Turtleheaded sea snake (Emydocephalus annulatus)

Also known as: annulated sea snake, egg-eating sea snake, turtle-headed seasnake
French: Emydocephale Annele
GenusEmydocephalus (1)
SizeLength: 60 - 120 cm (2)
Weightup to 1.5 kg (2)
Top facts

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

A slender, medium-sized sea snake (3), the turtleheaded sea snake (Emydocephalus annulatus) is named for its short, blunt head and plate-like upper lips, which give it a unique, turtle-like profile (3) (4). The scales on its body overlap each other and are smooth (3), while the wide scales on its underside have small bumps on them, and are keeled in the centre. The scale on the tip of the snout, known as the rostral scale, bears a conical projection, which forms a conspicuous blunt spine in the male turtleheaded sea snake (3) (4).

The turtleheaded sea snake is notable for its highly variable colouration (2) (3) (5), which ranges from uniform blue-grey, brown or black to having blotchy or banded patterns of creamy white or yellow (3) (4) (5) (6) (7). Uniformly blue-grey individuals of the turtleheaded sea snake are the most common form throughout its range, while a striking ringed form has been recorded in parts of the Great Barrier Reef, and a rare black form occurs on isolated reefs further east in the Coral Sea (2). Turtleheaded sea snakes are known to become darker as they grow larger (7).

Male and female turtleheaded sea snakes are generally quite similar in appearance, but there are some differences. Female turtleheaded sea snakes tend to grow larger than males, while the black form of this species is more commonly found in males than in females (7). The scales of the male turtleheaded sea snake have also been found to be more wrinkly or creased than those of the female (7) (8), particularly during the breeding season (8).

Unlike many other similar species, the turtleheaded sea snake has tiny fangs, measuring less than one millimetre in length (2).

The turtleheaded sea snake occurs in the Indian and Pacific Oceans, from the tropical waters of northern Australia to Fiji, New Caledonia, the Philippines and Vietnam (1) (2) (3) (4) (5).

Although the turtleheaded sea snake has a wide geographic range, it has a highly disjointed distribution throughout (1). For instance, in Australia, the turtleheaded sea snake is found in the Great Barrier Reef on the east coast (1) (3) and on the Timor Sea reefs on the west coast, but it is not found in the Gulf of Carpentaria which lies on the country’s north coast (1).

Shallow waters of coral reefs are the preferred habitat of the turtleheaded sea snake (2) (4) (6) (7), although it is also found within rocky or coral-rubble areas and over sand banks (1) (2) (7). The water it inhabits is generally less than 10 metres deep (3), but in the Philippines and other areas it has been recorded at a maximum depth of 40 metres (1).

The turtleheaded sea snake is generally found on reef flats during high tide, and it often uses drainage channels to travel to deeper water as the tide begins to ebb, although some individuals remain in tidal pools (3).

Studies have shown that juvenile turtleheaded sea snakes tend to be found in shallower water than adults (7).

The turtleheaded sea snake is a fully aquatic species, spending its entire life in the water (7). Despite being an air-breathing animal, the turtleheaded sea snake is capable of remaining underwater for up to two hours before surfacing to breathe again, and it has specialised valves which prevent water from entering the nostrils when the snake is submerged. 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 turtleheaded sea snake has a specialised gland under its tongue which enables it to excrete excess salt from its body (3).

Unusually among sea snakes, the turtleheaded sea snake shows complex social behaviour, often moving about in distinct groups. It also demonstrates high site fidelity, with the same individuals being found repeatedly within small home ranges on coral reefs (1) (3). The turtleheaded sea snake is not an aggressive species, and when confronted by a predator it tends to hide in reef crevices rather than strike back at its attacker. Although venomous (5), the turtleheaded sea snake only has tiny fangs, less than one millimetre in length (2), and its venom is one of the weakest among sea snake species (2) (9).

The turtleheaded sea snake does not require large fangs or potent venom as its diet consists solely of fish eggs (2) (3) (4) (6) (7) (9). This species mainly forages during the day (4), slowly moving among corals and investigating crevices or burrows for fish nests containing egg masses (2) (3) (10). The eggs on which it feeds are tiny (7) (10), and the turtleheaded sea snake feeds frequently, sometimes several times per hour (10). This species is thought to locate its food by scent (3) (10), and once an egg mass is found the turtleheaded sea snake scrapes the eggs off the substrate using an enlarged scale on its jaw, which functions much like a blade (1) (2) (3) (4) (7). The turtleheaded sea snake is known to consume the eggs of various fish species, particularly those of damselfish, blennies and gobies (1) (3) (7).

Male turtleheaded sea snakes tend to swim more rapidly than females, and a male will actively court any female it encounters (7). Little is known about the specific reproductive habits of the turtleheaded sea snake (2), although like most species of sea snake it is known to be viviparous, which means that it gives birth to live young rather than laying eggs (2) (3) (7). The female turtleheaded sea snake is thought to produce two to five young in each litter (3).

Population declines have been recorded in the turtleheaded sea snake in some parts of its range, including Ashmore Reef, but the reasons for these declines are as yet unknown (1). However, the primary threat to this species is likely to be associated with the loss or degradation of its coral reef habitat (1) (3). Although it is unclear exactly how this will impact upon the turtleheaded sea snake, as this species tends to feed upon fish eggs that are laid in nests, it is believed that any process which affects nest-laying fish species could negatively impact upon the turtleheaded sea snake (1).

In addition, the population declines of the turtleheaded sea snake on Ashmore Reef could be a result of the effects of climate change, such as coral bleaching, increased sea surface temperatures and an overall decline in habitat quality. Unfortunately, as there appears to be a great divide between the populations on the east and west coasts of Australia, any local extinctions of this species are unlikely to recover through dispersal from other areas (1).

Trawler fisheries are not considered to be a major threat to the turtleheaded sea snake, as it is only very occasionally trapped as incidental bycatch due to the fact that it inhabits coral reefs (1) (3).

Although there are currently no conservation measures in place targeted specifically towards the turtleheaded sea snake (1), this species is offered some protection through its occurrence on Ashmore Reef in Western Australia, which is a Commonwealth Reserve (3). To identify its conservation needs, continued monitoring of turtleheaded sea snake populations on Ashmore Reef has been recommended, as well as studies to obtain baseline data on the abundance of this species throughout the rest of its range (1).

All sea snake species in Australia are protected under their classification by the Department of Environment and Water Resources as ‘Listed Marine Species’. In addition, sea snakes are protected under the Environment Protection and Biodiversity Conservation Act 1999, while the Australian Fisheries Management Act 1991 requires fisheries to avoid impacting on protected or threatened species, including sea snakes. A three-year study has been instigated to develop and implement a long-term bycatch monitoring programme for Australia’s Northern Prawn Fishery, which has the largest impact of any Commonwealth-managed fishery on protected sea snake populations (1).

Since 2003, industry workshops have been jointly run by Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and Australia’s Fisheries Management Authority (AFMA) to train prawn fishery crew members on how to identify, photograph and record information regarding sea snake capture during the main prawn seasons (1).

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  1. IUCN Red List (October, 2012)
  2. Cousteau, F. (2008) Ocean: The World’s Last Wilderness Revealed. Dorling Kindersley, London.
  3. Department of Sustainability, Environment, Water, Population and Communities (2012) Emydocephalus annulatus.In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
  4. Wilson, S. (2005) A Field Guide to Reptiles of Queensland. New Holland Publishers, Sydney.
  5. The Reptile Database (October, 2012)
  6. Smith, M.W. (2009) Cobras and their Kin. Dorrance Publishing Company, Inc., Pennsylvania.
  7. Shine, R., Shine, T. and Shine, B. (2003) Intraspecific habitat partitioning by the sea snake Emydocephalus annulatus (Serpentes, Hydrophiidae): the effects of sex, body size, and colour pattern. Biological Journal of the Linnean Society, 80: 1-10.
  8. Avolio, C., Shine, R. and Pile, A. (2006) Sexual dimorphism in scale rugosity in sea snakes (Hydrophiidae). Biological Journal of the Linnean Society, 89(2): 343-354.
  9. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.
  10. Shine, R., Bonnet, X., Elphick, M.J. and Barrott, E.G. (2004) A novel foraging mode in snakes: browsing by the sea snake Emydocephalus annulatus (Serpentes, Hydrophiidae). Functional Ecology, 18: 16-24.