Do circle hooks reduce bycatch?...It depends.
Last week, NOAA hosted over 160 marine scientists, fisheries managers, gear experts, and commercial and recreational fishermen, from 20 countries, in Coral Gables, FL, for the first international symposium on circle hooks in research, management and conservation. While we all came away more informed about circle hooks, we left with more questions about their effectiveness for catching target species and reducing bycatch.
What is a Circle Hook?
A circle hook is traditionally defined as a fishing hook with the point turned inward to the shank at a 90° angle, giving it a circular shape. Geir Sivertzen, known as "Dr. Hook," immediately shook up that generalized definition. He informed us that not all circle hooks are alike - they vary in size, point angle, offset, gape width, bend, AND their specifications vary between manufacturers and are often defined differently in different places.
While we may all think of the J hook as the traditional fishing hook, the circle hook has actually been used in the Pacific since people first began fishing. It was adopted by many recreational fishers in the 1970s and 80s for catch and release fishing to reduce hooking mortality. Commercial fisheries are now seeing regulations requiring circle hook use for certain target species or in areas with bycatch problems.
Why use Circle Hooks?
The J hook can be become hooked deeply in fish and other animals and cause damage or death by becoming set in the gills, esophagus, or other vital organs. The shape and point of the circle hook is designed to prevent deep-hooking and to only hook in the corner of an animal's mouth. In recreational fisheries, the circle hook can reduce hooking injuries and mortality in catch and release fishing. In commercial fisheries, circle hooks may decrease bycatch and post-release mortality of bycatch. Circle hooks have specifically been used to prevent sea turtle bycatch in longline fisheries.
Do Circle Hooks Work?
Are circle hooks effective for maintaining target catch and reducing bycatch? The message from over 50 presentations and poster was - sometimes. Here are some examples:
Do circle hooks reduce deep-hooking?
In the southeastern Asian longline fishery, circle hooks caught 85% of fish in the mouth and only 4% in the gut, while J hooks caught 25% in the gut. Another study in the Canadian pelagic longline fishery found no difference in mouth and deep-hooking in sea turtles caught on circle hooks.
Do circle hooks reduce mortality?
In most studies, circle hooks were effective for reducing the mortality of animals caught because internal hooking was less frequent. In one Canadian longline fishery, the odds of survival on a circle hook were two to five times more likely for bycatch than on a J hook. However, a study of the reef fish vertical line fishery in the southeastern US resulted in more dead discards due to circle hooks than J hooks.
Do circle hooks decrease sea turtle bycatch?
In the Indonesian longline fishery, switching from J hooks to 16/0 circle hooks reduced sea turtle bycatch by 78%, while retaining target fish. In the southwest Atlantic longline fishery, circle hooks were also successful, decreasing loggerhead bycatch by 55% and leatherbacks by 65%. Using smaller hooks (13/0) instead of J hooks in an artisanal fishery in Italy did not lead to significantly fewer sea turtle captures.
Do circle hooks reduce other bycatch?
A comparison of circle hooks and J hooks in the equatorial Atlantic pelagic longline fishery found that circle hooks increased bycatch of blue sharks. The fishery actually caught more blue sharks than their target species. But in Hawaii, large circle hooks reduced the catch of sharks. Circle hooks also significantly reduced pelagic stingray bycatch in all studies where they were captured.
Do circle hooks maintain target catch?
Most studies found no difference between targe catch rates using circle hooks or J hooks. In the Cook Islands, circle hooks increased the catch of the target species - albacore tuna and swordfish. In other studies, target catch - mahi mahi, swordfish, tarpon - decreased.
There are other factors that complicate our understanding of the effectiveness of circle hooks: hook size, hook offset, type of bait used, how the hook was baited, capture and handling methods, soak time, species feeding behaviors, the position of the hook in the water column, and other environmental conditions.
Researchers have gone a step further with circle hooks and have experimented with modifications to see if they can reduce bycatch further. One modification is decreasing circle hook strength to release larger bycatch species, while maintaining enough strength to retain smaller target species. The New York Times recently reported on the new rule requiring "weak" circle hooks on longline vessels in the Gulf of Mexico targeting yellowfin tuna to reduce the bycatch of bluefin tuna. David Kerstetter, whose work is supported by the Consortium, is testing weak "whale-safe" circle hooks in the Hawaiian longline fishery where there is a false killer whale bycatch problem. Shark Defense presented their new SMART hook, which is designed to deter sharks from the bait. Researchers from NMFS presented their research on circle hooks with a wire extension "appendage" that increases the dimensions of the circle hook, making it more difficult for sea turtles to swallow.
To sum up the symposium - circle hooks are not a magic solution for bycatch prevention, but they are promising in many situations. Future research will need to determine how they can be used in conjunction with other management tools or gear modifications. Additionally, the effectiveness of circle hooks is limited by their acceptance by fishermen. Maintaining "fishability" - keeping costs low, retaining target catch, and not complicating fishing techniques - is important for circle hooks to be successfully adopted.
For more information on the circle hook symposium: www.circlehooksymposium.org
Photo: Kate McClellan