Chemoreception in loggerhead sea turtles: an assessment of the feasibility of using chemical deterrents to prevent sea turtle interactions with longline fishing gear
The mechanisms by which sea turtles are attracted to and become hooked and entangled in commercial fishing gear are not well understood. Identification of sensory attractants and repellants may prove useful in developing gear and bait modifications to reduce sea turtle bycatch in commercial fisheries. We conducted experiments to investigate the ability of loggerhead turtles (Caretta caretta, Linnaeus 1758) to use chemical and flow cues to successfully locate squid bait and also tested to see if chemical modification of squid bait would reduce the turtles' ability and/or willingness to track and locate bait. Captive reared juvenile loggerhead turtles were placed in a seawater-filled flume tank with a current of 3-5 cm sec-1. A nylon bag containing either nylon (control), squid, or squid that had been marinated in 2-phenylethanol or shark-derived compounds was placed in the current upstream from the turtle. Trials were conducted in darkness, and the behavior of turtles was monitored and recorded using an IR-sensitive video surveillance system. The presence of squid bait in the tank elicited feeding and searching behavior; however, turtles showed limited ability to locate squid bait in the absence of visual cues. Only 25-33% of turtles located and ate the squid bait during the 10-minute trial period. These results indicate that visual cues are important for foraging success in loggerhead turtles, and chemoreception likely plays a secondary role. Treatment of squid with 2-phenylethanol or shark-derived compounds did not prevent turtles from eating squid bait. There was no significant difference in the number of turtles that located and ate bait between control, squid, and chemically modified squid trials. An effective chemical deterrent for sea turtles has yet to be identified.