Study Identifies Pacific Danger Zones for Critically-Endangered Leatherback Sea Turtles

Leatherback turtle. Image credit: Ricardo F. Tapilatu.

The majestic leatherback turtle is the largest sea turtle in the world, growing to more than 6 feet in length. It is also one of the most threatened. A major new study of migration patterns has identified danger zones in the Pacific Ocean for this critically endangered species. This new understanding could help inform decisions about fishing practices to help reduce further deaths of this fragile species. Drexel University’s Dr. James Spotila, a leading sea turtle expert and professor of biology in the College of Arts and Sciences, was coordinator for the study involving collaborators worldwide.

“The study shows that leatherbacks can be found throughout the Pacific Ocean and identifies high-use areas that are of particular importance to their survival,” said lead author Dr. Helen Bailey of the University of Maryland Center for Environmental Science. “This information on their movements is essential for identifying hot spots and assessing where limiting fishing at particular times of year may be effective for protecting leatherbacks.”

Leatherbacks are the widest-ranging marine turtle species and are known to migrate across entire ocean basins. Female leatherbacks lay their eggs on tropical nesting beaches, but then migrate to foraging areas to feed on jellyfish. These long-distance migrations are likely to increase the risk that these animals may be caught in fishing gear, undermining conservation efforts to protect turtles on their nesting beaches. Interaction with fisheries is believed to be a major cause of death, which is of particular concern in the eastern Pacific Ocean, where the number of leatherback turtles has dropped by more than 90% since 1980.

 “Leatherback turtles are long-lived animals that take a long time to reach maturity, so when they are killed in fishing gear it has a huge impact on the population,” said Spotila. “Their numbers are declining so rapidly it is critical that measures are taken quickly to ensure these animals don’t go extinct.”

Leatherback turtles can travel enormous distances between their nesting and feeding sites. In the Pacific Ocean there are two populations of leatherback turtles that nest in the eastern and western Pacific. The study used state-of-the art satellite tracking, the largest satellite telemetry data set ever assembled for leatherbacks, to track 135 turtles. Leatherbacks in the eastern Pacific were tagged at the nesting sites in Costa Rica and Mexico. The western Pacific population was tagged at two nesting sites in Indonesia and at foraging grounds off the coast of California. The tracks were combined with oceanographic satellite data provided by NOAA, NASA, and a number of international partner space agencies to provide important insights into their long distance migrations.

The study found that the western Pacific population nesting in Indonesia traveled to many different feeding sites in the South China Sea, Indonesian seas, southeastern Australia, and the U.S. West Coast, mainly in highly productive coastal areas. This wide dispersal allows for a greater likelihood to find food. It also means that the turtles are more vulnerable to being caught unintentionally by fishing gear in coastal and offshore areas.

The study found that the western Pacific population nesting in Indonesia traveled to many different feeding sites in the South China Sea, Indonesian seas, southeastern Australia, and the U.S. West Coast, mainly in highly productive coastal areas. This wide dispersal allows for a greater likelihood to find food. It also means that the turtles are more vulnerable to being caught unintentionally by fishing gear in coastal and offshore areas.

The eastern Pacific population had a very different migration pattern, traveling from their nesting sites in Mexico and Costa Rica to the southeast Pacific. These turtles migrated south and tended to feed in offshore upwelling areas where their food, almost exclusively jellyfish, may be concentrated. The more limited feeding areas of the east Pacific turtles makes them more vulnerable to any changes that occur to the distribution or abundance of jellyfish in this area. Deaths caused by human activities, such as being caught in fishing gear, also pose a greater risk of causing this population to go extinct because they have a smaller range than the western Pacific leatherbacks.

Renowned experts from around the world joined together to work on this landmark study of leatherback turtle migration. The collaboration included Helen Bailey of the University of Maryland Center for Environmental Science; James Spotila of Drexel; George Shillinger and Barbara Block from Hopkins Marine Station of Stanford University; Stephen Morreale of Cornell University; Frank Paladino of Indiana-Perdue University; Scott Eckert of the Wider Caribbean Sea Turtle Conservation Network; Rotney Piedra of Parque Nacional Marino Las Baulas; Creusa Hitipeuw of the World Wildlife Fund for Nature-Indonesia; Ricardo Tapilatu of The State University of Papau; and Peter Dutton, Scott Benson, Steven Bograd, Tomoharu Eguchi and David Foley of the National Oceanic and Atmospheric Administration (NOAA).

The study, “Identification of distinct movement patterns in Pacific leatherback turtle populations influenced by ocean conditions,” appears in the March issue of Ecological Applications.

The study was supported by funding the from Lenfest Ocean Program, the Leatherback Trust, the Tagging of Pacific Predators program of the Census of Marine Life, and the NOAA-Fisheries Service.

Spotila is a pioneer in the field of sea turtle research who has made key contributions to the understanding of their physiology and behavior, and brought awareness to the threats they face. He was part of the team that attached a transmitter to a sea turtle for the first time, was first to recognize the impending disappearance of the leatherbacks from the Pacific Ocean and the first to document the connection between sex determination and nest temperature. He is the author of the award-winning illustrated book Sea Turtles: A complete guide to their biology, behavior and conservation (2005) and of Saving Sea Turtles: Extraordinary stories from the battle against extinction (2011).