The effect of circle hooks vs J hooks on the at-haulback survival in the U.S. Atlantic pelagic longline fleet
Observer data from the U.S. pelagic longline fleet was used to analyze the effect of circle and J hooks on the at-haulback survival of swordfish, shortfin mako, blue and white marlin. The probabilities of survival were estimated from odd ratios. Full models included water temperature, soak time, and fish length as continuous covariates. When only the effect of hook type is taken into consideration, circle hooks resulted in a significantly higher probability of survival for all species except for white marlin where the difference was not significant. Temperature, soak time, and fish length were significant depending on the species. When significant, in general these covariates had a negative effect on survival (i.e., higher values resulted in lower survival). The results show that circle hooks, which were adopted as a sea turtle bycatch mitigation measure by the U.S. pelagic longline fleet in both the Pacific and Atlantic oceans, also increase the at-haulback survival of other species and, therefore, it addresses some of the research needs to develop and implement Ecosystem Based Fisheries Management.