Olive-brown sea snake (Aipysurus laevis)

Also known as: olive sea snake
French: Aipysure Lisse
GenusAipysurus (1)
SizeLength: 1 - 2.2 m (2)
Weightup to 3 kg (2)
Top facts

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

The largest and bulkiest member of its genus (3), the olive-brown sea snake (Aipysurus laevis) has a stout, rounded body (4) and, unlike land snakes, a flattened, paddle-like tail suited to swimming (4) (5) (6). Its head is not distinct from the body, giving this species a worm-like appearance (5). The olive-brown sea snake’s scientific name, laevis, is derived from the latin word for ‘smooth’ (7), which presumably refers to its smooth skin (5).

One of six closely related species found in the beautiful reefs and shallow coastal waters of northern Australia (2), the olive-brown sea snake is highly variable in colour (3), ranging from plain brown to olive-brown, purplish-brown or grey on the upperparts, and becoming paler on the underside (2) (4) (8). The head is often olive-coloured (8), while the flattened tail is creamy white with a brown ridge along the upper surface (4).

The juvenile olive-brown sea snake is much less uniform in colour than the adult, showing a strongly banded pattern throughout its first year of life (8). This pattern is gradually lost as the juvenile matures (2).

The nostrils of the olive-brown sea snake are located on the top side of the snout (6), are semicircular in form (8), and have valves that allow them to be closed when underwater to prevent water from entering (9). This species has the longest fangs of any sea snake, growing to a length of about 4.2 millimetres (3).

The olive-brown sea snake is a common and widespread species (1), found in the eastern Indian Ocean and the western Pacific Ocean (1) (2). Its distribution encompasses the waters around eastern Indonesia and New Guinea, and extends throughout tropical Australian waters east to New Caledonia (3) (7).

The olive-brown sea snake is found around coral reefs (1) (2) (4), estuaries (2) and tropical coastal shallows (2) (5). Around coral reefs, this species occurs in a variety of habitat types, including the reef edge and sandy bottoms adjacent to deeper reefs (1).

Although the olive-brown sea snake has been recorded to depths of up to 68 metres (1), this species generally favours reef waters that are between 4 and 45 metres deep (4).

Although the olive-brown sea snake is a venomous species (7) (10), it is generally known to be quite docile (3), often being inquisitive and approaching divers (2).

The olive-brown sea snake hunts for its food by weaving among large corals on the reef, searching for unsuspecting prey resting in crevices and recesses (1) (2) (4). This species usually remains within a small patch of coral, and does not roam across large areas of the reef. It rarely ventures out into the open water, except after dark (2).

The olive-brown sea snake feeds on a wide variety of prey, including fish, fish eggs, crustaceans and molluscs (1) (3) (4) (5), and it incapacitates its victims with its venom. Olive-brown sea snake venom affects the muscles and nerves of its prey (10), and contains enzymes that break down the prey from the inside, making it easier for the sea snake to digest once swallowed (4).

Male olive-brown sea snakes reach sexual maturity in their third year (1), whereas females do not mature until they are four or five years old (1) (10).  The breeding season of this species generally runs from May to July (3). Courtship in the olive-brown sea snake takes place in the open water, often with several males vying for the same female (4), while mating takes place on the reef floor (4) (11). Fertilisation is internal (5), and following a gestation period of nine months (2) (10), the female olive-brown sea snake gives birth to up to five live young (2) (5). Female olive-brown sea snakes are only thought to breed every second year (10) (11).

The principal threats to the olive-brown sea snake are the loss and degradation of its habitat, and mortality as a result of being taken as bycatch in trawl fisheries (1).

Climate change causes various alterations to coral reef habitats, including the death of corals following mass bleaching, which in turn leads to a reduced abundance of prey and a reduction in suitable habitat for the olive-brown sea snake (1).

The olive-brown sea snake is known to be accidentally captured in trawl fisheries throughout its range, and given that this species takes a long time to mature, many individuals are caught before they have bred. In addition, the low reproductive output of the olive-brown sea snake, with just two to six offspring produced per female every other year, means that the species cannot sustain high levels of incidental capture (1).

The olive-brown sea snake is the most commonly found sea snake on Australia’s coral reefs (1), and there are currently no known conservation measures in place specifically targeting this species. However, recommendations have been made to monitor bycatch of this species, and for fisheries to use exclusion devices to reduce the levels of incidental catch (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 (1). 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 (August, 2012)
  2. Cousteau, F. (2008) Ocean: The World's Last Wilderness Revealed. Dorling Kindersley Ltd., London.
  3. Gopalakrishnakone, P. (1994) Sea Snake Toxinology. National University of Singapore Press, Singapore.
  4. Walker, P. and Wood, E. (2005) The Coral Reef. Infobase Publishing, New York.
  5. Marshall Cavendish (2000) Aquatic Life of the World, Volume 9. Marshall Cavendish, Singapore.
  6. Morrissey, J. and Sumich, J. (2011) Introduction to the Biology of Marine Life. Jones and Bartlett Publishers, Massachusetts.
  7. The Reptile Database (August, 2012)

  8. Hutchings, P., Kingsford, M. and Hoegh-Guldberg, O. (Eds.) (2008) The Great Barrier Reef: Biology, Environment and Management. CSIRO Publishing, Victoria, Australia.
  9. O’Shea, M. (2008) Venomous Snakes of the World. New Holland Publishers, London.
  10. Heatwole, H. (1999) Sea Snakes. University of New South Wales Press, Sydney, Australia.
  11. Greene, H.W. (2000) Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley, California.