Juveniles de salmón chinook (Oncorhynchus tshawytscha Walbaum, 1792) en ríos y lagos de la patagonia chilena

the presence of feral chinook salmon has been reported in chile since 1995, since when it has been reported an increase in the frequency of runs into rivers of patagonia and the consequent temporary settlement of juvenile populations. in order to understand the ecological significance of the presence of these new populations of juvenile chinook in rivers and lakes, we analyze the diet, condition and age of individuals present in four basins of southern chile (puelo, blanco, aysen and river basins). we analyzed 104 individuals, 67 from 37 from lakes and river systems. some juveniles caught in the aysén watershed (river aysén) and (lake yelcho) had ages greater than 1 year, which correspond to "stream type" populations. by contrast, in the basins of blanco, puelo and futaleufú (river systems) only age 0 + individuals were found. juveniles of both ages coexisted only in lake yelcho. the individuals of age 1 + showed high condition factors and piscivorous diets, based in native galaxids. individuals of less than 1 year showed lower condition factors and diets based mainly on insects of allochthonous origin. among individuals of age 0 +, only those greater than 8.5 cm in total length had fish in their stomachs. we conclude that age 1 juvenile chinook enter patagonian systems as piscivore predators, and if they reach sizes greater than 8.5 cm before the completion of the first year they also behave as piscivores. in all cases, prey fish were composed of native fish. this suggests a new negative interaction for the native fish fauna of patagonia, mediated by the size of exotic fish, such as predation, and possibly also competition for allochthonous organisms, which are an important source of energy in oligotrophic systems as the patagonian.