Science Advisory Report  2011/025

Management procedures for the multi-gear sablefish (Anoplopoma fimbria) fishery in British Columbia, Canada

Summary

• Fishery reference points are based on a target spawning biomass at maximum sustained yield, B_MSY, with limit and upper stock reference points at 0.4B_MSY and 0.8B_MSY, respectively;
• Quantitative conservation objectives relate to (1) maintaining the spawning biomass above the limit reference point of 0.4B_MSY in 95% of years projected over two sablefish generations (~36 years), and (2) implementing an acceptable probability of stock decline over 10 years that is scaled from 0.5 at the target biomass to 0.05 at the limit reference point;
• A multi-gear, age-structured, catch-at-age model is fitted to historical data to create stock scenarios that captures uncertainty in natural mortality, growth, and future recruitment variability;
• Stock reconstructions suggest that stock status is currently below B_MSY for all scenarios, with the stock currently positioned in the mid-Cautious to low-Healthy zones;
• A closed-loop feedback simulation approach is used to evaluate the relative performance of candidate management procedures that are distinguished by the choice of survey data, assessment model assumptions, harvest control rule specifications, and future regulations related to at-sea release of sub-legal sablefish;
• Candidate management procedures were robust to the uncertainties considered as indicated by a consistently low probability (p < 5%) of breaching the limit reference point over two sablefish generations (~36 years) regardless of the management procedure or stock scenario;
• Expectations for stock growth toward the target reference point over two sablefish generations range from B_MSY or greater to levels near, but not above B_MSY under the more pessimistic scenarios;
• Performance of management procedures based on the stratified random trap survey alone suggested the legacy standardized trap survey could be discontinued without creating a conservation concern, and could also achieve reduced catch variability relative to the use of both surveys;
• Increases in expected conservation and catch performance due to adopting an avoidance option for sub-legal sablefish, or a full retention option, were small relative to the performance attained by the existing size limit tactic, but these effects are likely underestimated due to suspected violations of assumptions related to trawl gear selectivity.

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Advisory Meeting of January 17, 2011 on Management Procedures for the Multi-Gear Sablefish (Anoplopoma Fimbria) Fishery in British Columbia.  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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