Post-Release Mortality of School-Size Atlantic Bluefin Tuna (Thunnus thynnus) in the U.S Recreational Troll Fishery
Master of Science (M.Sc.)
Virginia Institute of Marine Science
Atlantic bluefin tuna Thunnus thynnus (ABFT) support commercial and recreational fisheries throughout the North Atlantic Ocean. Due to heavy fishing pressure over the course of several decades, the eastern and western stocks of ABFT were overfished and the current biomass of the western stock is estimated to be approximately 19% of the biomass necessary for maximum sustainable yield. Despite a variety of management measures, including the implementation of minimum sizes and reductions of the total allowable catch (TAC) and country-specific quotas, little change was observed in the status of the western stock. The U.S. commercial and recreational ABFT fisheries are managed by the National Marine Fisheries Service (NMFS), which distributes the U.S. quota among domestic fisheries by gear type. The U.S. recreational fishery, which has historically targeted small or “school-size” (69-119cm) ABFT, is managed by open seasons, a minimum size, and bag limits (the number of ABFT allowed to be landed per vessel per day). Over the past 20 years, bag limits have been severely reduced due to decreased annual quotas, increasing the number of ABFT released each year, mostly within the school-size category. It is important, for the management of ABFT, to account for all sources of fishing mortality and the large number of releases in the recreational fishery each year could be a significant source of mortality. However, there is very little information available to assess post-release mortality of school-size ABFT in the U.S. recreational fishery. In this study, twenty pop-up satellite archival tags (PSATs) were deployed to estimate the post-release mortality of school-size ABFT captured under normal fishing conditions in the recreational fishery. PSATs recorded pressure (depth), temperature, and light data and were deployed on school-size ABFT caught using trolling methods. These tags were programmed to record data approximately every five minutes for a 31-day deployment. Nineteen tags (95%) reported to the satellites of the ARGOS system and approximately 85% (range: 34-100%) of all archived data were transmitted from each tag. Depth and temperature profiles were used to infer the survival of all 19 individuals whose tags reported (mortality=0% 95% CI=0%, 10%). Data from these tags were also used to investigate the short-term habitat utilization of school-size ABFT. During June to October, these fish spent the majority of their time in the upper 40m of the water column and at temperatures between 18 and 24oC.Individuals were more likely to make vertical excursions to depths exceeding 30m during the day than at night.
© The Author
Marcek, Benjamin Jon, "Post-Release Mortality of School-Size Atlantic Bluefin Tuna (Thunnus thynnus) in the U.S Recreational Troll Fishery" (2013). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539617936.