A diamondback terrapin swims after being released July 6 on Chenier Ronquille Island near Grand Isle, Louisiana. The turtle was one of 31 rescued as eggs last summer because the island was being restored. (Scott Threlkeld/The Advocate via AP)

Twenty-one 11-month-old turtles returned this week to the Louisiana barrier island where their mothers laid the eggs from which they hatched.

The diamondback terrapin nests were dug up to protect the eggs during restoration of Cheniere Ronquille after the 2010 oil spill. Now that work is finished, and the 4- to 5-inch-long turtles — hatched and raised by volunteers — returned Thursday.

Diamondback terrapins, which live along the coast from Texas to New England, are the only U.S. turtle that lives in brackish waters. They may be best known as the University of Maryland’s mascot and as the turtles that stop traffic at New York’s John F. Kennedy Airport when females trundle across the tarmac to look for sandy ground to lay their nests in June and July.

They’re listed as “near threatened” by the International Union for Conservation of Nature, as a species that could become threatened unless commercial trade is restricted. Habitat loss and sales to the Asian pet trade are among the biggest problems, according to the U.S. Fish and Wildlife Service’s application for that listing.

These turtle eggs were turned up about a year ago, when restoration crews supervised by the National Oceanic and Atmospheric Administration dug trenches around the island to ensure that no ground-nesting shorebirds would be laying eggs there, said Keri Landry, an endangered species biologist with the Louisiana Department of Wildlife and Fisheries.

A diamondback terrapin turtle released to a grassy area looks for the water July 6 on Chenier Ronquille Island. Twenty-one of the turtles that hatched in captivity 11 months ago were released on the barrier island. (Scott Threlkeld/The Advocate via AP)

She said dredged sediment was to be layered over the island, which would have buried the turtles’ nests about two feet deep, far beyond a hatchling’s ability to escape.

The crews turned up 10 or 12 nests, roping off each so Landry could collect the eggs. When she did, she marked each egg to show which end was up.

“After maybe a day or so, if you roll them, they’re not going to be viable,” said Stephen Creech, who hatched and raised the eggs. He said he and wife Rachael, owners of Adventure Pets in Mandeville, Louisiana, received 31 from Dave and Karen Milliken, whose incubators held the eggs for about a week last July.

Twenty-four hatched in August, and three hatchlings died. The rest have been growing since then in 150-gallon tubs with shallow brackish water, rocks and oyster shells for them to climb on, and ultraviolet lights and heated water to keep them warm.

“They’re beautiful. Mostly black and tan. Their heads are gray,” Creech said.

Creech says he also has a 10-inch-long full-grown female but plans to return her to the breeder who gave her to him.

He said he’d love to keep her in the pond in front of his store, “but she keeps chomping on my koi.”