Abstract

During heavy storms in 1994-1995, salmon farms in southern Chile lost several million fish from the most commonly farmed species, rainbow trout (Oncorhynchus mykiss), coho salmon (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar). To determine the abundance and distribution of such exotic salmon populations in the wild and their effect on native organisms, we conducted experimental fishing, in six locations in the salmon farming regions (41°-46° S) in the inner seas of Chiloé (X Region) and Aysen (XI Region), between November 1995 and December 1996. At the same time, we collected information from salmon farms and insurance companies about escaped individuals. During the experimental fishing we captured 2602 coho salmon, 984 trout, and 271 Atlantic salmon. Captures of the three species declined through the duration of the study; thus in November 1996 we captured <10% of initial catches. Population projections based on three possible mortality 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 observed available biomass in 1996. Thus, artisanal fishing may control escaped salmon. Of the three species, coho salmon had the best chances of becoming established in the remote XI Region where the artisanal fishing pressure was less intense. The three salmon species showed feeding similarities, since each kept feeding on pellets beneath the farms, particularly Atlantic salmon, while coho salmon showed greater preference for schooling fish, and rainbow trout fed more often on crustaceans. Thus, the three species, particularly coho salmon, could compete with native southern hake and mackerel: As a management approach to avoid salmon colonization and naturalization in southern Chile, local artisanal fishing should be encouraged because it is probably the most efficient way to remove escaped individuals and reduce the chance of populations becoming self-sustaining.