Venomous Snakes Ride Ocean Currents Around the World

It has no arms and is about as long as a baguette, but that hasn’t stopped the yellow-bellied sea snake from conquering the world’s oceans.

Now, there's new evidence that the reptiles travel around the globe by just going with the flow.

The venomous snake can drift on ocean currents for thousands of miles—possibly clocking distances of 20,000 miles (32,190 kilometers) and more over 10 years, computer simulations show. That means that, at least theoretically, a snake could float from near the Philippines to east of Hawaii or from Mexico to the island of Mauritius in the western Indian Ocean. (Related: "What's This Tropical, Venomous Sea Snake Doing in California?")

“I’m impressed, especially because it’s a really small species,” says study co-author François Brischoux, a biologist at France’s National Center for Scientific Research.

At only a hundred to 200 grams (three to seven ounces), the snake “is not comparable with a whale, but the distances traveled are comparable” to those of a whale.

Overall the yellow-bellied sea snake boasts an incredible resume for an animal that weighs less than a mango. It breathes air, but can stay underwater for three and a half hours. Its arsenal includes venom that can kill a person—though deaths are not common—and a paddle-shaped tail that helps steer the animal through the water. It never lives on land and can survive for months in a state of dehydration.

Snakes on a Sea

Still, those skills don’t explain how the species managed to migrate from its evolutionary birthplace in southeastern Asia to the Americas to Africa. No other snake, land or sea, has a broader range.

Complicating matters, the yellow-bellied sea snake has flipped its tail at efforts to track it. In one experiment in the 1970s, a scientist tagged almost a hundred snakes and recaptured exactly four.

While at sea off Costa Rica, Brischoux and colleagues have seen large numbers of the snakes amid shoals of drifting flotsam, suggesting the animal drifts where the water carries it. (Watch fishermen catch huge numbers of live venomous sea snakes.)

So, using computer programs that simulate ocean currents, the researchers followed the progress of more than 10,000 “virtual snakes” set adrift from 28 different sites where the species is known to live.

After a decade of riding the waves, 12 percent of the “virtual snakes” were still alive, the researchers report in this week’s Biology Letters.

What’s more, their spread in the computer simulation is a good match for the snake’s current range.

Mixing It Up

The results also help explain why sea snakes from the eastern and western Pacific are genetically similar, despite the vast space between them. Drifting snakes would help ensure genetic mixing between populations, Brischoux adds.

Long-distance reptile rafting is known to science, even by species that live mostly on land—though these voyages occurred when the continents were closer together. Iguanas on the eastern Pacific island of Fiji originated in South America, and crocodiles rafted from Africa to the Americas, says Peter Uetz, curator of the Reptile Database and a professor at Virginia Commonwealth University. (Also read how some mammals may have rafted to Madagascar from mainland Africa.)

Such epic journeys make the study’s results plausible, Uetz says, but he’s “a little bit skeptical” because most data on sea snakes comes from animals seen close to the coasts. What happens to them in the open ocean may be very different, he says.

For instance, it's well known that the tropical snakes have trouble tolerating cold water.

But Brischaux responds his model showed many of the animals managed to drift for 10 years without spending too much time in lethally chilly waters.

“I was not expecting this high survival rate … and the really long distances the [simulated snakes] were able to travel.”