Science Advisory Report 2022/043

Assessment of 4Vs and 4W Offshore Whelk (Buccinum undatum) Stock Status

Summary

• Whelk populations differ in genetic structure and life-history traits over small spatial scales, making it important to consider sub-population structure when developing appropriate management areas to protect from local depletion of Whelk on the Scotian Shelf.
• The primary indicator of stock status is non-standardized catch-per-unit-effort (CPUE, kg/trap), which is used as a proxy for stock biomass.
• Limit Reference Points (LRPs) were established for all regularly fished areas (4W Middle Bank, 4Vs Area 1 and Area 2) and were estimated based on a proportion of B₀ proxy, which is the maximum mean annual CPUE value of the time series.
• In 4Vs Area 1, the mean annual CPUE estimates have declined since the high in 2017 of 17.41 kg/trap but increased again in 2021 to 15.84 kg/trap, just below the B₀ proxy, and remains above the LRP of 5.22 kg/trap.
• In 4Vs Area 2, mean annual CPUE estimates have declined from a maximum value of 16.9 kg/trap in 2018 to 13.25 kg/trap in 2020 and were above the LRP for the entire time series. There was no fishing in Area 2 in 2021.
• For 4W Middle Bank, the CPUE indicator in 2021 is consistent with the recent time series at 4.67 kg/trap and is above the LRP of 2.37 kg/trap.
• Secondary indicators of stock status were used to help identify changes that may occur in the primary indicator, including changes in catch, effort, and annual spatial distribution of catch rates. The use of additional secondary length-based indicators was approved for future monitoring, but these indicators require new data collection of length frequencies of the retained catch, and no data are available yet for reporting.
• In 2021, landings were from 4Vs Area 1 (329 mt), Area 3 (202 mt), and a new fishing area west of the boundaries of Area 1 (160 mt). In 4W, landings have declined from 211 mt in 2018 to 146 mt in 2021 and continue to be concentrated on the southern portion of Middle Bank.
• The detailed samples previously collected from industry included discarded catch, so are not representative of the retained catch and cannot be used to estimate length-based indicators. Therefore, new sampling protocols were developed to monitor the length frequencies of the catch so that this approved method can be applied in the future.
• Detailed sampling will continue to be important for new fishing areas to inform on maturity, growth, parasitism, and sex ratios based on the differences observed at small spatial scales.
• Since Whelk populations are susceptible to local depletion, it is suggested that Total Allowable Catch (TAC) limits be placed on specific fishing areas to encourage exploration outside of current fishing areas, and that indicators continue to be monitored as annual TAC limits increase slowly.

This Science Advisory Report is from the June 14, 2022, regional peer review on the Stock Assessment of Offshore Whelk in 4Vs and 4W. 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 2022/043 (PDF, 539 KB)

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