First stock assessment for Antarctic toothfish approved

Scientists from NIWA have developed the first fisheries assessment for Antarctic toothfish, and the first for any exploratory Antarctic fishery. The 2005–06 quota for the Ross Sea Antarctic toothfish fishery, which opened on 1 December, has taken account of this new assessment.

20 December 2005

Fishermen hauling in Antarctic toothfish - Jack Fenaughty, Sanford Ltd.

The Commission for the Conservation of Marine Antarctic Living Resources (CCAMLR), which manages fisheries around Antarctica, accepted NIWA’s assessment of Ross Sea Antarctic toothfish stock levels and yields at their annual meeting in Hobart in October, and endorsed NIWA’s assessment model (CASAL) for use in other toothfish fisheries. CCAMLR commissioner Trevor Hughes, of New Zealand’s Ministry of Foreign Affairs and Trade (MFAT), describes it as a ‘huge achievement which has shown the way forward to CCAMLR for its management of exploratory fisheries.’

NIWA scientist Dr Stuart Hanchet says that the key to the adoption of the assessment by CCAMLR has been the good collaboration between scientists at NIWA and the Ministry of Fisheries, strong advocacy by MFAT, as well as good cooperation with the toothfish fishing industry, which independently initiated the tagging programme in 2001.

New Zealand longliners initiated a small-scale fishery for Antarctic toothfish – a close relative of the Patagonian toothfish, but found further south – in 1996–97. Since then, New Zealand vessels and, more recently, vessels from other countries have returned each summer to fish in the area. The fishery is managed by CCAMLR as an exploratory fishery, with a strong emphasis on data collection and research.

NIWA scientists used their CASAL population model to estimate initial and current levels of the Ross Sea Antarctic toothfish stock, as well as long-term yields, based on fisheries data and information collected as part of a tag-release programme. They estimated the initial Ross Sea Antarctic toothfish spawning stock at 69 000 t, and current biomass at roughly 61 000 t (the equivalent of about 2.3 million mature fish). Based on their yield estimate, CCAMLR recently set a quota for the 2005–06 season of just under 3000 t. This equates to about 100 000 fish and a total wholesale value of NZ$50 million.

With CASAL, New Zealand has introduced a new methodology to CCAMLR for assessing fish stocks. ‘Within 18 months, it has become widely accepted and is now being applied to a range of other toothfish fisheries by overseas scientists, including Patagonian toothfish around South Georgia in the South Atlantic,’ says Dr Hanchet, who led the research.

CCAMLR’s scientific committee was struggling to come up with advice on catch limits for any exploratory fishery, says Mr Hughes. ‘Some people were highly skeptical of arriving at an estimate within 10 years,’ but New Zealand ‘came to the rescue’ in just 18 months, he adds.

Background

1. Toothfish are large, bottom-living fish found only in Antarctic and sub-Antarctic waters. There are two main species, the Antarctic toothfish (Dissostichus mawsoni) and Patagonian toothfish (Dissostichus eleginoides), otherwise known as Chilean sea bass. Antarctic toothfish are found in higher latitudes south of the Antarctic Convergence. Antarctic toothfish feed on a wide range of prey, mostly fish, but also squid and crustaceans.
2. The Patagonian toothfish fishery is notoriously plagued by illegal, unreported and unregulated fishing (IUU), but this is not yet a problem for Antarctic toothfish.
3. CCAMLR is responsible for managing fisheries in Antarctic waters, and is part of the Antarctic Treaty system. CCAMLR aims to ensure that fisheries do not develop at a rate faster than data can be acquired to determine sustainable catch levels. The Antarctic toothfish quota was set by CCAMLR at the level that minimises risks to the stock from fishing while accounting for any uncertainty. Once sufficient data have been collected during the exploratory fishing phase to allow for a full stock assessment, a CCAMLR fishery may be managed as an ‘assessed’ fishery, and subsequently as a commercial fishery. No exploratory fishery has been assessed in the CCAMLR area before. For more information on CCAMLR, see: http://www.ccamlr.org/. For information on New Zealand’s involvement in CCAMLR, see: http://www.mfat.govt.nz/Foreign-Relations/Antarctica/2-Antarctic-Treaty-System/0-conservation-of-resources.php. For information on the toothfish fishery, see: http://www.colto.org/.
4. CASAL stands for C⁺⁺ Algorithm Stock Assessment Laboratory and was developed by NIWA scientists to assess fish stock levels and long-term yields. The model for Antarctic toothfish incorporates fisheries data (such as catch/effort and age frequencies), as well as tag-release and recapture data from a New Zealand industry-initiated tagging programme, which began in the 2000–01 fishing season. The beauty of CASAL, says Dr Hanchet, is that it has a ‘phenomenal amount of flexibility for incorporating different population structures in the model and testing the effects of different scenarios, such as different catch levels, on the stock.’
5. The work was funded by New Zealand’s Ministry of Fisheries. Another NIWA project is modelling Ross Sea ecosystems with a view to determining the likely impacts of environmental changes and human impacts, including those of the toothfish fishery.