Research Document - 1999/016

Slope Rockfish assessment for the West coast of Canada in 1998.

By J.T. Schnute, N. Olsen and R. Haigh

Abstract

For assessment purposes, slope rockfish include seven species: Pacific ocean perch, yellowmouth rockfish, redstripe rockfish, rougheye rockfish, shortspine/longspine thornyheads, and shortraker rockfish. These are managed within six major areas (3C, 3D, 5AB, 5CD, 5ES, 5EN), giving a total of 42 species-area combinations. Historically, these 42 assessment units have been managed with reference to a benchmark stock of Pacific ocean perch in Area 5AB. A catch-at-age analysis of this stock played a central role in the assessment. This assessment differs from past reports in three principle respects. First, we use a new trawl observer database to examine abundance ratios among species and areas. Second, we use information gathered from experienced members of the industry, and we record some of their concerns. Third, we do not include a new catch-at-age analysis of the benchmark stock. No new survey data are available to alter substantially the 1997 analysis.

We draw several conclusions from our analysis of the trawl observer database. First, as stated by industry members, CPUE varies substantially with depth. Second, commercial slope rockfish tows that occur in similar times and places as research survey tows sometimes exhibit lower CPUE profiles in relation to depth, confirming observations by fishermen that a system of IVQs may induce avoidance fishing. Third, analysis of heavily fished blocks shows little evidence of stock depletion, except possibly for longspine thornyheads. Finally, industry abundance estimates conform more closely to recent yield and quota recommendations than to various computed indices based on effort qualification and spatial stratification.

Recognizing the need for further analysis and lacking evidence for substantial change at this time, we recommend that the 1998 yield options be extended to 1999.

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