A survey of antipredator controls at marine salmon farms in Scotland

A questionnaire survey was sent to managers of marine salmon farm sites in Scotland to update knowledge on problems from predators and the use of antipredator controls. Of the 195 respondents, 5 had no antipredator controls with the remaining 190 having some level of control. Throughout Scotland, managers reported 12 species of predator. Seals were reported to be predators at 81% of sites. In total, 19 different types of antipredator control were used. Top nets were employed most widely, being used by 88% of the 195 respondents followed by seal scarers (52%) and shooting (49%). Shooting was considered to be very effective by 45 (62%) of the 73 site managers who expressed an opinion on its effectiveness. Views on the effectiveness of seal scarers varied markedly among site managers, and only 21 (23%) of 92 managers considered them to be very effective. There was also considerable variation in the perceived effectiveness of different types of antipredator nets. Comparison with previous studies showed that although there was a significant increase in the proportion of farms at which seals were reported to have caused loss or damage between 1985 and 1987, there has been no further increase. There were no significant changes over time in reported problems from other species of predator. The proportions of farms using nets and shooting to deter predators are remarkably consistent between the study periods. However, the use of seal scarers has increased significantly from 10% in 1985 to 52% in 2001. The survey suggests that the degrees of protection afforded by predator control methods vary appreciably between sites. There is a need for a range of antipredator devices to be tested under controlled conditions to determine under which circumstances each is most effective. This is particularly the case regarding seal scarers. (C) 2004 Published by Elsevier B.V.