The yellow-bellied sea snake has the widest range of any snake on the planet. And if the last few years are any indication, its range might be getting even bigger—thanks to climate change.
In January, one of the highly venomous, brightly colored serpents washed up on southern California's Newport Beach—only the fifth such snake ever recorded in the region.
Native to the world's tropical oceans, the reptile was several hundred miles north of its typical range, from southern Mexico north to Baja California. It follows three others that washed up in the winters of 2015 and 2016, and a fourth from 1972.
The previous four snakes all had something in common: They washed up during El Niño years, when ocean currents change and sometimes carry unwitting species far from home.
"Currents are doing weird things, and ocean temperatures are much warmer, so that kind of makes a lot of sense," says Greg Pauly, a herpetologist at the Natural History Museum of Los Angeles County.
What makes less sense is why one would show up in 2018, which is not an El Niño.
The Occasional Waif
The yellow-bellied sea snake is the only sea snake that lives in the open ocean, feeding on small surface fish and floating on currents, according to University of Florida biologist and sea snake expert Harvey B. Lillywhite.
The animals survive by drinking rainwater that falls on the sea surface, and give birth to live young—typically three to six offspring at a time—right into the water.
The species is happiest in waters above 65 or 66 degrees Fahrenheit; any colder and they're unable to digest food. Still, because ocean currents largely dictate their movements, the reptiles sometimes float outside of their preferred habitat, Lillywhite explains. (See what happens when a sea snake battles a deadly stonefish.)
"So periodically one will show up in New Zealand, one will show up in California. What we're talking about is the appearance of an occasional waif," Lillywhite says.
The Davidson Current runs from south to north deep below the surface about 10 to 20 miles off Baja and southern California, along the edge of the continental shelf.
From October through February, the current rises toward the surface, where it can pick up snakes floating near Baja and scoot them northward. Historically, there haven't been a lot of snakes along Baja's Pacific Coast to begin with. (Read how pollution is turning sea snakes black.)
But Pauly suspects that warming waters are causing yellow-bellied sea snakes to creep northward along the Pacific coast—increasing the chances that more animals get swept up into the Davidson Current.
"This is all speculation," he admits, but it's one that Lillywhite agrees with. "With global warming, we anticipate that some sea snakes' ranges are going to expand," Lillywhite says.
It makes sense that climate change would affect wide-ranging, open-water species first, says Pauly. Take the brown booby, an open-water seabird.
"For decades [it] has been moving northward up the Pacific coast, and just this past November was documented on this little chunk of rock off the Channel Islands," he adds.
Fun... But Terrifying
Stressed out, exhausted, and with bodies ill-suited for slithering on sand, yellow-bellied sea snakes are usually dead or dying by the time a beachgoer notices them. (See "Spiny, Venomous New Sea Snake Discovered.")
On the day the most recent snake washed up, the local sea surface was a frigid 61 degrees Fahrenheit—likely why it was close to death.
The animal was first reported to biologists at the Pacific Marine Mammal Center, who then contacted Pauly.
Humanely euthanized and added to the collections of the Natural History Museum of Los Angeles County, the specimen could help biologists gain insight into how climate change may be altering wildlife communities off southern California.
"On the one hand, I'm pretty excited that we've got yellow-bellied sea snakes showing up off of the coast. As a herpetologist, that's kind of fun," says Pauly.
"But the underlying cause is pretty terrifying."