Updated models of the habitat use of Patagonian toothfish (Dissostichus eleginoides) on the Kerguelen Plateau around Heard Island and the McDonald Islands (Division 58.5.2)

The Kerguelen Plateau supports the largest fishery for Patagonian toothfish (Dissostichus eleginoides) in the CCAMLR area, with landings of  >5000 t.yr^-1 from the French EEZ (Division 58.5.1) around îles Kerguelen and 2730 t.yr^-1 from the Australian EEZ around Heard and McDonald Islands (HIMI, Division 58.5.2). This paper provides a synthesis of the spatial distribution of the Patagonian toothfish drawn from biological data collected in the HIMI area (Division 58.5.2) on more than 500,000 fish caught since 1997 during fishery operations and research surveys. Statistical analyses were used to quantify the effect of bathymetry in structuring the spatial distribution of different length classes and sex composition, when controlling for gear selectivity, year and sex effects. Fish length increased with depths suggesting spatial segregation of life stages. Spatial predictions showed that small, immature, fish were mostly found over the Plateau (<400m) and banks tops (i.e. Shell Bank), whereas larger fish inhabit deeper waters (>1500m) especially on the eastern part of the Plateau, where the continental slope is steep. Being slightly biased towards females, sex ratio was also influenced by fishing depth. Proportion of females increased at shallower (<500m) and deeper (>1200m) depths, whereas a sex ratio of 0.6 was found in between. The recent discovery of extensive areas of spawning activity in the Australian EEZ revealed the importance of the western margin of the Plateau as spawning habitat. These results allow us to further refine hypotheses about the spatial segregation of life-stages and sex in the HIMI part of the Kerguelen Plateau. The distribution and ecology of the early life history stages, up to 2-3 years old, and the implications of sexual and phenotypic variability in growth and movement stand out as the priority for future research into the biology and management of Patagonian toothfish in this region.