By Amanda Orr

HOUSTON (Reuters) - More than 50 green sea turtles were released into the Gulf of Mexico off the Texas coast on Friday after recovering from cold-stunning, or hypothermia, brought on by a drastic drop in water temperature.

The release has taken place in phases, with Friday being the last major release for sea turtles rescued after a mid-November cold snap in Texas sent temperatures below freezing in large parts of the state.

"We wait until the Gulf waters are warm enough to prevent a repeat cold-stunning event for these individuals," said Donna Shaver, chief of the Division of Sea Turtle Science and Recovery at Padre Island National Seashore.

As with other reptiles, sea turtles rely on their external environment to regulate body temperature and cold-stunning occurs when water temperatures drop below 50 degrees Fahrenheit (10 degrees Celsius), she said.

Symptoms include decreased heart rate and lethargy, which renders the turtles virtually paralyzed and leaves them vulnerable to injury or death by predators and boats.

Over 100 cold-stunned green sea turtles were found floating or washed ashore on the Padre Island National Seashore this month. Rescuers brought turtles swaddled in towels to the rehabilitation facility where they received treatment that included intravenous fluids in the most severe cases.

"I hope that there are no more events this year but we just don't know," Shaver said.

(Editing by by Jon Herskovitz and Sandra Maler)