Yellowtail Rockfish (Sebastes flavidus) stock assessment for British Columbia in 2024

Abstract

Status The probability that the female spawning stock biomass at the beginning of 2025 (B₂₀₂₅) was greater than the limit reference point (LRP, 0.4_msy; B_msy is the equilibrium female spawning biomass at maximum sustainable yield) was >99%. The probability that B₂₀₂₅ was greater than the upper stock reference (USR, 0.8B_msy) was >99%, placing the coastwide stock in the Healthy zone. At the beginning of 2025, the stock status relative to BMSY (B₂₀₂₅/B_msy) was 2.31. The 90% credibility interval for this estimate was 1.25 to 4.59. At the beginning of 2025, the ratio of biomass relative to unfished female spawning biomass (B₂₀₂₅/B₀) was estimated to be 0.56. The 90% credibility interval for this estimate was 0.33 to 0.91. Fourteen sensitivity analyses that tested alternative assessment assumptions all showed the coastwide stock to be in the Healthy zone. The probability that the exploitation rate in 2024 (u₂₀₂₄) was below the removal reference (RR) exploitation rate at maximum sustainable yield (u_msy) was 94%. Trends Annual median stock status (B_t /B_msy) trended down from 4.0 times B_msy in 1935 to 2.0 times B_msy in 1983 and then fluctuated between values of 1.7 and 2.8 times B_msy until 2025. Since 2015, there has been an increasing trend in stock status. At no time did the 90% credibility envelope breach the USR. Since 2005, recruitment remained relatively stable compared to other Sebastes species, with more frequent strong recruitment years compared to longer lived species in the Sebastes genus. Exploitation rate has remained stable since 2000 with total annual catches between 3,500 and 5,000 t/y. Ecosystem and Climate Change Considerations Six large-scale environmental index series and one local upwelling series were used as independent variables to predict recruitment. Overall, these environmental series had low predictive power because of the considerable associated uncertainty and the relatively small amount of contrast across the range of available observations. Further work is required before these indices are capable of providing predictive power for recruitment in future stock assessments. Stock Advice Advice to managers was presented in the form of decision tables with ten-year projections using constant-catch policies up to 7,000 t/year. The stock was projected to remain above the LRP and USR with a probability of 99% and 93%, respectively, over the next 10 years at current levels of catch (4,000 t/year). The stock was projected to remain below the RR with a probability of >50% over the next 10 years at catches of 5,500 t/y or less.