Ornate reef sea snake (Hydrophis ornatus)

Also known as: Cochin banded sea snake, Gray’s sea snake, ornate sea snake, ornate seasnake
Synonyms: Aturia ornata, Chitulia ornata, Disteira ornata, Distira andamanica, Distira godeffroyi , Distira mjobergi, Hydrophis ellioti, Hydrophis inornatus, Hydrophis laevis, Hydrophis lamberti, Hydrophis ornata
French: Hydrophidae Orne
GenusHydrophis (1)
SizeMale total length: 95 cm (2) (3)
Female total length: 86 cm (2) (3)
Length at birth: 19 - 34 cm (1)
Top facts

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

A venomous species (2) (4), the ornate reef sea snake (Hydrophis ornatus) belongs to the largest genus of sea snakes, Hydrophis (5) (6), which comprises more than 30 species (6). Members of this group of marine reptiles are also known as ‘banded sea snakes’ (5).

The ornate reef sea snake is a large-headed, robust marine snake (2) (4) (7) (8) of roughly uniform thickness (4) (7), although the front part of its body is cylindrical in shape while the rear part appears more compressed and heavy (3). A characteristic feature of sea snakes is the vertically flattened, paddle-like tail (9).

Young ornate reef sea snakes are greyish, blue-grey or light olive to almost white, and patterned with 30 to 60 broad, dark cross-bands or blotches on the back (2) (3) (4) (7) (8) and large spots on the sides (4) (10). These wide markings are separated by narrow interspaces (2). While the base colour of the adult ornate reef sea snake is the same as in the young, the darker markings may become less conspicuous or even be altogether absent in adults (4) (8). In both adults and juveniles, the underparts of the ornate reef sea snake are yellowish (2) (3) or whitish (2) (3) (10).

In the central section of the body, the scales overlap slightly in 39 to 59 rows (2) (4) (7) (10) and are somewhat hexagonal in shape (2) (11). These scales are smooth in young ornate reef sea snakes, but are keeled in adults (10). The scales on the underside of this species are roughly twice as wide as those found on the sides (4) (7).

The taxonomy of this species is still in dispute (1), with some scientists recognising three subspecies (1) (12) and others recognising a fourth (2). In some cases, one of the subspecies is treated as an entirely separate species (1).

The ornate reef sea snake is a relatively widespread species, ranging from the Arabian Gulf (1) (2) (4) (10) (13) eastwards to countries including Indonesia, China, Taiwan and the Philippines (1) (3) (7) (12), and south to northern Australia (2) (3) (4) (8) (13). In the summer, this species extends its range even further southwards to Tasmania (3) (7) (12), being one of just three sea snake species to do so (7). The ornate reef sea snake has also been recorded in New Caledonia and the Loyalty Islands (1) (2).

The ornate reef sea snake is found in a range of marine habitats (7) (13), from coral reefs to turbid inshore waters and estuaries (1) (3) (7) (13). This species is generally found in deep water at depths of between 18 and 55 metres (14), most commonly at depths greater than 30 metres (3).

The ornate reef sea snake is active by day and night (3), and is known to adopt a generalist feeding strategy (15), eating a wide variety of fish (1) (3) (4) (15). It tends to feed on free-swimming fish that are found in habitats close to coral reefs, such as sandy areas, but is also known to feed on benthic and demersal species, including fish from the Apogonidae, Nemipteridae and Mullidae families. In addition, the ornate reef sea snake has been recorded eating fish discarded from prawn trawl fisheries (7).

Despite being an air-breathing animal, the ornate reef sea snake is capable of remaining underwater for up to two hours at a time, before surfacing to breathe again. Its single, elongated lung, which extends for almost the entire length of its body, is highly efficient for gas exchange, and sea snakes are also able to absorb oxygen through their skin when underwater. As in other sea snake species, the ornate reef sea snake has specialised valves which block off the nostrils while underwater (7).

Living in the marine environment poses several other challenges, and like other sea snake species, the ornate reef sea snake has a specialised gland under its tongue which enables it to excrete excess salt from its body. A sea snake sheds its skin approximately once every two to six weeks. By shedding its skin so frequently, a sea snake can get rid of the many marine species, such as algae and barnacles, which become attached to it (7).

Mating in sea snakes is a lengthy affair, and the male is unable to disengage from the female until copulation is complete. Like most species of sea snake, the ornate reef sea snake is viviparous, meaning that it gives birth to live young rather than laying eggs (7). In northern Australia, the gestation period for this species is around six to seven months, with births occurring in September (7), while off the east coast of India and around Thailand, gravid females have been found between March and April (3).

Although litter sizes in this species vary from 1 to 17 young (3), the ornate reef sea snake generally produces small clutches of relatively large offspring (1). This species is reported to commonly produce between two and five young at a time (1), although in northern Australia the average number of young per litter is six (3) (7). It is thought that female ornate reef sea snakes reproduce every year (7).

A widespread species (1) (8), the ornate reef sea snake is not considered to be at risk of extinction (1). However, it is known to be caught as bycatch by trawl fisheries (1) (7). It is the most commonly captured sea snake species in many Australian trawling zones, where the air-breathing reptiles get caught in the trawl nets and often drown or become crushed by the weight of the catch. Research has shown that the ornate reef sea snake has the highest mortality rate after trawling of any sea snake species tested (7).

Although there are currently no conservation measures in place specifically for the ornate reef sea snake (1), this species, along with all other sea snakes in Australia, is nationally protected through its listing under the Environment Protection and Biodiversity Conservation Act 1999 (1) (7). This species is also thought to occur in some Marine Protected Areas (1).

Marine Bioregional Plans have been developed for four of Australia’s marine regions to improve understanding of Australia’s oceans, identify the conservation values of each marine region, and set out broad biodiversity priorities and objectives. As part of these plans, the ornate reef sea snake has been identified as being of conservation value in the Temperate East, North and Northwest Marine Regions (7).

In addition, it has been recommended that further research be conducted into the design and placement of Bycatch Reduction Devices (BRD) to reduce the impacts of trawling on sea snake populations (7).

Find out more about sea snakes:

Learn more about marine conservation in Australia:

Find out more about conservation in Australia:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (May, 2013)
  2. The Reptile Database (May, 2013)
  3. Karthikeyan, R. and Balasubramanian, T. (2007) Species diversity of sea snake (Hydrophiidae) distributed in the Coramantal coast (east coast of India). International Journal of Zoological Research, 3(3): 107-131.
  4. Wilson, S. (2005) A Field Guide to Reptiles of Queensland. New Holland Publishers, Sydney.
  5. O’Shea, M. (2008) Venomous Snakes of the World. New Holland Publishers, Sydney.
  6. Rasmussen, A.R., Auliya, M. and Böhme, W. (2001) A new species of the sea snake genus Hydrophis (Serpentes: Elapidae) from a river in West Kalimantan (Indonesia, Borneo). Herpetologica, 57(1): 23-32.
  7. Department of Sustainability, Environment, Water, Population and Communities (2012) Hydrophis ornatus. In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
  8. Gopalakrishnakone, P. (1994) Sea Snake Toxinology. National University of Singapore Press, Singapore.
  9. 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 Organization of the United Nations, Rome. Available at:
  10. de Rooij, N. (1970) The Reptiles of the Indo-Australian Archipelago. Brill Archive, Leiden, The Netherlands.
  11. Cooke, F. (Ed.) (2004) The Encyclopedia of Animals: A Complete Visual Guide. University of California Press, Berkeley and Los Angeles, California.
  12. Tomascik, T. (1997) The Ecology of the Indonesian Seas. Oxford University Press, Oxford.
  13. Heatwole, H. (1999) Sea Snakes. University of New South Wales Press, Sydney, Australia.
  14. Hutchings, P., Kingsford, M. and Hoegh-Guldberg, O. (Eds.) (2008) The Great Barrier Reef: Biology, Environment and Management. CSIRO Publishing, Collingwood, Australia.
  15. Somaweera, R. and Somaweera, N. (2009) An overview of Sri Lankan sea snakes with an annotated checklist and a field key. Taprobanica, 1(1): 43-54.