Sea Snakes: A complete guide

Have you ever seen a sea snake in the wild?

These rare and beautiful creatures are often very hard to find and in some cases are mistaken for eels. Their preference for warmer waters also confines them to more tropical regions which makes them even harder to find.

This blog will touch on the lives of these little sea snakes, use the headings below to guide you through the blog article. 

General 

Sea Snake facts 

Where do Sea Snakes live?

Sea Snake Bites

Ecology and Conservation

Summary 

General

Sea Snake

In the ocean, Sea snakes are no more than 60 species of highly venomous marine snakes of the cobra family (Elapidae). There are two independently evolved groups: the true sea snakes (subfamily Hydrophiinae), which are related to Australian terrestrial elapids, and the sea kraits (subfamily Laticaudinae), which are related to the Asian cobras.

Although these snakes venom is the most potent of all snakes, human fatalities are relatively rare because sea snakes are not aggressive, their venom output is small, and their fangs are very short.

Of the 55 species of true sea snakes, most adults are between 1–1.5 metres in length, although some individuals may grow to 2.7 metres. 

In adaptation to marine life, true sea snakes have a flattened body with a short oarlike tail, valvular nostrils on top of the snout, and elongated lungs that extend the entire length of the body. Their scales are very small and usually not overlapping, abutting against one another like paving stones.

The belly scales are reduced in size in the primitive species, whereas in the more advanced forms they are absent. As a result, the advanced species cannot crawl and are thus helpless on land. When swimming, a keel is formed along part of the belly, increasing surface area and aiding propulsion, which occurs by lateral undulation. Sea snakes can remain submerged for several hours, possibly as much as eight or more. This remarkable feat is partly due to the fact that they can breathe through their skin. More than 90 percent of waste carbon dioxide and 33 percent of their oxygen requirement can be transported via cutaneous respiration. 

Moreover, a 2019 study of the blue-banded sea snake found a highly vascularized area between the snout and the top of the head, which allows oxygen to be transported directly from the water to the snake’s brain. Sea snakes give birth in the ocean to an average of 2–9 young, but as many as 34 may be born. 

The six species of sea kraits are not as specialized for aquatic life as the true sea snakes. Although their tail is flattened, the body is cylindrical, and the nostrils are lateral. They have enlarged belly scales like those of terrestrial snakes and can crawl and climb on land. The typical colour pattern consists of alternating bands of black with gray, blue, or white rings. The yellow-lipped sea krait is a common species that possesses this pattern and has a yellow snout.

Sea kraits are nocturnal, feeding primarily on eels at depths of less than 15 metres (49 feet). They go ashore to lay their eggs, climbing up into limestone caves and rock crevices, where they deposit 1–10 eggs. Adults average 1 metre in length, but some grow to more than 1.5 metres. The longevity record in captivity is seven years.

Sea Snake Facts

Sea Snake
  1. Sea snakes are front-fanged and highly venomous.
  2. A fold in the gums of a sea snake hides the fangs, and the fangs quickly emerge when biting something. Sea snake fangs are fragile and may break off and remain in the wounds of their victims. To counter the problem of having weak fangs, sea snakes have potent venom that can easily paralyse, kill, and begin the digestive process of the fish they target.
  3. Sea snakes evolved from two different snakes (the cobra in Asia and Australian terrestrial elapids)
  4. Marine sea snakes are viviparous: They give birth to fully-formed young at sea, without laying eggs
  5. Sea snakes require fresh water for drinking and will dehydrate at sea without it.

Where do sea snakes live?

They are restricted to coastal areas of the Indian and Western Pacific oceans, from the east coast of Africa to the Gulf of Panama. Except for the yellow-bellied sea snake, which is found in the open ocean from Africa eastward across the Pacific to the west coast of the Americas. All other species live mainly in waters less than 30 metres (about 100 feet) deep, as they must dive to the seafloor to find their food among coral reefs, among mangroves, or on the ocean bottom. Some species prefer hard bottoms (corals), while others prefer soft bottoms (mud or sand) in which to hunt their prey. Most sea snakes feed upon fishes of various sizes and shapes, including eels. Two primitive groups (genera Aipysurus and Emydocephalus) eat only fish eggs whereas,  Hydrophis specialize in burrowing eels.

Sea Snake Bites

Sea Snake

A Sea snake bite is the cause of some fatalities in the Western Central Pacific. Typical victims are fishermen handling gape nets, sorting fish on a trawler, or dragging a net while wading in muddy coastal waters or river mouths. Some sea snakes are gentle, inoffensive creatures which bite only when provoked, but other species are much more aggressive.

Even though sea snakes rarely inject much of their venom, so that frequently no or only trivial severity of poisoning is recognizable, all sea snakes should be handled with great caution.

If a snake bite has occurred, the following first-aid procedures are recommended:

  1. If the bite is on an arm or leg, a broad crepe bandage (or material of similar type) should be wrapped immediately around the area of the bite. The bandage must be very tight and extended over the entire arm or leg.
  2. Then a splint should be used to immobilize the arm or leg and hospital treatment must be sought as quick as possible.
  3. If the bite is on the body, firmly press the area of the bite and look for hospital treatment immediately. 

Ecology and Conservation

Sea Snakes

Sea snakes are exploited for their skin, organs, and meat. Although some species are taken in great numbers, they are not protected by CITES (A Washingon convention). Since 1934, meat and skin of sea snakes have been used commercially in the Philippines and local protection of sea snakes became necessary to avoid overexploitation. 

Sea snakes are also exploited in Australia, Japan, Taiwan Province of China, Thailand, and Vietnam. The local government in Queensland, Australia has introduced a special licence to collect sea snakes. However, most sea-snake fisheries in the Indian and Pacific oceans have not been reported in the literature and are not controlled by local governments.

With the exception of the Philippines, the impact of exploitation on populations of sea snakes is almost unknown and some populations may already be in danger of extinction. Monitoring and control of the commercial catch is the only way to maintain a sustainable yield, giving local governments a chance to intervene before a catastrophic collapse of local populations occurs. 

However, management of sea-snake fisheries and protection of the endangered species is not possible without a basic knowledge of the group and the ability to identify to the species level.  

There are many sea snake species in the Indian and Pacific oceans, but none in the Atlantic or Caribbean. Why is this?

Ocean Current and Climate Barriers

Not all sea snakes spend their entire lives in the ocean. Some species, called sea kraits -the non-true sea snakes-, can live on land or in water and lay their eggs on land. This limits their range because they need to stay near land to reproduce. 

In contrast, all entirely marine sea snakes are viviparous: They give birth to fully-formed young at sea, without laying eggs. This essential trait allowed the pelagic yellow-bellied sea snake to extend its range across the entire Indo-Pacific from an area of origin somewhere in the Coral Triangle of Southeast Asia. 

By the time it reached Central America’s Pacific coast however, the “Isthmus of Panama” had formed, fully separating the Pacific and Atlantic oceans. When the Panama Canal opened in 1914, it became possible for an occasional sea snake to enter Caribbean waters accidentally.

However, this species tends to drift with currents, so it is highly unlikely that enough could pass through the canal and find one another to the east to establish a breeding population. In fact, no population of sea snakes has been established on the eastern side of the canal since its completion in 1914.

Sea Snakes

Sea snakes also could enter the Atlantic Ocean by swimming from the Indian Ocean around the tip of Africa at the Cape of Good Hope. Yellow-bellied sea snakes do occur in the waters immediately east of the cape, but two major obstacles prevent them from traveling farther west. 

First, just west of the cape, the Benguela Current brings upwelling of very cold water to the coast of southwestern Africa. This current is 200 to 300 kilometres wide, and its water is too cold for these snakes– about 55 to 64 degrees Fahrenheit at the surface – for sea snakes that might drift there to survive for long or reproduce. 

Second, as research has shown, sea snakes require fresh water for drinking and will dehydrate at sea without it. They drink from “lenses” of fresh or brackish water that form temporarily on the ocean’s surface after large downpours of rain. But the climate of coastal southwest Africa is characterized by a large zone of permanent high pressure, which makes the region very dry with almost no rainfall.

Evolving from land to sea

Sea Snakes

Sea snakes also could become established by making evolutionary transitions from terrestrial or freshwater habitats to marine habitats in the island systems of the Caribbean. We know that elapid snakes – a family of venomous snakes with short, fixed-front fangs, such as cobras – have done this in the Coral Triangle region. 

Indeed, most of today’s sea snakes originated and evolved into different species in this part of the globe between 2 to 16 million years ago. At that time, this region was a vast wetland complex associated with Southeast Asia and the Australasian archipelago. 

Land and sea are interlaced throughout the Coral Triangle, and have been so for several million years. This region is also characterized by high rainfall, low and variable water salinity, and relatively stable tropical warm temperatures. Throughout much of its geological past, sea levels rose and fell many times, opening and closing marine corridors and causing mangrove fringes and mud flats to form and disappear. All of these conditions are favorable for evolutionary transitions from land to sea, and stable, shallow marine habitats have persisted for the past 3 million years.

Similar changes occurred in the Caribbean, but the Coral Triangle is a much larger and more complex system. Multiple ancestral lineages of snakes occur in Southeast Asia, and there are four to five times more viviparous (live-bearing), estuarine species within the Coral Triangle than occur in the Caribbean. 

In my view and that of my co-authors, the presence of appropriate lineages of snakes and a dynamic of ecological conditions favored speciation of sea snakes in the Coral Triangle much more so than in the Caribbean or anywhere else in the Atlantic Ocean. Indeed, the Coral Triangle, broadly defined, appears to be the only region where viviparity is characteristic of the majority of estuarine snakes. These snakes live in coastal waters contacting freshwater habitats, and they were most likely to undergo an evolutionary transition from terrestrial or freshwater to marine habitats and give rise to sea snakes.

Navigating changing oceans

Could future oceanic and weather conditions permit sea snakes to disperse from the Indo-Pacific to the Atlantic Ocean? It is believed to be quite unlikely. Thus, we do not expect any sea snake to show up on the beaches of Florida, like those occasional snakes that have drifted to land on beaches in California. There is simply no source.

There are already signs that some populations and species of sea snakes are in decline or have gone extinct, owing to changes in rainfall patterns, water temperatures, environmental contamination or human exploitation. Future climatic changes might bring negative as well as positive impacts on the biogeography of sea snakes. 

From my own experience watching sea snakes swim with graceful undulations over coral reefs, losing them (or any other marine organism) would be tragic and could threaten the health of coral reefs where sea snakes are top predators and considered to be harbingers of ecosystem change.

Summary

It can be said that seeing a sea snake in the wild is exceptionally special and rare. Tour groups are not necessarily available to see only sea snakes however, in some cases spotting a sea snake may be a by-product of another tour in the tropical regions in which they reside.

If you enjoyed reading this blog, why to visit our other blogs about Where to see manatees and dugongs; The Best Places to swim or dive with Orcas or Explore The Azores .

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