sea, has been extensively studied, partly because it is home to the research stations of New Zealand (Scott Base) and the United States (McMurdo Station)
- it sits close to the Antarctic Slope Front, a bathymetric feature that forms a buffer between the Southern Ocean and the Ross Sea continental shelf.
We provide scientific advice to help manage Antarctic fisheries. This includes research on Antarctic toothfish to understand the potential effects of the fishery on other parts of the Ross Sea ecosystem. Research on Antarctic toothfish and bycatch species is funded by the Ministry for Primary Industries.
The Ross Sea trophic modelling project is supported by the Ministry of Business, Innovation, and Employment ‘Ross Sea Sustainability’ programme, and co-funded by Ministry for Primary Industries projects on the effects of fishing on the region's ecosystem.
Our research in the Ross Sea region is allowing us to identify possible effects of the longline Antarctic toothfish fishery on the toothfish population and on the local ecosystem, and in turn identify more efficient tools for monitoring it, and managing it sustainably, based on the following areas of study:
1. Antarctic toothfish stock modelling
The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) uses two criteria to set the annual catch limit:
- the spawning fish stock must not fall below 50% of its unfished level in the long term
- the risk of the spawning fish stock falling below 20% at any time in the next 35 years should be less than 10%.
The catch level is set according to these criteria, using a stock assessment model. This involves estimating the number of fish in the stock, and how the population will change under different levels of fishing. Research is aimed at improving the accuracy and reliability of this modelling.
We helped introduce a programme into CCAMLR that stipulates that a proportion of caught toothfish be tagged and released. The subsequent recapture rate of these tagged fish helps us estimate the size of the toothfish population in the Ross Sea region.
2. Biology and ecology of Antarctic toothfish
NIWA scientists have undertaken a considerable amount of research on the biology and ecology of Antarctic toothfish including distribution and abundance, age and growth, reproduction, and feeding and have developed a working model of its life history.
3. Assessing and reducing by-catch impact
A number of other demersal (bottom-dwelling) fish are caught as by-catch of the fishery. These include grenadiers, skates, blue antimora, moray cod, and icefish. We have carried out research on their basic biology but there is still some uncertainty about the size of these populations, and how they may be affected by the current level of by-catch.
CCAMLR 'move-on' rules are in place so that too much by-catch of any species means the fishing vessel must move to a different location.
Tag-release experiments for skate have been underway for a number of years. Results from this will help us estimate their numbers and determine whether by-catch is likely to adversely affect them.
4. Ecosystem effects of fishing toothfish in the Ross Sea
We are developing a food web model to consider how the fishery for Antarctic toothfish may affect other parts of the ecosystem. What we learn in this research is used to improve the management of the fishery, and this will help reduce the detrimental effects of the fishery on other organisms.
5. Managing risk: the unknown effects of fishing
NIWA developed a risk assessment of fishing for Antarctic toothfish in the Ross Sea and presented it at a CCAMLR meeting of the Working Group on Ecosystem Monitoring and Management. We identified the risks of ecosystem damage from fishing, considering the following categories:
- Target species harvest: Risks of depletion of Antarctic toothfish to below a level that ensures stable recruitment.
- By-catch species harvest: Risks of depletion of other harvested species to below a level that ensures stable recruitment.
- Ecosystem impacts: Risks of changes to the marine ecosystem relationships due to the removal of harvested and by-catch species.
- Exogenous effects: Risks of change in the marine ecosystem due to, or exacerbated by, exogenous effects (e.g. the introduction of alien species, effects of associated activities on the ecosystem, and effects of environmental change).
6. Effects of fishing on habitat
Vessels fishing for Antarctic toothfish are only allowed to use long-lines – sections of rope with hundreds of baited hooks attached lying over the sea bed. This method is less damaging to vulnerable sea bottom structures such as coral than the effect of bottom trawling, but will have some impact on sea bed organisms. CCAMLR, together with New Zealand scientists, have been evaluating the effects of this fishing method in the Ross Sea region.
7. Supporting spatial management of Ross Sea
The fishery is managed differently across the region. For example, the permitted catch rate is lower around the northern seamounts (undersea mountains) and the Ross Sea shelf than it is along the Ross Sea slope.
Bioregionalisation may help to design a spatial management framework for the Southern Ocean. NIWA and other New Zealand scientists are engaged in research to support bioregionalisation and in investigations on how to design spatial management of fisheries, both in the Ross Sea and across the whole Antarctic Ocean.