The effectiveness of a seal scarer at a wild salmon net fishery

Abstract

During 2009 and 2010 an Acoustic Deterrent Device (ADD) was tested at a salmon bagnet. Treatment blocks when the ADD was either on or off were randomly assigned and observations were carried out from shore. During periods when the ADD was switched on, there were fewer seals observed and approximately a third more fish were landed per hour than when the ADD was switched off, these differences were both significant. Model results indicated that the higher fish landings when the ADD was operating were a direct result of the reduction in the number of seals in the vicinity of the net. Photo-identification of the seals resulted in ten grey seals and four harbour seals being identified, and showed that the majority of these were identified on one occasion, and that two grey seals made up 63% of the visits to the study area when individuals were identified. Seal-damaged fish were only found within the bagnet during off treatments. Overall, the ADD was found to be an effective seal deterrent. Refinement in the method of ADD deployment could further increase effectiveness.