Novel behavioral responses of sea turtles to gillnet fishing gear

Abstract

• 1.
  Fisheries bycatch, or the incidental capture of non-target organisms, results in high sea turtle mortality and is believed to be a contributor to population declines. Field studies have shown visual stimuli to reduce sea turtle bycatch in gillnets. These studies have focused on bycatch outcomes specific to net-gear modifications and have not explored behavioral mechanisms driving sea turtle entanglement.
• 2.
  To study these behaviors, we used wild-caught green (Chelonia mydas) and loggerhead (Caretta caretta) turtles in controlled tank experiments. We ran binary-choice trials with netted and unnetted passageways in a controlled tank environment. Underwater and overhead cameras recorded initial and subsequent treatment choices in addition to detailed behavior. Trials occurred in daylight, when turtles could presumably see the net. We also recorded time per treatment area, speed and acceleration in the presence of a net, and avoidance behaviors.
• 3.
  Turtles reduced their speed in the presence of a net, which suggests that they see and respond to it before each encounter. Both species initially avoided the netted passageway. Avoidance included U-turn and reversal behaviors, which have not been described in previous literature. Green turtles exhibited more U-turn behaviors and net interactions, whereas loggerheads became entangled more frequently.
• 4.
  By using controlled experiments with wild-caught animals, we provide novel insights on fine-scale behavioral interactions with fishing gear.