Abstract: Acoustic deterrent devices (ADDs) have often been considered a benign solution to managing pinniped predation. However, ADDs have also been highlighted as a conservation concern since they can inflict large‐scale habitat exclusion in toothed whales (odontocetes). We tested a new method that selectively inflicted startle responses in harbour seals (Phoca vitulina) at close ranges to the loudspeaker but not in a non‐target species, the harbour porpoise (Phocoena phocoena), by using a frequency range where porpoise hearing was less sensitive than that of phocid seals. The sound exposure consisted of isolated 200 ms long, 2–3 octave‐band noise pulses with a peak frequency of 1 kHz, which were presented at a source level of ∼180 dB re 1 μPa. Field tests were carried out within a 2‐month period on a fish farm on the west coast of Scotland where marine mammal behaviour was observed within three distance categories. Seal numbers dropped sharply during sound exposure compared with control observation periods within 250 m of the sound source but were unaffected at distances further away from the farm.
Carnivore depredation on human livestock is a worldwide problem with few viable solutions. Non‐lethal management tools such as acoustic devices show highly varying success and often pose a conservation risk due to noise pollution and habitat degradation. We tested the long‐term effectiveness of a deterrence system which harnesses an autonomous reflex (startle) to selectively inflict avoidance responses in a target species (phocid seals) by emitting band‐limited noise pulses with sharp onset times. Seal predation was monitored at a marine salmon farm (test site) over a full production cycle (19 month) with a multi‐transducer deterrent system deployed for the final year. Predation was also monitored for several months at two control sites and additional short‐term tests were carried out at sites which suffered higher predation rates.
