A Preliminary Comparison of the Relative Mortality and Hooking Efficiency of Circle and Straight Shank (“J”) Hooks Used in the Pelagic Longline Industry
B. Falterman and J. E. Graves
Abstract.—The fishing characteristics of circle hooks and straight shank or “J” hooks were investigated in the pelagic longline fishery during two successive trips. In one trip, circle hooks and J-hooks of comparable size were alternated along the length of the longline on six sets of approximately 400 live-baited hooks each, allowing a preliminary comparison of catch per unit effort (CPUE), hooking location, and mortality between the two hook types. On a previous trip, records of hooking location and mortality were obtained for J-hooks on nine additional longline sets. Yellowfin tuna Thunnus albacares accounted for 60% of the catch; the remainder was composed of 15 other species, none of which was represented by more than eight individuals. There was higher CPUE for all species combined, using circle hooks (5.05 fish/100 hooks) as compared with using “J” hooks (2.28 fish/100 hooks). Similar results were observed with the catch of the target species (yellowfin tuna), for which CPUE was approximately 2.5 times higher with circle hooks (3.33 tuna/100 hooks) as compared with J-hooks. Circle hooks also resulted in a lower mortality for all species (31% versus 42%) and for the target species (21% versus 39%). For all species, 95% of the fish taken on circle hooks were hooked in the jaw. Hooking location varied by species, but for all species combined, circle hooks consistently had a higher frequency of jaw hooking and a lower frequency of gut hooking than J-hooks. These preliminary results suggest that use of circle hooks in the pelagic longline fishery targeting yellowfin tuna may not only increase CPUE and survival of this species but also improve the survival of incidental catch and bycatch.