Research Document 1997/146

Sablefish stock assessments for 1997 and recommended yield options for 1998

By V. Haist, M.W. Saunders, R. Hilborn, and M. Maunder

Abstract

This paper represents a major assessment for sablefish. Two stock assessment models are developed for the analysis of B.C. sablefish fisheries and research data. The first is a mark-recapture model that explicitly accounts for fish movement between both spatial and depth strata. The second is an integrated catch-age mark-recapture model where only movement out of the assessment region is modelled. The two analytical methods employ some different assumptions and hence allow for alternate fits to the data observations. Separate analyses are conducted for northern and southern areas of the B.C. coast due to observed differences in age and length compositions, growth and evidence from juvenile tagging that recruitment to the areas are drawn from different origins.

Estimates of the 1996 exploitation rates from the two assessment models are not substantially different but the estimated trends in abundance from 1991 to 1996 differ significantly. For the southern B.C. stock the estimated 1996 exploitation rate is 0.056 from the integrated model and 0.05 (range of 0.04 - 0.07) from the mark-recapture model. For the northern B.C. stock the estimates are 0.18 and 0.11 (range of 0.09 - 0.15) from the integrated mode and mark-recapture model, respectively. The mark-recapture model analyses suggest significant declines in stock abundance between 1991 and 1996 for both stocks. The stock reconstructions from the integrated model indicate relatively stable abundance for the southern stock and only a slight decline in abundance for the northern stock over the same period.

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