Behavioral responses of juvenile leatherbacks Dermochelys coriacea to lights used in the longline fishery
Sea turtles are injured and sometimes killed because of interactions with pelagic longlines, such as hook ingestion, entanglement in the lines, and forced submergence. Stimuli from bait, gear and lights (often used at night on swordfish lines) might attract sea turtles. Previous experiments with loggerheads Caretta caretta demonstrated that the turtles were attracted to the lights, but no comparable studies have been done with other species. Our goal in this study was to determine whether juvenile leatherbacks Dermochelys coriacea, reared in the laboratory for 5 to 42 d post-emergence, responded to the lights in the same way as loggerheads. Each leatherback was presented once in varying order with 3 different colored light stimuli from either chemical lightsticks (n=16 turtles) or battery powered LEDs (n=16 turtles) commonly used in the fishery. Most leatherbacks, in contrast to loggerheads, either failed to orient or oriented at an angle away from the lights. These results imply that the capture of leatherbacks on longlines might occur for other reasons (by accident, through attraction to bait odour or to concentrations of natural prey located near the lines). Alternatively, older turtles might show responses that differ from those of juvenile turtles. We review previous studies based upon logbook data and conclude that because of confounding factors, there is no convincing evidence that marine turtles are attracted to the longlines by lights. We recommend that better-designed field experiments be carried out to determine whether fishery lights have an effect on marine turtle capture rates.