CHAPEL HILL -- Thousands of loggerhead turtles die every year when they get tangled or hooked in commercial fishing longlines meant for tuna or swordfish. New research suggests a possible reason why turtles swim into the lines. The glowing light sticks that lure fish to longlines also attract turtles, according to a University of North Carolina at Chapel Hill study.
The light sticks used in longline fisheries resemble the disposable plastic tubes popular with children on Halloween. The steady glow draws fish, which then find baited hooks and are caught on the lines. The lights also seem to fascinate turtles, however, which are equally likely to chomp on fish bait, or get snagged in the hooks and lines.
Juvenile turtles are indiscriminant eaters and bite nearly everything small that they encounter, said Ken Lohmann, UNC-Chapel Hill professor of biology and senior author of the study. Under natural conditions, most small objects floating or swimming through the sea are potential sources of food. But nowadays, with fishing lines, plastic, and garbage in the ocean, biting everything is not such a great strategy.
The study appears in the May 2007 issue of the journal Animal Conservation. John Wang, a former graduate student at Carolina and now a research associate with the Joint Institute for Marine and Atmospheric Research at the University of Hawaii, was the lead author of the study. Grants from the National Oceanic & Atmospheric Administration (NOAA) and the National Science Foundation provided funding.
The new findings may help fisheries decrease the number of turtles caught on lines, the researchers said. Most longlines deploy their hooks below the depths where turtles usually swim, so shading the lights to direct illumination downward instead of upward might make the lights harder for turtles to see. Similarly, switching to colors that turtles cant detect very well might also reduce turtle deaths.