Science Advisory Report  2015/010

Yellowtail Rockfish (Sebastes Flavidus) Stock Assessment for the Coast of British Columbia, Canada

Summary

• Yellowtail Rockfish is an important component of the multi-species and multi-gear groundfish fishery in British Columbia (BC). This species is the second-most important rockfish caught by midwater and bottom trawl gears in terms of total landings, after Pacific Ocean Perch (Sebastes alutus), and is also taken incidentally by the midwater trawl fishery directed at Pacific Hake (Merluccius productus).
• The BC population is assessed as a single stock using a two-sex statistical catch-at-age (SCA) model. Model inputs include reconstructed catches starting in 1940, one gear-type (bottom + midwater trawl), fishery-independent indices of relative biomass derived from six bottom trawl surveys spanning 40 years, and proportion-at-age data from commercial and survey sources. The model is implemented in a Bayesian framework to quantify uncertainty of estimated quantities and management parameters.
• The spawning biomass (mature females only) at the beginning of 2015 (B₂₀₁₅) is estimated to be 0.50 (0.30-0.76) of unfished spawning biomass (B₀), where numbers denote median and (5-95 percentiles) of the Bayesian estimates of parameter uncertainty. Also, B₂₀₁₅ is estimated to be 2.20 (1.12-4.41) of the equilibrium biomass at maximum sustainable yield, B_MSY.
• Forecasts of stock status relative to MSY-based, unfished, minimum and current biomass outcomes are presented. These outcomes include the provisional reference points from the decision making framework (DFO 2009), namely a provisional limit reference point of 0.4B_MSY and upper reference point of 0.8B_MSY. For the BC coast, B2015 is estimated to have a 1.0 probability of being greater than 0.4B_MSY, and a 0.995 probability of being greater than 0.8B_MSY (i.e., of being in the Healthy Zone). The ratio of the exploitation rate in 2014 relative to that associated with MSY is 0.40.
• Advice to management is presented in the form of decision tables using ten year projections from 2016 to 2025 for a range of constant annual catches from 0 to 6,000 t. Annual catches at levels near the recent 5-year (2009-2013) mean of 4,333 t are predicted to cause a gradual decline of the population over the forecast period.
• Alternative model cases investigated the effects of
1. separating data for bottom and midwater trawl gears,
2. including the West Coast Vancouver Island shrimp trawl survey,
3. increasing Yellowtail Rockfish catches during a period where actual catches were uncertain, and
4. doubling the standard deviation on the prior distribution used to estimate the natural mortality parameter.

This Science Advisory Report is from the November 18-19, 2014 Stock assessment for Yellowtail Rockfish (Sebastes flavidus) in British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Complete document (PDF, 777 KB)

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