Friday, October 7, 2011

SEA SNAKES Beutiful Dangerous

Sea snakes occur in the tropical and subtropical waters of the Indian and Pacific oceans from the east coast of Africa to the Gulf of Panama. Most species are found in the Indo-Malayan Archipelago, China seas, Indonesia, and the Australian region. They inhabit shallow waters along coasts and around islands, river mouths, and ascend into rivers up to more than 100 miles from the sea. They have also been found in lakes in Thailand, Cambodia, the Philippines, and Rennell Island (Smith, 1926; Dunson, 1975; Alcala, 1986; Ineich, 1996; pers. observ.). There is considerable variation in the number of species and species composition reported from the Western Central Pacific and precise information on geographical distribution for many species is still lacking. Most species feed on fish, a few prefer fish eggs, and a single species takes crustaceans and molluscs (Voris, 1972; Voris and Voris, 1983; McCosker in Dunson, 1975; Rasmussen, 1989, 1993). The genus Laticauda is oviparous (egg-laying) while all other sea snakes are viviparous (livebearing).

The most typical feature of a sea snake is the vertically flattened paddle-like tail, which is absent in all other aquatic or terrestrial snakes. However, the taxonomic status of “sea snakes” is still under review and there is no general agreement at the moment. Traditionally, sea snakes have been regarded as belonging to a single family, Hydrophiidae, with Laticauda as the most primitive genus. However, some experts consider that the Laticaudinae and Hydrophiinae evolved from different terrestrial representatives of the family Elapidae. Even more confusingly, some results indicate that the Hydrophiinae can be separated into 2 quite different groups, indicating that sea snakes may have evolved 3 times from terrestrial elapids (Rasmussen, 1997).

On a higher taxonomic level, all sea snakes are most closely related to terrestrial elapids, which include some of the most poisonous snakes of the world (e.g. brown snakes, taipan, death adder, cobra, Krait, mambas). Sea snakes (or aquatic elapids) and terrestrial elapids are both named “proteroglyphous snakes” because of the position of the poison-fangs in front of the upper jaw (maxillary bone).

Sea snake bite is the cause of fatalities in the Western Central Pacific. Typical victims are fishermen handling
gape nets, sorting fish on a trawler, or dragging a net while wading in muddy coastal waters or river mouths.
Some sea snakes are gentle, inoffensive creatures which bite only when provoked, but other species are much more aggressive (e.g. Aipysurus laevis, Astrotia stokesii, Enhydrina schistosa, Hydrophis ornatus) (Guinea, 1994; Heatwole and Cogger, 1994; Toriba, 1994; Warrell, 1994; pers. observ.). Even though sea snakes rarely inject much of their venom, so that frequently no or only trivial severity of poisoning is recognizable, all sea snakes should be handled with great caution.

If a snake bite has occurred, the following first-aid procedures are recommended: if the bite is on an arm or leg, a broad crepe bandage (or material of similar type) should be wrapped immediately around the area of the bite. The bandage must be very tight and extended over the entire arm or leg. Then a splint should be used to immobilize the arm or leg and hospital treatment must be sought as quick as possible. If the bite is on the body, firmly press the area of the bite and look for hospital treatment immediately.

Sea snakes are exploited for their skin, organs, and meat. Although some species are taken in great numbers
(e.g. Laticauda spp., Lapemis spp., and some Hydrophis spp.), they are not protected by CITES (Washington convention). Since 1934, meat and skin of sea snakes have been used commercially in the Philippines (Dunson, 1975) and local protection of sea snakes became necessary to avoid overexploitation. Sea snakes are also exploited in Australia, Japan, Taiwan Province of China, Thailand, and Viet Nam (Dunson, 1975; Warrell, 1994; Tim Ward, pers. comm., 1993; pers. observ.). The local government in Queensland, Australia has introduced a special licence to collect sea snakes. However, most sea-snake fisheries in the Indian and Pacific oceans have not been reported in the literature and are not controlled by local governments. With the exception of the Philippines, the impact of exploitation on populations of sea snakes is almost unknown and some populations may already be in danger of extinction.

Monitoring and control of the commercial catch is the only way to maintain a sustainable yield, giving local governments a chance to intervene before a catastrophic collapse of local populations occurs. However, management of sea-snake fisheries and protection of the endangered species is not possible without a basic knowledge of the group and the ability to identify to the species level. It is the purpose of the present contribution to provide a tool for correct identification of sea snakes in the Western Central Pacific. Nonetheless, the following identification keys must be regarded as tentative, due to the lack of distribution data from many regions and because there is no general agreement on the validity of certain species.

Identification of sea snakes to the species level is very difficult. The genus Hydrophis especially shows wide
interspecific variation which makes it difficult to exclusively use external characters for identification. For the
separation of genera, only characters that are visible without using a microscope are included in the keys. The shields on the head and the number of scale rows around the body are particularly important, as well as the shape of head, the size and number of ventral scales, and the position of the maxillary bone.

When counting scale rows around the neck and body it is important to remember that the count around the neck is a minimum count, while the count around the body is a maximum count. To be sure of the minimum
count around the neck it is necessary to count the scale rows 3 or 4 times, starting 1 ½ head lengths behind the head and then 2, 2 ½, and 3 head lengths behind the head. When counting scale rows around the body
the maximum count is normally found just behind the midbody. However, to be sure of the precise maximum
count it is helpful to count 3 or 4 times between midbody and anus. All scale rows are counted in a straight
line around the body, starting at a ventral and counting each scale along this line. The ventral is not included
in the scale-row count.

In the key to species of Hydrophis it was necessary to include the count of maxillary teeth behind the poison-fangs. Use a needle to push the gum around the teeth to above the maxillary bone and keep the gum in this position by fixing the needle at the roof of mouth (sometimes it is necessary to use 2 needles). A microsope is required to count the maxillary teeth.


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