PIFSC Sea Turtle Longline Research EA June 1, 2009
Summaries of records of turtle bycatch in shallow-set longline fisheries compiled by Beverly and Chapman (2007) document that most sea turtles hauled in alive are released alive. However, turtles that swallow the hook have a higher risk of dying after release. Modified gear, including large diameter circle hooks with fish bait, used on boats with dehooking equipment by a trained crew such as is required in the Hawaii-based longline fishery, substantially reduced sea turtle bycatch and mortality of bycaught turtles (Boggs and Swimmer 2007, Read 2007, Gilman et al. 2007, Figure 3, Figure 4). In addition to substantially decreasing sea turtle bycatch, changing bait from squid to fish also decreased shark bycatch substantially (Boggs and Swimmer 2007, Gilman et al. 2007). More sea turtles were lightly hooked than deeply hooked after the Hawaii- based regulations requiring circle hooks and fish bait were implemented (Gilman and Kobayashi 2007, Figure 5, Figure 6), resulting in an apparent decrease in post-release mortality, although mortality rates are difficult to determine long-term (Ryder et al. 2006, Beverly and Chapman 2007). These general trends were also found in studies conducted in Italy, Brazil, Uruguay, and Indonesia (Boggs and Swimmer 2007).
Figure 5. Severity of hooking of hardbacked sea turtles before and after implementation of sea turtle bycatch regulations in Hawaii longline fishery
Figure 6. Severity of hooking of leatherback sea turtles before and after implementation of sea turtle bycatch regulations in Hawaii longline fishery