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.