Science Advisory Report 2018/049

Redstripe Rockfish (Sebastes propiger) stock assessments for British Columbia in 2018

Summary

• Two stocks of Redstripe Rockfish were identified along the British Columbia (BC) coast based on observable, consistent differences in mean length and growth models between the areas. The two stocks are called BC North (or BCN) in Pacific Marine Fisheries Commission (PMFC) 5DE and BC South (or BCS) in PMFC 3CD5ABC.
• Both Redstripe Rockfish stocks were assessed using a single fishery, annual two-sex catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated quantities.
• The median (and 5 and 95 percentiles of the Bayesian results) female spawning biomass at the beginning of 2018 (B₂₀₁₈) is estimated to be 0.91 (0.69-1.13) of unfished female spawning biomass (B₀) in BCN and 0.62 (0.47-0.81) of B₀ in BCS. Also, B₂₀₁₈ is estimated to be 3.16 (2.02-4.00) of the equilibrium spawning biomass at maximum sustainable yield, B_MSY, in BCN and 2.43 (1.51-3.79) of B_MSY in BCS.
• At current catch levels, there is an estimated probability of >0.99 that both B₂₀₁₈ > 0.4B_MSY and B₂₀₁₈ > 0.8B_MSY for both stocks (i.e. of being in the healthy zone). The probability that the exploitation rate in 2017 was below that associated with MSY is also >0.99 for both stocks
• Advice to management is presented in the form of decision tables using the provisional reference points from the Fisheries and Oceans Canada Sustainable Fisheries Framework (SFF) Precautionary Approach. The decision tables provide five-year projections across a range of constant catches (Table 5, Table 6).
• The appropriateness of the MSY based reference points for long lived low productivity species is uncertain, consequently advice to management relative to reference points based on 0.4 and 0.2 of B₀ (unfished spawning biomass) is also presented as an alternative option.(Appendix F Tables: F11, F12, F25, F26).
• It is recommended that the next assessment occur in 2023, with three new indices available from each of the four biennial synoptic trawl surveys and five additional years of ageing and catch data. No appropriate indicators for this stock are recommended that would trigger an assessment earlier than scheduled. Advice for the interim years is explicitly included in the decision tables.
• Recommended future work includes the investigation of alternate reference points due to the sensitivity of B_MSY based reference points to assumptions about model parameters and functions, including: catchability (q), natural mortality (M), recruitment variability (σR), and commercial and survey selectivities.  It is also recommended that future assessors review the informative priors used in this stock assessment and investigate alternatives with the intent of developing more appropriate priors.

This Science Advisory Report is from the June 13-14, 2018 Regional Peer Review on Stock Assessment for British Columbia Redstripe Rockfish (Sebastes proriger) in 2018. 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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