Sea snakes of a species not seen for 15 years and believed extinct have been found alive and kicking — well, swimming — in the ocean waters off Australia's west coast, researchers report.

Short-nosed sea snakes have not been seen in a decade and a half since they disappeared from the only native habitat of the species on Ashmore Reef in the Timor Sea, they say.

However, two examples of the species, alive and healthy, have been identified on another reef, Ningaloo Reef, more than a thousand miles from Ashmore.

"We were blown away. These potentially extinct snakes were there in plain sight, living on one of Australia's natural icons, Ningaloo Reef," says Blanche D'Anastasi from James Cook University.

"What is even more exciting is that they were courting, suggesting that they are members of a breeding population," she says.

Another surprising discovery, the researchers said, was a substantial population of another rare sea snake species, the leaf scaled snake, living in lush sea grass in the same region.

Both the short-nosed and leaf scale snakes are classified as critically endangered under Australia's threatened species legislation.

"This discovery is really exciting; we get another chance to protect these two endemic Western Australian sea snake species," says D'Anastasi at the university's ARC Center of Excellence for Coral Reef Studies.

Despite their excitement of the findings, reported in the journal Biological Conservation, the researchers say there has been ongoing concern over a decline in sea snake populations in a number of marine areas.

Why they are disappearing is unknown, although some scientists suggest coral bleaching caused by climate change could be a factor.

Human activity may also be a reason, says Vimoksalehi Lukoschek of the ARC Center.

"Many of the snakes in this study were collected from prawn trawl by-catch surveys, indicating that these species are vulnerable to trawling," she says.

However, the disappearance from the protected Ashmore Reef cannot be because of trawling and cannot at present be explained, she notes.

"Clearly we need to identify the key threats to their survival in order to implement effective conservation strategies if we are going to protect these newly discovered coastal populations," she says.

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