Safeguarding the ocean road

Sea turtles could go extinct unless key migratory routes protected.

14 February 2004 - JIM GILES

Protecting the ocean routes used by turtles and other endangered species is vital if marine life is to be conserved, a group of marine biologists argued at the American Association for the Advancement of Science meeting in Seattle on Thursday.

Loggerhead turtles are accidentally    caught by fishermen.

Evidence for these offshore highways has emerged over the past few years, as data roll in from experiments to tag and track creatures such as turtles and dolphins. The studies show that the sea's largest animals follow well-swum paths, and are often caught by boats fishing for smaller species in the same areas.

The extent of the problem is revealed in an analysis of the effect of fisheries on protected species of turtles, due to published next month1. More than 200,000 loggerhead and 50,000 leatherback turtles are estimated to have been caught by accident in 2000, and both species could be extinct by the middle of the century.

"We know where these highways are," says Larry Crowder of Duke University, an author on the fisheries paper and one of the researchers behind the conservation proposal. "The only question is whether we can act in time."

One route follows the edge of the Gulf Stream as it run along the eastern coast of the United States. Others include paths to areas far from land where cold, nutrient-rich water is pulled upwards by surface currents. The arrival of the nutrients prompts a growth in plankton, attracting larger marine animals.

Moving target

Protecting these highways would be difficult, the researchers admit. The paths, which have been revealed by placing satellite communication devices on the back of migrating turtles and the fins of dolphins, are not precisely fixed in the water. And some cover vast distances - one bluefin tuna route crosses the entire Atlantic.

"There are challenges galore," admits Elliott Norse, president of the Marine Conservation Biology Institute in Redmond, Washington, who is also backing the conservation plan. He says that the problem of shifting routes can be solved by constantly tracking the movement of turtles and dolphins, and comparing data on ocean currents and temperature. By predicting where the animals will go, argues Norse, we can adjust fishing practices to reduce the number caught.

References

Lewison, R. L. et al. Quantifying the effects of fisheries on protected species: the impact of pelagic longlines on loggerhead and leatherback sea turtles. Ecology Letters, in press, (2004).