Fishing kills a third of turtles
Satellite-tracked tags hint at threatening mortality rate.
November 10, 2003
JOHN WHITFIELD - Nature
Nearly one in three sea turtles may be killed by fishing each year, suggests a new global study.
Tagged turtles have turned up in restaurants. © Corbis
"At this rate of mortality, you can project that some populations will go extinct in a few decades," says Graeme Hays of the University of Wales, Swansea, UK. Hays' estimates are based on records from turtles carrying satellite tags. These broadcast an animal's position, and record its dives.
Tags also record turtles being eaten - animals that suddenly move inland to a fishing village and stay there, for example, have almost certainly been taken for food. "Tourists have photographed turtles being barbecued with the transmitter still attached," says Hays.
His team pooled the data from eight tagging projects, covering 50 green, loggerhead and leatherback turtles for a total of nearly 6,000 days(1). During this time, six perished at human hands - three in Mexico and one each in Japan, Indonesia and South Africa. That equates to an annual mortality of 31%.
International trade in turtles is prohibited, but subsistence fishers still kill them for their meat and eggs. Some Mexican villages have rubbish dumps piled high with turtle shells. And many turtles die as 'bycatch', caught accidentally in fishing nets.
The studied animals were probably killed deliberately, as tags must be on land and out of doors for several days to guarantee an upload to the satellite. Corpses discarded at sea would not be able to do this.
Conservationists are alert to the dangers of bycatch, but often overlook the impact of turtle hunting illustrated in this study, believes turtle researcher Karen Bjorndal of the University of Florida in Gainesville. "Thousands and thousands are taken for food," she says.
Conservation policies should try to reduce hunting through education, legislation and working to provide alternative incomes, she says.
"People can make more money from turtles alive than dead," agrees Hays. He works on green turtles in Brazil and Ascension Island, where the animals get good protection, and conservationists and researchers have helped to establish ecotourism projects.
As the risks to turtles are so different from place to place, the team plans a study covering hundreds of animals, to get a fuller picture.
References:
(1) Hays, G. C. et al. Satellite telemetry suggests high levels of fishing-induced mortality in marine turtles. Marine Ecology Progress Series, 262, 305 - 309, (2003). http://www.int-res.com/abstracts/meps/v262/p305-309.html
Source: http://www.nature.com/nsu/031103/031103-17.html
