Amusing Monday: Evolution of sea snakes takes twists and turns

I’ve always felt fortunate that residents of Western Washington need not worry about encountering a deadly snake while hiking in our home territory. The same goes for divers and sea snakes — which are even more venomous than terrestrial snakes. The cold waters of Washington and Oregon tend to keep the sea snakes away.

The same used to be said for California, where sea snake sightings were once extremely rare. That has been changing, however, the past few years — especially during years when higher ocean temperatures encourage tropical creatures to make their way north. Is it just a matter of time before Washington scuba divers begin to report the presence of sea snakes?

A little more than a year ago, a highly venomous yellow-bellied sea snake was seen slithering on the sand in Newport Beach south of Los Angeles. It was the third report of the species since 2015, according to an article in the LA Times.

“Oceans are warming and the species that respond to that change will be those that are the most mobile,” said Greg Pauly, a snake expert quoted in the story by Louis Sahagun. “So the big question now is this: Are sea snakes swimming off the coast of Southern California the new normal?”

If you peruse the Internet for stories and videos about sea snakes, you will quickly learn that sea snakes are far more venomous than their land-based counterparts. You will see statistics such as this from Kidzone: “The most poisonous one is the beaked sea snake. Just 3 drops of venom can kill about 8 people!”

On the positive side, sea snakes rarely bite humans. And, when they do, they don’t deliver a lot of venom.

Folks working on fishing vessels in many tropical locations encounter sea snakes in their nets on a regular basis. Fishermen carefully remove the snakes and set them free. Unfortunately, a 23-year-old British man was killed last fall on an Australian prawn trawler when he was bitten while trying to remove a snake from a net. It was the first death of its kind in Australia since 1935, according to a researcher quoted by the Australian Broadcasting Company.

Steve Fisher, an underwater photographer who lives in Bremerton, told me about a few encounters he had with sea snakes while diving near Palau Manuk — also called “Snake Island” — in Indonesia last fall. It’s a place known for hundreds of green sea snakes.

The snakes tend to congregate around volcanic vents where the water is warm, Steve said. He likes to go night diving to capture images of exotic sea creatures in the glare of his lights. But the diving guides leading the dive trips in Indonesia made it abundantly clear that they would not immerse themselves during congregations of sea snakes after dark.

During daylight hours, Steve spotted as many as three snakes at one time swirling around together, but he never got to see the legendary “balls” of hundreds of snakes intertwined together at one time.

Steve Fisher of Bremerton took this photo of a green sea snake last fall while diving near Palau Manuk — also called “Snake Island” — in Indonesia. The diver in the foreground is a local guide. (Click to enlarge)
Photo: Steve Fisher

Steve said he counts on relatively slow reactions from the sea snakes and other potentially dangerous creatures that he encounters on his dives. That way he can capture his best photos of sea life.

“I’m kind of a fool when it comes to wildlife,” he told me. “When they are laying on the bottom and resting, I will reach over and touch them, causing them to look at me.” That’s when he gets the shot.

I became interested in this subject of sea snakes a few weeks ago after reading a new research paper about how the snakes keep themselves hydrated. Sea snakes are evolved from land snakes, which means their blood is based on freshwater and they breathe through lungs, not gills.

Sea snakes are seen swimming to the surface to take in a breath of air, although some apparently are able to absorb some oxygen from the water through their skin. But if they never return to land, how do they get enough freshwater to keep their bodies functioning?

Sea snakes have long been known to have salt glands to help excrete excess salt in their blood, and some scientists speculated that the snakes could be drinking seawater. But previous studies concluded that the salt glands are too small to excrete all the salt in the water needed for proper hydration.

The answer to the question of how the snakes get enough freshwater apparently is that they drink rainwater from the sky. Harvey Lilliwhite, a biology professor at the University of Florida, was studying yellow-bellied sea snakes in Costa Rica with his colleagues when the six-month dry season suddenly ended with a deluge of rain.

The researchers had already captured some snakes before the rain fell, and they captured others afterward — 99 snakes in all. Each time they brought snakes into the lab, they offered them a drink of freshwater. About 80 percent of snakes that were captured before the rains would take a drink, but that percentage declined as the rains continued. Only about 13 percent wanted a drink when captured eight days after the rains started.

The research paper was published in the journal Plos One. By the way, the snakes were released after the experiment.

So far, Lillywhite has not observed the snakes drinking water in the wild, but the presumed source of supply is the thin layer of freshwater that temporarily becomes layered over the heavier seawater when it rains. With wave action, the freshwater tends to accumulate in discrete locations, called lenses.

How do the snakes find these lenses of freshwater? How thick do the lenses need to be for the snakes to drink? Do lots of snakes suddenly come to the surface all at once when it rains? And what does the future hold for these specialized creatures, as climate change extends the periods between rainfall events? These answers must come later.

“How these animals locate and harvest precipitation is important in view of the recent declines and extinctions of some species of sea snakes,” Lilliwhite said in a University of Florida publication. “The question remains: How will climate change and its effects on precipitation impact the sea snakes?”

Jake Buehler, a writer with National Geographic, provided a nice account of the research with additional perspectives from folks not involved in the study.

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