Science Advisory Report  2011/056

Recovery Potential Assessment for Western Atlantic Bluefin Tuna (Thunnus thynnus) in Canadian Waters

Summary

• Atlantic bluefin tuna migrate seasonally to Canadian waters between July and December with occurrences on the Scotian Shelf, in the Gulf of St. Lawrence, in the Bay of Fundy, and off Newfoundland with considerable variation from one year to the next as a result of interactions between biological factors and environmental variations.
• Atlantic bluefin tuna migration and aggregation are related to oceanographic fronts and to the distribution of their prey.
• Spawning stock biomass (SSB) shows an initial steep and steady decline from 1970 to the mid-1980s and relative stability since then; with indications of a possible slight increase in recent years.
• Under the International Commission for the Conservation of Atlantic Tunas (ICCAT) low recruitment scenario, western Atlantic bluefin tuna is not overfished; under the ICCAT high recruitment scenario western Atlantic bluefin tuna is overfished.
• Fishery catch per unit of effort (CPUE) information indicates that local abundance of Atlantic bluefin tuna off southwestern Nova Scotia and in the southern Gulf of St. Lawrence is high in recent years.
• The proposed recovery target for abundance is to increase spawning stock biomass compared to 2012. ICCAT projections suggest that the 2025 SSB would be equal to or larger than the 2012 SSB for total allowable catches (TACs) of 2,250 metric tonnes (mt) or less.
• The proposed distribution target for recovery is to maintain habitat conditions allowing for a broad distribution in Canadian waters.
• The National Marine Fisheries Service (NMFS) of the USA concluded that there is a low probability of extinction at the TAC agreed for 2011 and 2012 (1,750 mt).
• Fishing is the only documented source of human induced mortality. Other potential sources are anthropogenic noise and oil and gas exploration and exploitation.
• Potential threats to habitat include overfishing of prey species, global climate change, and anthropogenic noise.
• Feasible mitigation measures to minimize the threat posed from fishing could include a reduction or elimination of landings of Atlantic bluefin tuna in directed fisheries or as a bycatch in other fisheries, and measures to increase the post-release survival of any Atlantic bluefin tuna released.
• Given that the proposed recovery target is an increase in SSB compared to 2012, maximum allowable harm was agreed to be the maximum removals by the fishery that would still result in the SSB in 2025 being greater than the SSB in 2012.

This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of July 13-15, 2011, on Recovery Potential Assessment (RPA) for western Atlantic bluefin tuna in Canadian waters. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

Complete document (PDF, 330 KB)

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