ASSESSMENT OF PATAGONIAN TOOTHFISH POPULATION IN THE NORTH OF SUBAREA 48.4 USING DATA FROM A FOUR-YEAR TAGGING EXPERIMENT

1. The bycatch TAC of 12 tonnes of macrourids was reached in 2008/09 triggering the early closure of the fishery with only 58.9 t of the 75 t TAC of D. eleginoides taken; 2. The target tagging rate of 5 fish per tonne was exceeded by both vessels, with 344 D. eleginoides tagged and released in 2008/09, slightly under the target of 375 for the full 75 tonnes of catch; 3. There were 29 D. eleginoides tag returns in 2008/09, bringing the total from all seasons up to 54 tag recaptures; 4. A total of 12 D. mawsoni and 269 rajids were tagged in all seasons combined though none were recaptured; 5. Evidence of gonad development in 2008/09 suggests that D. eleginoides may spawn in the North of 48.4 in some years; 6. Analysis of tagging and biometric data suggests that D. eleginoides at 48.4 have similar growth parameters to those of 48.3; though the bulk of the current vulnerable biomass may be composed of a limited number of cohorts. 7. CASAL confirms that the vulnerable biomass is dominated by a single cohort spawned in the early-1990s and that growth parameters are similar for D. eleginoides caught in 48.4 and 48.3. 8. CASAL estimates of D. eleginoides population size in the North of 48.4 agree with simple Petersen and local CPUE estimates, with a B0 of 1143 t and B2009/B0 of 85%. 9. The sustainable yield calculated according to CCAMLR decision rules is 47 tonnes.