Assessment of the South African anchovy resource using data from 1984 - 2015: results at the posterior mode

de Moor, Carryn L

Assessment of the South African anchovy resource using data from 1984 - 2015: results at the posterior mode

Working Paper

2016-10

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The operating model (OM) for the South African anchovy resource has been updated from that used to develop OMP-14 given four more years of data. The model has been altered from previous assessments to now fit directly to length frequency data, removing the earlier need for estimates of proportions of anchovy-at-age 1 during the annual November hydroacoustic survey. A Beverton Holt stock recruitment relationship is used for the base case. Time-invariant natural mortality is assumed to be 1.2year^(-1) for both juvenile and adult natural mortality as before; this provides a better fit to the data than other options considered. The resource abundance is estimated to be near the historical (1984-2014) average, with a total biomass of 3.3 million tons in November 2015. Recruitment reflects three major peaks over the past 20 years, although the lowest points in these fluctuations were still large, being similar to the maximum recruitment prior to 2000.

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