A comparison between ADAPT-VPA and ASPM-based assessments of the Gulf of Maine cod stock

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University of Cape Town

ADAPT-VPA and ASPM assessment methods are applied to the same data set for the Gulf of Maine cod stock to attempt to ascertain the reasons for the rather different results provided by past applications of the two approaches. A number of sensitivity tests for the ASPM assessment are also conducted. Results indicate the primary reasons for the past differences to be the longer period of data which the ASPM approach is able to take into account, and the fact that this approach estimates selectivity to be decreasing at larger ages whereas the ADAPT-VPA method assumes the selectivity at such ages to be flat. Arguments are presented that an ASPM-based assessment of this resource would provide a better basis for management advice than the current ADAPT-VPA method. Since the former consistently indicates current status of the resource to be appreciably better relative to the sp BMSY reference point than does the latter, such a suggestion has important implications for current management measures for the Gulf of Maine cod fishery.