Syntypes: AM R454 and R6633
Type-locality: probably the Australian Seas. Given as Loyalty Islands by Welch, 1988, Snakes Orient, 183 pp..
Turtle-headed sea snake
Egg-eating sea snake
Distribution: Indonesian sea (Timor), New Caledonia, Australia (North Territory, Queensland, West Australia)
Type locality: "probably the Australian Seas."
Marine waters of northern Australia from the Timor Sea to the Coral Sea.
Habitat and Ecology
Feeds exclusively on fish eggs and seems to prefer eggs that are laid in nests attached to corals and rocks by species such as damselfish, blennies and gobies (Voris 1966). This is accomplished by scraping the eggs from the substrate with the enlarged scale on each side of the upper lip (Guinea 1996). This species forages over open sand plains at the junction of sand and coral and is typically found close to the benthos and shelters on the bottom edge of corals (Shine et al. 2004, Heatwole 1999).
This species has been noted to have complex social behaviour (Shine et al. 2005). Studies in New Caledonia have found that individuals of this species appear to move about in distinct social groups. Moreover, the species appears to have extremely high site fidelity and estimates of genetic distance between east and west Australian populations (Lukoschek and Keogh 2006) suggest it has very low dispersal potential; thus, it is unlikely to be able to re-establish isolated populations following local extinctions.
IUCN Red List Assessment
Red List Category
Red List Criteria
Populations on Timor Sea reefs have undergone recent population declines, particularly on Ashmore Reef. The reasons for this decline are unknown. The extent of declines on other Timor Sea reefs is unclear as regular detailed surveys have only been conducted at Ashmore Reef.
This species is common in other parts of the range, and although there have been declines in some places, the declines do not reach the thresholds for the threatened categories.This species is listed as Least Concern.
There have been large population declines of this species at Ashmore Reef over the past eight to ten years (M. Guinea pers. comm. 2009). Abundance estimates in the vicinity of the inner mooring at Ashmore Reef in 1994, 1996 and 1998 from mark-recapture surveys were ~100 to 200 individuals (Guinea and Whiting 2005). Sighting rates during the same survey periods were 10 to >25 per hour (Guinea 2006, 2007). Although no subsequent mark-recapture abundance estimates are available, subsequent sighting rates (2001-2005) have dropped to 1-2 per hour for this species at the same location (Guinea 2006, 2007). This reduction in population size is also associated with major declines in abundance of other sea snake species at Ashmore Reef (Guinea 2006, 2007).
The main threat to this species is likely to be associated with loss or degradation of coral reef habitats, however there is no direct evidence about the nature or extent to which this is the case (Lukoschek et al. 2007). Nonetheless, the highly specialised diet and habitat preference of this species suggests that it will be threatened by all processes resulting in loss of fish species that lay eggs in nests (such as damselfish) as it forages exclusively on fish eggs and tends to prefer fish eggs in demersal nests.
In addition, it has been suggested that increased sea surface temperatures, coral bleaching, and resulting changes in habitat complexity may be linked to localized population declines of sea snakes on Ashmore Reef, northern Australia (Francis 2006) and suggests that climate change may impact sea snake populations (Francis 2006). However, there is little direct evidence about the nature and extent to which the effects of climate change will affect E. annulatus.
There is limited gene flow between populations of this species on the east and west coasts of Australia (Lukoschek and Keogh 2006), suggesting that populations are unlikely to recover from local extinctions by dispersal.
No sea snake species is currently listed by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora).
The Turtle-Headed Sea Snake (Emydocephalus annulatus) is a species of sea snake that can be found in waters of Oceania near Australia and some Pacific Islands like the Philippines and the Loyalty Islands of New Caledonia. The range is sporadic, for example, with populations distributed in the Eastern and Western coasts of Australia in the Great Barrier Reef and the Timor Sea reefs respectively. They do not, however, occur in the Gulf of Carpentaria along the North coast. Named for its short, blunt head, the medium-sized snake has a slender build and varies in color. A single snake may exhibit only one color or may have banded patterns of white or yellow with dark rings. The scales on top of the head are large, regular, and entire. The rostral scale on the tip of the snout is conical in shape, and the second of three supralabial scales is the largest. The body has 15-17 rows of smooth, overlapping scales. It has 125-145 ventral scales, a single anal scale, and 20-33 single subcaudal scales. It may grow to 75 cm in length.
According to a recent study, an individual snake's color affects the amount of algal fouling that accumulates on its body. A snake of a darker, more monotonous color will have a higher amount of algae build-up than those of a paler, patterned variety. The added weight of algae affects an individual's speed, reducing it by 20%. It was observed that those whose locomotive skills were affected had a tendency to be more inactive and choose to hide among the coral, while those with little to no algal fouling were found actively foraging. The inactivity, however, did not affect their survival rates as the study did not find significant evidence that lighter-colored snakes were more likely to survive than their darker-colored counterparts.
In recent years, there is still, however, a steady decline in populations in and around the New Caledonian Lagoon. About twice a week for nine years (2003-2011 inclusive), scientists have counted the number of individual sea snakes within the protected coral reef snorkeling area in the lagoon. In 2003, volunteers spotted an average of more than six snakes per day, which decreased to less than two per day in 2011. In 2006, similar studies were also done in Ashmore Reef in northern Australia that exhibited a decline in population as well. The cause of the decline is indistinct in either case, though the authors of both studies attributed it to human interference, habitat degradation due to tourism, coral bleaching, and habitat and diet complexity.
The Turtle Headed Snake feeds solely on immobile demersal fish eggs, such as damselfish, blennies, and gobies. The larger the snake, the more probable they are to feed on damselfish eggs, which lie in exposed areas, rather than blennies and gobies whose eggs are located in narrow crevices. Interestingly, E. annulatus populations tend to stay where they are and rarely move between each other. This could possibly have something to do with the spatial memory of snakes and their ability to remember where nests are located. If they stay in the same area, then the snakes are able to feed regularly on the same sites. Curiously, Emydocephalus is the only sea snake that does not possess palatal teeth. Contrary to the foraging habits of other snakes, the turtle head tends to eat smaller, more frequent meals rather than larger, infrequent prey. In this respect, Emydocephalus feeds more like a grazing mammal than a snake. This atypical method of feeding is evidence of the great adaptive radiation of snakes.
Terrestrial snakes use pheromones to locate potential sexual partners with a male often tracking a female's scent over large distances. Tracking scents over long distances, however, not possible in the aquatic environment of the Turtle Headed Snake. E. annulatus uses visual cues to search for mates. These includde the size, movement, and color pattern of the object holding its attention. Upon locating females, the reception of female skin lipid pheromones by tongue-flicking males is necessary for males to continue courtship and mating
- Emydocephalus annulatus (2010). The IUCN Red List of Threatened Species. International Union for Conservation of Nature.
- Emydocephalus annulatus - Turtle-headed Seasnake. Department of the Environment. Australian Government.
- Shine, R., F. Brischoux, and A.J. Pile (2010). "A seasnake's colour affects its susceptibility to algal fouling". Proceedings of the Royal Society B. 277(1693): 2459-64. doi:10.1098/rspb.2010.0255.
- Goiran, C., R. Shine (2012). "Decline in sea snake abundance on a protected coral reef system in the New Caledonian Lagoon". Journal of the International Society for Reef Studies. doi:10.1007/s0038-012-0977.
- Goiran, C., S. Dubey, and R. Shine. "Effects of Season, Sex and Body Size on the Feeding Ecology of Turtle-headed Sea Snakes (Emydocephalus annulatus) on IndoPacific Inshore Coral Reefs." Coral Reefs 32.2 (2013): 527-38. Web of Knowledge. Web. 24 Oct. 2013.
- Voris, Harold K. "Fish Eggs as the Apparent Sole Food Item for a Genus of Sea Snake, Emydocephalus." Ecology 47.1 (1966): 152-54. J Stor. Web. 24 Oct. 2013.
- Lukoschek, Vimoksalehi, and Richard Shine. "Sea Snakes Rarely Venture Far from Home."Ecology and Evolution 2.6 (2012): 1113-121. Web of Knowledge. Web. 24 Oct. 2013.
- Barrot, E.G. et al. “A Novel Foraging Mode In Snakes: Browsing By The Sea Snake Emydocephalus Annulatus (Serpentes, Hydrophiidae).” Functional Ecology 18.1 (2004): 16-24. Academic Search Premier. Web. 24 Oct. 2013.
- Shine, R. (April 2005). "All at sea: aquatic life modifies mate-recognition modalities in sea snakes (Emydocephalus annulatus, Hydrophiidae)". BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 57 (6): 591–598.