Science Advisory Report 2020/001

Assessment of Spiny Dogfish in the Northwest Atlantic

Summary

• In Canadian waters, discards from otter trawl, gillnet and longline fisheries for groundfish are the primary source of fishing mortality of Northwest Atlantic Spiny Dogfish. Total discard estimates have been declining since the 1990s. In 2017, reported landings were 53 mt and dead discards were estimated as 606 mt.
• Since 2012, US landings of Spiny Dogfish have increased to approximately 10,000 mt annually, with dead discard estimates ranging from 3,200-5,800 mt per year.
• Two Research Vessel (RV) surveys provide estimates of Spiny Dogfish abundance. The National Marine Fisheries Service (NMFS) Spring survey in US waters serves as the primary index of population abundance. The Fisheries and Oceans Canada (DFO) Summer survey is thought to primarily index changes in distribution as the population moves northward in the summer months.
• The majority of survey catches in Canada are adult males, with lower but similar numbers of female and male juveniles. Female adults form the smallest component of the survey catches throughout the time series.
• The assessment model developed for the Northwest Atlantic Spiny Dogfish Framework Part 2: Review of Modelling Approaches and Assessment (June 27-28, 2018) was not accepted for a number of reasons, including: the predicted abundance trajectory was very sensitive to survey catchability estimates on upper bounds, residual patterns on maturation and pupping rate estimates, and a retrospective pattern for adult female abundance estimates in recent years.
• The US regularly undertakes assessments of the Northwest Atlantic Spiny Dogfish population to provide advice for their directed fishery.  Participants at the December 2018 Canadian stock assessment meeting felt that relying on the US update to assess status and provide advice had several advantages over developing a new empirical approach based on US data. There was agreement that, until a joint or Canadian modeled approach could be developed, relying on the US assessment would be more informative than reviewing the survey index of adult female abundance without the context of a population model. 
• Adopting the US reference points was considered to be appropriate under the Canadian Precautionary Approach Framework. The target Spawning Stock Biomass (SSBtarget) was used as the Upper Stock Reference (USR) given that SSBtarget represents a proxy for adult female biomass at Maximum Sustainable Yield (MSY) under the US assessment model. The USR becomes 159,288 mt. The Lower Reference Point (LRP) would be the threshold Spawning Stock Biomass (SSBthreshold) value, calculated as 50% of the USR, with a value of 79,644 mt. This would put the biomass estimates in the Cautious Zone since 2015.
• The US model that was used as the basis for advice included 2017 survey data but did not apply the Kalman filter when calculating swept-area biomass. Results suggest that biomass of mature females has been declining since 2012 and is estimated as 106,753 mt in 2018.
• The US assessment update concluded that the stock is not overfished and that overfishing is not occurring. The Allowable Biological Catch (acceptable level of removals) for 2017 was 23,045 mt and actual removals from all sources (other than Canadian discards) were estimated at 14,326 mt. For comparison, estimated Canadian removals (including discards) in 2017 were 659 mt.
• The 2018/19 Canadian total allowable catch (TAC; 4000 mt for directed fishery, 4000 mt for retained bycatch) is very unlikely to be reached in 2019/2020. There is currently no directed fishery, and any Canadian landings are from bycatch in other fisheries.
• As the stock is in the Cautious Zone, a significant increase in removals (landings or discards) beyond levels seen in the last 10 years could warrant a reevaluation of fishery impacts. However, at this time, removals from bycatch in Canadian waters are not expected to be at a level that would hinder stock rebuilding, particularly given the US assessment that total stock removals are at an acceptable level.
• While current removals in Canadian waters are very low, the determination that the stock is in the Cautious Zone and the decline in recent adult female biomass estimates warrants consideration of reducing the TAC to a more precautionary level.
• Full assessment of the Northwest Spiny Dogfish stock requires information from both the Canadian and US surveys and fisheries. Participants agreed that a modelled approach to determining stock status would be valuable, ideally jointly with US colleagues. It was also noted that the Mid Atlantic Fishery Management Council is planning a review of their data inputs and assessment approach (a "Benchmark") in 2022.
• In the interim, science advice to management on Spiny Dogfish will be provided by reviewing the US stock assessment along with recent Canadian landings, as well as information about Spiny Dogfish from the DFO Summer survey.

This Science Advisory Report is from the December 11, 2018, and February 13, 2019, Assessment of Spiny Dogfish in the Northwest Atlantic. 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 2020/001 (PDF, 759 KB)