Distribution

Various species in the coastal regions of the Persian Gulf through India to Japan, southwards to Indonesia, New Guinea and western, northern and eastern Australia. Sometimes also at river mouths and further upstream.

H. cyanocinctus not found in the coastal waters of the Philippines, eastern Indonesia, New Guinea or Australia.

H. semperi found only in Lake Taal on Luzon, in the Philippines.

Map 8 Hydrophis cyanocinctus.

Biology

With 48 species this is by far the largest genus among the Hydrophiidae. They are found primarily in coastal waters with a soft seabed, but sometimes also in brackish water at the mouths of rivers (H. semperi only in freshwater, see above "Distribution"). Head relatively small, fangs barely longer than 4 mm. Depending on the species, the body is slender to sturdy, with a length from 50 cm to 2 m. H. cyanocinctus is a relatively slender species with blueish bands on a light background. Bands widest over the spine. Feed mostly on elongate fish, chiefly eels.

Fig. 4.50 Hydrophis cyanocinctus.

Risk

Most accidents occur in fishermen while they are emptying their nets. Hydrophis species have relatively small venom glands. H. cyanocinctus is an exception, as it may have up to 80 mg (dry weight) of venom. The Hydrophis venoms investigated to date have proven to be strongly toxic in animal experiments.

In Reid's clinical study of sea snake envenoming in northwest Malaysia, 23 Hydrophis sp. bites are recorded, of which 1 caused severe envenoming (H. cyanocinctus) (Reid 1975b). In a retrospective study from the same region, of a total of 65 patients with Hydrophiidae bites, 16 died. On the basis of statements by patients or witnesses, 7 fatalities were connected with Hydrophis sp. (H. cyanocinctus 4, H. spiralis 2 and H. klossi 1) (Reid and Lim 1957). A serious case of envenoming due to H. cyanocinctus was documented in Japan (Higa et al. 1990).

A retrospective study in a fishing village on Lake Taal, in the Philippines, found that over a period of around 5 years, 8 fishermen suffered envenoming by H. semperi, one of whom was reported to have died. These numbers carry particular weight considering that the actual group at risk in this study consisted only of the 150 fishermen who lived in the village (Watt and Theakston 1985).

Literature (biological)

Cogger 1975, 1987, 2000, Dunson 1975b, Gasperetti 1988, Limpus 1975, 1987,  Minton 1975, Reid 1975b, Reid and Lim 1957, O'shea 2005

The Reptile Database