Science Advisory Report  2014/028

Stock Assessment for Silvergray Rockfish (Sebastes brevispinis) along the Pacific Coast of Canada

Summary

• Silvergray Rockfish (Sebastes brevispinis) is a commercially important species of rockfish that has supported a domestic trawl fishery since 1940, with periods of heavy fishing in the mid-1960s and during 1985-1995.
• All areas of Canada’s Pacific coast, excluding waters between Vancouver Island and the British Columbia mainland, were assessed as a single stock using an annual two-sex catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated quantities.
• The spawning biomass (mature females only) at the beginning of 2014 (B₂₀₁₄) is estimated to be 0.56 (0.41–0.70) of unfished spawning biomass (B₀); numbers denote median (and 5-95 percentiles) of the Bayesian results. Also, B₂₀₁₄ is estimated to be 2.04 (1.22–3.00) of the equilibrium biomass at maximum sustainable yield, B_MSY.
• Two periods of high recruitment, 1982-1984 and 2000–2001, were estimated for this stock. Increased catch followed the large recruitment of 1982-1984, but not the large recruitment of 2000-2001.
• Decision tables are presented using the provisional reference points from the Fisheries and Oceans Canada Sustainable Fisheries Framework Precautionary Approach, namely a limit reference point (LRP) of 0.4B_MSY and upper stock reference (USR) point of 0.8B_MSY.
• Advice to management is presented in the form of decision tables using ten-year projections for a range of constant catch strategies up to 3,000 t/year, where t is tonnes; the mean annual coastwide catch was 1,408 t from 2008-2012. The probability of remaining above the LRP at the beginning of 2024 is estimated to be at least 0.99 for all catch strategies tested. The probability of remaining above the USR at the beginning of 2024 is estimated to be at least 0.89 for all catch strategies tested. Stock sizes are predicted to likely decrease at catch levels of at least 1,750 t/year. The probability that the exploitation rate at the beginning of 2024 will be below that associated with MSY at equilibrium is at least 0.56 for all catch strategies tested.
• Catches at levels of 1,500 t/year, slightly above recent mean catch levels, essentially predict no change in stock size over the next 10 years, with the stock remaining well above the USR.

This Science Advisory Report is from the Regional Peer Review meeting on ‘Assessments of British Columbia Rock Sole and Silvergray Rockfish Stocks’, held on November 20-22, 2013. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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