Sea snakes occur mainly in the warm tropical waters of the Indian Ocean and western Pacific Ocean (the Atlantic, Caribbean and Red Sea have no sea snakes), with a few species found well out into Oceania.
Sea snakes, part of the elapids group of snakes, are thought to have evolved from a family of Australian land snakes. Unlike eels, they have lungs, instead of gills, and need to come to the surface to breathe air. For that reason, sea snakes usually live in shallow waters where they swim about the bottom feeding on fish, fish eggs and eels.
They have a huge left lung, though, that stretches over much of their body length, and allows them to stay underwater for a few hours. They may also swim up rivers and have been seen as far as 160 km from the sea.
Sea snakes have specialized flattened tails which act as a paddle, for swimming and valves over their nostrils which are closed underwater. On top of all, like other creatures living in a very salty environment -such as seabirds and sea turtles- sea snakes have special glands that collect the extra salt from their blood. A sea snake's salt glands are situated beneath its tongue, so that each time it flicks it, it ejects salt back into the ocean.
Most sea snakes are venomous, and many highly so. Most sea snakes are venomous, and many highly so. Close cousins to the land kraits and cobras, sea snakes have the same type of venom, only much more potent. This venom contain neurotoxins which act on the nerve cells of the victim, paralyzing the respiratory system and ultimately causing death. Sometimes the venom also contains myotoxins which affect the skeletal muscles.
Even 'dead' specimens found at the beach should not be touched, because some species are known to feign death when stranded by the tide. Besides, some dead and even decapitated snakes can still administer a reflex bite.
Sea snakes feed mostly on fish which they swallow whole. This explains why a sea snake venom is usually so toxic: it must kill quickly or else a thrashing fish could either escape or its sharp spines might poke a hole in the snake's stomach.
However, cases of envenomation by sea snakes are very rare.
The first reason is that encounters with humans are not very common. Most sea snake bites occur on trawlers, when the snakes are sometimes hauled in with the catch.
The second reason is that even those snakes entangled in a net don't always try to bite. Indeed, most species are shy and far less aggressive than their land cousins, except maybe during the mating season, in winter - divers can sometimes be bitten if they disturb nesting areas-.
A third reason is that most bites - between 65 and 80%- are 'blank', meaning envenomation does not occur.
Thus, though a number of sea snakes have largely the potential to kill humans, they can hardly be considered as truly dangerous to man. Nevertheless, they should be treated with respect and left alone.
Caution must be also taken in the instance of a bite: because of the small size of their fangs, bites are not extremely painful, at first, and might even go unnoticed. The first symptoms can appear only 30 minutes to a few hours after the bite. A specific antivenin exists and Australian tiger snake antivenin can be used as a substitute.
TRUE/AQUATIC SEA SNAKES (Hydrophinae)
16 genera, 57 species
These snakes have laterally compressed tails used to propel them through the water, nostrils with valve-like flaps which can be closed upon submersion, and lack any ventral plates.
True snakes are viviparous, and bear 2 to 20 live young per litter. Born at sea after an extended gestation period - 4 to 11 months-, the young sea snakes are independent from the start and immediately swim away from their mother.
- Spiny-headed Sea Snake (Acalyptophis) 1 species
It is found in the Gulf of Thailand, the South China sea, the Strait of Taiwan, and the coasts of Guangdong, as well as in the waters of Indonesia, the Philippines, New Guinea, New Caledonia, Australia (Northern Territory, Queensland, Western Australia).
- Olive Sea Snakes (Aipysurus) 7 species
Those snakes occur in the Timor Sea, South China Sea, Gulf of Thailand, Indonesia, western Malaysia, Vietnam, southern New Guinea, the coasts of Australia (North Territory, Queensland, West Australia), New Caledonia, Loyalty Islands.
Generally, pelagic sea snakes have scales that do not overlap, unlike terrestrial snakes which scales imbricate to protect against abrasion; however, Olive Sea Snakes, which are reef dwelling species, do have imbricate scales to protect against the sharp coral.
* Olive Sea Snake (Aipysurus laevis)
This species is a familiar sight in the region about the swain Reefs and the Keppel Islands in the Australian Barrier Reef (which hosts 32 sea snake species).
An adaptation from this snake - and possibly other sea snake species- to its life is the coral reef are the photoreceptors in the skin of its tail: this allows the Olive Sea Snake to detect light and probably helps it while it remains hidden inside coral holes during the day.
Unlike most sea snakes, the Olive Sea Snake is reputed to be quite aggressive.
* Marbled Sea Snake or Spiny-tailed Sea Snake (Aipysurus eydouxii)
This 1 meter long snake occurs throughout Southeast Asia and parts of Australia. It frequents shallow waters and coral reefs, where it feeds almost exclusively on fish eggs. The Marbled Sea Snake might also be encountered some distance up mangrove inlets and, though it is a true sea snake which never emerges on land, it can sometimes be stranded in the iner-tidal zone by receding tides.
- Stoke's Sea Snake or Large-headed Sea Snake (Astrotia stokesii) 1 species
It is yellowish to pale brown with a large dark olive-colored head and a stout body with broad black or dark brown bands. This species is thought to be rather aggressive.
In 1932 a steamer in the Strait of Malacca, off the coast of Malaysia, spotted millions of Stoke's Sea Snakes, forming a line 3 meters - 10 feet- wide and 100 kilometers - 62 miles - long! Though the reason for this remarkable aggregation is unknown, it is presumed to be linked to reproduction.
- Turtlehead Sea Snakes (Emydocephalus) 2 species
Those sea snakes are found off the coasts of Timor (Indonesian sea), New Caledonia, Australia (North Territory, Queensland, West Australia), and in the Southeast Asian Sea along the coasts of China, Taiwan, Japan, and the Ryukyu Island.
- Beaked Sea Snakes (Enhydrina) 2 species
Beaked Sea Snakes are thought to be the most common of all sea snakes. They live in the Persian Gulf (Oman, United Arab Emirates, etc.), south to the Seychelles and Madagascar, south east Asian Sea (Pakistan, India, Bangladesh, Myanmar, Thailand, Vietnam), northern Australia (North Territory, Queensland) and Papua New Guinea.
Yet this snake is especially common in the coastal waters of India (which is home to 20 other sea snake species).
* Beaked Sea Snake or Common Sea Snake, Hook-nosed Sea Snake (Enhydrina schistosa)
This species is found in deep sea, where the bottom is sandy or rocky. It can also be found in tidal creeks and other sheltered spots during the monsoon.
The Beaked Sea Snake measures 47 to 116 cm, it is a dirty white to a pale greenish gray with some 40-50 dark round blotches on its back.
The Beaked Sea Snake is one of the most venomous snakes either on land or in the sea. Indeed, scientists have estimated its venom to be 4 to 8 times more lethal than that of a cobra. It is thought that one drop of it would be enough to kill three men. Though the initial bite is not painful - as it is normally the case with sea snakes- the Beaked Sea Snake's venom attacks the muscles of the body, causing excruciating pain, and death, if the victim is not treated.
However, though the Beaked Sea Snake is considered more aggressive than most sea snakes, this is all relative and this species is often handled without fear of being bitten by local fishermen, who accidentally capture it in their nets.
- Grey's Mudsnake (Ephalophis) 1 species
This snake is found in north-western Australia.
- Port Darwin Mudsnake (Hydrelaps) 1 species
This species occurs in northern Australia and southern New Guinea.
- Sea Snakes (Hydrophis) 34 species
This large group of snakes live in Indo-Australian and Southeast Asian waters.
* Faint-banded Sea Snake, or Sea Snake, Belcher's Sea Snake (Hydrophis Belcheri)
The Faint-banded Sea Snake is now thought to be, not only the most venomous sea snake, but the most venomous snake in the world. Its venom is said to be as much as 100 times more lethal than that of any other snake - including the Inland Taipan-. By comparison, one drop of venom from the King Cobra can kill up to 160 people in 30 minutes, but the myotoxic venom of the Faint-banded Sea Snake is thought strong enough to kill more than 1800 people!
However, fatalities are rare, because people and sea snakes rarely come into contact, and all the more since this the snake has the reputation of being quite friendly is must be subjected to severe treatment before it actually bites.
The Faint-banded Sea Snake is usually encountered entangled in nets, so that most bites are inflicted on fishermen. Even then, only some 25% of bites are accompanied by a venom injection. So, though the Faint-banded Sea Snake is extremely venomous, it is by no means a "dangerous" species to humans.
* Yellow Sea Snake (Hydrophis spiralis)
The Yellow Sea Snake inhabits off-shore water.
This species has the particularity of being the largest sea snake: it can measure up to 3 meters (10 feet), though the average size is 115-150 cm. It has a large head and a broad body which is olive on the back, yellow on the stomach, with 34 to 74 black bands.
* Annulated Sea Snake or Ringed Sea Snake (Hydrophis cyanocinctus)
This snake is common along the coast of Pakistan. It lives in shallow, muddy and mangrove swamps during the monsoon and feeds on fish and eels in particular.
It measures 85 to 119 cm and has a horse-shoe shape marked on the crown of its black head.
This species, as opposed to most sea snakes, does relatively well in captivity.
* Cochin Banded Sea Snake (Hydrophis ornatus)
This rare snake lives in mangrove swamps, notably along the coast of Pakistan.
Its head is olive, its stomach whitish, and it has 41 to 45 black cross bars. The Cochin Banded Snake measures 1 to 1.8 meters, and some 31 cm at birth.
This species has the reputation of being quite aggressive for a sea snake.
* Hydrophis mamillaris
This small snake - 55 to 110 cm - is found in muddy mangrove swamps and along sandy beaches. It is yellowish to grayish with a black tail and a very small head.
* Small-headed Banded Sea Snake (Hydrophis fasciatus)
This rare snake inhabits shallow water where the bottom is either sandy or rocky.
It has a very small head, a long and slender body with 48 to 71 black bands, and measures 47 to 120 cm.
* Many Toothed Sea Snake (Hydrophis caerulescens)
This rare species can be found in muddy creeks with mangrove swamps.
It measures 70 to 120 cm, has a small head and a slender bluish to grayish back and yellow stomach, with 35 to 58 deep bluish black bands.
* Persian Gulf Sea Snake (Hydrophis lapemoldes)
This snake lives in muddy mangrove swamps.
It is olive brown with curved yellow marks on the top of its head and 45 black bands. It measures between 68 and 113 cm.
* Hydrophis semperi
This snake has the particularity of being one of the two landlocked fresh water species of sea snakes. Indeed, it is found in Lake Taal in the Philippines.
- Jerdon's Sea Snake (Kerilia) 1 species
This snake is found in southeast Asian waters.
- Bighead Sea Snake (Kolpophis) 1 species
It is a species of the Indian Ocean.
- Shaw's Sea Snake or Short Sea Snake (Lapemis curtus) 1 species
This common species ranges from the Persian Gulf to the Indian Ocean, in the South Chi Sea, Indo-Australian archipelago and the western Pacific. lt likes rocky coasts and comes to the surface to take fresh air.
It is a small snake - 67 to 90 cm - displaying 45 to 55 dark greeninsh brown crossbars.
- Small-headed Sea Snakes (Microcephalophis)
* Common Small Headed Sea Snake (Microcephalophis gracilis)
This rare species is notably found along the coast of Pakistan where it inhabits sandy bottoms and muddy mangrove swamps.
It has a long body measuring between 126 and 149 cm, is usually grayish above and paler below, with 40 to 60 bands.
* Cantor Small-headed Sea Snake (Microcephalophis cantoris)
This uncommon species lives in shallow waters with a muddy or sandy bottom, notably in the waters of Pakistan.
It is a big snake - 115 to 150 cm-, light olive to yellow on top, and paler on the stomach, with 49 to 61 gray or black crossbars.
- Northern Mangrove Sea Snake (Parahydrophis) 1 species
This species is found in northern Australia and southern New Guinea.
- Hediger's Snake (Parapistocalamus) 1 species
This snake seems limited to the Bougainville and Solomon islands.
- Yellow-bellied Sea Snake or Black-and-yellow Sea Snake, Pelagic Sea Snake (Pelamis platurus) 1 species
An explanation for such a wide range might be that this species, which normally inhabits coastal waters, drifts far out to sea, where it gives birth to its live babies. It is the only sea snake which can be found beyond the tropical parts of the Indian and Pacific Ocean. It is sometimes, but rarely, encountered in Hawaiian waters (it is the only kind of sea snake ever found there).
The Yellow-bellied Sea Snake is a small snake black and yellow snake with an elongated head. It measures 53 to 88 cm.
This pelagic species can be found in drift lines, slicks of floating debris - seaweed, driftwood - brought together by the wind and surface currents. Fish like to shelter under these slicks and thus provide food for the snakes.
Now and then, Yellow-bellied Sea Snakes get washed up on beaches after storms and can pose a hazard to children, especially since they sometimes congregate in massive groups of hundreds to thousands of snakes.
Though sea snakes like warm, tropical waters, they need to cool down if the water gets too warm. The Yellow-bellied Sea Snake likes to spend time at the surface of the water, but is known to dive to depth of up to 50 meters - 150 feet - in search of cooler waters when the surface temperature exceeds 25 °C. It can stay submerged for more than three hours. This is made possible thanks to most sea snakes ability to breath through their skin. In the case of the Yellow-bellied Sea Snake, experiments have shown that 20% of its oxygen needs are satisfied in this manner.
Because the Yellow-banded Sea Snake feeds by simply gulping down its prey, it is more likely to bite under stress and provocation since its venom seems to be used essentially for defense.
The Yellow-bellied Sea Snake has a potent venom, estimated to be roughly one-fourth as strong as that of the Beaked Sea Snake. This venom is still more toxic than the Mojave rattlesnakes and King cobras, and, for instance, more potent than the venom of any terrestrial land snake found in Costa Rica.
However, despite the abundance of Yellow-bellied Sea Snakes of the western coast of this country, very few human fatalities due to this species have been recorded (some say only one, worldwide).
- Viperine Sea Snake (Praescutata viperina 1 species
This snake is found from the Persian Gulf to the Indian Ocean, in the South Chinese Sea, and the northeast to the coastal region of Fujian and Strait of Taiwan. It inhabits coastal waters and creeks.
The Viperine Sea Snake measures 86 to 97 cm, is a pale peach to greenish white in color with 25 to 35 rhomboid dorsal blotches. The throat is white, and the tail black.
- Anomalous Sea Snake (Thalassophis) 1 species
This species inhabits the south Chinese Sea (Malaysia, Gulf of Thailand) and the Indian Ocean around Indonesia (Sumatra, Java, Borneo).
SEA KRAITS (Laticaudinae)
1 genus, 5 species
Like other sea snakes, Sea Kraits have evolved from a land species into aquatic reptiles having smooth-scaled bodies, yet they are thought to be more "primitive", as their transformation into sea snakes is not complete.
Indeed, the Sea Kraits are not considered true sea snakes as they alone, have retained the ability to come to shore, thanks, notably, to enlarged ventral scales which provide them with the necessary grip.
They are also the only sea snakes which nostrils are not situated dorsally. Another exception among sea snakes: Sea Kraits lay eggs, instead of giving birth to live young, and come to land for that reason.
Sea Kraits, that use their venom for prey immobilization are generally very docile snakes and are frequently handled with impunity by local fishermen.
- Sea Kraits (Laticauda) 5 species
Sea Kraits are found in southeast Asian, Indo-Australian waters and the Pacific islands.
* Banded Sea Snake or Amphibious Sea Snake, Yellow-lipped Sea krait (Laticauda colubrina)
The Banded Sea Snake is easy to recognize with its shades of light blue - or silver- and black bands running the full length of its body. It measures 75- 200 cm (2.5-6.5 ft). Its tail is laterally compressed and rudder-like, making this snake an efficient underwater swimmer. Banded Sea snakes do not have eyelids but rather modified scales to protect their eyes.
Like other Sea Kraits, the Banded Sea Snake spends most of its time at sea, where it frequents shallow tropical reefs and surrounding estuaries. There, it feeds primarily on the crabs, cuttlefish, eels, fish, fish eggs, and squid.
Yet, it is not rare for the Banded Sea Snake to come ashore, especially during the breeding season, to lay its eggs on land.
This species is not reputed aggressive. However, it will defend itself when threatened and has a powerful myotoxic venom which paralyzes the muscles of its victims.
* Laticauda crokeri
This Krait species is one of only two sea snakes that are known to live in landlocked fresh water. Indeed, it is found in Lake Te Nggano on Rennell Island in the Solomon Islands.
Another notable fact about this snake is that it is the only sea snake to be classified as vulnerable according to the IUCN Red List of Threatened Species. Despite the fact that sea snakes ar exploited for their meat, skin and internal organs, and that they are killed in great numbers, CITES does not afford them any protection.
Introduction to Dive Medicine Dangerous Creatures of the Sea
Banded Sea Snake (Laticauda colubrina)
Sea snakes are gentle and shy but venomous
Snakes of Pakistan
Ms. Fahmida Iffat, Marine Biologist at Zoological Survey Department, Karachi.
The World Record for the Most Venomous Sea Snake
So what is the most poisonous snake?