Use of underwater playback to reduce the impact of eiders on mussel farms

Abstract

One of the most commonly employed methods of reducing damage by diving ducks to mussel stocks on mussel farms in Atlantic Canada and in Scotland is chasing birds by boat. While effective in the short term, the frequency of chases is often restricted by high costs, both in time and fuel. Tests in Scotland used underwater recordings of chase-boat engines replayed at regular intervals on continuous loop tapes through an underwater loudspeaker in an attempt to reduce predation pressure by eiders on mussel farms. Trials of the underwater playback system (UPS) gave significant reductions in eider numbers of 50-80%, while a control trial with the playback of an unassociated noise gave no reduction in numbers. The mean return time of birds to the farm after chasing by boat also increased significantly. As the presence of workers on mussel farms reduces the number of eiders feeding there, the UPS is a useful deterrent when workers are not present. The long-term habituation of ducks to the system was negligible when workers are absent, providing there is occasionally reinforcement of the deterrent by boat chasing. Potential factors effecting the efficacy of the UPS are discussed.