Stock assessment of the Patagonian toothfish, Dissostichus eleginoides, harvested by the French fishery at Kerguelen Islands (Division 58.5.1 of the CCAMLR)

A stock assessment of the Patagonian toothfish (Dissostichus eleginoides) at Kerguelen Island (division 58.5.1 of the CCAMLR) was undertaken with the modeling software CASAL, using different statistical and biological datasets: abundance estimation from the POKER 1 and 2 scientific cruises, catch per unit effort of the commercial fishery, tagging survey, sample size frequencies… CASAL is a simple population-modeling tool, applied to a single area and based on sex combination. The spatial complexity of the fishery is modeled using different functions for fishery selectivity depending on the fishing zone and the type of fishing vessels (trawlers, long-liners). The fishing zone for the long-liners is divided in four areas (North, East, South, Skiff Bank) and in two depth categories: less than and more than 1,500m. Commercial catches are integrated in the model by CCAMLR season. A weighted combination of datasets was integrated using the effective samples’ size calculated at the level of each haul. An iteratively estimated process error was applied to the length frequency data. With an initial biomass of about 200,000 tons, the modeling tends to present results which are consistent with the stock assessments undertaken by the Australian scientific team at Heard (subarea 58-5-2) and over the Kerguelen Plateau. The biomass long-term projection, done for the Patagonian toothfish with a simulated 5,100 tons catch by long-liners, fulfils the CCAMLR management rules. However, these results should be considered with caution and research studies aiming at collecting more biological data and getting a better understanding of the population spatial complexity should be continued.