Workshop Convened to Review Sea Turtle Post-release Mortality

Incidental capture in longline fisheries is a recognized threat to sea turtles in all major ocean basins. The magnitude of the threat is not well understood due, in part, to uncertainty about the rates of turtles' post-interaction mortality—the likelihood a turtle will die as a result of the interaction after being released alive but injured. In assessing impacts of longline fisheries on sea turtles, NMFS uses established criteria to determine what level of post-release mortality will be assumed. In November 2011, PIFSC convened a webinar to review current post-release mortality criteria and determine whether new scientific information exists to recommend modifications.

Post-interaction mortality can be estimated through field studies, but such studies are difficult. Conditions that may influence outcomes of interactions are highly variable, tracking turtles released at sea is difficult, costs are high, and detection of mortality using remote sensing technology is problematic. Recent research has aimed to overcome these challenges and provide estimates of post release survival with higher levels of confidence. Despite extensive international research using a variety of methods, our ability to definitively determine a turtle's likelihood of survival based on location of hooking, amount of gear remaining attached at release, and the turtle's species and size, remains limited, and research findings are highly variable.

Initial criteria for estimating post-release survival were established by NMFS in 2001. In January 2004, the NMFS Office of Protected Species convened a workshop and expert panel to review the criteria and revise them (reported in Ryder et al., 2006, NOAA Technical Memorandum NMFS-OPR-29). Since 2004, additional scientific papers and anecdotal information on the subject have become available. Accordingly, the primary goals of the November webinar were to: 1) critique methods and findings of recent research on sea turtle post-release longline mortality; 2) confirm current understanding of best-practice handling and release methods to maximize turtles' probability of survival; 3) compare the relative certainty of results from alternative methods to measure or estimate post-release survival; and 4) identify information gaps and future research priorities to improve the accuracy of estimates. A workshop report was prepared. The report conveys comments offered by a variety of participants; however, individual comments do not necessarily reflect group consensus. Several key findings were identified: