Leatherback sea turtle Dermochelys coriacea visual capacities and potential reduction of bycatch by pelagic longline fisheries

Abstract

Leatherback and other marine turtles are classified as Critically Endangered or Endangered by the International Union for Conservation of Nature (IUCN), largely due to anthropogenic factors (e.g. poaching, habitat destruction and incidental mortality in fisheries). A need to understand the visual capacities of marine turtles has arisen from mortality caused by attraction of these turtles to chemiluminescent lights used by swordfish longline fisheries. Finding light sources that do not attract turtles, but enhance swordfish catch, could remove a major source of anthropogenic mortality to the Critically Endangered leatherback sea turtle. Using field-adapted non-invasive electrophysiology (corneal electroretinogram), we determined that leatherback spectral sensitivities differ significantly from those of green and loggerhead turtles with peak sensitivity in the shorter wavelengths. Leatherback temporal sensitivities also differ greatly from those of green turtles and peak at lower frequencies. Our results show that while leatherback and swordfish spectral sensitivities are similar, temporal response frequencies are very different. This difference provides a possible means to reduce the attraction of leatherbacks to swordfish longline gear by switching to electroluminescent attractants that use rapidly flickering light sources. Light sources flickered at >16 Hz should be difficult for leatherbacks to detect as flickering, while remaining readily seen as flickering by swordfish.