Sea Snakes and Fish Spines

[Abhishek Jamalabad]

I am fortunate enough to live in a place where a biologically rich beach lies between my workplace and my home, and the walks to work and back offer quite a lot of new sightings every day. On my walk home a couple of days ago, I came across a hefty adult Hook-nosed Sea Snake (Enhydrina schistosa) lying a few metres away from the constantly receding tide line (the tide transitioning from high to low). I am more used to seeing this common reptile as carcasses or dying specimens caught in nets, but was glad to see upon approaching this one that it was very much alive and fairly active. Unlike most other sea snakes, the hook-nosed sea snake is a hardy species that tends to move about when stranded, even thrashing about violently if disturbed. I wondered how it could have got stranded, since the nets are not used at this time of year. Perhaps the odd net being used off-season, I thought.

This specimen was about 3 feet long and quite hefty. It also had a large fish in its belly. I did not have a snake stick with me, so I tried lifting it up with my umbrella to return it to the water– firstly, it was hard to do so since the umbrella doesn’t have a hooked handle, and secondly, the snake thrashed about as expected, and I didn’t want to risk handling it improperly. The only other way was to nudge and push it back to the water, which I managed to do. The snake did not swim off, though, which was when I started thinking it might have suffered some internal injury- and then I noticed that it had a fish spine sticking out of its abdomen.

Sea snakes are a group of elapid snakes (relatives of the cobras, kraits, coral snakes etc.) that have evolved to live almost entirely in the sea. Most of them have a diet composed primarily of fish, which can be more dangerous than one would imagine, considering the erectile spines that most of them have on their fins. It is common knowledge that sea snakes are some of the most venomous snakes on the planet, and one theory to back this is that fish are very active prey capable of easily escaping or injuring the snake by thrashing about if not killed swiftly. They are also swallowed head-first by the snake, to avoid injury from the backward-pointing spines.

Moreover, the hook-nosed sea snake is a specialist that prefers catfish, which have one of the nastiest spines of all fish. So what could have caused this seemingly unusual accident? The potent venom would have ensured the death of the fish before it reached the belly, so it is unlikely it acted in defense after being swallowed. My speculation is that the snake was in distress (either before or after landing on the beach) and attempted to regurgitate the fish, in which case the spine (now moving the wrong way) could easily pierce it. I have seen injured specimens of this species throwing up small fish before. A large enough fish with strong enough spines would surely be much harder to regurgitate.

Unfortunately, I had to leave the scene as it was, and couldn’t keep a track of what happened next. It was raining a lot that day, so the snake would have been safe from sun exposure. I had placed it as close to the tide line as possible, but not in deep water where it would be helpless if unable to swim. Given how active it was on land, and considering I did not find any carcass on the beach the following day, perhaps it swam off.

Image of the snake with a heavy meal.