Exploratory Catch-at-Age Assessments of Gulf of Maine-Georges Bank Witch Flounder

Butterworth, Doug S; Rademeyer, Rebecca A

Exploratory Catch-at-Age Assessments of Gulf of Maine-Georges Bank Witch Flounder

Working Paper

2016-10

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

License

http://creativecommons.org/licenses/by/4.0/

Abstract

Exploratory Statistical Catch-at-Age assessments of the Gulf of Maine-Georges Bank witch flounder stock indicate possibly unrealistically high q values (in the range of 3-5) for surveys, suggesting substantial herding by the net. If q is forced to be lower, the primary lack of fit that arises originates from the larger numbers of 11+ fish predicted compared to observed for the spring survey. All of treating the Albatross and Bigelow abundance index series as independent, including LPUE data, and forcing a lower value for q suggest the resource at present to be larger and of better status relative to pristine. Even if both the first two of these factors are incorporated, however, a strong retrospective pattern remains. During the meeting, a further base case run was developed to mimic the specifications agreed for the ASAP base case run as closely as possible, and some sensitivities to that also run. Of interest is that for a combination of the sensitivity factors (allowing selectivity doming, including LPUE data and downweighting the proportions-at-age data) the retrospective pattern is considerably reduced (especially for spawning biomass), the survey indices are fit better, and values of q drop, approaching 3.

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