Science Advisory Report 2020/025

Bocaccio (Sebastes paucispinis) stock assessment for British Columbia in 2019, including guidance for rebuilding plans

Summary

• A single Bocaccio rockfish (BOR) stock has been identified along the BC coast, based on no observable differences in mean weight, observed length, or growth models between North (5ABCDE) and South (3CD) and among three regional areas (5DE, 5ABC, 3CD). There were also no observable differences in BOR biology by trawl fishing gear type.
• The BOR stock was assessed using a two-fishery, annual two-sex catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated quantities. A composite base case that combined three models using three fixed values for natural mortality (M) to incorporate the uncertainty in this parameter was used to evaluate this stock.
• The median (with 5 and 95 percentiles of the Bayesian results) female spawning biomass at the beginning of 2020 (B₂₀₂₀₎ is estimated to be 0.028 (0.013, 0.058) of unfished female spawning biomass (B0). Also, B₂₀₂₀ is estimated to be 0.096 (0.042, 0.23) of the equilibrium spawning biomass at maximum sustainable yield, B_MSY.
• There is an estimated probability of <0.01 that B₂₀₂₀ > 0.4B_MSY and a probability of 0 that B₂₀₂₀ > 0.8B_MSY (i.e. of being in the Healthy zone). The probability that the exploitation rate in 2019 was below that associated with MSY is >0.99.
• There is evidence from the two most important trawl surveys and from the commercial fishery that a strong BOR cohort was spawned in 2016. This stock assessment estimates that this cohort is 44 times (5–95% range: 30–58) the average recruitment (1935-2019) estimated over the 85 year reconstruction period.
• Advice to management is presented in the form of decision tables using the provisional reference points from the DFO Decision Making Framework Incorporating the Precautionary Approach (DFO 2009). The decision tables provide ten-year projections across a range of constant catches up to 600 tonnes/year.
• The strong 2016 year class is projected to rebuild this stock above the limit reference point (LRP) (0.4B_MSY) with a 0.95 probability by 2023 at catch levels up to 600 tonnes/year. Catch levels above 600 tonnes/year were not evaluated. It is projected to rebuild this stock above the Upper Stock Reference (USR) (0.8B_MSY) with at least a 0.68 probability by 2023 over the same range of catch levels. Decision tables for stock rebuilding out to three generations (60 years) are presented in the Research Document.
• The size of the 2016 year class was a major source of uncertainty discussed during the review, this uncertainty was addressed with projections from the lowest 5th percentile of recruitment estimates. These projections extended the period to rebuild above the (USR) by 2 years.
• 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 0.2 and 0.4 of B₀ is also presented as alternative options in the Research Document.
• It is recommended that a stock status update be prepared biennially, with a full re-assessment occurring after 2025 or longer. Intermediate progress on rebuilding can be tracked by the two primary trawl surveys which sample this species as well as by the commercial trawl fishery.

This Science Advisory Report is from the December 17-18, 2019 regional peer review on the Bocaccio (Sebastes paucispinis) stock assessment for British Columbia in 2019, including guidance for rebuilding plans. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2020/025 (PDF, 760 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.