Assessment of the South African sardine resource using data from 1984-2015: Results at the joint posterior mode for the two mixing-stock hypothesis.

de Moor, C L; Butterworth, Doug S

Assessment of the South African sardine resource using data from 1984-2015: Results at the joint posterior mode for the two mixing-stock hypothesis.

Working Paper

2016-07

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 sardine 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 model infection of sardine by a “tetracotyle”-type metacercarian parasite, and includes data on this parasite prevalence-by-length in the likelihood. A Hockey-Stick stock recruitment relationship is used for this OM, with a different median recruitment and higher variability estimated for the west stock during “peak years”. Time-invariant natural mortality is assumed to be 1.0 year-1 for juveniles and 0.8 year-1 for adults as before. The total resource abundance is estimated to be 688 thousand tons in November 2015, with the west stock consisting of 142 thousand tons and the south stock consisting of 546 thousand tons. These biomasses are well below the long term average of 1 039 and 492 thousand tons for the total resource and west stock respectively, and near the long term average of 547 thousand tons for the south stock. The west stock has experienced below average recruitment in 11 out of the 12 most recent years.

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