(This article was originally published on OceanLines on August 29, 2008.)
Leatherback Turtles have been around for more than a hundred million years but in the last 20 years, the population of leatherbacks in the eastern Pacific Ocean has declined by more than 90%.
Until recently it has been difficult for conservationists to help these turtles because their migratory patterns span the entire ocean. A new effort to tag and track leatherbacks that nest on the Pacific coast of Costa Rica has shed new light on the situation.
Unlike most turtles, the leatherbacks from Playa Grande in Costa Rica seem to follow a more specific migratory pattern past the Galapagos and into the South Pacific.
“Given that the turtles seem to move in a predictable way from the nesting beach through the equatorial region from roughly February though April, we could potentially suspend fishing in certain areas while the leatherbacks are passing though that part of the eastern Pacific,” said George Shillinger, doctoral candidate in biology at Stanford University’s Hopkins Marine Station. This could potentially save these Pacific leatherbacks.
Shillinger is the first author of a paper published in the July 15 issue of Public Library of Science Biology, and part of a team of other biologists and oceanographers from the U.S., France, and Costa Rica who participated in this study.
By comparing the turtle’s movements with the fishing activity in the areas they migrate through, the researchers can locate the exact times and places where the turtles face the greatest risk. With this information changes could be made to protect the leatherbacks.
Fishing activity is a severe problem with the leatherbacks because they often turn up as bycatch. They can easily get hooked on longlines. “What often happens with longliners is that it is just inconvenient to hassle with a turtle and they don’t want to lose the hook, either, so what people will do is just cut the flipper off with a machete and just send the turtle away to die,” said Shillinger. “A turtle without a front flipper is a dead turtle.”
In three sessions from 2004-2007 Shillinger and co-author Bryan Wallace of Duke University and Conservation International, along with a team from Playa Grande National Park, tagged 46 female leatherback turtles. The tags emitted signals that were picked up by satellites, allowing the team to track the turtles’ position.
The leatherback tagging study is part of the Tagging of Pacific Predators (TOPP) program. TOPP is part of the Census of Marine Life, a global network of researchers from more than 80 nations participating in a 10 year program to “assess and explain the diversity, distribution, and abundance of life in the oceans.”
Shillinger and his colleagues also worked with research oceanographers and co-authors Steve Bograd and Helen Bailey at NOAA and Daniel Palacios, at NOAA from the University of Hawaii. They studied turtle speeds and movements and found that they were heading in a south-southwesterly direction to the South Pacific Gyre year after year.
The South Pacific Gyre is a vast, barren region. Satellite images, often used to determine levels of chlorophyll by the color of the water, show crystal clear water with no good reasons why the leatherbacks migrate here. However, the satellite can only penetrate about 25 meters below the surface so it is possible that the turtles are targeting something deeper in the water.
“What they are doing there is a big question,” said Shillinger. “Perhaps the tremendous water clarity may work to the advantage of these leatherbacks because they are visual predators,” he said.
Whatever the reason, they always return to Costa Rica to lay their eggs on the shores of Playa Grande. Progress is being made there because the locals who used to take the turtle eggs to sell for profit are now being paid to protect them. The leatherbacks are also bringing in new tourism, helping the economy and drawing more attention to their problems.
This is a step in the right direction but more needs to be done. “It is still at the early stage globally, putting together large transboundary, transnational, plans for protecting highly migratory species like turtles,” Shillinger said. “First and foremost, you need political will and a framework in which to operate.” There is hope though because international conventions have already set agreements on the need to save other endangered ocean species. Shillinger says that as more people become aware the governments are slowly starting to take action, “I wouldn’t write these turtles off.”
Copyright © 2008 by OceanLines