Population assessment of Patagonian toothfish in the north of Subarea 48.4 – 2010 update

The target tagging rate of 5 fish per tonne was exceeded by both vessels, with 232 D. eleginoides tagged and released in 2009/10, bringing the total to 1,547 in all seasons; There were 18 D. eleginoides tag recaptures in 2009/10, a total of 72 in all seasons; The length-frequency of 2009/10 captures is consistent with the theory that the bulk of the biomass is dominated by a small number of cohorts. CASAL estimates a large recruitment event in early the early 1990s and faster growth rates than those currently assumed for the 48.3 population CASAL estimates of D. eleginoides population size in the North of 48.4 are very similar to that from the previous season with a B₀ of 1,123 t (compared to 1,127 t in the 2009 assessment) and B₂₀₁₀/B₀ of 92.8%. Sustainable yield calculated according to the CCAMLR decision rules is 41 tonnes. A lower than anticipated number of tag recaptures have come from 2007/08 releases. Removing these from the CASAL assessment reduced B₀ to 963 tonnes though had a minimal effect on B₂₀₁₀/B₀ (89.7%). Sustainable yield omitting 2007/08 tags is 37 tonnes.