Ancient Mariners

DON’T TRY THIS AT HOME, it’s a bloody stupid thing to do.” I felt obliged to start with a line borrowed from The Young Ones (the Rik Mayall/Ade Edmondson TV comedy, not the Cliff Richard movie). Human interaction is rarely positive for the animal, and more often rather negative.
The animal in question happens to be unreasonably, ludicrously venomous. In a world of liability and disclaimers, I have to suggest that handling the animal with the deadliest bite on Earth should never, ever be attempted. It seems obvious.
That said, I and dozens of other divers I know have found sea snakes to be rather relaxed and inoffensive snorkelling and diving companions.
Malcolm grew up in the UK, and adders seemed to like his back garden. He grew up scared of snakes. “I never associated snakes with diving – the English Channel is snake-free – but while diving in Ningaloo Reef, Western Australia, in 2005, to my horror I came across a large olive-coloured snake on the seabed.
“Nothing happened. It just ignored me. Back on board, I showed the guide my shots: ‘That’s an olive sea snake, mate – rarely aggressive but highly venomous.’ My snake paranoia was immediately restored.”
“In October 2010 a Fiji guide picked up a snake. It seemed relaxed enough. The guide afterwards told me it was a banded sea krait, and its venom ranks among the most toxic in the world.
“In September 2013 on the Great Barrier Reef and on dive after dive we saw olive sea snakes. I would happily have avoided each and every one, but my buddies were determined to show me that if gently approached, they would be perfectly relaxed. So they picked some of them up.
“The snakes didn’t seem stressed, but I was and kept my distance.”
I like to help people overcome phobias, particularly those involving sea animals. Much of our hype about the dangers they pose is unrealistic, and distracts us from looking at their fascinating lifestyles, forms and elegant functions.
Apart from clownfish, other damsels and triggerfish defending territories, I have never in 20 years had any marine animal come at me with intent to do harm. All the sea snakes I have encountered have been completely unaffected by me following them rather closely around.
I also think the zealous “thou shalt not touch” culture popular with divers in recent years with regard to marine life should not be absolute. It over-rides understanding individual situations and distracts from more important concerns. However, in the case of sea snakes I’m happy to encourage Malcolm and others (although not, apparently, his guides) to give them plenty of room.
Sea snakes are venomous not in a ruin-your-day kind of way, but in a you-will-die-within-an-hour kind of way. Why would you deliberately harass an animal, the only defence of which is a bite that can kill you so easily?
The most venomous species that has been assessed, the faint-banded sea snake, has venom a hundred times more toxic than that of the inland taipan, the most venomous land snake. It is 400 times more toxic than the most venomous cobra and 1000 times more than a mamba.
There are 33 more species in the same genus, and most have not been properly studied for the potency of their venom, or any anti-venom developed.
Their venom seems to be highly prey-specific, which would account for the huge differences in toxicity towards laboratory mice. So with an unfamiliar species you may be lucky – it might “only” be as toxic to humans as a viper.
I have heard many times that sea snakes are “back-fanged” and can bite only where they can work the back of their jaws – like the skin between your thumb and forefinger. This is a myth.
I talked recently to a snake specialist who works with every group of venomous land snakes, and he said this is simply not true, and showed me the structure of sea-snake jaws. Yes, they have small mouths and small fangs, but the jaw is basically the same as that of a mamba or cobra. This is no coincidence – sea snakes belong to the same family.

Returning to the sea
It was relatively recently in evolutionary terms – just a few million years ago – that snakes returned to the sea. If they were around when the Panama isthmus closed 3 million years or so ago, any snakes in the Caribbean didn’t make it – today they are restricted to tropical waters of the Indian and western Pacific oceans.
To become marine, they developed a mechanism to lift up the trachea to breathe through the nose and then to seal the nostrils to hold their breath.
The mouth seals reasonably tightly, but a small gap allows the short forked tongue to just poke out, tasting odours on the water currents and expelling salt, which is pumped out of a special gland at the tongue’s base.
The single lung is hugely expanded compared to that of land snakes and runs almost the length of the body, providing buoyancy and an on-board oxygen supply for extended dives.
Their relatively thin skin means that they can absorb a certain amount of oxygen directly from the water, perhaps a quarter of their needs, though this probably helps only when they are resting – active foraging uses more oxygen, and probably limits dive-time to a few minutes.

Land-tied sea kraits
So sea snakes are basically big-lunged, nostril-sealing, salt-excluding cobras with flattened tails, adapted to moving through the sea. There are two subfamilies, representing different levels of adaptation to a marine existence.
The five species of commonly seen sea kraits that make up the smaller subfamily still have relatively well-developed belly scales, allowing them to move around a little on beaches and in caves. Sea kraits need to come ashore to breed, laying eggs in damp caves.
There are a handful of islands, some with porous rock and coral caves, some of them volcanic, that attract breeding aggregations.
The warmth provided by the volcanic activity may help to speed up the incubation of the eggs. These islands, such as Gunung Api and Gili Manuk in the Banda Sea, have become hotspots for visits by a handful of liveaboards.
I’ve had some fabulous snorkels following banded sea kraits foraging over coral reefs from the mid-Pacific to Indonesia. They’ll surface to breathe every five to 10 minutes or so, so I find myself doing many dives to each one of theirs.
They are sleek and built to weave through tiny cracks in reefs, hunting for small reef fish hiding in crevices. Considering how rich in fish these reefs are, I am amazed how rarely the snakes catch a meal. You can follow one foraging intently for an hour or so and not see a kill.
The sea kraits have always ignored me, weaving, prodding and exploring through the reef intent on their task and barely giving me a glance, even when I try to come in low and close for a macro shot.
That said, I try to keep myself a little off to the side and not cut them off. Once in a while I’ve had a snake at close range swim straight towards me. Their heads look rather similar to their mamba cousins, and I’ve had a couple of “oh shit!” moments.

Breaking the land link
The majority of sea snakes – 50-odd species – belong to a second subfamily, more distantly removed from their land-based cousins. They have lost the “crawling” belly scales, making them helpless out of the water, and have become adapted solely for a marine existence.
They tend to be somewhat heavier-bodied and looser-skinned than sea kraits. They hatch their eggs inside the body, giving birth to live young in breeding rafts out at sea.
Certain of these sea snakes are hugely abundant – by far the most numerous reptiles on Earth, far more successful than their land-bound cousins – and rafts of tens of thousands of yellow-banded sea snakes and their relatives have been seen in open water in the west Pacific and the Strait of Malacca.
The snakes being handled by the guides in Malcolm’s photos are from one of the seven species of olive sea snake in the genus Aipysurus – “only” about as venomous as a king cobra.
Divers are so far removed from what sea snakes eat, and sea snakes are pretty laid-back beasties, fascinating and elegant. But handling them leads them nowhere good, and can go to really bad places. Just watch and enjoy.

THAT TOXIN
Sea-snake bites are usually painless, apparently. Unlike their closest land-based relatives they usually don’t inject very much venom. In that case you might well survive – as long as you can keep breathing.
There’s little or no swelling, but the venom quickly starts to digest your muscle and, more dangerously, paralyse you.
You start with a headache, a thirsty, swollen mouth, and you tend to throw up.
As your muscles start to fail, your whole body hurts, your muscles incapable of either contracting or relaxing.
The breakdown of muscle floods your body with calcium, playing havoc with cell membranes and muscle and nerve function, and your blood and urine go dark dirty red from the myoglobin released from your dissolving muscles. Your heart, kidneys and breathing all give up at about the same time.
This can take a couple of minutes, or a few hours (which gives you enough time to get medical care). For perspective, however, perhaps two people a year die worldwide from sea-snake bite, about 50 times fewer than people killed by the bite of man’s best friend.
There are very good reasons for sea snakes to be so unreasonably venomous. Venom is expensive to make in terms of protein and energy, and the sea is a perfect medium to dilute and wash it away if it were given out in the volumes cobras do.
At the same time, sea snakes’ foraging grounds – coral reefs – are tighter and more labyrinthine than terrestrial hunting grounds.
Small reef fish are adept at running and hiding in this maze, so it makes sense to produce and inject tiny amounts of venom, so you don’t waste it but make sure it is toxic enough that your prey has no chance to escape into the maze – because it dies instantly.