By Jonathan Amos
BBC News Online science staff, in Seattle
Longline fishing is taking a terrible toll on sea turtles in the Pacific.
Hooks are a major hazard to the turtles
Loggerhead and leatherback turtles have an annual 40-60% chance of meeting a longline hook, and thousands are dying as a result, Dr Larry Crowder says.
The Duke University researcher told a Seattle conference that urgent action
was needed to prevent these creatures from disappearing from the ocean.
The US marine ecologist says tracking technology reveals that turtles use the same areas as fisheries vessels.
Dr Crowder made his comments at the annual meeting of the American Association for the Advancement of Science here in Washington State.
He says the impact of longlines on turtle populations has emerged from research he and colleagues have just submitted for publication in the journal Ecology Letters.
Although turtles clearly lose large numbers because of habitat loss, egg poaching and predation at their nesting sites, he says the idea that so many are also being killed at sea in fishing gear is quite shocking.
"In the year 2000, longline fishermen from 40 nations set at least 1.4 billion hooks on longlines that average about 40 miles long," he said. "That's 3.8m hooks per night that are set globally."
Although not every encounter with a hook results in death, the losses are nevertheless substantial. The latest estimate suggests that globally loggerheads (Caretta caretta) are being killed at a rate of about 200,000 a year. In leatherbacks (Dermochelys coricea), the number is about 50,000.
In the Pacific, where the animals are critically endangered, these losses are especially serious.
"More loggerheads and leatherbacks are estimated to be killed in the longline fishery alone than nest annually in the Pacific," Dr Crowder said.
New tracking and remote-sensing technologies are revealing new information about where marine organisms congregate and how this brings them into conflict with the fishing industry.
"If you think about these turtles being homogeneously distributed in the largest ocean in the world, it is impossible to imagine they would ever run into a hook. The answer to that is they aren't homogeneously distributed - they're in very particular places," Dr Crowder said.
"If you saw Finding Nemo, it is a cartoon characterisation but not a bad one, in the sense that organisms like sea turtles orient themselves to 'highways'.
"Unfortunately these habitats, these highways, are also locations where there is intensive fishing."