Uncertainties and associated concerns relating to using short-term projections to advise on the 2020 sardine TAC and TABs

de Moor, Carryn; Coetzee, Janet; Butterworth, Doug S

Uncertainties and associated concerns relating to using short-term projections to advise on the 2020 sardine TAC and TABs

Report

2019

Abstract

The analyses undertaken to provide a scientific recommendation for the 2019 sardine TAC and TAB, under Exceptional Circumstances were subject to a number of more serious uncertainties than would normally apply. Given the critically low level of the sardine resource, care should be taken to either recommend catch limits that are robust to these uncertainties, or to undertake further research to minimise such uncertainty. One key uncertainty is how survey (and commercial) length frequencies should be weighted given that concerns frequently arise that one or other (or both) may be unrepresentative of the population length structure. Future recruitment to this short‐lived resource is another key uncertainty. While the primary uncertainty surrounding the weight‐at‐length has been alleviated, and the growth curve adjusted, some uncertainty surrounding the choice of growth curve remains. Finally, under Exceptional Circumstances, the decision‐making process involves a greater degree of subjectivity. While the Small Pelagic Scientific Working Group aimed at making this as objective as possible to recommend 2019 sardine catch limits, that approach could possibly be further improved. This document is aimed at providing current research and analyses to assist discussion on the key questions to the panel at the MARAM International Stock Assessment Workshop.

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