Escaped salmon in the inner seas, southern Chile: Facing ecological and social conflicts

During heavy storms in 1994-1995, salmon farms in southern Chile lost sever al million fish from the most commonly farmed species, rainbow trout (Oncor hynchus mykiss), coho salmon (Oncorhynchus kisutch), and Atlantic salmon (S almo salar). To determine the abundance and distribution of such exotic sal mon populations in the wild and their effect on native organisms, we conduc ted experimental fishing, in six locations in the salmon farming regions (4 1 degrees -46 degrees S) in the inner seas of Chiloe (X Region) and Aysen ( XI Region), between November 1995 and December 1996. At the same time, we c ollected information from salmon farms and insurance companies about escape d individuals. During the experimental fishing we captured 2602 coho salmon , 984 trout, and 271 Atlantic salmon. Captures of the three species decline d through the duration of the study; thus in November 1996 we captured < 10 % of initial catches. Population projections based on three possible mortal ity rates (0.4, 0.8, and 1.2) predicted the disappearance of salmon by year 2000, and the highest mortality rate was the best predictor of the observe d available biomass in 1996. Thus, artisanal fishing may control escaped sa lmon. Of the three species, coho salmon had the best chances of becoming es tablished in the remote XI Region where the artisanal fishing pressure was less intense. The three salmon species showed feeding similarities, since each kept feedi ng on pellets beneath the farms, particularly Atlantic salmon, while coho s almon showed greater preference for schooling fish, and rainbow trout fed m ore often on crustaceans. Thus, the three species, particularly coho salmon , could compete with native southern hake and mackerel. As a management app roach to avoid salmon colonization and naturalization in southern Chile, lo cal artisanal fishing should be encouraged because it is probably the most efficient way to remove escaped individuals and reduce the chance of popula tions becoming self-sustaining.