Annulated sea snake  (Hydrophis cyanocinctus)

The annulated sea snake is classified as Least Concern (LC) on the IUCN Red List (1).

Sea snakes are amongst the most venomous of the world’s snakes, and are highly adapted to life at sea, being the most completely marine of all reptiles and never voluntarily coming ashore (3) (4) (5). All possess a flattened, paddle-like tail for swimming, as well as valved nostrils, which can be closed when the snake is underwater. Sea snakes lack the expanded belly scales that most other snakes use for moving on land (2) (3) (4). The body of the annulated sea snake (Hydrophis cyanocinctus) is variable in colouration, but usually bears 50 to 75 black bands or rings on a yellow or olive background (3) (6), the bands being broader towards the upper surface of the body and usually tapering to a point on the flanks. The species is one of the longest of all sea snakes (2), and the female is larger than the male (6).

The annulated sea snake is reported to occur in the Indian Ocean, including in the Arabian Gulf, east to Thailand, Malaysia and the Philippines, and in the Western Pacific Ocean, the South China Sea and East China Sea (1) (2) (3).

The annulated sea snake usually inhabits warm, shallow waters over reefs, seagrass or sand (3).

Little information is available on the biology of the annulated sea snake. Other sea snakes have been recorded diving to depths as great as 100 metres, and remaining underwater for up to 2 hours before surfacing to breathe (3). Like other sea snakes, it is likely that the powerful venom is used to overcome prey, which in this species includes eels and other elongate fish (2), and it may also have a secondary role in aiding digestion (3) (5). Studies in captivity suggest prey is located by movement-sensitive receptors in the skin, rather than using vision, with captive individuals able to catch fish in total darkness (6) (7).

All sea snakes give birth to live young (3) (4). In captivity, the annulated sea snake has been shown to give birth, at night, during January and February. Three to five young are usually produced, and measure around 43 centimetres at birth, although females are larger than males even at this young age (6) (7).

Very little is known about the conservation status of this and other sea snakes (3). The annulated sea snake is believed to be relatively common, but has been reported to occur as bycatch in commercial trawleries (7). The extent of this threat is unknown, as is the extent to which other threats to marine ecosystems, such as overfishing, reef destruction, pollution and climate change, may impact this species. Many sea snakes are exploited for the skins, organs and meat (2), but it is not known whether this poses a threat to the annulated sea snake.

Research into most sea snakes has been minimal (3). Most sea-snake fisheries in the Indian and Pacific Oceans are unregulated, and their impacts are virtually unknown (2). Despite some species being taken in large numbers, no sea snakes are listed under the Convention on International Trade in Endangered Species (CITES) (8).

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View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more about the annulated sea snake and other sea snake species:

• Carpenter, K.E. and Niem, V.H. (2001) The Living Marine Resources of the Western Central Pacific. Volume 6: Bony Fishes Part 4 (Labridae to Latimeriidae), Estuarine Crocodiles, Sea Turtles, Sea Snakes and Marine Mammals. Food and Agriculture Organisation of the United Nations, Rome. Available at:
  ftp://ftp.fao.org/docrep/fao/009/y0870e/y0870e65.pdf
• Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.

For more information on the conservation of snakes and other reptiles:

• International Reptile Conservation Foundation:
  http://www.ircf.org