Australian Sea Snakes Really Go Down Under

A sea snake, spotted by an ROV, at a record (sea snake) depth of nearly 800 feet off northern Australia.

AS OCEAN-DWELLING, AIR-BREATHING REPTILES, SEA SNAKES NEED TO RETURN TO THE SURFACE periodically to take in air, a factor that makes them largely shallow-water animals common to reefs and river estuaries in the Indo-Pacific basin.

So it was a reptilian phenomenon when two sea snakes were spotted at depths of some 800 feet/240 meters off the coast of northern Australia, as reported recently in the journal Austral Ecology.

That places them in the mesopelagic zone, often called the “twilight zone” because of the minimal amount of light that reaches it.  The conventional wisdom was that they shouldn’t have been there.

NEW DEPTHS, NEW RECORDS

“Sea snakes were thought to only dive between a maximum of 50 to 100 metres because they need to regularly swim to the sea surface to breathe air, so we were very surprised to find them so deep,” says Dr. Jenna Crowe-Riddell, lead author of the Austral Ecology article.

“We have known for a long time that sea snakes can cope with diving sickness known as ‘the bends’ using gas exchange through their skin,” she says. “But I never suspected that this ability allows sea snakes to dive to deep-sea habitats.”

ROVS ON PATROL

Observed separately at some 800 feet/240 meters deep, they set new records for the depths at which sea snakes are known to dive. One was found at 820 feet/250 meters, the other at 784 feet/239 meters. The previous known record was a mere 436 feet/133 meters.

They were spotted with remotely operated vehicles operated by IMPEX Australia, an energy exploration and production company working in the region. The company passed data and images of the snakes to the University of Adelaide researchers. The snakes were spotted in 2014 and 2017.

PICNICING IN THE DARK

Some of the footage showed the snakes poking their heads into burrows in the sand, obviously hunting for prey But it’s dark in the mesopelagic zone, and difficult to discern what that prey would be. Snakes mostly dine out on small fish and other small animals, Dr. Crowe-Riddell says.

Lack of light at 750 feet is most likely not a problem for the snakes; they rely strongly on tongue-flicking to sense stuff in their underwater world.

PRINCIPAL SOURCES: “First records of sea snakes (Elapidae: Hydrophiinae) diving to the mesopelagic zone (>200 m),”  Austral Ecology; “SEA SNAKES MAKE RECORD-SETTING DEEP DIVES,” University of Adelaide News Office; “The weird, wonderful and worrying world of sea snakes,” Australian Broadcasting Company; “Sea snake,” Wikipedia.com.

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