Photo copyright Tim Nicholson.
Lady Bowen, Australia.
You mostly find sea snakes in shallow, tropical waters. They look a little like eels but they are reptiles not fish and must come to the surface regularly to breath. Some types of sea snake have the most potent venom of all snakes.
It has been a long-standing dogma that all sea snakes satisfy their drinking needs with seawater, their internal salt glands filtering and excreting the salt. Experiments published this month with three species of sea snake captured near Taiwan, however, found that the snakes refused to drink saltwater even if thirsty - and then would drink only freshwater or heavily diluted saltwater.
The research may help explain why sea snakes tend to have patchy distributions and are most common in regions with abundant rainfall. Although unlike most other sea snakes, the sea kraits can still return to land.
Researcher Professor Lillywhite believes the sea snakes that spend their lives in the open ocean drink water from the "lens" of freshwater that sits atop saltwater during and after rainfall, before the two have had a chance to mix. That would explain why some seawater lagoons, where the waters are calmer due to protection from reefs, are home to dense populations of sea snakes — the freshwater lens persists for longer periods before mixing into saltwater.
Sea snakes are reptiles that have returned to the sea from the land. Of the 15 living families of snakes, four contain marine species. Altogether there are 70 known species of sea snake.
The bite of the sea snake is painless. However, half an hour later stiffness, muscle aches and spasm of the jaw or pain in the bitten limb may occur. This is followed by blurred vision, drowsiness and respiratory paralysis.
Sea snakes are are generally not agressive and will not bite unless provoked. Even then they tend not to use their venom, and their short fangs cannot penetrate a neoprene wetsuit. Although many are shy and will not approach divers, some can become very curious - swimming close to you to get a better look. If this happens to you remain calm and enjoy watching these elusive animals.
The Underwater Photographer: Digital and Traditional Techniques, by by Martin Edge, Paperback, 536 pages (2009)