Research Document - 2004/055
Sablefish (Anoplopoma fimbria) in British Columbia, Canada: Stock Assessment for 2003 and Advice to Managers for 2004
By Haist, V., A.R. Kronlund, M.R. Wyeth
Sablefish (Anoplopoma fimbria) stock status in British Columbia for 2003 was assessed and advice to managers provided for the 2004/2005 fishing year. Four stock abundance indices were evaluated, including (1) standardized survey catch rates, (2) trap vulnerable biomass estimates derived from tag recovery data, (3) standardized commercial catch rates based on fisher logbooks, and (4) nominal catch rates based on commercial trap fishing logbooks and landings. A biomass dynamics model was used to integrate the stock indices and allowed estimation of annual production parameters, where the production terms represent the net changes in biomass resulting from fish growth, recruitment, immigration, emigration, and changes in trap vulnerability. Performance measures were presented in decision tables to allow stock status at different future catch levels to be compared. The performance measures adopted in this assessment were related to biomass levels that should be avoided to ensure conservation concerns for sablefish do not arise.
There was substantial improvement in the standardized survey and commercial catch rates indices in 2003, following the modest improvement observed in 2002. General agreement among the time series of indices indicated that sablefish vulnerable to trap gear experienced a decrease in abundance from higher levels in the early 1990s to low levels in the mid 1990s. The rate of decline slowed in the mid 1990s in both the north and south stock areas. For the north stock area, a period of relative stability occurred in the mid 1990s until 2001 when historically low commercial CPUE and standardized survey results were observed. Standardized survey catch rates in the north increased modestly in 2002 and then improved substantially in 2003. The decline in commercial trap and survey indices for the south stock area was more gradual through the mid 1990s and continued through 2002. However, significant improvement of the 2003 survey index for the south stock area was observed. An increase in the northern standardized commercial catch rates was in agreement with the upturn seen in the standardized survey results. The pattern of tagging model estimates of trap vulnerable biomass was generally consistent with the trends indicated by the commercial catch rates and standardized survey series through 2002.
Production model outputs suggested there was little risk that the TAC levels investigated will lead to a short-term conservation concern for sablefish. However, the model projections are strongly influenced by the substantial increase observed in the 2003 standardized survey and northern trap fishery indices relative to results in 2002. It is not known whether the stock index results in 2003 signal the beginning of period of sustained higher abundance for the B.C. sablefish stock. Support for a sustained period of (relatively) higher sablefish production, and potentially higher TACs, will be drawn from the accumulation of high stock index values over several years.
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