Meeting Abstract

P3.68  Friday, Jan. 6  Dwindling Sea Snakes at Ashmore Reef: Searching for the “Elephant in the Room” GUINEA, M/L; Charles Darwin University

At least 17 species of sea snakes are recorded from reefs, lagoons and channels at Ashmore Reef on Australia’s Sahul Shelf. Three species are regionally endemic (Aipysurus foliosquama, A. apraefrontalis and A. fuscus) with another two species also endemic to Australia. Surveys to 1998 indicated a stable population of 6 to 17 snakes per hectare of reef flat at low tide and from 1 to 3 snakes per hectare on the sand flats at high tide, but from 30 to 70 snakes per hectare in the lagoons at low tide. Tagging studies over three years estimated from 94 and 192 Turtle-headed Sea Snakes (Emydocephalus annulatus) used a single coral head 30 meters in diameter. Spawning events by Damselfish (Chromis) attracted feeding aggregations of Turtle-headed Sea Snakes. The reef was prolifically abundant with new individual sea snakes swimming into view each minute. By 2008 Ashmore Reef supported less than 1 sea snake for 10 hectares, regardless of habitat, with only three snakes seen in three weeks of survey. Sea snake populations on neighboring reefs, at 30 to 250 nautical miles distant, appeared unaffected. The cause of this decline at Ashmore Reef remains unknown. Possible, but unsubstantiated, causes include: changes in sea level with erosion of reef flats and increased sedimentation in lagoons; changes in water temperature over the expansive reef flat; changes to rainfall patterns; altered management regimes due to increased surveillance of border security; changes to fishing practices by artisanal Indonesian fishers; increased frequency and closer proximity of seismic surveys and gas well construction by petroleum companies. Sea snakes are the marine equivalent of the miner’s canary for reef health. Yet the cause of their decline in numbers and species at Ashmore Reef remains the “elephant in the room” until examined afresh.