Should We Be Worried About Sea Snakes?

This discussion topic submitted by George Gardner ( at 9:33 am on 6/1/00. Additions were last made on Wednesday, December 18, 2002.


The world would be less interesting if there were no creatures that instilled fear in us humans. Any organism that can devour, bite, sting, poison, or in any way potentially harm us can cause these fears. Human beings also have the ability to imagine fears of things just because we have little knowledge of them. In other words, we often fear organisms and kill them just because they appear ugly, or menacing to us. Snakes certainly are among those at the top of the list of organisms that man has been fearful of, and, in some cases, for good reason. Snakes or serpents display an appearance and movement that promotes a primeval fear in many of us. "Depending on the civilization, snakes have been seen as demons, monsters, gods, ancestors, or sacred protectors." 1. "Their ability to move without limbs, swallow prey in one piece, inflict venomous bites, constrict, ever-open eyes, and changing skin set them apart from other animals." 1. Serpents have symbolized every theme from immortality to death.
Surely many sea-stories and legends are the result of actual encounters with the only serpents who have actually adapted to a totally marine environment - the sea snakes. Overall, most people have little knowledge of these creatures. I myself have never seen one. The purpose of this paper is to gain insight into the understanding of these creatures and to find how fearful of them we should be.
There are 2,600 species of snakes, making them one of the most successful groups of reptiles. The Antarctic is the only continent that they have not conquered. Their range includes deserts, dense forests and aquatic environments. The oldest known reptile fossil dates back to the carboniferous about 350 million years ago. Evolutionary success is probably due to a remarkable ability to swallow their prey whole, unique locomotion, and venom toxicity. Snakes most likely evolved from lizards, but the missing common ancestor has not been found in the fossil record. 1 Many scientists believe that sea snakes once were in the same family as the cobra. 5. There are two main theories suggesting how they became totally aquatic. They could have been terrestrial and begun looking for food in the open sea, or maybe they are descendants of a family of extinct water snakes. 6.
Sometimes confused as true sea snakes is the Sea Kraits sub family ( laticaudinae) which is less aquatic. The sea kraits must come to land to lay eggs and are more mobile on land than true sea snakes. Their range includes coastal waters of Southeast Asia and the Southwestern Pacific islands. 2. True sea snakes sub family (hydrophine) is included in the large group of venomous snakes called the elapids. There are at least 50 species of sea snakes, most of which are venomous. The adaptations of this amazing creature for life in the open sea are what truly enable it to be called a sea snake. Their paddle shaped tail allows for quick movement through the water but leaves the creature virtually helpless and immobile on land. Supposedly, the sea snake cannot curl up to bite if it is held by the tail out of the water, although I do not recommend trying it. The lungs of a sea snake extend almost the entire length of its body, allowing large amounts of oxygen to be stored. Also, up to 22% of needed oxygen is absorbed through the skin from sea water. The lungs also play a role in buoyancy. The presence of enlarged lungs leads me to believe that these creatures evolved from land snakes. Depending on how active they are, most species can remain underwater up to 2 hours without surfacing. The nostrils can be closed with valve-like flaps to prevent water from entering the lungs.
Evolution has also solved the salt problem for sea snakes. The sea water has a higher concentration of salt than their bodies. Extra impermeable skin and a specialized gland under the tongue called the sublingual gland prevents dehydration through osmosis. 2 This gland disposes of excess salt from the body. The heart of a sea snake is found in the middle of the body. In contrast, the heart of a terrestrial snake is located closer to the head. Water pressure helps compensate for blood pressure so that blood does not accumulate in the tail. 1
Sea snakes are top predators, feeding mostly on fish, eels, crabs, squids, and fish eggs. They can become a meal themselves for sea eagles, sharks, moray eels, saltwater crocodiles, crabs, and humans. 7. Interestingly, large masses of sea snakes are sometimes spotted, numbering in the thousands, intertwined at the surface, forming huge "slicks." Although scientists are not completely sure why this behavior occurs, one theory suggest that it may provide shaded shelter for unsuspecting fish which wind up becoming a meal for the sea snakes. 2. The largest slick found in my research occurred in the Straits of Malaca on May, 1932, in which a 10 ft wide 60 mile stretch of sea snakes was observed. 8. Most would-be predators of sea snakes end up victims themselves, as often the snake bites the stomach of whatever swallows it and escapes out of the predators mouth as the poison takes affect. 9.
True sea snakes are vivitarious (live bearing), mating and bearing their young at sea. The over-sized lungs of sea snakes only allow for relatively small litters, numbering from 2 to 20. The young are born close to shore in a protected place where there is plenty of fish to eat. 6. As they grow, they shed their skin often, about every 2-6 weeks. This carries into their adult life, helping to rid them of parasites. Most sea snakes reach adulthood in 1 year and live 3-4 years. Olive sea snakes may live up to 10 years. 6. The majority of species grow to the 1-2 meter range.
Sea snakes come in a variety of colors, some of which probably aid in absorption of radiation to elevate body temperature. This could be the main reason why sea snakes are found only in tropical regions where the water temperature is suitable for survival. So, where are they? Will we run into one off the coast of San Salvador? They can be found in the waters of Australia, Indonesia, Southeast Asia, India, Gulf of Arabia, and the Gulf of Oman. They can be found from the Cape of Good Hope to Central American Pacific waters. 9. Sea snakes are not found in the Atlantic ocean or in the Caribbean. All but one species is found in coastal waters. 2. So, the good news is that we will not have to worry about sea snakes during the course. There has been some concern about possible migration through the Panama Canal. This has not occurred so far, maybe because of a lack of suitable food in the fresh water of the canal. Sea snakes seem to be lazy travelers floating with the current, and the water flow of the Panama Canal prevents their intrusion. It could be possible for their migration if another canal is ever constructed in Panama. 9. What would be the ecological effects to the Caribbean with the influx of sea snakes?
So, how dangerous are they? Should we limit ourselves to the Atlantic and Caribbean or the Mediterranean, which is too salty and lacks food for the sea snake? On paper they seem extremely deadly. Sea snake venom is the deadliest of all snake venoms. Snake venoms are an evolutionary success also aiding in digestion. One drop (0.03mi) of venom from the beaked sea snake can kill 3 men. A single beaked sea snake carries enough venom to kill 52 people. This neurotoxin is 4 times more deadly than a cobra's. 6. Neurtoxins affect the nervous system, especially respiration and the heart. The victim of an untreated, highly venomous bite can expect convulsions, paralysis, respiratory failure and death. 9. The neurotoxins in sea snake's venom prevents the binding of the neurotransmitter, acetylcholine which blocks nerve impulses. 7.
Okay, now that it seems like the worst creature you could ever come across and that you should kill every sea snake, there is good news. For the most part, sea snakes don't want anything to do with humans. They are relatively non aggressive, and there are very few deaths attributed to sea snake bites. Most bites occur from careless handling of nets and lines by fisherman or on occasion stepping on one. Antivenin is an accepted treatment if available. Also on a positive note, only 25% of those bitten develop any symptoms of poisoning. 9. Sea snake fangs lie at the back of the mouth rather than at the front and the venom delivery system is poor. 7.
Sea snakes continue to be studied, as we still have much to learn. Unfortunately, their study is difficult because of the harshness of the conditions in which they live. Also, they do not do well in captivity. The exploitation of sea snakes will also hinder their study, as they are being hunted at an alarming rate. Their leather is in much demand, especially in the United States. Some cultures consider them a delicacy, resulting in millions of Asiatic sea snakes being slaughtered each year. In 1974, Philippine divers were catching 450,000 sea snakes a month, which of course has led to a massive decline in population.
Your chances of being bitten by a sea snake are extremely rare, especially if you only dive or snorkel off the east coast of the United States or in the Caribbean. Those who venture to tropical parts of the world where sea snakes exist are not likely to be bitten. The best advice for divers in these areas is to just be cautious while wading in water where you can stand up. Very few bites have occurred in the open water. If you dive in waters where sea snakes are numerous it may be a good idea to have antivenin available.
Just about every animal that captures my attention because of it's uniqueness, size, beauty, ferociousness, or ability to kick my ass seems to be in some kind of trouble. I'm getting tired of hearing how human greed is reducing these creatures to near extinction. You would think that a snake, of all animals that live in the ocean would be left alone. Of course this is not the case, and, unfortunately, sea snakes are not cute enough to gain much sympathy. I mean everybody considers a baby mountain gorilla an adorable site, and you know where they are headed. If we would plaster a picture of baby sea snakes on cereal boxes, it would be futile. How do we fight exploitation that occurs on such a large scale in remote parts of the world? What I do is try to get the message across to my students, and, of course, refuse to purchase products which lead to the annihilation of creatures such as the sea snake. I can hear my critics now, " I bet he wears leather shoes and eats at Mcdonald's!"

Literature Cited

1. Bauchot, Roland. "Snakes a Natural History", New York, New York. Sterling Publishing Co., Inc., 1997
2. Mattison, Chris. "The Encyclopedia of Snakes". New York, New York: Facts on File Inc.,1995
3. Phelps Tony. "Poisonous Snakes". New York, New York: Sterling Publishing Co., Inc., 1981
4. Mattison Chris."Snakes of the World". New York, New York: Facts on File., Inc., 1986
5. "Sea Snakes"., Dolphin Log/May 1997. New York: The Cousteau Society, May 1997
6. Souza D.M. "Sea Snakes".Minneapolis Minnisota: Carol & Hoda Books., Inc., 1998
8. Minton, Sherman., and Heatwole, Harold, "Snakes and the Sea", Oceans,11:55 April 1978
9 .


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