Research Document - 1999/184
Slope Rockfish Assessment for the West Coast of Canada in 1999.
By J.T. Schnute, N. Olsen, and R. Haigh
Abstract
This year's report does not provide a new assessment, but rather a series of steps essential for future assessments, based on industry-sponsored surveys for slope rockfish. Our research follows a strategic plan for collaborative work with the groundfish industry. The report presents the latest available data and makes the following major advancements on past work. First, we have developed a bathymetric database, cross-referenced with the observer data, from which we can calculate bottom area available to fishing as well as actual bottom areas swept and impacted. We have also provided estimates of biomass for each slope rockfish species by extrapolating observed estimates of density at depth to all available coastal bathymetry. Second, in collaboration with the Canadian Groundfish Research and Conservation Society, we have initiated the development of an industry-sponsored slope rockfish survey, independent of the fishery. To date, we have developed maps that record fishermen's impressions of trawl characteristics of the ocean floor. These classifications and preliminary estimates of fish density provide essential prior information in designing a survey that minimizes the variance of biomass estimates for a given level of available resources. Third, we have used biological data to calculate rough estimates of key reference points for the slope rockfish species. The report presents the complete mathematical framework for calculating reference point values from underlying biological parameters.
Analyses extended from last year suggest a continuing decline in the density of longspine thornyheads in the most heavily fished blocks in assessment unit region 3C. Although these results are not definitive, they suggest a cautious approach to the development of a new fishery on this species.
In response to a request from industry and management, we examine the possible justification for shifting the 5CD/5ES boundary 20 minutes north of its present location at 52°N. If the quota remains unchanged in each area, the impact on quota holders would be minimal. Furthermore, fishing pressure on the Morseby Gully region would be somewhat alleviated if 5CD quota holders shift some of their effort to the region off the southwest Queen Charlotte Islands.
Although we have observed a number of significant trends in CPUE, we do not specifically recommend that current TAC levels be adjusted. CPUE trends may indicate changes in abundance; however, there are so many confounding factors that we can only advise managers to be aware of potential problems. Until controlled surveys are implemented and/or confounding factors are statistically incorporated in CPUE measurements, we cannot with any degree of confidence provide reliable measures of stock abundance at this time and recommend that the 1999 yield options be extended to 2000.
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