Research Document - 2000/157
Sablefish Stock Assessment for 2000 and Recommended Yield Options for 2001.
By V. Haist and R. Hilborn
Abstract
This document represents a major assessment for B.C. sablefish. The principle data source on trends in abundance is the tagging program, and in particular the percentage of tags returned in the year following tagging. Coastwide, this percentage remained steady at 9-11% from 1991 to 1997, rose to 19% in 1998, and decreased to 8% in 1999.
Three analytical methods, all based on the tag release-recapture data, are used to estimate stock abundance. The methods differ in the degree that biological and fishery structure is incorporated in the estimation process, and in the choice of tagging data subsets used in the analyses. Different tagging data subsets are chosen to minimize potential bias in the alternative estimation methods.
All three methods suggest that B.C. sablefish decreased in abundance from the early 1990's through 1997, followed by a substantial increase in 1999. These trends are consistent with those observed in commercial fishery CPUE and survey CPUE indices, except that the fishery and survey indices did not show significant increases in 1999. However, the fishery CPUE is not adjusted for the effect of escape-rings, used in the commercial fishery in 1999, and therefore will not reflect abundance trends.
Stochastic stock projections are conducted for the 2000 to 2002 period at three levels of harvest (3800 t, 4000 t, 4500 t). The expectation, at all harvest levels, is an increase in abundance for both stocks.
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