Lightsticks May Hold Deadly Attraction for Sea Turtles

RALEIGH, N.C. _ Longline fishermen use lightsticks similar to the glowing tubes that delight trick-or-treaters to lure tuna and swordfish to baited hooks. New research by University of North Carolina-Chapel Hill scientists suggests that for endangered sea turtles the lights may hold a fatal attraction.

Lab experiments by Ken Lohmann, a University of North Carolina biology professor and John Wang, a graduate who is now a research associate at the University of Hawaii and National Marine Fisheries, found that young loggerhead turtles in a tank tended to swim toward lights.

It’s well known that hatchling turtles on a beach will crawl toward lights as they try to find the surf. But researchers did not know whether juvenile loggerheads in the water shared that attraction. Young loggerhead and leatherback sea turtles, which are protected because of declining numbers, are inadvertently hooked during longline fishing.

"Juvenile turtles are indiscriminant eaters and bite nearly everything small that they encounter," said Lohmann, a study co-author whose expertise is turtle navigation. "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."

Longline fishing, which uses a single line hung with hundreds or thousands of baited hooks over miles of ocean, is the preferred fishing gear for tuna and swordfish in federal and international waters off the Atlantic and Gulf of Mexico. Lightsticks are tied to the lines to mimic the nighttime luminescence of squid to draw big fish to the bait.

On the Atlantic coast, longline fishing is concentrated in the North Atlantic hundreds of miles off the coast of New England and Canada. Even so, sea turtles that hatch on beaches in North Carolina and Southeastern states may encounter the hooks.

Sea turtles spend years of their lives following a circular current that takes them north to Nova Scotia and east to the Azores off Portugal, researchers believe.

"There is a big longline fishery that operates in the Azores," Lohmann said. "Many juvenile turtles from the U.S. Southeast are caught there."

When the researchers tested the turtles with unactivated lightsticks in the tanks at the National Marine Fisheries Laboratory in Galveston, Texas, and at Florida Atlantic University, the loggerheads swam in circles.

"Once you start adding glowing lightsticks, the turtles started swimming toward those lightsticks," said Wang, lead author of the study. "We’ve conducted several tests. With each tests, we’ve run 12 to 20 turtles."

Worldwide, Duke University researchers have estimated that 250,000 loggerhead turtles and 60,000 leatherback turtles were snared in 2000 by commercial longline fishing, based on partial data from nations that collect such information. They say that other commercial fishermen using gill nets and trawling are responsible for large or larger catches of turtles.

Dewey Hemilright of Kitty Hawk, a longline fishermen who works waters from Florida to New York for swordfish and tuna, said the study merited further research under ocean conditions.

"What works on land doesn’t always happen on the ocean," Hemilright said.

Hemilright said U.S. longline fishermen face heavy environmental regulations, unlike those of many countries, and are required to use circle hooks to avoid catching turtles. The hooks also reduce catches of swordfish. That may mean other countries eventually are given part of the U.S. fishermen’s allotment of swordfish catch, he said.

Hemilright said the capture of turtles was a much bigger problem in countries with weak or no environmental regulations than with commercial fishermen here.

"Just because other countries are catching that many turtles doesn’t mean it’s happening in the U.S," Hemilright said. "Our fishery would be shut down if they hooked many turtles."

The new UNC findings, if confirmed by field studies, may help fisheries decrease the number of turtles caught on lines, the researchers said. The research appeared in the current issue of the journal Animal Conservation.

Lohmann said there are simple steps to reduce the problem. He said most longlines deploy their hooks below the depths where turtles usually swim, so shading the lights to direct illumination down might make the lights harder for turtles to see.

"The turtles spend most of their time in water close to the surface," Lohmann said. "The fish are found at much greater depths. If the lights are shaded so that the lights are directed downward, the turtles may not see them."

Similarly, switching to colors of lights that turtle can’t detect might also reduce turtle deaths.

David Bernhart, chief of protected resources for National Marine Fisheries in the Southeast region, said the inadvertent catch of protected turtles had long been a concern with longline fishing.

Part of the Atlantic fishery had been closed in 2000 and 2001 because of the problem, Bernhart said. Since 2004, U.S. longline fishermen working the Atlantic have been required to use less destructive circle hooks. He said the change reduced the number of turtles captured by 50 percent.