Acoustic protection for marine mammals: new warning device PAL

Their inability to detect gillnets in time is due to various reasons. The water is often murky and the nets are hard to see. However, toothed whales, just as bats, are able to orientate themselves with their biosonar: They produce clicks, whose echoes provide information on prey and obstacles. However the thin nylon yarns of the nets only reflect a weak echo at close range and only if directly ensonified. And the sonar beam t fi of “vi w” of harbour porpoises is very narrow, ranging from 11-13 degrees [2]. This is further aggravated by the fact that animals often are distracted by their search for food or by social interactions. Also, they may remain mute as they engage in passive acoustics in order to avoid attracting the attention of predators or aggressors, like killer whales or dolphins.