Research Document - 2003/071
Sablefish (Anoplopoma fimbria) in British Columbia, Canada: Stock Assessment for 2002 and Advice to Managers for 2003
By Kronlund, A.R., Haist, V., Wyeth, M., and Hilborn R.
There is general agreement among the trends in stock indices that sablefish vulnerable to trap gear experienced a decrease in abundance from (relatively) high levels in the early 1990s to low levels in the mid 1990s. The rate of decline slowed markedly in the mid 1990s for both 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 indexing survey results were observed. Index survey catch rates in the north improved in 2002, and were comparable to those observed in the mid 1990s. In contrast, the decline in commercial trap and survey indices for the south stock area was more gradual through the mid 1990s, but has continued through 2002. The pattern of monthly tagging model estimates of vulnerable biomass was generally consistent with the trends indicated by the commercial catch rate and index survey series, though it is variable through the late 1990s.
This assessment incorporated the results of the fall 2002 abundance indexing survey, a new standardized commercial catch rate index, and a new tag-recovery model that adjusts tag returns for month effects. Analysis of sablefish recruitment indicators from various sources in British Columbia and the United States suggested that future production of sablefish should improve over low levels experienced in the 1990s. A simple biomass dynamics model was used to combine the stock indices and to examine the consequences of assumed levels of future production on projected stock biomass, where production was considered to be the combined effects of recruitment, immigration, emigration, and growth. Advice to managers was cast in the form of decision tables. By necessity, frequent review of the stock indicators will be required pending the development of a satisfactory population dynamics model for examining the consequences of long-term harvest strategies for sablefish.
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