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Hawaii Longliners Reduce Sea Turtle Bycatch
Photo Credit: NOAA
by Lance Smith
Longline fishing poses one of the greatest threats to threatened and endangered Pacific sea turtles. This fishing method typically consists of suspending a large number of baited hooks attached at regular intervals over a horizontal mainline more than a mile in length. Sea turtles are incidentally hooked or entangled in the gear, or in other words, become bycatch.
The National Marine Fisheries Service (NMFS) manages the limitedentry (maximum of 125 vessels) Hawaii longline fishery, which targets tuna and swordfish – species of high market value – across a large area in the central Pacific Ocean. Longlining for tuna is done during the day at 150 to 400 meters (about 500 to 1,300 feet) of depth, generally to the south of Hawaii, while longlining for swordfish is done at night in areas north of Hawaii less than 100 meters (about 330 feet) in depth. Because of the different gear and methods used, tuna and swordfish longlining are managed separately, although the same vessel may switch between the two species. The "Hawaii longline fishery" is a general term that refers to both the tuna and swordfish longline fisheries based in Hawaii.
Photo Credit: NOAA Fisheries Observer Program, Honolulu
All five sea turtle species living within United States Pacific waters are listed as threatened or endangered under the Endangered Species Act. The species caught most commonly in the tuna fishery is the olive ridley (Lepidochelys olivacea). The tuna fishery also results in bycatch of leatherback (Dermochelys coriacea) and green (Chelonia mydas) sea turtles. The sea turtle species caught most commonly in the Hawaiian swordfish fishery is the loggerhead (Caretta caretta), although incidental captures include leatherbacks from the Pacific’s severely depleted population. Hawksbill sea turtles (Eretmochelys imbricata) occur in Hawaiian waters but are not known to be incidentally captured in either fishery.
Because of high bycatch rates of sea turtles, particularly loggerheads, the Hawaiian swordfish fishery was closed by court order in 2001. The Hawaiian tuna fishery was seasonally restricted by the same order due to high bycatch rates of olive ridley sea turtles. Both fisheries were also catching substantial numbers of leatherback sea turtles.
After longliners incorporated measures to reduce sea turtle bycatch, the Hawaiian swordfish fishery reopened in 2004. These measures included the use of large circle hooks (a hook designed to reduce mortality in non-target species) and mackerel-type bait (which reduces the likelihood of attracting turtles), the stationing of observers on every boat, and protocols for handling and releasing hooked or entangled turtles. Some turtle conservation measures were also adopted by the Hawaiian tuna fishery. As a result, bycatch of loggerhead and leatherback sea turtles was reduced by approximately 90 percent in the Hawaii longline fishery as a whole.
Sea turtle bycatch rates tend to be higher in swordfish longline fisheries than in tuna longline fisheries, especially for loggerheads. That’s because juvenile loggerheads congregate in the same area of the ocean as swordfish, where prey for both species is abundant. In addition, loggerheads usually forage on the surface or in shallow water, whereas other sea turtle species, such as leatherbacks and olive ridleys, typically dive deeper in search of food. However, when the proper protocols are used to handle and release a hooked loggerhead, studies have shown that survival is approximately 80 percent.
Sea turtle bycatch rates in the Hawaii tuna and swordfish longline fisheries are lower than those in other longline fisheries operating in the Pacific. Bycatch rates of seabirds, such as several albatross species, have also been reduced in the Hawaii longline fishery in recent years as a result of several seabird conservation measures. These include dying bait blue and attaching weights to baited hooks to make them sink faster.
As part of a broad international program for the conservation of sea turtles and seabirds, NMFS is working with other countries that manage Pacific longline fleets to encourage the adoption of conservation measures in their waters. The Hawaii longline fishery provides an example of how sea turtle and seabird bycatch can be reduced as part of an economically viable fishery.
Kaneko, J.J. and P.K. Bartram. 2008. What if you don’t speak "CPUE-ese"? Pelagic Fisheries Research Program Newsletter, University of Hawaii. 13(2):1-3.
Lance Smith, the Endangered Species Team Leader in the Protected Resources Division of the NMFS Pacific Island Regional Office, can be reached at email@example.com or 808-944-2258.
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