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Two experiments were conducted to determine 1) if UV illumination reduced green sea turtle (Chelonia mydas) capture rates in large mesh gilllnets and 2) the impact of UV illumination on target catch rates in bottom-set gillnets.  Paired tests were conducted using a control net and an experimental net with UV LEDs placed every 5 m on the floatlines for the sea turtle experiment.  In the target catch experiment, inactive LEDs were also placed on the control net at 5 m spacing.  Sea turtle catch rates were significantly higher in the control nets and there was a 39.7% reduction in mean catch rates with the experimental net.  There was no significant difference in catch rates of target species between the control and experimental nets.

An observer program assessed the impact of the Costa Rican longline fishery on bycatch species from 1999 to 2010. Observers recorded species, sex, reproductive state, and dimensions of all animals captured. They also recorded information about individual longlines, including location, set and haul back times, hook type, hook number, bait used, target species, and total number of hooks. The longline fishery caught a large number of silky sharks (Carcharhinus falciformis), olive ridley turtles (Lepidochelys olivacea), and pelagic stingrays (Pteroplatytrygon violacea). The authors estimate that 699,600 olive ridleys were caught between 1999 and 2010, including 92,300 adult females. The captures correspond with a decline in nesting populations nearby and statistically significant size decreases in mature turtles. They also observed a decline in the average size of silky sharks. Geospatial analysis of the data indicated that there were temporal shifts in mahi-mahi (Coryphaena hippurus) abundance, but fishing efforts did not shift with abundance. The authors suggest marine protected areas and/or time area closure to reduce the bycatch of sea turtles and sharks.  

An analysis of the performance of circle hooks in comparison to J-style and tuna hooks on the hooking rates of target and non-target species, specifically sea turtles, in the artisanal surface longline fisheries of Ecuador, Panama, and Costa Rica was performed. The target fisheries were mahi-mahi and a combination of tunas, billfishes, and sharks (TBS). In the TBS fishery, tuna hooks were compared to 16/0 circle hooks from Ecuador and Panama and 18/0 circle hooks from Costa Rica. For the mahi-mahi fishery, 14/0 and 15/0 circle hooks in Ecuador and 16/0 circle hooks in Costa Rica were compared to traditional J-style hooks. Circle hooks reduced sea turtle hooking rates in most of the comparisons. Hooking rates for target and non-target species were not consistent.

Use-intensity distributions for 135 satellite-tracked adult leatherback turtles (Dermochelys coriacea) were combined with longline fishing effort to estimate predicted bycatch risk over space and time in the Pacific Ocean. For western Pacific nesting populations, the greatest risk was adjacent to primary nesting beaches in the tropical seas of Indo-Pacific islands. For eastern Pacific nesting populations, the greatest risk was in the South Pacific Gyre. Targeted management should be based on these predicted hotspots to reduce leatherback bycatch.  

Experimental studies were conducted over a three year period (August 2008-December 2011) to determine the effects of changing traditional J-hooks baited with squid bait to circle hooks (offset and non offset) with mackerel bait on sea turtle interactions. Studies were carried out aboard pelagic longline vessels targeting swordfish (Xiphias gladius) in the tropical northeast Atlantic Ocean. Overall, sea turtle interactions were reduced when circle, compared to J-hooks, were used. However species specific differences did occur. Leatherback (Dermochelys coriacea) interactions were only reduced when circle hooks with an offset were used. Leatherback interactions can be reduced by 55% in this fishery by switching from J-style to circle hooks. Hardshell turtle interactions (loggerhead Caretta caretta, olive ridley Lepidochelys olivacea, Kemp ridley Lepidochelys kempii) were reduced when both circle hook styles and mackerel bait were used. Interactions with hardshelled turtles can be reduced by 50-55% in this fishery by switching from J-style to circle hooks.  A 55% reduction in hardshell turtle bycatch is expected to occur in this fishery by switching from squid to mackerel bait.

Experimental studies were conducted over a three year period (August 2008-December 2011) to determine the effects of changing traditional J-hooks baited with squid bait to circle hooks (offset and non offset) with mackerel bait on sea turtle interactions. Studies were carried out aboard pelagic longline vessels targeting swordfish (Xiphias gladius) in the tropical northeast Atlantic Ocean. Overall, sea turtle interactions were reduced when circle, compared to J-hooks, were used. However species specific differences did occur. Leatherback (Dermochelys coriacea) interactions were only reduced when circle hooks with an offset were used. Leatherback interactions can be reduced by 55% in this fishery by switching from J-style to circle hooks. Hardshell turtle interactions (loggerhead Caretta caretta, olive ridley Lepidochelys olivacea, Kemp ridley Lepidochelys kempii) were reduced when both circle hook styles and mackerel bait were used. Interactions with hardshelled turtles can be reduced by 50-55% in this fishery by switching from J-style to circle hooks.  A 55% reduction in hardshell turtle bycatch is expected to occur in this fishery by switching from squid to mackerel bait.

18/0 circle hooks when compared with J hooks significantly reduce loggerhead (Caretta caretta) and leatherback (Dermocheles coriacea) sea turtle bycatch in Atlantic longline fisheries for pelagic swordfish (Xiphias gladius). Circle hooks also reduced the rate of hook ingestion by loggerhead sea turtles. The combination of circle hooks and mackerel (Scomber scombrus) bait was the most effective in reducing sea turtle bycatch and had no negative effect on swordfish catch. Loggerhead sea turtle (Caretta caretta) bycatch in the Atlantic longline fishery increased with an increase in total soak time. Soak time was insignificant for swordfish but it was significant for bigeye tuna (Thunnus obesus).

The effect of circle hooks and J-style hooks on the catch composition, catch rates, hooking location and status of release of target and bycatch species were compared on pelagic longline vessels.  There were significant differences in catch rates between the two hook types for bigeye tuna, which had higher catch rates on circle hooks and sailfish (Istiophorus spp.), pelagic stingrays (Pteroplatytrygon violacea), and leatherback sea turtles (Dermochelys coriacea), which had higher catch rates on J-style hooks. Survival of bigeye (Thunnus obesus) and yellowfin tunas (Thunnus albacares) was significantly higher when circle hooks were used, and bigeye and yellowfin tunas, swordfish (Xiphias gladius) and sailfish had significantly higher external hookings when circle hooks were used. The results suggests using 18/0 circle hooks with a zero degree offset could increase the survival of bycatch species while having minimal effects on the catches of target species.

The effect of circle hooks and J-style hooks on the catch composition, catch rates, hooking location and status of release of target and bycatch species were compared on pelagic longline vessels.  There were significant differences in catch rates between the two hook types for bigeye tuna, which had higher catch rates on circle hooks and sailfish (Istiophorus spp.), pelagic stingrays (Pteroplatytrygon violacea), and leatherback sea turtles (Dermochelys coriacea), which had higher catch rates on J-style hooks. Survival of bigeye (Thunnus obesus) and yellowfin tunas (Thunnus albacares) was significantly higher when circle hooks were used, and bigeye and yellowfin tunas, swordfish (Xiphias gladius) and sailfish had significantly higher external hookings when circle hooks were used. The results suggests using 18/0 circle hooks with a zero degree offset could increase the survival of bycatch species while having minimal effects on the catches of target species.

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.