Journal of the Marine Biological Association of India

Volume 14 Issue 2

The role of sea snakes (Hydrophidae) in the trophic structure of coastal ocean communities.

Harold K. Voris

This Hydrophiidae is a family of poisonous marine snakes consisting of 51 species placed in 16 genera. The center of the geographic range for the family is the Straits of Malacca where 27 species coexist. Because essentially all species are associated with coastlines, the range is more or less linear. As their range extends from the Straits of Malacca along the east and west coast of India to the Persian Gulf, the number of species present steadily decreases from 27 to 11. The coastal waters of southern India harbour 20 species, representing 8 genera.


Although the taxonomy of this group is comparatively well understood, our knowledge of its ecology is sorely lacking. In this study, the feeding habits of sea snakes are examined. Data on 13 genera and 39 species were obtained from the stomach contents of 95 sea snakes collected during the International Indian Ocean Expedition and from specimens borrowed from over 19 museums. Also data from 84 additional snakes were extracted from the literature. Prey have been identified and then classified according to body form and ecology. Body forms fall into four general categories: (1) eels (e.g. Apodes) and eel-like fish (e.g. Synodus); (2) bullet-shaped fish (e.g. mullet); (3) vertically or laterally oversized fish (e.g, puffers and flatfish); (4) other than fish (e.g. birds' eggs, fish eggs and prawns). Five general categories were constructed to describe prey ecology: (1) inshore, on or near bottom; (2) rock dweller; (3) reef dweller; (4) pelagic inshore; (5) pelagic offshore. The fact that sea snakes utilize such a wide range of food types demonstrates their niche diversity.


Correlation studies on the relationships of prey class, prey ecology, snake dentition and snake girth reveal the extent of feeding specialization. Generally, species in which the adult males have an average neck circumference of more than 30 mm, the average fang length is greater than 1.7 mm. These species are taxonomically diverse and include most of the monotypic genera and numerous Hydrophis species. Their feeding habits are diverse and include every class of food. The Aipysurus and Emydocephalus whose average neck circumference is greater than 30 mm, have average fang lengths of only 1.4 mm and 0.8 mm respectively. These forms feed on eels and demersal fish eggs. The microcephalic species have neck circumferences of less than 30 mm and fang lengths of less than 1.7 mm. These forms belong to three genera, Mkrocepfialophis, Kerlia and Hydrophis yihich feed almost exclusively on bottom dwelling Apodes eels. From such data and that in the literature, a preliminary qualitative picture of the role of sea snakes in ocean communities can be constructed.

Date : 30-12-1972