Research Document - 2004/41
Analyses of survey catchability and fishery selectivity in the SPA for the Northern Gulf of St. Lawrence (3Pn, 4RS) cod stock
By Cadigan, N.
Abstract
We explore two issues in the sequential population analysis (SPA) for the cod stock in the Northern Gulf of St. Lawerence (3Pn+4RS). In recent assessments the SPA for this stock has been an ADAPT formulation. The first issue we explore involves how to model the fishing mortality at the oldest age in the SPA. The second issue involves possible changes in the catchability of indices used in the SPA to estimate stock size. We conclude that there is some evidence from the SPA that the fishery selectivity has changed since the moratorium, and now has a "dome" shape. We also conclude that there is statistically significant evidence in the SPA that the catchability of the NGulf indices is not constant over time. This nonstationarity is somewhat consistent with annual changes in the spatial distribution of the stock, which may have become more concentrated in inshore areas. The Sentinel gillnet index has an opposite trend to that predicted by the SPA.
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