Sonar Sees a Good Idea

Hector's Dolphin by Steve Dawson, NEW ZEALAND WHALE AND DOLPHIN TRUST

Gillnets are made from nylon and are almost invisible (acoustically and visually) to animals in the water, which is why fishers have long employed them for gathering important food resources from oceans worldwide. For dolphins, however, that has meant decades of dangerous and often deadly entanglements. In Aotearoa/New Zealand, gillnets have been identified as the highest threat to the Maui or Popoto subspecies of Hector's dolphins, found only on the west coast of the North Island, and numbering only about 50 individuals. Conservation organizations there have worked hard to get on-board electronic monitoring installed on fishing vessels to help decrease "by-catch".

Maui dolphin by Ben Haarmann

Off Brazil's coast, researchers have discovered something far better than monitoring: actual prevention. And it comes with the added bonus of turning floating garbage into up-cycled dolphin alert systems. Since dolphins navigate by echolocation, plastic bottles that fishers zip-tye to their nets will bounce sonar signals back, giving them audible warning. Without any reduction in fish harvest, dolphin deaths declined almost 90%. Glass bottles with metal bolts inside also are being successfully used to help dolphins detect and avoid nets.

Irrawaddy dolphin tours in Cambodia

Per Berggren, emeritus professor of marine megafauna conservation in the School of Natural & Environmental Sciences at Newcastle University, said, "It's also rewarding to know that we are using some of the plastic waste that spoils our oceans. The bottles are securely attached to the nets, and we did not lose any plastic bottle during the trials." New studies are now spreading to Cambodia and Congo too, where such win-win opportunities for affordable mitigations are welcomed.