Malcolm Smith recognized the high diversity and abundance of sea snakes in his 1926 Monograph of Sea Snakes. In 1973 Alpha Helix expedition collected more than 350 sea snakes representing nine species in less than two weeks and observed many more In 2005 the standing stock of sea snakes was estimated at about 40,000 snakes on the 174 km2 reef ﬂat of Ashmore Reef.
Besides high species diversity and abundance, there are high levels of sea snake endemism at Ashmore Reef. Half of the species (3/6) from the Aipysurus lineage recorded from Ashmore Reef are restricted to the Timor Sea. Endemics that almost certainly evolved in the Timor Sea highlighting the role this region has played in the evolutionary history of the Aipysurus lineage. Additionally four of the nine resident species and three of the ﬁve vagrant species are Australasian endemics.
In a new study, Lukoschek et al. (2013) report on surveys conducted between 1973 and 2010. They recorded the highest abundances (average 42–46 snakes day) and species richness (nine species) in 1973 and 1994. In 2002 abundance had declined by more than 50% (21 snakes day) and only ﬁve species were recorded. Since 2005 abundances have been consistently low (1–7 snakes per day) with just two species, Aipysurus laevis and Emydocephalus annulatus, recorded in signiﬁcant numbers. Extensive searches since 2005 (especially in 2010) ﬁve species of sea snake historically abundant at Ashmore Reef have not been observed and are presumed locally extinct. These species include three Timor Sea endemics Aipysurus apraefrontalis, Aipysurus foliosquama, Aipysurus fuscus, and one Australasian endemic Aipysurus duboisii. Declines in sea snake abundance and diversity at Ashmore Reef cannot be attributed to differences in survey methods over time.
The authors discuss habitat loss, illegal harvesting, decline in prey, disease, invasive species, and pollution as possible causes for the decline. But it is important to note the declines happened in spite of Ashmore Reef's National Nature Reserve (IUCN Category 1a) status that was declared in 1983 and, although the causes for the declines are not known, this protection has not prevented their disappearance.
Lukoschek V, Beger M, Ceccarelli D, Richards Z, Pratchett M, 2013. Enigmatic declines of Australia’s sea snakes from a biodiversity hotspot, Biological Conservation, 166, 191-202, ISSN 0006-3207,