Nearly two-dozen turtles that were stranded by cold weather last year in Massachusetts have successfully undergone rehab and returned to waters off Louisiana’s coast.

More than 1,200 young and “cold-stunned” Kemp’s ridley sea turtles were stranded in November and December. According to the National Oceanic and Atmospheric Administration, “cold-stunning” occurs when the circulatory systems of sea turtles exposed to frigid water temperatures for several days slow down to a point where the turtles cannot function.

Various sea-turtle rehabilitation facilities along the east and Gulf coasts joined in the effort to care for the stunned turtles.

Suzanne Smith, stranding-and-rescue coordinator for the Audubon Nature Institute for Marine Mammals and Sea Turtles, said 21 of the 27 turtles she and her colleagues received were released into the Gulf of Mexico, 24 miles off the coast of Grand Isle, on Thursday.

“It was a beautiful day,” she said. “We couldn’t have asked for a more beautiful day.”

The turtles were placed in open produce boxes and carefully transported for about 100 miles from the institute’s aquatic centre before being loaded on to the back of two boats, one provided by Audubon and the other by the state Department of Wildlife and Fisheries. Carefully shielded from the sun, they were then transported 24 miles out to sea, where the boats’ engines were shut off to ensure the turtles’ safe re-entry into the wild.

A released Kemp’s ridley turtle dives into the warm waters of the Gulf of Mexico. Photograph: Gerald Herbert/AP

Each turtle was released by hand on a cloudless, sunny day with temperatures in the low 70sF and calm seas – a sharp contrast to the conditions that existed when they were stranded in New England.

The turtles immediately swam from the boats, disappearing into the sun-warmed water as Smith and Audubon Nature Institute veterinarian Dr Tres Clarke exchanged a triumphant high-five.

One of the 27 turtles the Audubon institute received did not survive, Smith said. The other five, which had suffered from pneumonia or problems with their shells and flippers, will remain in the rescuers’ care for about a month to receive antibiotics and nutrition.

“Their prognosis, though, is good,” she said.