Research Document - 2002/074
Review of survey, commercial fishery and tagging data for sablefish (Anoplopoma fimbria) in British Columbia (Supplement to the November 2001 sablefish stock assessment)
By A.R. Kronlund, Malcolm Wyeth, Ray Hilborn
Catch rates observed during the 2001 sablefish (Anoplopoma fimbria) survey have declined significantly compared to those observed in the previous five years. In response, fishery managers requested a review of the 2001 survey data in the context of historical survey and fishery information, as well as an updated tag-recovery analysis. This paper was prepared as a supplement to the most recent assessment of sablefish (Haist et al. 2001) to accommodate the new survey information and to help evaluate whether the current assessment of sablefish stock status should be revised.
Survey catch rates showed declines from 1990 to 2001 in seven of nine localities and generally showed declines at all depth strata surveyed. The decline was steepest in the first half of the time series, and slowed from 1996 to 2000. Catch rates in 2001 were the lowest in the time series, and generally exhibited much smaller variance in comparison to previous years. Commercial catch rates calculated from logbook records showed trends similar to the survey data within the survey localities. Trends were less well defined outside of the survey areas, but suggested a decline from 1990 to 2001 and reduction in variance in the latter few years of the series. Interpretation of these trends is complicated by the adoption of escape rings in trap gear in 1998. Estimates from the tagging program for 2001 indicated a biomass of 37,300 t with an exploitation rate of 0.096. The estimates of abundance were without trend from 1995 to 2001, with no significant outliers evident within this period. The tagging program estimates showed no evidence of a dramatic decline in abundance from 2000 to 2001.
Recent assessments of sablefish in British Columbia have relied primarily on the results of tag-recovery analysis to provide estimates of stock biomass and harvest rate. Trends in survey and commercial catch rates were used to corroborate the trend in estimates from the tag-recovery analysis. This review of sablefish stock indicators, prompted by the low 2001 survey results, resulted in a re-interpretation of stock status that reflects the concern that the stock has experienced continuous decline during the 1990s. Recommendations to managers for the current 2001/2002 and 2002/2003 fishing years are provided.
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