Trials with Different Hooks and Bait Types in the Configuration of the Surface Longline gear used by the Spanish Swordfish (Xiphias Gladius) Fishery in the Pacific Ocean

Three hook types and two bait types were tested on two surface longline vessels targeting swordfish (Xiphias gladius) for 240 days at sea in areas of the SE Pacific Ocean. The use of circle hooks instead of conventional ones led to losses in swordfish catch rates of -23.1%, while moderate increases of up to +5.5% were found for the shortfin mako (Isurus oxyrinchus) and billfish catches rose substantially +55.5%. Few changes in catch rates were observed in the sea turtle Caretta caretta with the use of the circle hooks being tested. The use of squid as bait instead of mackerel would generally cause a decrease in the catch rates of most fish species with the exception of billfish and the sea turtle Caretta caretta, which exhibited values of up to +31.7% and +8.2%, respectively. Mean standardized CPUE data suggest that the use of the alternative hook-bait combinations tested would cause a drop in the catch rates of the target species ranging from -15.8% to -36.4%, but, in general, an increase in the catch rates of billfish up to +86.8%, as compared to the use of the traditional combination of reference. Owing to the scarce interaction on sea turtles, it was not possible to draw robust conclusions for these species. However the results do suggest that the use of squid as bait tends to increase the catch rates of sea turtles as opposed to the use of mackerel. There was no interaction with sea birds during the whole experiment.