Research Document - 2012/095
Stock assessment and recovery potential assessment for Yellowmouth Rockfish (Sebastes reedi) along the Pacific coast of Canada
By A.M. Edwards, R. Haigh, and P.J. Starr
Yellowmouth Rockfish along the Pacific coast of Canada has been designated as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), with commercial fishing being the primary threat. The purpose of this document is to be the Recovery Potential Assessment that formulates the scientific information concerning the current status of the species, threats to its survival and recovery, and the feasibility of its recovery. This document also serves as a stock assessment for the provision of advice to fisheries managers.
We used an annual catch-at-age model tuned to five fishery-independent survey series, annual estimates of commercial catch since 1940, six years of age composition data from two survey series, and 18 years of age composition data from the commercial fishery. The model started from an equilibrium state in 1940, and the survey data cover the period 1967 to 2010 (although not all years are represented). The two-sex model was implemented in a Bayesian framework (using the Markov Chain Monte Carlo procedure) under two main scenarios which were considered equally plausible, in which natural mortality was either estimated or fixed (termed run ‘Estimate M’ and run ‘Fix M’, respectively).
Both model scenarios imply a slow-growing, low productivity stock that has undergone periods of high recruitment in the early 1960s and the early 1980s. For run ‘Estimate M’, the estimate of B2011/B0, where B2011 is the spawning biomass (mature females only) at the beginning of 2011 and B0 is the unfished equilibrium spawning biomass, is 0.614 (0.431-0.829), denoting median and 5th and 95th quantiles of the Bayesian posterior distribution. For run ‘Fix M’, the estimate of B2011/B0 is 0.409 (0.289-0.547). Denoting the estimated spawning biomass at maximum sustainable yield as BMSY, the estimate of BMSY/B0 is 0.233 (0.149-0.314) for run ‘Estimate M’, and 0.216 (0.147-0.298) for run ‘Fix M’.
The exploitation rate (ratio of total commercial catch to vulnerable biomass) for 2010 is estimated to be 0.020 (0.010-0.036) for run ‘Estimate M’ and 0.038 (0.026-0.059) for run ‘Fix M’, compared to respective historic highs of 0.090 (0.059-0.123) and 0.130 (0.110-0.154) estimated for 1966 during intense fishing by foreign fleets.
Current and projected probabilities of the status of the population are given with respect to (i) the DFO Sustainable Fisheries Framework provisional reference points of 0.4BMSY and 0.8BMSY, (ii) reference points of 0.2B0 and 0.4B0, and (iii) reference criteria given by COSEWIC assessment indicators A1 and A2.
Projections are presented for up to three generations (90 years) for both model runs. For each level of constant catch, these give probabilities of future population status with respect to the above reference points and reference criteria, as well as estimates of the time taken to attain them (with different levels of confidence) assuming random recruitment.
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