Science Advisory Report 2020/047
Rougheye/Blackspotted Rockfish (Sebastes aleutianus/melanostictus) Stock Assessment for British Columbia in 2020
Summary
- Two spatial stocks of the Rougheye/Blackspotted (REBS) Rockfish complex have been identified along the BC coast, based loosely on the spatial distribution of genetically confirmed specimens from surveys: the northern stock in 5DE is predominantly comprised of Blackspotted Rockfish or REBS north (previously Rougheye Rockfish Type I). The southern stock in 3CD5AB is largely comprised of Rougheye Rockfish (Type II) or REBS south.
- The REBS stocks were assessed using a two-fishery, annual two-sex catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated quantities. For each stock, a composite base case that combined nine models for REBS north and six for REBS south, using three fixed values for natural mortality (M), to incorporate the uncertainty in this parameter, and three values of CPUE process error, were used to evaluate stock status.
- For REBS north, the median (with 5th and 95th percentiles) female spawning biomass at the beginning of 2021 (B2021) is estimated to be 0.595 (0.405, 0.840) of unfished female spawning biomass (B0). Also, B2021 is estimated to be 2.21 (1.50, 3.15) times the equilibrium spawning biomass at maximum sustainable yield, BMSY.
- For REBS south, the median (with 5th and 95th percentiles) female spawning biomass at the beginning of 2021 (B2021) is estimated to be 0.286 (0.155, 0.680) of unfished female spawning biomass (B0). Also, B2021 is estimated to be 1.07 (0.582, 2.61) times the equilibrium spawning biomass at maximum sustainable yield, BMSY.
- For REBS north, there is an estimated probability of 1 that B2021 > 0.4BMSY and a probability of 1 that B2021 > 0.8BMSY (i.e., of being in the Healthy zone). The probability that the exploitation rate in 2020 was below that associated with MSY is 1 for both groundfish trawl and commercial non-trawl (Other) fisheries.
- For REBS south, there is an estimated probability of >0.99 that B2021 > 0.4BMSY and a probability of 0.74 that B2021 > 0.8BMSY (i.e., of being in the Healthy zone). The probability that the exploitation rate in 2020 was below that associated with MSY is 0.42 for the groundfish trawl fishery and 0.64 for the combined commercial non-trawl (Other) fisheries.
- 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 1200 tonnes/year for REBS north and up to 600 t/y for REBS south.
- It is projected that the REBS north stock will remain above the LRP (0.4BMSY) and USR (0.8BMSY) with a probability of ≥0.99 over the next 10 years at current levels of catch (600 t/y). For REBS south , it is projected that the stock will remain above the LRP with a probability of 0.85 and above the USR with a probability of 0.53 over the next 10 years at current levels of catch (300 t/y). For the REBS south stock, this catch strategy is not sustainable over the long-term (1.5 generations or 75 years).
- The appropriateness of the MSY-based reference points for long-lived, low productivity species is uncertain; consequently, advice 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 full re-assessment occur in 10 years or less, subject to the availability of new information. During intervening years, the trend in abundance can be tracked by surveys which sample this species, as well as by commercial fishery CPUE.
This Science Advisory Report is from the May 26-27, 2020 regional peer review on Blackspotted / Rougheye Rockfish (Type I and Type II) stock assessment for British Columbia in 2020. 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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