Why does the current hake assessment indicate the extent of depletion of the M. paradoxus population to be high, but that of M. capensis to be much less?

Rademeyer, Rebecca A; Butterworth, Doug S

Why does the current hake assessment indicate the extent of depletion of the M. paradoxus population to be high, but that of M. capensis to be much less?

Working Paper

2008

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The relatively high extent of depletion estimated for the M. paradoxus population is found to be robustly determined, with all five sources of data contributing to the assessment suggesting that both this extent and current fishing mortality are relatively high. However these fives sources lead to appreciably differently perceptions for the extent of depletion of the M capensis population. The GLMstandardised CPUE series commencing in 1978 is found to be the most influential of the five in leading to present estimates of both a relatively low extent of depletion and fishing mortality for this population. However if there is a trend in bias over time in this index as a measure of abundance, irrespective (almost) of the direction of this bias, the extent of depletion of the M. capensis population would be estimated to be notably higher. Research priorities indicated by this analysis are a focus on ageing and sex-differentiation for M. paradoxus, and on the possibility that factors responsible for an increase in catching efficiency may have been omitted from the M. capensis CPUE GLM standardisation.