| 1 | Elegant sea snake |
Maximum length: 260cm.
A common sea snake found in Australasia, which easily reaches 2 metres, and may push to 2.6m. This is a dangerously venomous species, with the usual paddle-shaped tail for powering effortlessly through water. Elegant sea snakes (Hydrophis elegans) can choose from several food groups, but lean strongly towards snake eels, loving any elongated fish.
Rather than clinging frightenedly to coral reefs, this is one of the more flexible sea snakes. Elegant sea snakes can be found at ocean depths of 80 metres, or even 145 metres. Yet they’re also at home in shallower waters, and have been found 12km upstream from the mouth of the Burnett River in Queensland.
Elegant sea snakes are most common in shallow waters off the northern coast of Australia, including Northern Territory and Queensland. They particularly like seagrass beds and mud flats at less than 3 metres in depth. One of their hotspots in Queensland is Cleveland Bay.
Elegant sea snakes are preyed on by sharks, namely the tiger shark, the main shark species to prey on sea snakes (great whites rarely bother). However, they have a keen ability to dodge these terrifying predators. Scientists found in 2008 that when tiger sharks approach, elegant sea snakes move intelligently to the safety of seagrass beds. These are inferior for their snake eel prey, yet are superior for camouflage. They usually spent their days foraging on the open mudflats, yet abandoned them at high tide when tiger sharks had easier access.
| 2 | Slender-necked sea snake |
Maximum length: 139cm.
The slender-necked sea snake (Hydrophis melanocephalus) is another common aquatic species, inhabiting coastal areas such as offshore mudflats. This species lies further north, occupying southern China, southern Japan (Ryukyu Islands), and South Korea. It’s possible, but still being debated whether they live in Queensland. Either way, this sea snake prefers cooler waters.
Slender-necked sea snakes are often found on shallow mud flats between coral reefs, rather than prowling through the reefs themselves. They have a flexible diet, including sand divers and gobies, but eels are their favourite, including conger eels and burrowing eels.
This species can swallow an eel incredibly quickly. One event was witnessed near Iriomote Island, southern Japan. The snake was pressing its head to the sea floor, until it suddenly whipped out a 30cm black-striped snake eel, from a hole invisible to human eyes. The sea snake floated to the surface, then commenced swallowing by the head, which it completed within 13 seconds.
Though fully aquatic like most Hydrophis members, slender-necked sea snakes can also swallow prey on land. One individual was witnessed swallowing a longfin snake eel, also near Iriomote Island, which was biting the sea snake painfully behind its head, but was still swallowed eventually. This happened on a muddy shore 3-4 metres from the water’s edge.
Slender-necked sea snakes are shorter than the elegant sea snake, with a standard of 1-1.2 metres, with females being slightly longer. One of their recognisable features is a yellowish streak behind each eye.
| 3 | Lambert’s sea snake |
Maximum length: 125cm.
A fairly widespread species, which skips Australia and lives further to the north, appearing along the coasts of Thailand, peninsuar Malaysia, Singapore and the Philippines. Lambert’s sea snake (Hydrophis lamberti) has the special feature of a large head, versus the short head of a Jerdon’s sea snake. This species is very common in certain spots, and is regularly scooped up by fishing trawlers by accident. Lambert’s sea snakes sometimes pop up in local markets, being sold on for their skin, or even as food.
At first glance, this is just another sea snake, but one of their signature features is a grey cap on their head, followed by an olive chin, which extends across their belly. The shape of the bands is another key, as they’re thicker along the spine, and thinner on the flanks (see above). Male Lambert’s sea snakes are generally larger than females.
Hydrophis lamberti’s closest relative is the plain sea snake (Hydrophis inornatus). Singapore is another of their bases. If you want to meet Lambert’s sea snake yourself, then avoid coral reefs – they favour the sandy bottoms of the sea.
| 4 | Greater sea snake |
Maximum length: 156cm.
One of the most abundant sea snakes worldwide. Alongside the elegant sea snake, the greater sea snake (Hydrophis major) is the most commonly encountered sea snake in the shallow coastal waters of northern Australia, away from coral reefs.
Like most Hydrophis members, this is a fully aquatic snake, which has no need to relax on dry beaches or rocky shores. The greater sea snake can move to deep water, but generally prefers shallow water, particularly areas 1-2 metres deep, where they can blast through schools of eeltail catfish and grab them with ease. One hotspot for this sea snake is the New Caledonian port city of Noumea, which is also a hotspot for the turtle-headed sea snake.
At 80-100cm, this isn’t the longest sea snake, and females are longer than males. Greater sea snakes have a strong taste for catfish, particularly eeltail catfish, which aren’t really eels, but are elongated and slimy like they are.
This species has an assortment of powerful neurotoxins, but life isn’t a cakewalk for them. A 2020 study found that in oceanic regions occupied by the greater sea snake, the local eeltail catfish have developed significantly longer spines. In some areas, this species has a highly focussed diet, as in the coral reefs of New Caledonia, the local greater sea snakes ate eeltail catfish exclusively.
| 5 | Persian Gulf sea snake |
Maximum length: 96cm.
One of the shorter sea snakes worldwide, with a maximum length of 96cm in males and 92.5cm in females. The Persian gulf sea snake (Hydrophis lapemoides) stretches from the Oman coast, through India and Bangladesh, all the way to Thailand. It’s particularly common off the coast of the United Arab Emirates, alongside the plain sea snake (Hydrophis inornatus).
Persian gulf sea snakes are fully aquatic, yet boast the ability to move into freshwater estuaries temporarily as well. This is a shallow water species, moving through areas just 3 metres deep over coral reef and rocks. They constantly mingle with fishermen, some of whom are probably terrified, and others less so, having learnt to tolerate their presence decades ago.
Persian gulf sea snakes have a base colour of light grey or very pale yellow. These are overlaid with rings, which are normally black, but sometimes have a greenish tint. The older the snake, the more these rings fade, and the rings are also fainter on the belly. Their prey isn’t too specific, featuring gobies, cardinalfish eels, flatfish, etc.
The Persian gulf sea snake has one interesting quirk: mass gatherings, which randomly appear on the ocean surface, and can contain hundreds or even thousands of individuals. These gatherings are often spotted by fishermen in the Arabian gulf, minding their own business.
Strangely, when dolphin pods move into town, this species mysteriously disappears. The theory is that dolphins are natural predators of Persian gulf sea snakes.
| 6 | Jerdon’s sea snake |
Maximum length: 105cm.
One of the more poorly researched sea snakes. Jerdon’s sea snake (Hydrophis jerdonii) lives off the east coast of the Indian subcontinent, but is one of the less abundant species, as you’ll never find hundreds swarming a single bay as fishermen try desperately to depart for the day.
This species is also found in the Gulf of Siam to the east of Thailand, and the South China sea, including the southern coast of Vietnam. Very little is known about Jerdon’s sea snake’s diet, venom or oceanic adaptions, other than their usual paddle-shaped tail. They appear at least 12-20 miles off shore, as prawn trawlers sometimes scoop them up there. They’re sometimes sold for skins by people who accidentally catch them.
Most of our knowledge is in their physical appearance. Jerdon’s sea snake has a particularly short head, and an olive base of colours, with a slight green tinge. Compared to other sea snakes, its black bands are “blurry” – rather than sharply contrasting against the olive base, they fade in gradually.
Originally, Jerdon’s sea snake was distinct enough from the pack to be part of its own genus – Kerilia. But now, it’s been moved back to its old position in the Hydrophis mob (which has 46 members worldwide).
| 7 | Annulated sea snake |
Maximum length: at least 2 metres.
This potentially dangerous species measures 120-160cm, and is the most common sea snake in the waters of the Indian subcontinent. This snake can be found along the entire mainland coast of India, from west to east, and its overall territory is equally vast.
Annulated sea snakes (Hydrophis cyanocinta) appear from the Gulf of Persia, through India, to the Philippines and southern China. The one place they skip is Australia, as the competition with the local greater sea snakes is just too high.
Though they prefer shallower waters, annulated sea snakes can be found up to 40km away from coastlines. They’re fairly aggressive for a sea snake, and are alert to their surroundings. They also move better on land than the majority of Hydrophis sea snakes. They skip coral reefs, preferring to inhabit the muddy, sandy bottoms of seas, where they constantly search for fish.
Annulated sea snakes have a mostly neurotoxic venom, but a 2021 study found that this varies by location. In Xisha, China, their venom consisted of 58.09% neurotoxins, compared to 81.1% in Hara, Iran. The theory was that their prey was to blame, as the fish in Hara tended to be fast-moving, making rapid paralysis all the more important.
The annulated sea snake has a wider diet than the eel-fest of the elegant sea snake. Their meals include gobies such as taileyed gobies, and especially mudskippers, including Indopacific slender mudskippers and Dussumier’s mudskippers.
| 8 | Yellow sea snake |
Maximum length: 275cm.
The yellow sea snake (Hydrophis spiralis) is believed to be the longest sea snake in the world, reaching a confirmed record of 2.75 metres, and averaging at over 2 metres. Yellow sea snakes were discovered in 1802, and are found along the coast of India, Sri Lanka and in the Persian Gulf. They favour deeper waters, usually below 10 metres, while surfacing regularly to warm themselves in the sun. Their diet is barely researched at all.
As usual, this is a venomous snake, and while nothing is proven, yellow sea snakes seem unusually aggressive compared to their fellows. A 2015 study found an individual off the coast of Kochi, southwest India, which was described as “very aggressive“, and “showed a ready to bite nature“. This snake measured 2.3 metres, which is perfectly ordinary for this species.
Yellow sea snakes are recognisable by their deep yellow colour, and black bands which number 41-65. Another ID sign is that their black rings are especially narrow compared to other Hydrophis members.
The Iranian port town of Jask and the southeast Indian Tamil Nadu coast are hotspots for this species. By their very nature, sea snakes hard to research, particularly Hydrophis members which are fully aquatic. What we know about the yellow sea snake is mainly its easily visible characteristics – its length, its bright colours, etc.
| 9 | Shaw’s sea snake |
Maximum length: 110cm.
One of the most widespread sea snakes. Shaw’s sea snake (Hydrophis curtus) stretches from the Persian Gulf through India, all the way to the northern coast of Australia.
Shaw’s sea snake measures 90cm, and is one of the thicker sea snakes. They have weirdly baggy belly scales, and blurry, indistinct banded patterns. This snake lives in such a different world that it might as well be on another planet. It spends its days on the sandy bottoms of seas in ambush posture, waiting for subtle water movements that indicate an oncoming fish. If a goby brushes against its scales, then Shaw’s sea snake will instantly strike and devour, unless the fish weaves out of the way.
One study compared Shaw’s sea snake directly to the elegant sea snake, in Australian waters. It found that Shaw’s sea snake preferred locations further from freshwater (at least 3km) such as river estuaries. The species liked seagrass beds, but usually slightly deeper ones, at up to 4 metres vs less than 3 metres.
The elegant sea snake was highly specific in its diet, targeting eels, while Shaw’s sea snake chose from 4 families of fish (gobies, jacks, pomfreys). This is a flexible sea snake, and that’s probably why it’s so common.
Shaw’s sea snake has an extremely high density of blood vessels in its skin, which are thought to be for underwater oxygen absorption. The scientists discovered so many blood vessels that they couldn’t make a proper incision without extremely heavy bleeding. Shaw’s sea snakes also have an incredibly hard skull capsule, which made it almost impossible for the scientists to analyse their brain tissue.
| 10 | Dwarf sea snake |
Maximum length: 82cm.
One of the shorter sea snakes, as the name suggests, with all known individuals measuring under 1 metre. This species is also called the many-toothed sea snake, as of all Hydrophis species, it has the highest number of maxillary teeth behind its fangs (14-18 rather than 13).
Dwarf sea snakes (Hydrophis caerulescens) are missing from most of Australia, but cover a large territory in southeast Asia. They have a small pocket in Queensland, and then spread through Vietnam, southern China, Sumatra, Thailand, to most of India. This species preys on the likes of burrowing gobies and worm eels, but a full study on its diet hasn’t been conducted yet. Nor has its venom been analysed in great detail.
Despite their large range, dwarf sea snakes are rarely observed by human beings. Their habitats tend to be seagrass beds rather than coral reefs, where they occupy positions from 0 to 25 metres below the surface.
Dwarf sea snakes are adorned with many white or sometimes yellow bands. With age, these gradually fade away, until the entire snake is a dull grey. This is possibly why they’re rarely observed, as they blend with the water surface from above just too well.