The new sonar built from the sounds of marine life
Whale skeletons stand guard around the coast of Fuerteventura in the Canary Islands, a stark reminder of the damaging effects of military sonar. Sonar from ships and submarines is believed to be one of the contributing factors to whale strandings, confusing the sonar of whales and causing them to wash ashore.
However, this whale-unfriendly technology may soon have a rival. Lori Adornato, project manager at the US military research agency Darpathink we could detect submarines by paying more attention to natural sound than by emitting sonar pings.
“Right now, we’re treating all of that natural sound as background noise, or interference, which we’re trying to suppress,” says Adornato. “Why don’t we take advantage of these sounds, see if we can find a signal?”
His project, Persistent Aquatic Living Sensors (Pals), eavesdrops on marine animals to detect underwater threats. Current droppable sonobuoys – deployed by the military to detect enemy underwater activity – only work for a few hours over a small area due to limited battery life. Rather, the Pals system could cover a large region for months. It could provide a near-constant means of monitoring coastlines and underwater channels. Adornato says reef-dwelling species that can be counted on to stay in one place are probably the best sentinels.
“You want to make sure your organism will always be there,” says Adornato.
Pals sponsors several teams that are studying different approaches using very different reef species.
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Laurent Cherubin is the principal researcher of the Grouper Guard Team at Florida Atlantic University, in collaboration with goliath groupers. These fish, which can weigh up to 300 kg (660 lb), are common in US waters and produce loud calls to deter intruders.
“It’s a loud, low-frequency boom,” says Cherubin. “They are territorial and will explode at any intruder on their territory.”
A booming grouper can be detected at 800 m (2,640 ft), although not all booms mean contact. In addition to alert calls specific to intruders and predators, the grouper’s repertoire includes courtship sounds to attract mates, threatening calls when establishing territory, and other sounds whose purpose remains a mystery.