Dusky Sea Snake

The dusky sea snake is a marine snake found in a small number of coral reefs offshore of Western Australia in the Timor Sea. The dusky sea snake is listed as endangered throughout its range under the Endangered Species Act.

The dusky sea snake is brown, or purplish-brown, with a few faint cross-bands on its sides. It has wide ventral scales and diamond-shaped body scales that are smooth and imbricate (i.e., overlapping). Imbricate scales probably help protect the snake from abrasion on sharp corals. There are generally 19 scale rows around the neck; 19 around the mid-body; and 155 or more ventral scales. There are 6 to 8 maxillary teeth behind the poison fangs. The dusky sea snake has a laterally compressed body to be used as a paddle and valvular nostrils located more dorsally. In addition to locomotion, the paddle-like tail is assumed to help with maintaining position in the water column with increased buoyancy.

The dusky sea snake has been seen resting, swimming, or foraging between reef and sand where it preys mainly on labrid (e.g., wrasses) and gobiid (e.g., gobies) fishes, as well as fish eggs. The dusky sea snake is venomous and may stick its head or tongue into a crevice or substrate to locate prey. The specialist tendencies of the dusky sea snake make it well adapted to living on the reef, but susceptible to changes in its ecosystem.

The dusky sea snake is a benthic, coral reef-associated species endemic to the shallow (less than 15 meters deep), emergent reefs of the Sahul Shelf off the coast of Western Australia in the Timor Sea, between Timor and Australia. These reefs are relatively isolated and lie at the edge of the continental shelf over several hundred kilometers from the mainland.

The dusky sea snake is viviparous, which means embryos develop internally and young undergo live birth. Because this species never ventures on land, mating occurs at sea and young are born alive in the water. Within the Aipysurus genus, the number of young per female is small (usually less than four) and young are relatively large at birth. Timing and seasonality of the dusky sea snake’s breeding cycles are unknown. Little is known about the juvenile life stage of dusky sea snakes. The dusky sea snake’s lifespan is 10 years.

Habitat Degradation and Loss

Increased water temperature is a threat to the dusky sea snake and its habitat. Temperature plays a large role in the health of a reef. The heatwave that hit northwest Australia in the summer of 2015-2016 caused the waters of Scott Reef to see a 2℃ increase in temperature during this time, with 92 percent of sampled sites along this reef system being at least 60 percent bleached. This level of mortality impacts the dusky sea snake since it is only known to reside on and around hard coral reef ecosystems and impacts its ability to find shelter and prey.