Seamount-specific biomass estimates from SSRU 88.2H in the Amundsen Sea derived from mark-recapture data

Mark-recapture data for Antarctic toothfish from individual seamount features in SSRU 88.2H were analysed to estimate biomass trends on isolated seamounts. Biomass estimates were also calculated for SSRU 88.2H as a whole. The analyses indicate that:

• Fish seldom move among seamounts within the complex, and residence time on particular seamounts declines rapidly over 1–4 years.
• Fishing has occurred on almost every seamount in every year and usually in proportion to the level of tagging on the seamount in the previous year.
• Trends in local biomass estimates for individual seamounts and SSRU 88.2H overall showed a decline in biomass through time with a slight increase in biomass since 2012.
• The pattern in recapture rates of annual cohorts of tagged fish through time in SSRU 88.2H indicates a decrease in the percentage of the population tagged due to the annual immigration of untagged fish, along with catch and emigration of tagged and untagged fish resulting in a decreasing trend in biomass overall.
• Annual immigration also results in a progressive inflation of biomass estimates from mark-recapture data, and therefore biomass estimates are most accurate after 1 year at liberty, but still overestimated due to immigration.