SEATTLE--Protecting endangered leatherback sea turtles has become a cause célèbre in environmental circles. But the first global assessment of the leatherback's more numerous cousin, the loggerhead sea turtle, shows that it's in even bigger trouble. The results, presented here 13 February at the annual AAAS meeting, suggest one way to save the loggerheads: Keep them away from fishing lines in the open ocean.
Tens of thousands of loggerheads still roam the world's oceans, and the species is listed as threatened but not endangered. Scientists learned a few years ago that the loggerheads flock to open-ocean sites where cold and warm water mix to feed on the cornucopia of jellyfish, squid, and other creatures--as do giant swordfish. Commercial fishing boats follow the swordfish, and loggerheads often die on their longlines--fishing hooks strung like Christmas lights from lines that stretch for kilometers.
To see how much harm fishers were inflicting on loggerheads--and gauge the loggerhead's chance of survival--marine biologist Larry Crowder of Duke University in Durham, North Carolina, and his colleagues first estimated the entire loggerhead population in the Pacific Ocean from counts of nesting females at all the known breeding beaches and by taking the turtle's life span of 80 years into account. Then they calculated how many turtles were killed by fishers each year by using commercial fishing data to create "a map of where the hooks are," Crowder says, and by collecting data on loggerheads accidentally hooked and killed by fishers. The numbers, which will be published in the March issue of Ecology Letters, were alarming: Of the 67,000 loggerheads in the world, 30,000 get tangled in longlines each year and between 3000 and 6000 die. That means that a typical loggerhead will encounter a fisher's hook every 2 years, and that between about 5% and 10% of the world's population is killed each year. Because loggerheads live until they're 80 years old and don't breed until they're 30, Crowder says, the results mean that saving the loggerhead "requires some real action--and soon."
"The evidence can't get any better," says marine ecologist Peter Etnoyer of Aquanautix Consulting in Los Angeles, a firm that plans and helps conduct oceanographic research expeditions. If nations don't cooperate soon to dramatically reduce the numbers of loggerheads killed by fishers, Etnoyer concludes, the species may never recover.