Sea snake homing instinct could nix translocation

September 24, 2002

Philippine researchers want to restore a sea snake that has been wiped out on Gato Island by translocating the species from other islands. But new research suggests that this may not work because these snakes have such a strong drive to return to their own islands.

"The fidelity of snakes to their home island was absolute," say Sohan Shetty, then at the University of Sydney, Australia, and now at Nanyang Technological University in Singapore, and Richard Shine of the University of Sydney, Australia, in the October issue of Conservation Biology.

Widely distributed in the Pacific Ocean, the snakes (yellow-lipped sea kraits) forage for moray and conger eels in the ocean, and typically return to land to digest their prey, mate, lay eggs. The up to 5-foot long snakes are prized for their meat and skins, which are used to make high-quality leather goods, and are easy to catch in huge numbers because they are concentrated on small islands and, although venomous, are so docile that they rarely bite or even try to escape.

Overexploitation has caused local extinctions of yellow-lipped sea kraits in the Philippines and Japan. While translocation has been proposed to restore these populations, no one knew if the relocated snakes would stay put.

To help assess the likelihood that translocation would restore these sea krait populations effectively, Shetty and Shine studied the snake's homing behavior on two small Fijan islands. The islands are about 2 miles apart and one (Mabualau) is uninhabited by people while the other (Toberua) has a resort.

Shetty and Shine caught 328 yellow-lipped sea kraits by hand on Toberua, marked them by clipping their scales and then released them on Mabualau. When the researchers recaptured the translocated snakes, they found that all of them had returned "home" within about a month. The researchers also caught, marked and released 674 snakes on Mabualau, and found that none of them were recaptured on Toberua.

These findings suggest that the populations on the two islands are separate, a conclusion that is supported by the finding that adult male sea kraits have different average growth rates and body sizes on the two islands (they grow faster and are larger on Toberua).

This work shows that it may take a long time for yellow-lipped sea kraits to recover from local extinctions. "Our data suggest that translocations may be ineffective because the snakes are likely to return to their original homes," say Shetty and Shine. Another implication of the snake's site fidelity is that populations are extremely vulnerable to local threats such as developing islands into resorts, introducing mongooses, and degrading the coral reefs where the snakes forage.

Shetty and Shine note that the flip side is sea kraits could be harvested if managed properly. "Simply stated, populations on certain islands can be left undisturbed while those on other islands can be harvested. That way, we can be certain we are not wiping out the entire species, and at the same time we are not depriving people of their livelihood," says Shetty.
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ADDITIONAL CONTACT INFORMATION:
*Richard Shine (61-2-9351-3772, rics@bio.usyd.edu.au)
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