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Geographic 27 Apr 07
Glow Sticks May Lure Sea Turtles to Death
Helen Scales for National Geographic News
The same glow sticks that lighten up raves and Halloween may be tempting thousands of sea turtles to their deaths, a new study says.
Used to attract fish to hooks on miles-long lines, the lights are apparently also irresistible to the reptiles.
Commercial longline fishing operations are known to contribute to the decline of sea turtle populations. Now researchers say that simply changing the type of light sticks could perhaps reduce the number of accidentally caught turtles.
The study is the first to demonstrate that sea turtles are attracted to the lights used by commercial longliners to lure swordfish and tuna. The paper appears in this month's issue of the journal Animal Conservation.
"Once the turtles are in the vicinity of the longlines, there's a high chance they will bite on the bait and become snagged," said study co-author John Wang of the University of Hawaii. "They can also get entangled in the fishing lines."
In 2000 alone, an estimated 200,000 loggerhead turtles and 50,000 leatherbacks were killed on longlines, according to the report. The World Conservation Union lists both species as endangered.
To investigate whether visual stimuli attract sea turtles to longlines, Wang and colleagues used electronic tracking devices to monitor the movements of loggerhead turtles as they swam in a large laboratory tank.
"We put various commercial light sticks at the edge of the laboratory pool to see if the turtles would swim toward them," Wang said, "which they did."
The turtles swam toward yellow, blue, and green chemical glow sticks as well as orange LEDs. An LED is a small type of light bulb usually used in groups. The bulbs are increasingly found in consumer applications such as car brake lights and flashlights—and in a more expensive, longer-lasting type of glow stick.
"Turtles might mistake the light sticks for glowing jellyfish," said co-author Ken Lohmann, from the University of North Carolina. "But it's equally plausible this is just an instinctive reaction to the unnatural continuous light," Lohmann said.
Searching for Solutions
"Light sticks are integral parts of some longline fisheries," study co-author Wang explained, "so limiting their use will not be a viable management solution."
Instead, researchers are working closely with industry leaders to develop modified glow sticks that would still lure swordfish and tuna but be less attractive to turtles.
One possible strategy, Wang said, "is shading the light sticks to direct the light downward. Sea turtles use the top portion of the water column, while most target fish are caught as they move upward from deeper water."
Pulsing lights are also being tested to see if they are less attractive to sea turtles.
"Fisheries in general are the biggest concern for sea turtles," said Roderic Mast, vice-president of Conservation International and co-chair of the World Conservation Union's Marine Turtle Specialist Group.
"Research like this that focuses on ways to limit the impact of particular fisheries is going to help us do a better job of solving these problems."
Yahoo News 8 May 07
Experts: Turtles drawn to light sticks
Endangered loggerhead turtles snared by longline fishermen may be inadvertently lured to the hooks because of an attraction to light sticks designed to attract tuna and swordfish, researchers said.
Scientists at the University of North Carolina at Chapel Hill found in lab experiments that young loggerhead turtles will swim toward lights similar to those used by fishermen to attract big fish.
"Juvenile turtles are indiscriminate eaters and bite nearly everything small that they encounter," said Ken Lohmann, a UNC biology professor whose expertise is turtle navigation.
Lohmann recommended that longline fishermen direct the lights, designed to mimic the nighttime luminescence of squid, toward the bottom of the ocean.
Turtles spend most of their time near the surface. "The fish are found at much greater depths," Lohmann said. "If the lights are shaded so that the lights are directed downward, the turtles may not see them."
He also suggested that fishermen switch to colors of light that turtles can't detect.
Lohmann conducted the study with John Wang, a graduate who is now a research associate at the University of Hawaii and National Marine Fisheries.
Inadvertent turtle catches have long been a concern, said David Bernhart, chief of protected resources for National Marine Fisheries in the Southeast region. U.S. longline fishermen working in the Atlantic have had to use circle hooks since 2004 to limit inadvertent catches, a change Bernhart said reduced the number of turtles captured by 50 percent. ___
Information from: The News & Observer, http://www.newsobserver.com
Related articles on Global: marine issues and sea turtles
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