Rennell Island sea krait  (Laticauda crockeri)

Classified as Vulnerable (VU) on the IUCN Red List (2).

The genus Laticauda (sea kraits) comprises seven species typically recognised by their strong colour banding and amphibious lifestyles (1) (3) (4). While six of the seven species fit this description, the Rennell Island sea krait is intriguingly different. Instead of having the conspicuous pattern of light and dark bands, this species is uniformly dark brown in colouration and only exhibits relatively faint banding. It is also considered a dwarf species, because of its relatively small size compared with the other Laticauda species (5). In common with the body shape of other sea kraits, and indeed most other marine snakes, it has a paddle shaped tail with which it propels itself through the water (3) (4).

Despite its partly misleading name, rather than occurring in the sea, the Rennell Island sea krait is restricted to a lake (Lake Te-Nggano) on Rennell Island in the Solomon Islands (2) (5).

The lake in which this species is found is narrowly separated from the sea and has a salt content about one third that of salt water. It mostly inhabits shallow parts of the lake, which lies within a limestone (raised coral reef) basin (1) (5).

Marine snakes in general exhibit a range of adaptations to their aquatic environment, of which the ability to stay submerged for long periods of time is particularly remarkable. They are able to avoid frequent trips to the surface to breathe because not only do they have a long, cylindrical lung that runs almost the length of their body, but they are also able to diffuse oxygen from the water through their skin (4). Although in sea kraits this form of respiration is less efficient than in other marine snakes (3), the Rennell Island sea krait frequently remains submerged for more than eight minutes (5). It forages in fairly shallow waters from a depth of only a few centimetres down to a recorded 13 metres. With frequent tongue flicking, it investigates crevices and holes, and the edges of submerged logs and branches for small fish, such as the native goby Eleotris fusca. Like many other marine snakes, this species has a potent venom, which it secretes from hollow fangs at the front of its mouth, and uses to immobilise prey before swallowing (3) (5).

While sea kraits are the only group of marine snake considered to be oviparous, that is, laying eggs instead of giving birth to live offspring, the mode of reproduction has never been reliably recorded in the Rennell Island sea krait (3) (5). Furthermore, local people maintain that in contrast with other Laticauda species, the Rennell Island sea krait does actually give birth to live young (5). Although the other sea krait species are all amphibious, an essential trait for oviparous snakes that must come ashore to lay their eggs (4), during the only field study conducted on this species it was never seen on land (5).

The Rennell Island sea krait is the only species of marine snake currently listed on the IUCN Red List. Despite the absence of any significant direct threats, it is classified as Vulnerable because it has a very small and restricted range (2).

Currently, there are no known conservation measures in place for this species. However, East Rennell which includes Lake Te-Nggano, is classified as a World Heritage Site because of its exceptionally diverse and unique fauna and flora. Consequently, the area is managed according to a management plan recommended by UNESCO (United Nations Educational, Scientific and Cultural Organisation) which should ensure its long-term preservation (6).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the East Rennell World Heritage Site see:

• UNESCO World Heritage – East Rennell:
  http://whc.unesco.org/en/list/854