Research Document - 2005/031
Sablefish (Anoplopoma fimbria) in British Columbia, Canada: Stock Assessment Update for 2004 and Advice to Managers for 2005
By Haist, V., A.R. Kronlund, M.R. Wyeth
Sablefish (Anoplopoma fimbria) stock status in British Columbia for 2004 is updated and advice to managers provided for the 2005/2006 fishing year. Four stock abundance indices are evaluated including (1) trap survey catch rates, (2) trap-vulnerable biomass estimates derived from tag-recovery data, (3) standardized catch rates based on commercial trap fishing logbooks, and (4) nominal catch rates based on commercial trap fishing logbooks and landings. Non-tagging based indices of abundance are integrated into a monthly tagging model which is used to conduct stock biomass projections. Performance measures are summarized in decision tables to allow the projected stock biomass to be compared at different levels of total annual catch. In general, performance measures adopted in this assessment are related to biomass levels that should be avoided to ensure conservation concerns for sablefish do not arise.
Trap survey catch rates in 2004 were similar to those observed in 2003 however commercial catch rates declined from 2003 to 2004. Beginning-year trap vulnerable biomass estimated for 2004 is estimated to be similar to levels in the mid-1990s. 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 areas. For the north area, a period of relative stability occurred in the mid 1990s until 2001 when historically low commercial CPUE and survey results were observed. 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 area was more gradual through the mid 1990s and continued through 2002. However, significant improvement of the 2003 survey index for the south area was observed. Survey catch rates observed in 2004 are similar to 2003 levels. Commercial catch rates declined in 2004, tempering the outlook for the stock. 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 and 2003, but diverges from the trap survey in 2004.
The decision tables allow evaluation of tradeoffs along the conservation, stability, and yield axes of fishery objectives. If greater importance is placed on long-term stability, at the expense of increasing yield, then a reasonable trade-off between catch stability and stock conservation objectives would support no change to the current TAC of 4,500 t for the 2005/2006 fishing year. Higher tolerance for variability in catches, perhaps requiring larger reductions in future TACs, may provide the rationale for the selection of a higher TAC.
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