[Phylum: Chordata] [Class: Reptilia] [Order: Squamata] [Family: Hydrophiidae (Water Lovers)]
Sea snakes are reptiles that live in water and need to breathe air. Even so, they are capable of staying underwater for long durations before they need to surface.
This section contains fun facts and information about the 60+ species of marine snake, including their diet, where they live, and which ones are venomous.
Even if you've seen a snake on land, you may not even know there are similar limbless reptiles swimming in the oceans.
But, for one reason or another, water snakes differ from the specimens that live on dry land (terra firma).
Regular sightings of these amazing sea life creatures occur in Australia, the Indo-Pacific Ocean, and New Guinea.
As a result, it is common for some scuba divers and snorkelers to have ophidiophobia (a fear of snakes) - especially when diving or swimming in shallow, warm-water coastal environments.
Note: Because they spend most of their lives living in water, you can also find snakes in freshwater rivers, lakes, and forested wetlands (swamps). Even though some snake species can travel on land, most sea snakes will die if they get washed ashore.
In fact, two distinct groups have evolved in independence. But, this section focuses on the subfamily Hydrophiinae (true sea snakes) that are related to Australian terrestrial elapidae (elapid snakes).
Often, they will swim together as a group, which can appear to be one, single, elongated snake. This could be why water snakes are regularly depicted as serpents of the sea.
It would be unusual to find a sea snake measuring more than 1.5 metres in length (about 5 feet). In actuality, the average length for venomous marine snakes is less than one (1) metre (3 feet).
Most of the species have a light-coloured body, many with dark rings encircling it. Some also have tiny belly scales that help them to crawl.
Having a flattish, oar-shaped tail means they can swim through the water column to the surface by moving it in a sideways motion. However, being able to store large amounts of oxygen inside their lungs means they can remain submerged for extended periods.
Most of the sea snake species can hold its breath for at least thirty (30) minutes. Whereas, many of the true sea snake species can stay below the surface for up to eight (8) hours before they need to breathe air.
They use their skin to absorb up to 33% of their oxygen requirements. Then, they use a similar process to expel 90% of the carbon dioxide.
In case you were wondering:
Sea snake poison is 'highly' potent. But, most species have short hollow fangs and venom output is small. Marine snakes are not aggressive by nature (unless threatened or provoked). So, human fatalities from snake bites are a rare occurrence (excluding careless fishermen).
Note: Another section has extra facts and information about sea kraits (subfamily Laticaudinae) which have closer relations with Asian cobras.
The typical diet and nutrition of a sea snake varies with the species. For example, the yellow-bellied sea snake is a carnivore and it will only eat fish.
Nonetheless, most coral reef snake species feed on a mixture of:
Besides consuming their usual diet, this sea reptile also needs to take in fresh water to avoid dying of thirst. Some will venture on land to drink. Whereas, others will swallow fresh water while swimming at the surface (e.g. while it is raining).
They can also use special glands to remove salt from the water that surrounds them. In fact, snakes use 'salivary' sublingual glands (situated underneath the tongue) to expel any unwanted deposits of sea salt.
The actual species of the snake will determine whether it has oviparous reproduction (egg birth) or ovoviviparous (fertilised internally). Nonetheless, these are the only reptiles that give birth in the ocean, and the general clutch size will be around three or four.
Almost all true sea snakes display ovoviviparous reproduction. In simple terms, it means the female will give live birth from the eggs stored inside her body.
The reason is because their eggs fail to incubate underwater and they rarely make a visit to dry land. This process differs from the female oviparous yellow-lipped sea krait which ventures on land to lay her eggs.
Sadly, the International Union for Conservation of Nature (IUCN) lists the crocker's sea snake (Laticauda crockeri) as being vulnerable (VU), and many more are close to extinction.
Furthermore, the critically endangered list includes the leaf-scaled sea snake (Aipysurus foliosquama) (Leaf-scaled sea snake) and the short-nosed sea snake (Aipysurus apraefrontalis). The major causes of the decline in sea snake populations, include:
Worse still, much of the Orient considers sea snakes as being a delicacy. They often use snakes' attraction to light to capture them for human consumption.
Interesting Fact: There are no sea snakes in the Atlantic Ocean, Caribbean Sea, nor in areas with high salinity (e.g. the Red Sea).
Sometimes, even trained scuba divers struggle to differentiate coral reef snakes with some eel species (e.g. moray eels). Check if there's a dorsal fin running down its body. If so, it's not a snake!
In a nutshell, YES! A somewhat surprising fact is that many of the sea snake species contain more venom than the average land snake, including the cobra and rattlesnake.
If you get a scuba diver's licence you will be qualified to dive deep enough to see snakes in the ocean. But, some members of the Elapid family can actually dive to kill their prey at depths around 250 metres (800 feet).
There is only one of the species that will swim huge distances from the shoreline. The yellow-bellied sea snake is the only known reptile that spends its entire life in water and swims hundreds of miles out into the ocean.
The yellow sea snake (Hydrophis spiralis) is the longest, growing almost to three (3) metres in length. The shortest is a species called shaw's sea snake (Hydrophis curtus).
There's a rare species of venomous sea snake that you can only find in the Philippines. In fact, it only lives in a single lake on the island of Luzon. It has several names, including garman's sea snake and lake taal snake (Hydrophis semperi).
Research in marine biology suggests that they can hear some sounds, albeit limited in their sensitivity to sound pressure.
The geographical distribution of aquatic sea snakes and sea kraits is large. However, you won't find any of these marine reptiles in the Atlantic Ocean, the Caribbean Sea, and areas with high salinity (e.g. the Red Sea, Egypt).
In essence, the best place for scuba divers to find sea snakes in the ocean is somewhat 'subjective'. Even so, check out seven locations listed in the scuba destinations section for useful facts and information.
Note: The short video [2:49 seconds] contains some quick answers to questions about common venomous reptiles, banded sea kraits facts, and information about coral reef snakes.