Analyses of the Hawaiian pelagic longline fishery were conducted to determine what factors, including hook type (J or circle) and location (sea mount v open ocean), have impacted the catch of both target and bycatch species. Standardized catch rates for all tuna species as well as for blue and oceanic whitetip sharks were significantly higher when the wider circle hooks were used. However, shortbill spearfish and striped marlin catch were significantly lower when circle hooks were used. No differences in catch rates between the two hook types were seen for bigeye thresher sharks or swordfish. The average swordfish lengths were significantly larger when circle hooks were used, while average lengths for bigeye and skipjack tunas were significantly smaller. There was no difference in the average length between the two hooks types for yellowfin or albacore tunas, spearfish or marlins. In addition, the change from J hooks to circle was likely a factor in decling sea turtle bycatch rates.
Hawaii longline tuna fishery temporal trends in standardized catch rates and length distributions and effects on pelagic seamount ecosystems
Aquatic Conservation: Marine and Freshwater Ecosystems