Post-capture survival of Atlantic wolffish (Anarhichas lupus) captured by bottom otter trawl: Can live release programs contribute to the recovery of species at risk?

Abstract

In 2003, the Atlantic wolffish (Anarhichas lupus), spotted wolffish (A. minor), and northern wolffish (A. denticulatus) were placed on Schedule 1 of Canada's Species at Risk Act which afforded them protection against harm. Consequently, it is mandatory to release both northern and spotted wolffish and it has been recommended that live-release protocols also apply to Atlantic wolffish. Catches in trawls comprise a significant threat to recovery of all three wolffish species and the Grand Bank yellowtail flounder (Limanda ferruginea) otter trawl fishery overlaps the most persistent high concentrations of Atlantic wolffish in the western North Atlantic. As a result, the trawl fishery initiated a voluntary live-release program. The current study investigated the post-capture survival of Atlantic wolffish captured incidentally in the Grand Bank yellowtail flounder otter trawl fishery. Short-term survival was monitored for wolffish placed in holding tanks onboard commercial vessels as well as wolffish returned to the ocean floor in cages. High (92–100%) post-capture survival was demonstrated in Atlantic wolffish following net entrainment in commercial tows up to 2.5h, haul back through a thermocline (range, 5.8°C), and exposure to 5–13°C air temperatures for up to 2h. High post-capture survival and similarities among all three species of wolffish with regard to morphology, physiology, post-capture activity levels, and tag returns in previous studies suggest live-release programs will help to rebuild populations of all three wolffish species. From a conservation perspective, release of wolffish can only be effective if it does not interfere with reproduction. Uncertainties with regard to the reproductive success of egg guarding male wolffish when returned to the ocean are discussed.