What do they look like?
With their streamlined, boat-shaped body and flattened, paddle-like tail, sea snakes are well adapted to marine life. In fact, they are completely helpless on land! Their nostrils are positioned on top of their snout and closed by fleshy valves when they dive to prevent water from entering their lungs. Sea snakes typically stay submerged for about 30 minutes, although some can dive to 100 m and remain underwater for up to 2 hours. A special gland under their tongue concentrates and excretes excess salt water from their body.
At least 22 species have been recorded in Western Australia, with 6 species found in the Shark Bay World Heritage Area. The three most common in Shark Bay are the:
Sea snakes vary in size and colour. The bulky olive-headed sea snake grows to 1.6 m long. It has a broad, yellowish head and 24–30 black bars along its back. The bar-bellied or elegant sea snake, which grows to almost 2 m, has a small head and slender body that gradually becomes stouter towards the tail. Its fawn or brown skin is marked with a series of alternating black bars and spots. The Shark Bay sea snake is a patternless species growing up to 1.5 m. Males are brown, with short keels along the dorsal scales. Females are larger, purplish in colour, and don’t have dorsal keels.
Where do they live?
At least 22 species have been recorded in Western Australia, concentrated in the warmer, shallower parts of the Indian and west Pacific Oceans. In Shark Bay sea snakes can be found in a variety of locations, from mangroves, muddy estuaries and reefs to the open ocean. They are often seen swimming around the Denham jetty, studying the people fishing above!
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How do they breed?
Instead of laying eggs, females produce live, swimming young at sea. This characteristic helps differentiate them from sea kraits, (another group of snakes that also live in the sea) which lay their eggs on land.
Are they dangerous?
Sea snakes evolved from elapids, land-dwelling snakes that inject venom through fangs at the front of their upper jaw. Although sea snake fangs are short, their venom is highly toxic and acts quickly to prevent prey – usually fish – from swimming away.
Sea snakes are curious and will readily approach divers, but they are generally placid and harmless to humans if left in peace. They will only bite people
if they are hooked, netted, entangled or otherwise frightened or harassed. Exhausted or injured sea snakes washed ashore after storms should also be left alone – their venom will still be dangerous.
Any threats to their survival?
Sea snakes are protected under Western Australia’s Wildlife Conservation Act. Like other sea creatures they are at risk of boat strikes, litter, stray fishing line and tackle. Please keep an eye out for sea snakes when you’re boating and dispose of litter responsibly. For more information about Western Australian wildlife check out the WA Museum Fauna Base
to download a printable PDF of this fact sheet.