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Local scientists tout success of 'revolutionary' way to tag sea turtles

A loggerhead sea turtle in rehabilitative care at the Aquarium’s Sea Turtle Hospital.
New England Aquarium
A loggerhead sea turtle in rehabilitative care at the Aquarium’s Sea Turtle Hospital.

Scientists at the New England Aquarium say they’ve developed a “revolutionary” way to monitor threatened and endangered sea turtles over long periods of time.

After rehabbing four loggerhead sea turtles that were found cold-stunned on Cape Cod beaches, researchers surgically implanted acoustic tags just under the turtles’ skin, and have since found them thriving in the wild.

“And yes, their names are hilarious. … We had Captain Kool-Aid, Popeye, Glossy Ibis and Peanut,” said Kara Dodge, a sea turtle expert and research scientist at the New England Aquarium.

While tagging turtles after rehabilitation is not a new concept, sedating and implanting an acoustic tag just above the animal’s hip —versus affixing a satellite tag to a shell — is a completely new method for sea turtles.

A typical satellite tag often only lasts about three or four months and can cost from $2,000 to $5,000.

“The advantage of an acoustic tag is that they are a longer duration tag. They can last up to — depending on the model— three to 10 years,” Dodge said. “They also are an order of magnitude less expensive. So these tags we used for this past round of loggerheads were about $400 apiece. So in theory, you could tag many, many more animals at a much lower cost.”

That prospect — which could better inform researchers about sea turtle migration, breeding, and rehabilitation patterns — is thrilling to Dodge.

“We really only get such limited amounts of data during our post-release monitoring with these turtles [using satellite tags], so being able to get three years of detection data will be amazing,” she said. “I don't want to sound dramatic, but it will be kind of revolutionary.”

One benefit of satellite tags, however, is that they provide researchers with real-time data about a sea turtle’s exact location. By contrast, researchers need to pull acoustic receivers from the water and download their data first, causing a delay.

“The satellite tags work with our polar orbiting satellites, so every time the turtle surfaces to breathe … [if] the antenna breaks the surface, and if there's a satellite in view of the tag, then we can get data transmitted from the tag to the satellite,” Dodge said.

“But acoustic telemetry is different in the sense that basically these turtles have acoustic pingers. I think the description of the E-Z Pass system is really good. … As a turtle is swimming along, [it’s] passing by these acoustic receivers that are out in the environment and those are listening for the pings from the acoustic tag on the turtle.”

For that technology to work, the turtle needs to be swimming through areas that have these acoustic receivers, but Dodge said there are thousands from the Gulf of St. Lawrence to the Gulf of Mexico, all along the Eastern Seaboard.

“The beauty of acoustic telemetry is that these receivers can listen to any acoustic tag, regardless of which animal is carrying it,” she said. “So it's really a multi-species listening system: a tuna passing by with a tag, or a sturgeon, or a sea turtle. The receiver is listening for all of those tags.”

Since the loggerheads were released off West Dennis beach, the receivers detected three of them nearly 100 times along the southern coast of Massachusetts between August and October. One turtle, Popeye, hasn’t been picked up by any of the acoustic receivers, but Dodge said it’s not cause for worry.

“In Nantucket Sound, we had 10 receivers out and they were sort of dotted throughout Nantucket Sound,” she said. “But there are plenty of places in the sound where we did not have receivers, so it could have easily … made its way out quickly. It could have easily bypassed our acoustic receivers.”

For the other three, Dodge said, so far, so good: while Peanut was detected on inshore and offshore receivers in the eastern part of Nantucket Sound, Captain Kool-Aid and Glossy Ibis were detected on inshore receivers off Waquoit, Hyannis Harbor, and Bass River.

A loggerhead undergoes surgery to implant an acoustic tag.
New England Aquarium
A loggerhead undergoes surgery to implant an acoustic tag.

The data gathered not only shows the turtles thriving in the wild, Dodge said, but is providing researchers with valuable information on where the turtles are traveling and likely feeding.

“The conservation goal for this work is for you to release an animal that is healthy, returns to a wild behavior state and then ultimately contributes to the breeding population, which is what we need for the species to recover,” she said.

Last year more than 1,000 turtles were found cold-stunned on beaches around Massachusetts, according to Mass Audubon Wellfleet Bay Wildlife Sanctuary. If the acoustic tags prove to be safe and effective, Dodge said she hopes the team will be able to implant internal tags in rehabilitated turtles of different species and sizes in the future.

“Then ultimately, I think we'd like to be able to see if this can be safely brought into a field setting, which would allow scientists who are working with wild-caught turtles to be able to actually put these tags on not just rehabbed turtles,” she said. “We need to do close monitoring and [keep] doing surgeries in a hospital setting, but I think ultimately that's where we'd like to see this go.”

Eve Zuckoff covers the environment and human impacts of climate change for CAI.