At-Vessel And Postrelease Mortality Rates Of Bluefin Tuna (Thunnus Thynnus) Associated With Pelagic Longline Gear In The Northern Gulf Of Mexico

Bluefin tuna (Thunnus thynnus) of the western Atlantic Ocean are often incidentally caught in the pelagic longline fishery that targets swordfish (Xiphias gladius) and yellowfin tuna (Thunnus albacares) in the Gulf of Mexico. Data on at-vessel and postrelease mortality are lacking. Using the database of the NOAA Southeast Fisheries Science Center's Pelagic Observer Program, we estimated the mortality rate occurring at-vessel to be 54% (95% confidence interval [CI]: 4662%) when the currently mandated weak circle hook (with a reduced diameter <= 3.65 mm) was used. To estimate rates of postrelease mortality, we deployed 41 pop-up satellite archival tags (PSATs) on bluefin tuna captured in the pelagic longline fishery operating in the northern Gulf of Mexico from May 2010 through April 2015. Data from the PSATs indicate that 29 fish survived for at least 30 d and that 4 fish died within 12 d of tagging. Six PSATs detached prior to the programed release date, and 2 PSATs did not report. We estimate a postrelease mortality rate between 12% and 29%. Combining the postrelease mortality estimate with the at-vessel mortality rate, we estimate a total mortality rate of 59% (95% CI: 47-71%) associated with capture and subsequent release of bluefin tuna in this fishery according to its current fishing practices.