Investigating the impact of seismic surveys on threatened sea snakes in Australia's North West Shelf
A project undertaken at the School of Earth and Environmental Sciences, The University of Adelaide, and supervised by Dr Kate Sanders
Australia's North West Shelf (NWS) reefs support the highest recorded diversity, endemism and abundance of sea snakes in the world. Surveys by co-investigator Guinea have revealed alarming declines of NWS sea snakes, most severely at Ashmore, where prior to 2000 there were ~70 snakes/hectare and there is now <1/10 hectares. Two species endemic to Ashmore and Hibernia reefs have not been sighted on surveys since 2001 and are listed as Critically Endangered. The cause of the declines is unclear: coral and sea grass habitats have remained intact and are not subjected to intensive fishing. A potential contributing factor that has hitherto been overlooked is increasing seismic survey activity in the NWS.
Australia is undergoing a boom in off-shore oil and gas exploration, with seismic surveys using air guns to direct intense impulses of sound at the sea floor. Sound waves can exceed 200dB (1 million times the safe level for humans) and have well documented impacts on marine organisms. Physical damage has been found in fish swim bladders and the inner ears of fish and cetaceans; cetaceans and turtles display avoidance behaviour, and startle behaviour has been observed in squid and fish.
Three characteristics suggest that sea snakes might be especially vulnerable to air gun impacts:
- Sealed nostrils and an air-filled lung extending the length of the body, plus slower swimming speeds than other marine vertebrates, might mean they are unable to avoid tissue damage at close range.
- Scale sensillae that allow sea snakes to detect the vibrations of their prey show peak sensitivity to low frequencies that overlap those produced by air guns, this may disrupt feeding (via acoustic masking) and provoke avoidance behaviour.
- Translocation (a common response to air guns) is associated with high mortality in sea snakes; habitat displacement might have long term consequences for highly isolated NSW populations.
Sea snakes are currently omitted from all protocols for environmental impact assessments for seismic surveys, including at the initial referal stage by proponents (oil and gas industry) and in recommendations by regulators (state and federal government).
This project will determine whether the extremely intense air-gun sound produced during seismic surveys influences behaviour, performance or health status of sea snakes. We will test the following hypotheses:
1a) Sea snakes display avoidance and/or abnormal behaviour in response to simulated air gun activity [there is a non random relationship between sea snake position and sound level in experimental aquaria].
1b) Sea snake hunting/feeding performance is negatively impacted by simulated air gun activity [prey location and/or striking differs significantly in undisturbed (control) versus experimentally sound impacted aquaria].
2) Sea snakes exhibit avoidance behaviour and negatively impacted hunting/feeding performance in their natural environment following exposure to actual air gun activities [1a&b above for free ranging snakes and snakes in field enclosures].
3) Body condition index (BCI) and characteristics of soft tissues (lungs and dermal sensillae) vary significantly between sound impacted and non-impacted sea snakes.
Kate Sanders (University of Adelaide, Australia), Michael Guinea (Charles Darwin University, Australia), Arne Rasmussen (Royal Danish Academy of Fine Arts, Denmark), Agustín Camacho (University of São Paulo, Brasil).
Contact: Kate Sanders (email@example.com)
|Figure 1. Aipysurus laevis surfacing for air on Scott Reef, March 2012.