PHUKET, Thailand (Reuters) - Off the shore of Thailand's resort island of Phuket, marine conservationists have released 11 baby leatherback sea turtles into the Indian Ocean, hoping they can thrive in the wild and return in two decades to reproduce.

The release of the year-old turtles, each about the size of a rugby ball, follows an intense conservation effort to boost the leatherback's survival chances after the discovery in 2018 that the endangered species had returned to lay eggs in southern Thailand.

The stronger turtles have successfully made their way into the ocean, while others perished after hatching, so a programme was launched to nurse the weak baby leatherbacks, according to Pinsak Suraswadi, Director-General of Thailand's Department of Marine and Coastal Resources.

Thailand is one of five countries, including Sri Lanka and Canada, that have been able to nurse this species of baby turtle up to their first year. A typical leatherback will lay eggs after 20 to 25 years.

They were released in April by conservationists and have satellite tags to monitor their progress, part of an international initiative by the non-profit conservation organisation Upwell Turtles.

"It's necessary for us to study the travel routes of the baby turtles to understand where they are going so that we can implement measures to protect the leatherback turtle while they are hatching from their nests," said Pinsak.

Despite having an evolutionary history of more than 150 million years and surviving the extinction of the dinosaurs, the species is now critically endangered in the Pacific region.

This type of turtle has an estimated population in the Pacific of fewer than 2,300 adult females, according to the World Wildlife Fund.

After their release, the turtles still face dangers from fishing gear, eating plastic waste, and exposure to toxins.

"I'm happy to know whether our effort in nurturing the leatherback sea turtles for a year proves fruitful or not," said senior fishery biologist, Hirun Kanghae.

"If they survive it answers everything about the conservation and population restoration of the leatherback sea turtles in the best way possible," he said.

(Writing by Chayut Setboonsarng; Editing by Martin Petty and Ros Russell)

By Napat Wesshasartar