Sea Snakes Stay Dehydrated up to 7 Months Waiting for Fresh Drinking Water

Dehydration may not seem like a problem sea snakes would encounter. After all, they live their lives in water. But according to a University of Florida researcher, sea snakes can be dehydrated for months at a time, waiting for fresh rainwater to quench their thirst.

The claim goes against a long-standing belief that marine vertebrates have evolved to use salt water to meet their hydration requirements, according to UF biologist Harvey Lillywhite, who reports his finding in the Proceedings of the Royal Society B.

"These snakes refuse to drink salt water, even when dehydrated," Lillywhite said in statement. "They need fresh water to survive."

Despite sea snakes being surrounded by water, they don't drink it, Lillywhite said, noting that the idea that the sea snakes use salt glands to distil the water of excess salt does not appear to be true.

While the snakes to excrete salt, "no sea snake we have tested drinks sea water," Lillywhite said.

Lillywhite and his colleagues spent three years conducting field studies in tropical waters, where they observed yellow-bellied sea snakes (Pelamis platura), one of the most widely distributed sea snakes. The researchers also studied the snakes in the laboratory, finding that in both environments the sea snakes shunned salt water and would only drink fresh water.

Because fresh rain water is less dense than sea water, it floats on the top of it, forming a thin lens of water. Sea snakes drink this instead of salt water.

The snakes appear to sense rainfall, Lillywhite said, noting a change in the snakes' behavior during the approach of a tropical storm.

The open ocean, during the dry season, is like a desert. A lack of rain can stretch for six or seven months in some regions, such as Guanacaste, Costa Rica, where the snakes were studied.

When fresh water is available for the snakes to drink, they may just take small amounts of it. But in other cases, the sea snake will gorge itself on fresh water, consuming up to 25 percent of its body weight in rainwater.

Lillywhite noted that diminishing rainfall may be linked to declining sea snake populations in some areas, such as Northern Australia, which has been struck by drought.

"Understanding the water requirements and drinking behaviors of marine vertebrates could help with conservation efforts," Lillywhite said. "In areas of intensifying drought, they will need to move or die out.