Washington, Nov 7 : Experiments have shown that sea snakes seek out freshwater when they are thirsty rather than saltwater.
The experiments were conducted by Harvey Lillywhite, a University of Florida zoologist, and his team.
It was previously believed that the roughly 60 species of venomous sea snakes worldwide satisfy their drinking needs by drinking seawater, with internal salt glands filtering and excreting the salt.
But, experiments with three species of captive sea kraits, captured near Taiwan, found that the snakes refused to drink saltwater even if thirsty, and then would drink only freshwater or heavily diluted saltwater.
In the lab studies, Lilywhite's team kept snakes caught in the wild near Orchid Island, Taiwan, away from freshwater for two weeks.
At the end of that period, dimpling of the snakes' scales indicated they were dehydrated.
The researchers weighed the snakes, freed them in saltwater tanks for up to 20 hours, then weighed them again.
None gained appreciably, indicating they didn't drink, despite their thirst. But when the researchers freed the snakes to swim in freshwater tanks, most immediately drank significant amounts.
More experiments revealed the snakes would drink only freshwater or highly diluted saltwater.
"Our experiments demonstrate they actually dehydrate in sea water, and they'll only drink freshwater, or highly diluted brackish water with small concentrations of saltwater - 10 to 20 percent," Lilywhite said.
Harold Heatwole, a professor of zoology at North Carolina State University and expert on sea snakes, has termed Lillywhite's conclusion "a very significant finding."
"This result probably holds the key to understanding the geographic distribution of sea snakes," he said.
According to Lillywhite, the sea snakes that spend their lives in the open ocean drink water from the "lens" of freshwater that sits atop saltwater during and after rainfall, before the two have had a chance to mix.
That would explain why some seawater lagoons, where the waters are calmer due to protection from reefs, are home to dense populations of sea snakes.
Sea snakes are members of the elapid family of snakes that also includes cobras, mambas and coral snakes.
They are thought to have originated as land-dwelling snakes that later evolved to live in oceans. Most spend all, or nearly all, of their lives in seawater, including giving birth to live young while swimming.