Yellowmouth rockfish stock assessment 2021

The Yellowmouth Rockfish (YMR) stock assessment evaluates a British Columbia (BC) coastwide population harvested by a single fishery dominated by bottom trawl. Midwater trawl catches (16% by weight over the period 1996 to 2020) of YMR were combined with bottom trawl for the purposes of this stock assessment. YMR catches by capture methods other than trawl were negligible, averaging less than 1% over the same period. Analyses of biology and distribution did not support separate regional stocks for YMR. The YMR stock was assessed using an annual two-sex catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated and derived parameters. The model framework adopted was National Oceanic and Atmospheric Administration’s (NOAA) Stock Synthesis 3, a change from the platform used for the 2011 YMR stock assessment. A composite base case, consisting of five models covering a plausible range of fixed values for natural mortality (M), was used to evaluate stock status because M could not be reliably estimated using the model platform. This stock assessment was primarily informed by the catch per unit effort (CPUE) abundance series and the commercial fishery age frequencies. The YMR abundance indices from the fishery independent surveys had too much relative error to reliably monitor abundance while the associated survey age frequency data showed inadequate continuity for use in estimating year class strength. The median (with 5th and 95th percentiles) female spawning biomass at the beginning of 2022 (B2022) was estimated to be 0.69 (0.44, 1.08) of the equilibrium unfished female spawning biomass (B0). Also, B2022 was estimated to be 2.39 (1.54, 3.73) times the equilibrium spawning biomass at maximum sustainable yield, BMSY. There was an estimated probability of 1 that B2022 > 0.4BMSY and a probability of 1 that B2022 > 0.8BMSY (i.e., of being in the Healthy zone). The probability that the exploitation rate in 2021 was below that associated with MSY was 0.95 for the commercial fishery. Advice to managers was presented in the form of decision tables using the provisional reference points from Fisheries and Oceans Canada’s (DFO) Decision Making Framework Incorporating the Precautionary Approach (DFO 2009). The decision tables provided ten year projections across a range of constant catches up to 3000 tonnes/year. The YMR stock was projected to remain above the limit reference point (LRP) (0.4BMSY) and USR (0.8BMSY) with a probability of >0.99 over the next 10 years at current levels of catch (1000-1250 t/y). Catches >1500 t/y were predicted to exceed the harvest rate limit (uMSY) in 10 years with probability >50%. 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 was also presented as alternative options. It is recommended that a full re-assessment occurs in no more than 10 years, subject to the availability of new information. During intervening years, the trend in abundance can be tracked by commercial fishery CPUE and, less reliably (because of the high relative error), by the fishery independent surveys used in this stock assessment.

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