NIWA’s Research on the Toothfish Fishery
NIWA is actively engaged in providing scientific advice to help in managing Antarctic fisheries. This includes research on Antarctic toothfish itself, and working to develop an understanding of the potential effects of the fishery on other parts of the Ross Sea ecosystem.
The following work is ongoing at NIWA into assessing and managing the longline fishery for Antarctic toothfish in the Ross Sea sector:
- Antarctic toothfish stock modelling
- Plausible early life history of Antarctic toothfish
- Assessing and reducing bycatch impact
- Ecosystem effects of fishing toothfish in the Ross Sea
- Managing risk: the unknown effects of fishing
- Effects of fishing on habitat
- Supporting spatial management of Ross Sea
1. Antarctic toothfish stock modelling
The current CCAMLR management uses two criteria to set the annual catch limit:
(a) the spawning fish stock must not fall below 50% of its unfished level in the long term;
(b) 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. Ongoing research is aimed at improving the accuracy and reliability of this modelling.
NIWA scientists have helped introduce a programme into CCAMLR that stipulates that a proportion of caught toothfish should have a small tag attached and be released. The subsequent recapture rate of these tagged fish allows us to estimate the size of the toothfish population.
stock assessment model fsa-07_37.pdf
2. Plausible early life history of Antarctic toothfish
NIWA scientists have summarised what little is known about the early life stages of Antarctic toothfish, and produced a plausible biological-hydrodynamic model.
Hypothetical early life history of Antarctic toothfish. (2.7 Mb)
3. Assessing and reducing by-catch impact
A number of other demersal fish are caught as by-catch by the fishery for Antarctic toothfish in the Ross Sea sector. These include Whitson's grenadier, blue antimora, moray cod, icefish, and skate. We have poor knowledge of how big these populations are, 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 of these by-catch 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. Knowledge gained in this research is used to improve the management of the fishery and aims to reduce the chance of detrimental effects of the fishery on other organisms.
Preliminary trophic model of the Ross Sea shelf (290 kb)
5. Managing risk: the unknown effects of fishing
A risk assessment of fishing for Antarctic toothfish in the Ross Sea was developed at NIWA and presented in 2007 at the CCAMLR Christchurch meeting of WG-EMM (Working Group on Ecosystem Monitoring and Management). We identified risks of ecosystem damage due to fishing and then looked at ways to evaluate and address the risk. The categories we considered were:
- Target species harvest: Risks of depletion of Antarctic toothfish to below a level that ensures stable recruitment.
- Bycatch 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 bycatch 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).
Ecological risk management and the fishery for Antarctic toothfish in the Ross Sea (180 kb)
6. Effects of fishing on habitat
The fishery for Antarctic toothfish only uses long-lines – sections of rope km long with hundreds of baited hooks attached lying over the sea bed.
This fishing method is much less damaging to vulnerable sea bottom structures like corals than bottom trawling, but is likely to still have some effect on sea bed organisms. CCAMLR is currently developing a strategy to evaluate the damage this may be doing and reduce its impact.
effect of long-line fishing on benthic habitats vme_risk.pdf
7. Supporting spatial management of Ross Sea
The fishery for Antarctic toothfish in the Ross Sea is managed differently in different parts of the region. For example, the permitted catch rate is lower around the northern seamounts than along the Ross Sea slope.
The role of protected areas, within which fishing is prohibited, is currently under debate within CCAMLR.
“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 investigations on how to design spatial management of fisheries, both in the Ross Sea and across the whole Antarctic Ocean.
Marine Classification: Lessons from the New Zealand Experience. (583 kb)
Use of Biological Data to inform Bioregionalisation of the Southern Ocean (5.4 Mb)