'Extinct' Highly Venomous Sea Snake Rediscovered in Ocean's Twilight Zone

Last week, scientists conducting research on Western Australia's Ashmore Reef became the first humans to lay eyes on a short-nosed sea snake at the site in more than two decades. Olive-colored and critically endangered, the snakes have been thought locally extinct for 23 years.

Like cobras, taipans, and death adders, the short-nosed sea snake is a member of the Elapidae family, meaning that it possesses short, hollow fixed fangs capable of injecting predominantly neurotoxic venom.

In short, it's not an animal you want to encounter in the course of a swim. Luckily for them, the scientists were safe inside a research vessel "equipped with advanced robotic technologies" at the time of rediscovery, according to ABC Science.

"The robot was looking at a dead shell and [the researchers] were trying to pick it up and it had a sea snake sitting next to it," Blanche D'Anastasi, a sea snake expert at the Australian Institute of Marine Science, said. "They asked to zoom in on it and they [both] realized straight away it was a short-nosed sea snake. They contacted me soon after and were like, 'Is this what we think it is?'"

It was, much to her surprise. Short-nosed sea snakes were once abundant on Ashmore Reef, according to D'Anastasi, but their numbers began to decline in the 1970s and bottomed out in the early 2010s. The downward trend is of significant concern to marine biologists.

"You used to find about 50 snakes per day if you were walking the reef site," D'Anastasi said. "By 2002 it was down to 20 snakes per day, by 2010 it was down to 10, and then in 2012 there were no snakes left in the shallows."

king cobra swimming through river
Patrick Aventurier/Getty Images

The species was presumed extinct in 1998 when it disappeared from Ashmore, but Kate Sanders, a reptile ecologist at the University of Adelaide, and her team managed to locate a few small, isolated populations along the coast in 2016.

"Cable Beach in Broome, we've had a single specimen from there, and scattered distributions from the Exmouth Gulf," she said.

However, their members differed from the animals that had been previously observed on the reef in several significant ways, raising the possibility that they represented a distinct species of sea snake entirely. For example, they had smaller heads.

From photos, it's impossible to definitively identify the new specimen as either a reef snake or a coastal snake. It was found curled up on the seabed about 220 feet below the surface in the ocean's twilight zone. Not to be confused with the 1960s sci-fi show of the same name, the twilight zone refers to the region of the ocean that receives only a minimal amount of sunlight.

That location, Sanders said, suggests one of two scenarios. In the first, the original short-nosed sea snakes have been inhabiting the reef all along at depths that put them out of the natural reach of humans. In the second, the coastal snakes have simply expanded their territory.

"Could they have recolonized from the coast? That's a really important question," Sanders said. "If it's the coastal population that's recolonized, that would suggest we've lost that historical diversity that used to be present on Ashmore."

Genetic testing should solve the mystery.