Research Document - 2012/002

Bluefin Tuna (Thunnus thynnus) in Atlantic Canadian Waters: Biology, Status, Recovery Potential, and Measures for Mitigation

By J.-J. Maguire and B. Lester

Abstract

In May 2011, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determined that Atlantic bluefin tuna (Thunnus thynnus) in the western Atlantic was Endangered. The reason for the designation is that the current abundance of spawning individuals is the lowest observed and the abundance of spawning fish has declined by 69% over the past 2.7 generations. COSEWIC concluded that the cause of the decline, overfishing, has not ceased and that it is not clearly reversible.  A Recovery Potential Assessment (RPA) was held 13-15 July 2011 at the St. Andrews Biological Station, St. Andrews, NB.  The purpose of the RPA was to provide information and scientific advice required to meet various requirements of the Species at Risk Act (SARA), including public consultations, decisions regarding the listing of western Atlantic bluefin tuna in Canadian waters under the Act, and developing a recovery strategy should the species be legally listed.

In Canadian waters there is no evidence that range has been reduced and the proposed distribution target for recovery is to maintain habitat conditions allowing for a broad distribution in Canadian waters. 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. The proposed recovery target for abundance is to increase spawning stock biomass compared to 2012. The International Commission for the Conservation of Atlantic Tunas (ICCAT) estimated that the 2025 SSB would be equal to or larger than the 2012 SSB for catches of 2,250 mt or less. 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. The only documented human induced mortality to Atlantic bluefin tuna in Canadian waters is fishing; feasible mitigation measures to minimize the threat posed include a reduction or elimination of landings of western 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. 

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