High connectivity of salmon farms revealed by aggregation, residence and repeated movements of wild fish among farms

Abstract

Marine fish farms are widespread in coastal waters throughout the world, yet how they modify the movement patterns of wild fish species is largely unknown. We determined the spatiotemporal distribution of saithe Pollachius virens in a fjord system with intensive salmon cage aquaculture in Norway. Abundances of 8000 to 18 000 saithe were estimated around 2 salmon farms in the fjord using an underwater video system. Residence of saithe around fish farms and movements among farms and throughout the fjord were studied using implanted acoustic transmitters and an extensive array of automatic receivers. Of the saithe equipped with acoustic tags, 63% were observed daily at one or more of the 3 farm..