Sharks have an incredible sense of smell, but it is their sense of hearing that could be one of the keys to protecting people at beaches, says a team of researchers led by Dr Christine Erbe from Curtin University’s Centre for Marine Science and Technology.
“We had this idea of trying to figure out what acoustic signatures humans make, whether the sharks can hear them, and, if appropriate, whether we can somehow interrupt that,” says Erbe. These interruptions could then potentially be used to ‘hide’ or ‘mask’ the noises people make in the water from the sharks.
Western Australia is a pertinent place to work on this project, given the debate over baited drum lines to cull sharks, and the project has been funded by Western Australia’s Department of Commerce.
Initial recordings have been made of people in a pool swimming and snorkelling past a hydrophone – a microphone designed to record or listen to underwater sound. Erbe’s team records people swimming and surfing at beaches to see how far their noises travel. These sounds can then be played to sharks in enclosures at Ocean Park Aquarium in Shark Bay to check for any responses.
“If we see responses from the sharks, the next step is to figure out if we can mask the sounds of people in the water using artificial signals,” says Erbe. These artificial signals are band-limited white noise, created digitally. “We can see which frequencies, or part of the human sound signature, could be detected by the sharks and calculate the range limits at which that might occur. We can then design masking signals that fill in around them so those frequencies can’t be detected,” she says. The team will test these masking signals by playing them back to the sharks at Ocean Park Aquarium.
This masking technique is different to other approaches where loud sounds are played at beaches to scare sharks away. The problem with the loud sound approach, says Erbe, is that it potentially interferes with an entire underwater ecosystem. The masking approach, on the other hand, is targeted at frequencies and levels that only sharks can hear in the surf zone. “We’re not looking at scaring the sharks away, we’re just limiting them from detecting humans,” she says.
According to Erbe, a multidisciplinary approach is crucial to solving problems such as shark mitigation, and her team ranges from physicists to acousticians, engineers and marine biologists.
Team member Dr Miles Parsons is leading another project on the sonar detection of sharks with the aim of building an early warning system. “The solution will have to be a combination of detecting sharks and preventing them detecting us,” says Erbe.
– Ruth Beran