The current assessment method for the mackerel icefish (Champsocephalus gunnari) in sub-area 48.3 employs the CMIX and GYM packages, deriving population numbers-at-age then projecting these numbers forward under the given harvest control rule to set a two-year TAC. One issue is the accurate identification of cohorts from the survey model, given the differential age structures observed in the population at Shag rocks and around South Georgia. In this paper we propose a length-based approach that removes this issue of determining cohorts, using stratified bootstrap techniques to estimate the length distribution of the population from the survey data which, in conjunction with the bootstrapped survey biomass data, yield an estimate of the population numbers-at-length. A length-based population projection is then used to estimate the two-year TAC, given the relevant harvest control rule.
Numéro du document:
Point(s) de l'ordre du jour