Sea Snakes and Sea Kraits (Subfamily Hydrophiinae and Laticaudinae)
Marine snakes are by some estimates the most common snakes in the world. This makes sense as three-quarters of the earth is marine! But little is known about these seagoing snakes.
Adaptations that help sea snakes live in sea include: Flattened tail and bodies, usually no “neck”, paddle-like tails.
Skin which is more impermeable to salt than land snakes, but allows water to pass in more easily than out.
Usually dark-coloured top to camouflage from above, and light-coloured belly to look like the sky from below.
Although they have among the most deadly toxins, snakes rarely bite humans. It is not true that the gape of their mouths are too small to bite people. They can if they want to. They are just gentle creatures that don't bite unless severely provoked.
They moult more frequently than land snakes, about every 2-6 weeks, probably to get rid of parasites and barnacles. Bottom feeding marine snakes moult by rubbing against rough surfaces, those that float on the surface twist their bodies into complex knots so the shed is often found in knots. They also remove barnacles this way.
Most are active to depths of only 30m although they can dive as deep as 150m.
All eat mainly fish: reef-bound snakes forage through holes and crevices for stationary prey rather than chase them down. They prefer long fish like eels, but also eat fish eggs, prawns, cuttlefish.
Their venom is more toxic than terrestrial snakes. This is because in the open moving sea, their prey would be washed far away if they don't succumb immediately to the venom.
Marine snakes are preyed on by sea birds and other sea creatures.
There is still some dispute about whether these snakes belong in the family Elapidae Subfamily Laticaudinae (Seakraits): 6 species, all marine, living in coral reefs and lagoons from the Bay of Bengal to the Pacific Ocean. They return to shore to mate and lay eggs, as well as to bask, particularly after eating. Sometimes they expose only the part of the body containing prey to the sun. They can be found under rocks and logs or even in trees along the shore. During the mating season, thousands of males wait on the shore for females to arrive at night. 5-6 males may pile up on each female writhing around her. As soon as one male succeeds, the rest leave to look for other females. Females lay eggs in cavities in exposed coral reefs or rocky areas, or in the warm sand. One species is restricted to a landlocked lake in the Solomon Islands (L. crockeri).
Subfamily Hydrophiinae (Seasnakes): 50 species. All are highly venomous to humans but they are gentle and rarely bite. Except for 2 species which live in lakes, all are marine and found throughout the Pacific and Indian Oceans. Most live in shallow waters around the coast, river mouths or around islands, feeding on fishes and their eggs in the coral reefs.
They are better adapted to aquatic life than seakraits. They have valved upward facing nostrils (in seakraits these are sideways) and a seal over the tongue groove to keep out water. They also have a salt gland beneath the tongue that concentrates sodium which is excreted when they protrude their tongue. Their single lung extends the entire length of the body to help them float and so they can hold their breaths under water, some up to 1 hour. Some species can take oxygen directly through the skin. Their scales all the same size (seakraits still have broad belly scales for moving on land); tail vertebrae with long spines to support their oar-like tails (seakraits don’t have these). Most give birth to live young, some massing in sheltered estuaries to give birth (seakraits lay eggs on shore). They are so well adapted to a life at sea that they are helpless on land. Seakraits are brightly banded while seasnakes are banded lengthwise. Seakraits still return to land but seasnakes can’t breathe or move on land. The seasnakes are believed to have evolved from Australian elapids.
The famous Yellow-Bellied Seasnake (Pelamis platurus) lives like plankton on the open ocean as passive travellers on the currents. Usually found at “slicks”, narrow strips of calm water where two ocean currents meet. Too slow to chase down fish, they ambush them, exploiting fish’s natural tendency to hide under floating objects, including the seasnake! The snake swims backwards so its head appears to be its tail. Fish that come within range are caught with a quick backward snap of the elongated jaws. They may also forage on the ocean bottom, diving up to 6-15m. They can stay underwater for 1.5-3.5 hours.
These snakes sometimes form huge groups, one was seen between Malaysia and Sumatra was 3m wide and 100km long. They are unable to move on land and if stranded on a beach, will die. Most sea creatures will not touch them and will release or regurgitate them. Probably because the skin tastes terrible.
They mate in warm water, near the surface. They give birth to live young. This is the only sea snake that occurs on both sides of the Pacific. It is also the only sea snake to have reached the Hawaiian Islands.
Size: Average 60cm, maximum 113 cm
Babies: 1-10 live young about 20cm long. Gestation: 5-6 months.
Distribution: Oceanic Islands, Pacific Ocean, Indian Ocean: Indian and Pacific oceans around eastern Africa, Madagascar, Arabia, and India. Throughout coastal south-eastern Asia, Indonesia, Japan, Australia, New Zealand, and the Pacific Islands. Extending to the western coast of the Americas from Ecuador and the Galapagos Islands north to Baja California and the Gulf of California.
Habitat: Prefer warm shallow coastal waters, although some are found far out at sea.
Role in the habitat: like other predators, sea snakes control the population of their prey. They are also a source of food for predators higher up on the food chain.
Status and threats: Like other venomous snakes, they suffer from bad press and are often persecuted as a result of misconceptions about them. Like other reef dwellers, they suffer from habitat destruction.
More about snakes
- What are snakes?
- Are snakes cold?
- Why are snakes long?
- What do snakes eat? Do they drink?
- How do snakes swallow?
- How do snakes hunt?
- Why and how do snakes kill?
Snake predators and how do snakes protect themselves?
Snake mating, eggs and babies
Where are snakes found?
Fascinating snake adaptations to various habitats
Snake bites and first aid
Snakes in danger: role and conservation and snakes in human culture
Snake records: biggest, smallest, deadliest and more
- More snakes
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- General snake links and references
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