A preliminary SCAA/ASPM assessment of white hake

Butterworth, Doug S; Rademeyer, Rebecca A

A preliminary SCAA/ASPM assessment of white hake

Working Paper

2008

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The ASPM (SCAA) methodology presented in Butterworth and Rademeyer (2008), with an adjustment to be able to incorporate data on proportions at length, is applied to white hake. In a preliminary and (for reasons of time) restricted analysis, four scenarios are consider for the period from 1963 when abundance indices first become available. These reflect the assumptions that spawning biomass in 1963 was at 25% and 50% of its pristine level, and that the catch of hake of length less than 60 cm was either all white hake or all red hake, with the latter assumption leading to somewhat more optimistic appraisals of the current status of white hake. Model fits to survey index trends are broadly reasonable, though there are some difficulties with proportions at length data which would likely be better addressed in future analyses by adopting a length-specific rather than an age-specific selectivity framework. All four scenarios considered suggest an increase in spawning biomass over the last decade, and that the current fishing mortality is less than FMSY. Nevertheless the preliminary nature of all results must be stressed, particularly as time has thus far allowed only a very limited number of variants of the assessment to be investigated.

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