Survey reveals plenty of young toothfish in the Ross Sea
A New Zealand-led survey of young toothfish in Antarctica has found high densities of the highly-prized fish in the southern Ross Sea, reports http://www.megafishnet.com/ with reference to NIWA.
Marine scientists Dr Stuart Hanchet, from NIWA, and Dr Hyun-Su Jo, from Korea, recently completed the first survey of young Antarctic toothfish.
Dr Hanchet says the successful survey is the first in a series that will monitor numbers of young Antarctic toothfish in the Ross Sea region.
He says, "To monitor fish abundance properly, it is necessary that the surveys be conducted in a controlled and rigorous way. For example, this means using the same fishing gear and the same bait, at the same time and location every year. It is also important that the survey is carefully designed so that it samples the main area in which the target population is found.
"This survey will be an important monitoring tool to make sure the level of fishing remains sustainable."
Antarctic toothfish (Dissostichus mawsoni) are found at depths down to 2000 metres. Fish mature at a length of 120-130 cm, and most adults live to an average age of 20 to 24 years.
"We're looking at both the number and size of fish that are between five and 10 years old and less than 100 cm in length", says Dr Hanchet. "We currently collect good information to monitor the abundance of adult toothfish, but we don't have the same quality of information for young fish. These fish are the adults of tomorrow, and by tracking this part of the population we can make sure that catch limits are set at the correct level in the future".
"Using the results of the survey, we will be able to model and forecast the future fish population. We need to develop a series of surveys over time because a single survey by itself tells us very little," says Dr Hanchet.
Under the provisions of the Antarctic Treaty, the Antarctic toothfish fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). CCAMLR sets the rules for fishing in the CCAMLR Convention Area, which includes the Ross Sea, and all participating member countries have to operate within these rules.
CCAMLR takes a precautionary approach to fishing in the Ross Sea. This means making careful and cautious decisions when there is uncertainty, so that the overall level of fish abundance remains high.
Countries fishing in the Ross Sea must tag a certain number of toothfish for scientific research, and carry out biological sampling of toothfish, as well as other fish species caught as by-catch.
"Tagging information has been critical to developing a comprehensive stock assessment model for the fishery to estimate biomass and set catch limits," says Dr Hanchet.
New Zealand vessels voluntarily introduced tagging in 2001, and tagging for all CCAMLR vessels became mandatory in 2004. New Zealand fishery scientists began assessing toothfish stocks in 2005.
The survey was a New Zealand-led scientific contribution to CCAMLR. It was designed by marine scientists in NIWA and the Ministry of Agriculture and Forestry (Fisheries science), and involved a collaboration with the fishing industry, which provided the platform for the survey - the Sanford vessel San Aotea II.
The main objective of this first toothfish survey was to establish the feasibility of developing a time-series of surveys to monitor young toothfish in the southern Ross Sea using standardised commercial long-line fishing gear.
Fifty-nine random locations were surveyed using long-lines, each comprising 4600 hooks, set for up to 24 hours, within a survey area of 30,000 square kilometres. They caught mainly 70-100 cm toothfish (at times over 100 individuals per line), in depths from 300-900 metres. The fish caught were then measured and sexed, with biological samples taken for further analysis back in New Zealand.
The survey also demonstrated the feasibility of collecting samples for wider ecosystem monitoring. A large number of samples of muscle tissue and stomachs were collected from Antarctic toothfish and several other fish species, and will be analysed to understand feeding habits and relationships with other organisms in the food chain.
The results of this survey will be presented at the next CCAMLR meeting, together with a proposal to continue the survey in future years.
Background facts
Fishing for Antarctic toothfish in the Ross Sea region began in 1997/8.
The number of licensed fishing vessels in the Ross Sea is carefully controlled by CCAMLR. In the current 2011/12 season, 18 vessels were permitted to fish, of which 15 actually fished.
The total catch limit this season was 3282 tonnes.
New Zealand's participation in the Ross Sea toothfish fishery is worth NZ$20-30 million per annum in export earnings.
The New Zealand delegation to CCAMLR comprises officials from the Ministry of Foreign Affairs and Trade, Ministry of Agriculture and Forestry, and Department of Conservation. Representatives from the fishing industry and environmental NGOs have been included in the New Zealand delegation in past years.
There are two toothfish species in Antarctica waters. The Antarctic toothfish is found around the Antarctic continent in Antarctic waters, and the Patagonian toothfish which is found further north in sub-Antarctic waters. In the mid to late 1990s the Patagonian fish was heavily over fished by illegal vessels. The stocks are believed to have stabilised, and in some cases re-built.