Framework review for the stock assessment of the Offshore Whelk (Buccinum undatum) in the 4Vs and 4W exploratory fishery

Abstract

Exploration for Offshore Whelk in Nova Scotia began in 2004 and exploratory licences were issued to Louisbourg Seafoods Ltd. in 2010 for 4Vs and 4W North Atlantic Fisheries Organization (NAFO) Divisions and to Premium Seafoods Ltd. for 4W in 2012. At the request of Fisheries and Oceans Canada (DFO) Maritimes Region Resource Management, a monitoring framework was developed for the exploratory Offshore Whelk fishery in 2020 to provide advice on future monitoring and research. In 2021–22, Science advice was requested for the completion of a stock assessment and the development of indicators and reference points to determine stock status of Offshore Whelk. Fishery dependent data from monitoring documents and industry-led detailed sampling were analysed to evaluate fishery trends, spatial distribution of the fishery, growth, maturity, prevalence of parasitism, and natural mortality. Based on these data a number of indicators were explored for monitoring the fishery using catch and length-based methods. Although several methods have been presented, catch-per-unit-effort (CPUE) was proposed as a proxy for biomass. Candidate limit reference points (LRPs) were estimated for all regularly fished areas (4W Middle Bank, 4Vs Area 1 and Area 2) based on a proxy for the unexploited biomass (B0), the maximum annual mean CPUE (kg/trap). Candidate LRPs were defined as 20% and 30% of the B0 proxy for all areas, although based on the risk of local depletion of Whelk, 30% was determined to be more appropriate as an LRP. Length-based indicators were recommended to use in addition to the catch-based indicator to monitor the number of juveniles in the catch but would require additional annual sampling of the length frequency of the catch. This Research Document was presented at the May 17–18, 2022, regional peer review meeting on Framework Review for Stock Assessment of Offshore Whelk in 4Vs and 4W.