Sea turtle and pelagic fish sensory biology: developing techniques to reduce sea turtle bycatch in longline fisheries
The high level of incidental capture of sea turtles in pelagic longline fisheries is of great concern to environmental groups, the fishing industry, and fisheries managers in the U.S. and other countries. Regulatory measures to protect sea turtles in both the Pacific and Atlantic Oceans have recently been introduced in U.S. fisheries, including longline gear modifications (e.g., use of large circle hooks) and time-and-area fisheries closures (U.S. Department of Commerce 1999, 2000; Watson et al., 2005).
Ways to reduce longline-turtle interactions and the mortality caused by such encounters are needed. Solutions may result from research on the behavior, distribution, and sensory physiology of sea turtles and the pelagic fish species targeted by longline vessels. Most promising are studies to define and exploit differences in sea turtle and fish sensory physiology. Sea turtles and pelagic fishes are evolutionarily distinct groups of animals with differences in vision, hearing, and olfaction that may influence the ways in which they interact with fishing gear. The factors that attract sea turtles and target fish species to longline gear and bait are not well understood, but numerous sensory cues may be involved. In 2001, scientists of NOAA Fisheries created the Sensory Biology Working Group and launched a multidisciplinary, interagency research program to investigate the visual, auditory, and chemosensory abilities of sea turtles and pelagic fishes. The purpose of the research was to identify differences between turtles and pelagic fish species that may be used to develop gear and bait attractive to fish but unattractive to sea turtles or undetectable by them. The overall plan has been to proceed simultaneously along several tracks employing modern molecular genetics techniques (to identify receptor molecules), standard electrophysiological methodologies (to record responses to specific stimuli and define detection thresholds), and behavioral experiments in several species of sea turtles and commercially important tunas and billfishes. The primary objective of the research is to develop techniques and/or commercially viable devices that eliminate or substantially reduce the interactions of sea turtles with longline fishing gear while not reducing catch rates of the targeted fish species to unacceptable levels.
Research projects have been underway since 2001, supported by funding from the Pacific Islands Fisheries Science Center (PIFSC), NOAA Fisheries, in Honolulu, Hawaii. Because of the complexity of the research, projects have necessarily involved a large and diverse team of scientists. Collaborating scientists have held three meetings to discuss research progress.
This NOAA Technical Memorandum presents scientific work produced by the working group including research discussed at the first meeting, hosted by the PIFSC in January 2003 in Honolulu, Hawaii. The contributions concern the development of gear modification that show promise in reducing interactions of sea turtles with baited longline fishing gear.