Sea Serpents and Sea Kraits: What’s the Difference?

Sea Serpents and Sea Kraits: What’s the Difference?

From a distance they are often mistaken for moray eels. But unlike morays, they are fish, and they often boldly swim up to divers. And once they are upon us, they often give what feels like a rather intense inspection before they move along.

Although some are drably colored, others are elegant and handsome. I would even say striking, but that is the one thing you hope that they are not. That’s because they are highly venomous. They are sea snakes and sea kraits, the marine reptiles that are the focus of this Ultimate Dive Travel’s blog.

The Big Picture

Upon first glance sea snakes and sea kraits certainly look alike to most lay divers, and many sport divers have never heard of the common name sea krait. However, specialists view sea snakes and sea kraits as different groups of animals. Even so, the two groups share many similarities with regard to significant adaptations and lifestyles. But a close examination of their lifestyles shows that they also exhibit some major differences.

All sea snakes and sea kraits are reptiles. Thought to have descended from lizards during the Jurassic period approximately 135 million years ago, snakes are believed to be the most recently evolved group of reptiles. It is highly likely that the first snakes were aquatic animals. But the early snakes left the aquatic world and crawled onto land. All living species of sea snakes and sea kraits are thought to have descended from terrestrial snakes that later invaded and adapted to life in the marine environment.

Worldwide, there are approximately 70 species of extant, or currently living, sea snakes and sea kraits. Most occur in warm, tropical waters of the Indo-west Pacific, although some species also inhabit the eastern Pacific. Neither group naturally occurs in the waters of the Atlantic Ocean and associated seas. The waters surrounding Indonesia and northwest Australia have the greatest number of species with each area being home to more than 20 species.

Sea Serpent Confusion

In biology the word ‘radiation’ refers to a species or group of animals that evolved into additional species or types. Herpetologists generally agree there are five major radiations of sea snakes.

Sport divers generally encounter two of these groups. One is referred to by specialists as marine hydrophiines, the “true” sea snakes. The second group is known as sea kraits. However, many lay divers commonly use the word sea snake to include both groups. Not surprisingly the inconsistency leads to some confusion.

“True” sea snakes are believed to have evolved from a group of highly venomous terrestrial snakes that inhabited Australia. All hydrophiines live their entire lives in the sea. And all bear live young. They are the only reptiles that give birth in the sea. These snakes are believed to have first appeared between 10 and 15 million years ago.

It is likely that sea kraits first appeared some 5 to 10 million years earlier than the sea snakes. They, too, are the descendants of land-dwelling elapid snakes. There are eight currently recognized species. Unlike sea snakes, sea kraits routinely leave the aquatic environment going onto land to mate, lay eggs, digest food and rest. The bodies of all sea kraits exhibit distinct bands.

Both sea snakes and sea kraits possess fixed fangs and are highly venomous.

Hunting And Feeding

While some species of sea snakes and sea kraits feed exclusively on a single prey species, collectively speaking these marine reptiles feed on a variety of bony fishes including some eels, fish eggs, shrimps, crabs and worms. All are limited to prey that can be swallowed whole, but it is worthwhile to note that snakes and sea kraits can swallow prey whose size is more than twice the diameter of their neck. Once they have bitten their prey these predators wait until the prey stops struggling so it can be swallowed head-first.

While sea snakes and sea kraits can easily out swim divers, they cannot swim fast enough to catch most swimming fish. So instead of swimming after prey, most sea snakes and sea kraits search in cracks and crevices of reefs for resting fish and other prey. However, the yellow-bellied sea snake hunts by floating at the surface where it waits for curious fish to seek shelter under its body, a hiding place that can prove fatal.

Sea snakes and sea kraits are preyed upon by a variety of relatively large fish such as some groupers, some sharks, and the birds known as sea eagles (ospreys).