Report on an investigation of reasons for differences between outputs from ASPM and ADAPT-VPA assessments of the Gulf of Maine cod stock

Butterworth, Doug S; Rademeyer, Rebecca A; Plagányi, Éva E

Report on an investigation of reasons for differences between outputs from ASPM and ADAPT-VPA assessments of the Gulf of Maine cod stock

Working Paper

2005

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The application of ADAPT-VPA and ASPM assessment methods to the same data set for the Gulf of Maine cod stock allows two primary reasons for earlier differences in assessment results from these two approaches to be identified: • the longer period of data which the ASPM method is able to take into account; and • decreasing selectivity at larger ages estimated by the ASPM approach, in contrast to the flat selectivity assumed by the ADAPT-VPA application of Mayo et al. (2002). Arguments are presented that the ASPM approach (with specific details of an application still to be discussed) should be preferred over ADAPT-VPA as the basis for management recommendations for this resource. Since the ASPM assessments consistently indicate the resource status to be appreciably better relative to the MSY biomass, this has important implications for what might constitute appropriate management measures at present.