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Gloucester scientists track migration of giant sea turtles

Gloucester-based scientists  Michael Dodge (left) and Kara Dodge preparing to release a satellite-tagged adult leatherback sea turtle.

Connie Merigo

Gloucester-based scientists Michael Dodge (left) and Kara Dodge preparing to release a satellite-tagged adult leatherback sea turtle.

Marine scientists in Gloucester have published new findings from the first successful satellite tagging study of the largest living turtle species, which can stretch to 10 feet long and weigh up to 2,000 pounds.

In the study — conducted from 2007 to 2010 — 20 migrating leatherback sea turtles were tagged and tracked, primarily off the Massachusetts coast.

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Researchers catalogued the turtles’ habitats, diving activity, and search behavior, which will help scientists develop their understanding of the breed, known for its size and its rubberlike shell, or carapace. The findings were published last month in a Public Library of Science academic journal, PLOS ONE .

“Up to this point, leatherbacks have been an enigma,” said Kara Dodge, a marine scientist at the University of Massachusetts Amherst’s Large Pelagics Research Center in Gloucester, who led the study as her doctoral project for the University of New Hampshire. “We can’t protect them unless we know where they are, and what kind of habitat they depend on.”

Listed as an endangered species by the US Fish & Wildlife Service, the leatherbacks’ unique biology and wide-ranging travel pattern makes it a particularly interesting species, said center director Molly Lutcavage, a research professor who has studied the turtles since 1985 and was part of the team that developed the attachment used to tag the turtles for satellite tracking.

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“The leatherback is the only living reptile that maintains a warm body temperature, like the extinct dinosaurs that were warm-bodied, and that means that even though it’s a so-called cold-blooded reptile, it actually functions like a mammal,” said Lutcavage, senior author and principal investigator for the project. “It keeps its body warm, which means it can stay as much as 15 or 18 degrees warmer than the ocean that it’s in. For that reason, leatherbacks can travel all the way up almost to the Arctic — they make their way all the way to Greenland — and they can also dive deeply to really cold waters, as cold as 49 degrees.”

The study points out their large body size, the ability to adjust their metabolic rate, and insulating layer of fat allows leatherbacks to maintain their core body temperatures.

“Not only does it get around the entire Atlantic Ocean, but it travels from the surface to over 4,000 feet’’ deep, Lutcavage said. “It’s a turtle that has very few restrictions on its travel.”

Most previous reports have focused on adult females in warmer climates, the paper noted, but the Gloucester-based study also followed immature and adult male leatherbacks in their northern US feeding grounds. Among the findings: The 20 leatherbacks tagged spent significant time along the Northeast continental shelf — which stretches from Cape Hatteras, N.C., to the Gulf of Maine — during the summer and fall, when jellyfish, their prime food source, are plentiful.

The turtles migrate from New England waters to subtropical and tropical habitat for the winter, and females lay their eggs on Caribbean and Florida beaches in the spring.

According to the National Oceanic and Atmospheric Administration, the biggest threats to the survival of leatherbacks are the harvesting of eggs by humans, and incidents where the turtles become entangled in fishing gear.

The information compiled in the Gloucester study is important, the paper published by the Large Pelagics Research Center states, because “coastal ecosystems are under intense pressure worldwide, with some of the highest predicted cumulative impact in the North American Eastern Seaboard and the eastern Caribbean. Parts of those regions constitute high-use habitat for leatherbacks in our study, putting turtles at heightened risk from both land- and ocean-based human activity.”

David Rattigan may be reached at drattigan.globe@gmail.com.
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