SEA SNAKES EAT MOSTLY MORAY EELS

by Whit Gibbons

June 10, 2007

Diversity, which refers to the numbers and kinds of plants and animals in a region, is a household word among ecologists. The Savannah River Ecology Laboratory (SREL) itself might be said to be ecologically diverse. SREL researchers include a geologist who studies meteorites from Mars, an ecologist who examines radiation in environments from South Carolina to Chernobyl, and ornithologists who use satellites to track endangered woodstorks. But what would an ecology lab be without an expert on sea snakes? The sea snake research that Bob Reed published while he was at SREL is worth hearing about again.

"Sea snakes are strange and wonderful critters distributed primarily in the Southeast Asian and Australian region. Related to the venomous cobra family, sea snakes have two main subgroups. The first includes the `true' sea snakes; these species are specialized for a fully aquatic existence, have live birth, and never leave the water. The second group includes about a half dozen amphibious species known as sea kraits, which hunt their food in the water but move into terrestrial shoreline habitats to digest food, mate, shed their skin, and lay eggs. Most sea kraits are elegantly attired in black and white bands. One species has black bands interspersed with brilliant DayGlo blue. These snakes can reach astonishingly high densities in some areas, and researchers have reported finding up to 600 in a single day.

"In collaboration with scientists from the University of Sydney, Australia, I studied sea kraits on the island of Efate in Vanuatu. The musical 'South Pacific' was modeled after the people of Vanuatu, a nation composed of hundreds of islands in the western Pacific Ocean.

"We mostly searched for snakes at night with the aid of headlights, catching the animals on shorelines as they left the water and moved toward shelter in limestone crevices. During the day, we weighed, measured, and marked the snakes, determined what they had eaten, and then released them at their original capture sites. On some nights I hired a local to drop me off on a tiny islet off the north coast of Efate, where I would catch snakes and then fall asleep on a beach to the sound of waves breaking on a reef. In the morning I played Robinson Crusoe, catching fish with a handline and cooking them over a driftwood fire in an empty giant clamshell while waiting for the boat to pick me up.

"An astounding fact about most sea kraits is that they are dangerously venomous yet unbelievably docile. Even while being unceremoniously picked up and placed in collecting bags, none tried to bite. If a laid-back attitude is characteristic of the tropics, these snakes have it in spades. However, although sea kraits are not usually dangerous to humans, they are unrelenting when after their favorite prey, moray eels. These eels are potentially dangerous to a hungry snake, as was evident from the hideous eel-inflicted bite scars on many snakes. But the snakes usually prevail; we found up to five small eels in the stomach of a single snake, and a five-foot female snake was able to subdue and swallow a four-foot moray eel!
" Our research was aimed at finding out how three outwardly similar species of sea kraits were able to coexist in one spot in Vanuatu. We found that the species eat different kinds and sizes of eels and apparently hunt at different water depths, thus effectively dividing up the available food resource without competing. Sea snakes also vary in their swimming speeds and body sizes, which may also contribute to their stable coexistence.

"Sea krait populations appear to be declining in many regions of the western Pacific. Perhaps overfishing of reef fish has reduced the food supply of moray eels, which would eventually affect the snakes. Or maybe humans have degraded the beaches so that suitable hidey-holes for snakes have disappeared. Or maybe too many of these relatively harmless snakes are still killed by people out of fear. I have designed a poster to distribute among native communities in Vanuatu to explain the relationship between snakes, eels, and healthy reef ecosystems. With a bit of help, perhaps these marvelous eel-eating snakes will persist in their island habitats for a long time to come."

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