Assessment of the South African anchovy resource using data from 1984 – 2010: results at the posterior mode

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University of Cape Town

The operating model (OM) for the South African anchovy resource has been updated from that used to develop OMP-08 given four more years of data and a revised time series of commercial catch. A Hockey Stick stock recruitment relationship, and the same median juvenile and adult natural mortality rates as in previous assessments are used. When considering the Beverton Holt, Ricker and Hockey stick stock recruitment relationships, AICc model selection criterion do not show strong support for one relationship over another, yet the carrying capacity at the posterior mode differs considerably between the Hockey Stick and other relationships. Two base case hypotheses are chosen: one estimates random effects about adult natural mortality over time while the other assumes time-invariant annual adult natural mortality. There has been a decrease in recruitment residual standard deviation and in recruitment autocorrelation for this updated OM compared to that used in previous OMs. The impact of this on the appropriate choices of a risk definition and threshold for the new OMP to be developed needs to be considered. The resource abundance remains above the historic average, with a model-estimated 1+ biomass of 2.2-2.4 million tons in November 2010, having provided 8 years of above average recruitment in the past 11 years. The harvest proportion over the past 11 years has not exceeded 0.13.