Hawaii longline tuna fishery temporal trends in standardized catch rates and length distributions and effects on pelagic seamount ecosystems

Analyses of the Hawaiian (U.S.) 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 (Prionace glauca) and oceanic whitetip sharks (Carcharhinus longimanus) were significantly higher when the wider circle hooks were used. However, shortbill spearfish (Tetrapturus angustirostris) and striped marlin (Kajikia audax) 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 (Alopias superciliosus) or swordfish (Xiphias gladius).  The average swordfish lengths were significantly larger when circle hooks were used, while average lengths for bigeye (Thunnus obesus) and skipjack tunas (Katsuwonus pelamis) were significantly smaller.  There was no difference in the average length between the two hooks types for yellowfin (Thunnus albacares) or albacore tunas (Thunnus alalunga), spearfish or marlins. In addition, the change from J hooks to circle was likely a factor in declining sea turtle bycatch rates.