Acoustic Harassment Devices (AHD) for salmon trap nets in the Baltic Sea

No abstracts are to be cited without prior reference to the author.

Many attempts have been made to use sound to reduce the conflict between mammals and human activities in the marine environment. AHD-s (Acoustic Harassment Devices) produce a sound intense enough to cause discomfort and avoidance and are used extensively in aquaculture. Some trials have also been made in fisheries operations (Mate and Harvey 1986, Jefferson and Curry 1996) with the aim of avoiding by-catch of marine mammals and of stopping damage to gear and catch. Generally, limited quantitative data have been presented on the long term mitigating effect of AHD-s. In order to obtain such data, a series of field trials were carried out at set traps for salmonids in the northern part of the Baltic Sea. This fishery is subject to heavy disturbance by grey seals (Westerberg et al. 2000, Fjälling 2005), and mitigation methods are under development (Lunneryd et al. 2003).