Science Advisory Report 2023/006

Development of Biological Reference Points and a Precautionary Approach Framework for the Dungeness Crab (Cancer Magister) Fishery in Crab Management Areas I and J

Summary

• Three methods were used to estimate reference points: an empirical method using biomass at maximum sustainable yield proxies, a stock recruitment-based method, and a simulation model-based method. Determinations of stock status were made for 2019.
• The stock status indicator and reference points were estimated primarily using fishery-independent survey data. Commercial data collected from service providers and logbooks were used to estimate model parameters such as exploitation rates, softshell periods, and sex ratios. A three year running median of female catch per unit effort (CPUE) was used as the indicator in order to account for cyclical fluctuations of the crab population.
• Reference points were expressed in terms of standardized CPUE. Female CPUE was used as the main indicator because it represents the reproductive potential of the stock. Sublegal standardized CPUE was used as a secondary indicator to provide additional information. Decision makers could consider the long- and short-term trends in annual sublegal male crab CPUE, but this indicator will not be used to formally describe stock status.
• Empirical limit reference points were estimated at 0.228 (B_mean) and 0.310 (B_max) standardized female CPUE.
• The stock recruitment limit reference point was estimated at 0.439 standardized female CPUE.
• The simulation limit reference point was estimated at 0.3 standardized female CPUE.
• The stock recruitment relationship is highly uncertain, and simulation reference points rely on many assumptions There are fewer concerns about the performance of the empirically derived reference points.
• The 2019 stock status for Dungeness Crab in Crab Management Areas (CMAs) I and J is in the Cautious zone between the Limit Reference Point (LRP) and the Upper Stock Reference (USR), using the empirical reference points. The work undertaken validates the methodologies for reference point estimation for CMAs I and J.
• The degree to which climate change will affect Dungeness Crab populations in British Columbia is unknown. Productivity may change due to fluctuations in ocean temperature, acidity, and oxygen concentration. Coastwide populations may also be affected by changes in larval transport due to changing ocean circulation.
• The degree of connectivity of subpopulations of Dungeness Crab in British Columbia is currently uncertain. Further analyses and definition of the stock is required before estimating reference points coastwide. There is a high degree of trap competition in CMA I and J. This competition likely decreases the survey CPUE, and may alter trends in survey CPUE through time. This observation should be accounted for in future analysis by including data from other sources (e.g., commercial data).
• The analysis recommends applying the empirically-based methodology for determining reference points for the Dungeness Crab in CMAs I and J using female CPUE. It also recommends using the three year running median of standardized female CPUE as the stock status indicator.

This Science Advisory Report is from the February 28-March 1, and October 26, 2022 regional peer review on the Development of biological reference points and retrospective evaluation of abundance trends in Fraser River Dungeness Crab (Management Areas I and J). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2023/006 (PDF, 497 KB)

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