Interaction between seals and marine fish‐farms in Tasmania, and management of the problem

Abstract

Abstract Seals that attacked fish on 15 marine fish‐farms in south‐eastern Tasmania were large subadult and adult male Australian fur seals Arctocephalus pusillus doriferus. From July to November 1988 there were 235 attacks on fish‐farms where Atlantic salmon Salmo salar and rainbow trout S. gairdneri were held in pens. Single animals usually attacked pens at night, irrespective of the size and species of fish in the pens. The seals damaged both pens and fish, and sometimes fish escaped as a result of the attacks. The vulnerability of fish‐farms was influenced by their proximity to seal haul‐out sites. Proximity to fishing ports and size of the fish‐farm had little influence. The use of shooting as a protection method was inefficient and ineffective because seals usually entered fish‐farms at night and showed no fear of shooters. There were many attacks in the presence of underwater acoustic seal scarers. Deterrents such as pursuit with boats, lights, seal crackers and emetics helped reduce the number of seal attacks. The only way totally to prevent seals from attacking fish‐farms is to exclude them from the vicinity of the fish pens with physical barriers that they cannot penetrate. These are currently in use, and include perimeter fences and protection nets made of steel mesh set around individual pens.