Serpent Research: Australia sea snakes and the absence of Laticauda

Globally there are about 70 species of sea snake (aquatic elapids, in the subfamilies Hydrophiinae and Laticaudinae), inhabiting tropical and subtropical waters of the Indian Ocean and the Pacific Ocean, from the east coast of Africa in the west to the Gulf of Panama in the east. Most species occur in the Indo-Malayan Archipelago, the China Sea, Indonesia, and the Australian region. The viviparous sea snakes (Hydrophiinae) originated in Australia, having descended from the country’s endemic front-fanged terrestrial hydrophiine snakes. The group has since radiated in shallow water marine habitats throughout the Indo-Pacific, with 62 recognized species in 7 genera. However, Australia supports the highest recorded diversity and endemism, with more than 35% of the described viviparous sea snake species recorded from its waters and five nationally endemic species: Aipysurus apraefrontalis, A. foliosquama, A. fuscus, Ephalophis greyae, and Hydrophis donaldi. Over the last 50 years 8 new species have been described from or adjacent to Australian waters, but large areas still remain much understudied. The addition of further species must be expected as the geographical ranges of existingspecies remain unknown and some of the published studies lack comprehensive review. The taxonomy of the Australian sea snake species has been debated for the last 50 years without consensus being reached. However, a recent phylogenetic study using six molecular loci for 39 sea snake species in 15 genera recovered Hydrophis as broadly paraphyletic with respect to several other genera. Instead of erecting multiple new genera, the authors recommended dismantling the mostly monotypic genera Pelamis, Enhydrina, Astrotia, Thalassophina, Acalyptophis, Kerilia, Lapemis and Disteira, and recognizing a single genus, Hydrophis, for these taxa. This classification system avoids confusion and better reflects the history of the recent and very rapid diversification of these snakes.

In a recently published paper Rasmussen and colleagues present an updated reviewed checklist and a new complete identification key to sea snakes in Australian waters. The identification key includes 29 documented species and four species of questionable occurrence. The authors report no evidence for breeding populations of Laticauda in Australian waters, but include the genus on the list of possibly occurring taxa.

The countries around Australia have at least six Laticauda species. In the literature two species are reported from Australian waters: L. colubrina and L. laticaudata. At least 3 specimens of L. colubrina are deposited in the Australian Museum, Sydney. Three of the localities are in New South Wales and suggests the specimens are waifs, one is from inland western Victoria (the desert town Northern Hill) indicating an error. At least three Australian specimens of L. laticaudata are deposited in museum collections, one in BMNH:55.10.16.439 from Tasmania, one in ZMUC: 66265 from Sydney and one in Museum Victoria, Melbourne 60287 from Torres Strait also indicating waif specimens. The authors found no further specimens reported from Australia suggesting Laticauda is not breeding in Australian waters despite breeding populations in surrounding countries. A previous author suggested that competition from the Aipysurus species might, at least in part, be responsible for the rarity of Laticauda in Australian waters. And another author suggested that it may be due to the absence of coastal limestone rocks in northern Australia which is the preferred sheltering and egg-laying sites for these species. Further investigation in the northern part of coastal Australia is much needed before we can include Laticauda in the checklist; however, Laticauda sp. is included in the possible list.