Effect of Circle Hooks and Bait on Target and Bycatch Species in Pelagic Longline Fisheries 2007 Inter-Sessional Meeting of the Subcommittee on Ecosystems February 19-23, 2007, Madrid Spain

The ability of circle hooks to reduce the bycatch of sea turtles is a function of hook style and size and for cheloniid (hardshell) turtles, turtle size. Relative to 9/0 “J” hooks, 18/0 circle hooks reduce sea turtle bycatch significantly (U.S. Atlantic, Pacific and Ecuador data). Relative to 9/0 “J” hooks, 18/0 circle hooks reduce sea turtle bycatch significantly (U.S. Atlantic, Pacific and Ecuador data).

The ability of circle hooks to reduce the bycatch of sea turtles is a function of hook style and size and for cheloniid (hardshell) turtles, turtle size. Relative to 9/0 “J” hooks 16/0 circle hooks do not reduce the CPUE of pelagic/oceanic stage loggerhead turtles (Azores data; Canadian data) Relative to 9/0 “J” hooks 16/0 circle hooks do not reduce the CPUE of pelagic/oceanic stage loggerhead turtles (Azores data; Canadian data) 16/0 circle hooks do reduce pelagic loggerhead turtle CPUE when compared with smaller “J” (7/0 & 8/0) hooks and 8/0 ringed tuna hooks. (U.S & Azores data) 16/0 circle hooks do reduce pelagic loggerhead turtle CPUE when compared with smaller “J” (7/0 & 8/0) hooks and 8/0 ringed tuna hooks. (U.S & Azores data) 16/0 circle hooks reduced the CPUE for turtles relative to “J” hooks in the eastern Pacific (IATTC data). 16/0 circle hooks reduced the CPUE for turtles relative to “J” hooks in the eastern Pacific (IATTC data).

The ability of circle hooks to reduce the bycatch of sea turtles is a function of hook style and size and for cheloniid (hardshell) turtles, turtle size. Feeding studies indicate that hook size has a significant effect on ingestion of hooks of the size encountered on pelagic longlines (U.S. data). Feeding studies indicate that hook size has a significant effect on ingestion of hooks of the size encountered on pelagic longlines (U.S. data).

The ability of circle hooks to reduce the bycatch of sea turtles is a function of hook style and size and for cheloniid (hardshell) turtles, turtle size. Because a circle hook results in less foul hooking than “J’ hooks and leatherbacks most often are foul hooked, it is likely that any size circle hook with minimal offset will result in a reduction in leatherback bycatch. Because a circle hook results in less foul hooking than “J’ hooks and leatherbacks most often are foul hooked, it is likely that any size circle hook with minimal offset will result in a reduction in leatherback bycatch. Canadian observer data indicates a significant reduction in leatherback CPUE with 16/0 circle hook when compared to “J” hooks. Canadian observer data indicates a significant reduction in leatherback CPUE with 16/0 circle hook when compared to “J” hooks.

The post-hooking mortality associated with circle hooks is estimated to be less than that of “J” hooks in cheloniid turtles. Circle hooks engage in the jaw and less often are swallowed by cheloniid turtles; a much higher proportion of “J” hooks are swallowed. Circle hooks engage in the jaw and less often are swallowed by cheloniid turtles; a much higher proportion of “J” hooks are swallowed. Post-hooking mortality associated with a mouth hook is estimated to be lower than a swallowed hook. Post-hooking mortality associated with a mouth hook is estimated to be lower than a swallowed hook. Hooks in the mouth can be removed; seldom can swallowed hooks be removed safely. Hooks in the mouth can be removed; seldom can swallowed hooks be removed safely.

The post-hooking mortality associated with circle hooks is estimated to be less than that of “J” hooks in cheloniid turtles. Effective gear and techniques have been developed to safely remove longline gear from entangled, foul hooked, and mouth hooked turtles. Effective gear and techniques have been developed to safely remove longline gear from entangled, foul hooked, and mouth hooked turtles.

More Seabirds May Be Caught on “J” Hooks Than On Circle Hooks Observer data from the U.S. Atlantic pelagic longline fishery indicates that sea bird CPUE was six times higher for “J” hooks than for circle hooks. Observer data from the U.S. Atlantic pelagic longline fishery indicates that sea bird CPUE was six times higher for “J” hooks than for circle hooks.

Effect of Circle Hooks on Blue Sharks Blue shark CPUE was nominally increased with 18/0 circle hooks and squid bait in the North Atlantic swordfish fishery (U.S. data) Blue shark CPUE was nominally increased with 18/0 circle hooks and squid bait in the North Atlantic swordfish fishery (U.S. data) Blue shark CPUE was significantly reduced with 18/0 circle hooks and mackerel bait (U.S. Atlantic and Pacific data). Blue shark CPUE was significantly reduced with 18/0 circle hooks and mackerel bait (U.S. Atlantic and Pacific data).

Effect of Circle Hooks on Bycatch Release Mortality Circle hooks engage in the jaw and less often are swallowed than “J” hooks resulting in a lower rate of release mortality for bycatch species. Circle hooks engage in the jaw and less often are swallowed than “J” hooks resulting in a lower rate of release mortality for bycatch species. Preliminary studies and anecdotal information suggest that circle hooks result in a better quality fish due to an increase in live fish boarded. Preliminary studies and anecdotal information suggest that circle hooks result in a better quality fish due to an increase in live fish boarded.

The effect of bait type varies by hook style and species. 300 – 500 gram mackerel bait significantly reduces turtle bycatch compared to squid bait. (U.S. data) 300 – 500 gram mackerel bait significantly reduces turtle bycatch compared to squid bait. (U.S. data)

The effect of bait type varies by hook style and species. 300 – 500 gram mackerel significantly increases the catch of swordfish compared to squid bait (U.S. Atlantic and Pacific data). 300 – 500 gram mackerel significantly increases the catch of swordfish compared to squid bait (U.S. Atlantic and Pacific data).

The effect of bait type varies by hook style and species. 300 – 500 gram mackerel bait significantly reduces the catch of bigeye tuna, albacore tuna, mahi mahi, opah, and wahoo (U.S. Atlantic and Pacific data). 300 – 500 gram mackerel bait significantly reduces the catch of bigeye tuna, albacore tuna, mahi mahi, opah, and wahoo (U.S. Atlantic and Pacific data).

Circle hooks effect target species catch. The CPUE of swordfish is reduced significantly by circle hooks with squid bait (U.S. Atlantic data). The CPUE of swordfish is reduced significantly by circle hooks with squid bait (U.S. Atlantic data).

18/0 circle hooks with squid bait significantly reduced mahi mahi CPUE (U.S. Atlantic data). 18/0 circle hooks with squid bait significantly reduced mahi mahi CPUE (U.S. Atlantic data). Circle hooks effect target species catch.

The CPUE of bigeye tuna in swordfish-directed sets is nominally increased with 18/0 circle hooks and squid bait (U.S. data). The CPUE of bigeye tuna in swordfish-directed sets is nominally increased with 18/0 circle hooks and squid bait (U.S. data).

16/0 circle hooks significantly increase yellowfin tuna catch compared to “J” hooks. (U.S. Atlantic data). 16/0 circle hooks significantly increase yellowfin tuna catch compared to “J” hooks. (U.S. Atlantic data). Circle hooks effect target species catch.

Results from Gulf of Mexico tuna-directed research indicates a significant reduction in yellowfin tuna catch with 18/0 circle hook compared to 16/0 circle hook when used with sardine bait (U.S. data) Results from Gulf of Mexico tuna-directed research indicates a significant reduction in yellowfin tuna catch with 18/0 circle hook compared to 16/0 circle hook when used with sardine bait (U.S. data)

Circle hooks effect target species catch. The CPUE of albacore tuna was significanly increased with 18/0 circle hooks and squid bait in swordfish-directed sets in the U.S. North Atlantic fishery (U.S. data). The CPUE of albacore tuna was significanly increased with 18/0 circle hooks and squid bait in swordfish-directed sets in the U.S. North Atlantic fishery (U.S. data).