Underwater sensors capture porpoises’ rare distress calls off Cornwall

Bycatch, the accidental capture of animals in fishing gear is considered the world’s greatest direct human-caused threat to dolphins and porpoises. Off the coast of Cornwall, a set of underwater sensors was listening to the ocean when it detected something researchers rarely get to see. According to an online report by Phys Org, two harbor porpoises swam around a fishing net, seemingly foraging for food and avoiding the gear, until one got caught up in it. What happened next was recorded in unusual detail, both acoustically and in terms of movement, providing researchers a rare insight into how these animals might react to a dangerous encounter. Scientists from the University of St Andrews’ Sea Mammal Research Unit and Scottish Oceans Institute found that their passive acoustic monitoring systems had inadvertently detected the bycatch event. Their results were published on August 26 in Royal Society Open Science. The devices had been deployed on a static gill net off Cornwall to detect marine mammal activity. Two harbor porpoises were observed foraging for several minutes around the gear and were recorded. The animals seemed to know how to avoid the net. Perhaps while chasing prey,...