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Science Trawl: Researchers Hunting Sea Turtles

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Hunting Sea Turtles - Mike Arendt measures the width of a turtle’s carapace. Photo By Jeff Dennis
Hunting Sea Turtles – Mike Arendt measures the width of a turtle’s carapace. Photo By Jeff Dennis

Hunting Sea Turtles


Hunting Sea Turtles is on in the coastal waters of South Carolina, Georgia and Florida. Two boat captains, two deckhands, one cook and four science personnel spend five days per week aboard Lady Lisa, a 75-foot St. Augustine shrimp trawler, catching sea turtles to submit to a brief scientific study before releasing them back into the ocean.

The National Marine Fisheries office both funds and permits the Southeastern U.S. turtle trawling operation headed by S.C. Department of Natural Resources biologist Mike Arendt in partnership with the University of Georgia’s Marine Extension Service.

Sea turtle nesting surveys conducted on barrier islands and beaches up and down the coastline only interact with mature females while laying eggs.

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“The sea turtle trawl survey covers about 500 randomly selected areas in these coastal waters,” says Arendt. “The survey is a relative abundance survey, and 85 percent sea turtles encountered are immature.”

On the very first trawl of a July cruise, a turtle from the other 15 percent comes aboard in the large-mesh nets. A male loggerhead estimated to be around 30 years old is gently lowered onto the deck and the science personnel spring into action. After acquiring a wealth of data recordings (see sidebar), the turtle deemed to be No. 674 caught by the Lady Lisa since 2000, splashes back into the Atlantic sporting two new flipper tags.

Deckhand Patrick Gerkin then resets the nets, which are dragged for 30-minute intervals before being winched up. No sea turtles are caught on the next three trawls.

“Seven to 12 sea turtles is what we average over a five-day sea turtle cruise,” says Arendt. “These are a long-lived species and the data sets that we are making now will benefit future studies as much as our immediate work. We will trawl between Winyah Bay, S.C. and St. Augustine, Fla., each season. We spend four nights each week on the boat so we can cover the greatest area per trip.”

The workdays are long, hot and arduous.

“The two Captains work a six-hour on and six-hour off rotation, while the two deckhands supervise the winches that operate the nets, and the cook is charged with providing three square meals a day in the galley,” Arendt says.

The science personnel share a unisex ‘condo’ below deck near where the fish boxes used to store loads of iced down shrimp. Trawling is normally conducted from 7 a.m. until 7 p.m. and an average workday might allow for 10 separate trawls. After a 7 p.m. clean up of the topside deck, the crew takes turns using the only shower and head aboard the trawler to get cleaned up and ready for sleeping in bunk beds.

Researcher Bree Tomlinson recalls that catching three loggerhead turtles during one trawl is one of her fondest recollections. “The first day at work I have to get my sea legs back, but by the third day I am fine,” Tomlinson says. “But after five days on the trawler, my legs are always wobbly when I get back on land.”

Tomlinson says smart phones help to dispel any feeling of isolation from being on the boat all week, and crewmembers sometimes watch a DVD movie to pass time at night.

All of the turtles encountered during this cruise, including several loggerheads and one Kemp’s Ridley, are observed to be in good health. However, if a turtle is weak or appears at-risk, then a photo of that turtle is sent to the sea turtle hospital at the S.C. Aquarium. If need be, the turtle will be brought in as a patient. This is just one example of how the sea turtle trawl combines with modern technology to make a difference one sea turtle at a time.

Overall, the findings are fairly positive. Each sea turtle encountered is tagged before being released, but the sea turtle trawls seldom recapture previously tagged specimens. Given the extensive tagging regimen applied, one might conclude that a bounty of juvenile sea turtles reside of the Southeastern coast.

“It will take decades before scientists can say if sea turtles are fully recovered,” says Arendt. “Currently loggerheads in the Southeast are listed as a threatened species.”

The trawler is an environmental education classroom at its best, keeping observers utterly fascinated. Guitarfish, long-spined urchins, starfish, egg cases and even a devilfish or manta ray came up in the nets as bycatch. Before being released, all of it is cataloged and entered into a database and, if unsure about a particular item, a photo is made to share with the correct specialist back in port. The variety of fish and invertebrates is stunning to see and it becomes apparent that sea turtles are one of the larger inhabitants found in these coastal waters.


Hunting Sea Turtles – Collecting Scientific Data


When a sea turtle is encountered, a physical examination begins with observations to determine if excessive barnacle build up exists or if scaling (peeling of the shell) is occurring. It’s not uncommon to see barnacles covering 25-percent of turtles’ bodies. A keratin biopsy is sometimes collected from the shell for a researcher in Florida who evaluates diet by analyzing stable isotopes. Twelve measurements of the carapace are taken including width and depth of shell.

“All our procedures are veterinarian-approved, and we keep the turtle onboard only as long as our tests require, making sure to keep the sea turtle wet with a saltwater hose,” says Arendt.

Antibacterial cream is applied to the carapace after taking a sample from the shell, and antiseptics are applied before drawing blood from the neck area.

“When drawing blood we try and be as gentle as possible with the turtle,” said Bree Tomlinson, who is then tasked with immediately processing the collection samples in the makeshift laboratory below deck. Spun in centrifuges for five minutes, the blood is separated into plasma, white blood cells and red blood cells for separate storage in liquid nitrogren. Special government permits allow for these tests, and other researchers across the Southeast rely on these sea turtle trawls to provide them with these crucial biological samples.

For more information, visit www.dnr.sc.gov/marine/sturtles/index.html.

Jeff Dennis is a Charleston native. Read his blog at www.LowcountryOutdoors.com.

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Jeff Dennis is an outdoor writer and photographer who grew up on a creek in Charleston loving the saltwater, and he contributes regularly to All At Sea Southeast. Read his blog at www.LowcountryOutdoors.com

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