Effects of 17/0 circle hooks and bait on sea turtles bycatch in a Southern Atlantic swordfish longline fishery

The incidental catch of marine turtles is a major problem in commercial pelagic longline fisheries. The present paper reports marine turtle bycatch composition and rates from a Portuguese commercial longline fishery targeting swordfish in the South Atlantic, and investigates the effects of changes in hook style and bait type. In total, 310 longline sets were carried out between 2008 and 2012. Three different hook styles were tested, traditional J hook (9/0) and two 17/0 circle hooks (a non-offset and a 10o offset), but only one bait type was used in each set (Scomber spp. or Illex spp.). Two species of sea turtles were caught, the leatherback Dermochelys coriacea, and the loggerhead Caretta caretta, the latter comprising the majority of the catches. The highest mean bycatch per unit of effort values for both species combined (1.693/1000 hooks) and for the individual species (1.505/1000 hooks for loggerheads) occurred with J-style hooks baited with squid. Changing from J-style to one of the circle hooks was only significant when using squid bait (with the odds-ratios decreasing between 54% and 63%). Hooking location was species-specific, with most loggerheads hooked by the mouth, while leatherbacks were mostly hooked externally by the flippers. Overall, 65% of all sea turtles were released alive (85% for leatherbacks compared with 63% for loggerheads). Significant reduction of sea turtle accidental catches on the swordfish longline fisheries can be achieved by changing the J hooks to circle hooks, especially if baited with mackerel. However, such gain is species-specific and area dependent. Copyright (c) 2013 John Wiley & Sons, Ltd.