Environment: Endangered sea turtles’ feeding grounds overlap with degraded areas in the Gulf of Mexico

Photo: Kim Bassos-Hull, Mote Marine Laboratory
A Kemp’s ridley sea turtle. Photo courtesy Kim Bassos-Hull, Mote Marine Laboratory.

Federal study may help conservation efforts

By Summit Voice

FRISCO — While Kemp’s ridley sea turtles mostly nest in protected areas, they may still be subject to threats in their key feeding grounds, according to National Park Service and U.S. Geological Survey researchers.

After tracking the turtles for 13 years, biologists found that the favored feeding grounds of the endangered turtles coincide with some Gulf of Mexico waters that are subject to oil spills, extensive commercial fishing and oxygen depletion.

The study is the first to offer details on foraging locations and migration patterns of the Kemp’s ridley sea turtles, considered to be the most endangered hard shell sea turtle in the world.

Scientists do not know why the turtles feed where they do, how human influences may affect turtle health or behavior, or whether human impacts on their chosen feeding areas might change their future foraging behavior.

The researchers identified the feeding grounds by analyzing 13 years of satellite-tracking data. The researchers tagged turtles at nesting sites between 1998 and 2011 and tracked them as they went on to foraging locations throughout the Gulf. Turtles from two major nesting sites in the study fed at specific locations off the coasts of Louisiana and Mississippi and at other locations in the Gulf.

“Protecting feeding grounds for adult female sea turtles is important for the recovery of the species and this new information is important for future planning and restoration decisions,” said Donna Shaver, chief of the National Park Service’s Sea Turtle Science and Recovery Division at Padre Island National Seashore.

Cooperative efforts between Mexico and several U.S. agencies have helped increase the population of this species of sea turtle. Species support includes protection of nesting turtles and their eggs on nesting beaches and reducing threats from fishing. The number of Kemp’s ridleys nesting in the region has increased from 702 nests in 1985 to about 22,000 in 2012.

The research, in which dozens of adult female sea turtles were tagged after they nested on the beach at Padre Island National Seashore offers a “first glimpse” of how and when the turtles feed, said Kristen Hart, a research ecologist for the USGS Southeast Ecological Science Center. “We were able to decipher Kemp’s ridleys foraging behavior in space and time using a combination of satellite telemetry and new statistical techniques.”

Previous tracking studies generally showed Kemp’s ridley migration from nesting beaches along the Gulf of Mexico coastline to northern Texas and Louisiana with some turtles migrating as far as peninsular Florida. Until the current study, it was not known whether turtles displayed movement behavior indicative of foraging or migration at a particular location. The modeling done as part of the study has allowed scientists to pinpoint where these turtles may be feeding, a key finding in terms of identifying important at-sea habitats for these imperiled turtles.

In addition to tagging turtles at Padre Island, Shaver said the researchers tagged turtles at nesting sites in Rancho Nuevo, Mexico, about 200 miles south of Padre Island.

“This is the first time we’ve tracked the Mexican turtles to habitats in the Northern Gulf of Mexico,” she said.

The feeding habitat discovery came when scientists differentiated time the sea turtles spent in feeding or breeding mode from the time spent migrating. Once scientists located when and where the turtles were feeding, they were also able to coarsely profile what type of habitat offered the best feeding grounds for Kemp’s ridleys.

“We have a lot more to learn about how and why Kemp’s ridleys use their foraging sites,” Hart said. “We don’t know enough about individual turtles yet to draw conclusions about their behavioral responses to conditions at foraging grounds, and we are just beginning to understand differences among different sea turtles species. For example, Kemp’s ridleys appear to migrate, then feed, and then migrate to a final feeding destination. Loggerheads, in contrast, seem to head straight for feeding hotpots.”

“We plan to continue fleshing out the major scientific gaps that managers need addressed in order to develop long-term survival and recovery plans for Kemp’s ridleys,” Hart said.

Read the study, “Foraging area fidelity for Kemp’s ridleys in the Gulf of Mexico,” in the journal Ecology and Evolution.

Background

The Kemp’s ridley turtles are considered the smallest sea turtle in the world, with adults reaching about 2 feet long and weighing up to 100 pounds. They are found in the Gulf of Mexico and the Atlantic seaboard and feed primarily on crab species living on the sea floor of shallow waters. Their name comes from a fisherman named Richard Kemp of Key West, Florida, who provided the specimen used to describe the species in 1880. They are related to olive ridleys, another small sea turtle found around the world.

Kemp’s ridley sea turtles are listed in the U.S. and internationally as endangered throughout their range due to dramatic population declines in the 20th century. The vast majority of Kemp’s ridleys converge on three major sites in the state of Tamaulipas, Mexico every year to nest. In the early 1960s, a film was discovered that showed an estimated 40,000 females nesting at one particular site – Rancho Nuevo – on one day.

Threats to Kemp’s ridleys once included egg collection, overhunting, and unintentional capture during fisheries operations.  Today, most of their nesting occurs on protected lands. Nonetheless, nesting habitat is still sometimes disturbed by natural and human events such as hurricanes, oil spills, or erosion. Also, activities that affect the seafloor (what scientists call benthic habitat) can disturb their feeding habitat. This includes bottom trawling and dredging. Another known threat is incidental capture, or unintentional by-catch, in fishing gear.

Although conservation efforts began in the 1960s, the number of nesting females continued to decline. By 1978, the U.S. and Mexico started a multi-agency effort to safeguard Kemp’s ridleys from extinction by encouraging nesting at Padre Island National Seashore in Texas. Biologists have since been monitoring nesting activity, and there has been an increase in the number of nests since 1985.

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