Ornate reef sea snake (Hydrophis ornatus)

Ornate reef sea snake
IUCN Red List species status – Least Concern LEAST

Top facts

  • The ornate reef sea snake is a relatively widespread species, found from the Arabian Gulf across to Indonesia and southwards to Australia.
  • A venomous species, the ornate reef sea snake feeds on a wide variety of fish, including species that live on the ocean floor.
  • The female ornate reef sea snake usually produces between two and five relatively large young per year, which are born live.
  • While young ornate reef sea snakes have broad, dark cross-bands and blotches on their back, this pattern tends to fade in adults.
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Ornate reef sea snake fact file

Ornate reef sea snake description

GenusHydrophis (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).

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

Ornate reef sea snake biology

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).


Ornate reef sea snake range

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).


Ornate reef sea snake habitat

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).


Ornate reef sea snake status

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

IUCN Red List species status – Least Concern


Ornate reef sea snake threats

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).


Ornate reef sea snake conservation

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).


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Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
Relating to the lowermost region of a body of water such as an ocean or lake, or to the organisms that live there.
In the fishing industry, the part of the catch made up of non-target species.
Fish that live on or near the ocean bottom. They are often called benthic fish, groundfish, or bottom fish.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
The state of being pregnant; the period from conception to birth.
An organ that makes and secretes substances used by the body.
Carrying developing young or eggs.
A projecting ridge along a flat or curved surface, particularly down the middle.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
The science of classifying organisms, grouping together animals which share common features and are thought to have a common ancestor.
Cloudy or muddy; not clear.
Giving birth to live offspring that develop inside the mother’s body.


  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.

Image credit

Ornate reef sea snake  
Ornate reef sea snake

© Huw Roberts

Huw Roberts
PO Box 17172
UGRU (Women's Campus)
UAE University
Al Ain


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