Research Document 1997/147

Slope rockfish stock assessment for the west coast of Canada in 1997 and recommended yield options for 1998

By L.J. Richards, N. Olsen, J. Schnute, and R. Haigh

Abstract

For assessment purposes, slope rockfish include Pacific ocean perch, redstripe rockfish, yellowmouth rockfish, rougheye rockfish, shortraker rockfish, and shortspine and longspine thornyheads. The best information pertains to the Goose Island Gully stock of Pacific Ocean perch. An age-structured analysis for this stock uses catch-age data available from 1963-96 and a series of trawl surveys, updated with recent surveys in 1994 and 1995. Based on this analysis, the foreign fishery of the late 1960s and early 1970s reduced the stock to about a third of the 1965 exploitable biomass by 1977. Between 1977-84, biomass remained relatively constant. Exploitable biomass then increased to more than half of the 1965 level by 1994, as a result of above-average recruitment and low fishing mortality rates. Point estimates of beginning of year biomass decreased slightly between 1994-97. Biomass is likely to decrease again for 1998, given the absence of incoming above average year-classes, but is anticipated to remain near the expected long-term average biomass.

Because of limited data, we are less certain about the status and potential yields of other stocks of Pacific ocean perch. Based on recent surveys, we have recommended decreases in the yields in Areas 3C and 5E-S and an increase in the Area 5E-N yield. We have not recommended changes to the yields in Areas 3D and 5C/D.

Yields for redstripe rockfish, yellowmouth rockfish, and shortspine thornyheads are derived from 25%, 38%, and 12%, respectively, of the Pacific ocean perch yield. These percentages are expanded from Goose Island Gully bottom trawl survey information, after considering potential midwater abundance and recent ratios in the catch. Yields for rougheye rockfish are based on the species longevity of up to 147 years of age. Yields for shortraker rockfish are determined from the ratio of shortraker to rougheye rockfish in monitored landings. We have no scientific basis for recommending yields for longspine thornyheads.

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