The banded sea krait (Laticauda saintgironsi) swimming over a seagrass bed in New Caledonia (Image: Xavier Bonnet)
Sea kraits (Laticaudine) are sea snakes. They’re front-fanged (proteroglyphous) venomous elapid snakes and are common through much of the Indo–Pacific region. When they’re pregnant, the females stop eating!
Seems like a strange thing to do when you need energy and nutrients to make eggs.
Why would they do that?
Francois Brisçhoux, Xavier Bonnet and Richard Shine set out to find out why by studying two of these kraits; Laticauda laticaudata and L. saintgironsi, on small islets in the Lagoon of New Caledonia. What a cool field site!
Apparently it’s not that uncommon for snakes to loose their appetite (anorexia) when they’re developing eggs. Why they do it has always been a good question and the answers are varied. Some have suggested that the eggs squash the gut making it difficult to fit any food inside the distended body. Another reason is that it’s an adaption to avoid predators; by not eating, the snakes can hide and reduce the chance of being eaten themselves before they lay their eggs.
These kraits can grow to 1.2 metres long and only eat fishes. In turn, they have to watch out for sharks and other large fish which will gladly eat them. Once they have caught and eaten a fish, which are often eels, they return to their home islet and get out of the water. They’re safe on the land, they’re not eaten by birds or other terrestrial animals and can warm up in the sun.
So in the water its ‘kill or be killed’ but on the land they can take a rest and warm up.
What a great place to visit! (http://www.flickr.com/photos/mylifeshow/ / CC BY 2.0)
After examining 1,300 of these snakes over 6 years Brisçhoux and his colleagues concluded that these species tend not to eat when pregnant, they do become anorexic. By palpating or gently feeling the snakes bodies with their fingers, they worked out that the snakes could eat if they wanted too, their stomachs weren’t squashed by the eggs.
What does happen though is that the snakes can’t swim as well when they are full of eggs. Their locomotion is inhibited!
A snake swimming in open water sticks out (check out the first picture). It’s not hidden and cryptic like a snake in the rainforest. Sea snakes in open water are easy prey for sharks, especially if they’re slow and swollen with eggs!
These snakes don’t breed that often, so they place considerable value on making sure they get to lay their eggs. What they think is happening is that the snakes find it difficult to swim well and they’d be ‘sitting ducks’ in open water. The snakes also find it difficult to chase their fishy prey through the small gaps in the coral.
So the costs of hunting (chances of being eaten) have gone up and the rewards (possibility of catching a speedy fish) have gone down. It’s not worth the risk. So the best strategy is to bask in the sun, conserving energy in a predator free environment, making sure they lay their eggs before they go back into the sea.
Once the eggs are laid it’s back to the hunt, risking the sharks and playing Nature’s game of life.
The video below shows a sea krait eating an eel..greedy or what?
References
Bonnet et al (2010) Conflicts between feeding and reproduction in amphibious snakes (sea kraits, Laticauda spp.), Austral Ecology, DOI: 10.1111/j.1442-9993.2010.02115.x
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