San Fransisco — The western Pacific leatherback turtle, the world’s largest turtle and a common sight every year in the waters around the Golden Gate Bridge, could go extinct within 20 years if more isn’t done to protect its habitat and nesting sites, a team of international experts concluded.
The worldwide population of the endangered Pacific leatherback has declined more than 90 percent since the 1980s because of commercial fishing, egg poaching, destruction of nesting habitat, degradation of foraging habitat and changing ocean conditions.
Marine biologists had believed the global population had stabilized, but the new study, published in the scientific journal Ecosphere, shows that turtle eggs are disappearing fast in one of its last bastions, the beaches of Indonesia.
“At least 75 percent of all leatherback turtles in the western Pacific Ocean hatch from eggs laid on a few beaches in an area known as Bird’s Head Peninsula in Papua Barat, Indonesia,” said co-author Peter Dutton, a marine scientist with the National Oceanic and Atmospheric Administration (NOAA). “Our analysis indicates the number of leatherback-turtle nests on this beach has declined 78 percent over the last 27 years.”
The researchers counted 1,532 nests on Bird’s Head in 2011 compared with 14,455 in 1984. Nests in Indonesia, including other beaches, dropped 78.3 percent since 1984, according to the study by NOAA’s National Marine Fisheries Service, the State University of Papua Indonesia, University of Alabama, Birmingham, and World Wildlife Fund Indonesia.
That averages out to a 5.9 percent decline every year. The study estimates there are 500 turtles nesting on the Indonesian peninsula each year. If the trend continues, researchers said, the reptiles are likely to be extinct in two decades.
“Our view is that if we don’t take dramatic action to eliminate threats to leatherbacks both in our waters and abroad, we will lose this incredible, iconic animal forever,” said Geoff Shester, the California program director for Oceana, a nonprofit marine-conservation group.
Leatherbacks, or Dermochelys coriacea, are the largest sea turtles in the world, measuring more than 6 feet long and weighing as much as 2,000 pounds. Their life span is not known, but biologists believe they live at least 40 years and possibly as long as 100 years in the wild.
The giant turtles usually lay several batches of about 100 eggs in nests they dig in the sands of Indonesia, the Solomon Islands, Vanuatu and Papua New Guinea.
The worldwide population of leatherbacks is relatively stable compared with the Pacific version, which was listed under the Endangered Species Act in 1970. There are 20,000 to 56,000 adult female leatherbacks in the Atlantic Ocean, said Bryan Wallace, a Duke University professor and director of science for the Marine Flagship Species Program of Conservation International.
The Pacific leatherbacks are in a much more difficult situation. The hatchlings emerge after about two months and eventually swim across the Pacific Ocean to California, where they feed on jellyfish off San Francisco, Monterey and Bodega bays in the summer and fall. The 6,000-mile journey is the longest known migration of any marine reptile.
The study shows that an increasing number of them aren’t making it. There are believed to be no more than 5,700 nesting female Pacific leatherbacks left.
Federal regulators designated nearly 42,000 square miles of ocean along the coasts of California, Oregon and Washington as critical habitat for the turtles last year. But it did not include the migration routes the turtles take to get to their feeding grounds.
Turtle advocates say the creatures are vulnerable to longline fishing and drift nets dragged by oceangoing vessels. Such fishing is banned on the West Coast during leatherback migration, but groups say they are fighting efforts by federal regulators to expand drift-net fishing into leatherback habitat.
“Leatherbacks are in big trouble, and every one that drowns in a gill net or on a longline hook is a major casualty,” said Teri Shore, program director at Turtle Island Restoration Network.