Seagoing Snakes
from the book, "Our Fascinating Earth"

Our Fascinating Earth

Seagoing Snakes

When the subject of snakes is raised, one immediately thinks of deserts, swamps, and jungles. Snakes do occur in these places, but the locale of their greatest abundance is the sea.

There are approximately fifty species of sea snakes, all members of the family Hydrophidae, that roam the waters of the Indo—Pacific region. As in so many groups of animals, there is always one type that is the wanderer. The habitat of one species, Aelamis platurus, extends into the western coastal waters of Central America and Mexico in considerable numbers. Its full range is from eastern Africa to western America, making it the most widely distributed reptile in the world. A few specimens have even been observed in Posieta Bay, Siberia.

Sea snakes do not seem able to survive in waters colder than 68 degrees Fahrenheit, so water temperatures form an invisible barrier, as effective as any material wall, that prevent them from entering the Atlantic Ocean around the Cape of Good Hope or Cape Horn.

North and South America were two separate continents prior to three million years ago. It was about then that the isthmus of Panama rose from the sea, joining the two continents and forming an effective land barrier that would separate the two great oceans. Scientists believe that before that time the sea snakes had not yet inhabited the eastern edge of the pacific. By the time their migrations finally took them there, the isthmus of Panama was already dry land and served as a barricade. Were it not for that thirty—mile—wide stretch of land, the sea snake would certainly inhabit the Atlantic today.

One might wonder why the snakes do not cross the isthmus through the Panama Canal. For them this would be impossible because freshwater lakes in the canal bar the passage of such marine organisms from one ocean to another. Sea snakes cannot enter freshwater because they would quickly lose critical amounts of body salts and die. Normally, salt from marine waters replaces the salt that is continuously eliminated by a special gland located in the sea snake's lower jaw. In this manner the intake and elimination of salt in the snake's body stay in balance.

Sea snakes are very highly specialized marine reptiles. They must come to the surface to breathe but can dive to considerable depths, remaining underwater for up to eight hours without breathing, an absolute record among air—breathing vertebrates. Their bodies are well adapted for such a feat because their right lung alone takes up most of the internal body space and extends even into the tail region. Their windpipe also has been modified into an auxiliary lung that, like a true lung, takes oxygen into the blood. Thus the snake uses its intake of air most efficiently.

These seagoing reptiles are generally coastal animals with a distinct preference for the mouths of rivers, harbors, beach areas, and coral reefs. The many species share one common characteristic — all are poisonous. As would be expected, the degree of potency varies among species, but even the least venomous is dangerous to man. Scientists report there is one known species that has a venom at least fifty times as potent as that of the king cobra!

A unique feature of the bite of the sea snake is that it is slow—acting and virtually painless. The lack of reports, especially in beach areas, may often be due to the victim's failing to realize he has been bitten. The delay in receiving medical attention is usually fatal.

Many Asians value sea snakes for their skin and meat, and fishermen take them by the hundreds of thousands each year, working their nets with bare hands. Here is where the greatest number of fatalities occur as many are bitten and few receive immediate medical attention. Still the fishermen seem reluctant to change their tactics.

Since the annual harvest of sea snakes is so great, it is natural to assume that this would affect the sea snake population. Although scientists cannot accurately estimate their number, there seems to have been no population decline. To illustrate their abundance, in 1932 ships sailing in the Strait of Malacca observed a continuous aggregation of sea snakes covering an area about ten feet wide and over seventy miles long — there must have been millions of them. All were swimming determinedly in one direction toward an unknown destination, probably their breeding grounds. Recently the number of reports from ships that have sailed through seas literally alive with sea snakes has increased.