Fish distribution in a southern Patagonian river invaded by Chinook salmon

Abstract

This study analysed the spatial–temporal abundance and distribution of exotic Chinook salmon (Onchorynchus tsawytscha) along the shore zone of the Lapataia River in relationship with the presence of non-native brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta), and native small puyen (Galaxias maculatus) during the four seasons of the year. These data were used to detect fish patchiness and spatial overlap and related to environmental characteristics to determine the habitat used by each species. Juvenile Chinook salmon was recorded only in spring and summer, showing a highly aggregated spatial distribution pattern. The native small puyen dominated fish assemblages all over the year, except in winter when brook trout showed the highest abundance. The highest overlap was detected between small puyen and Chinook salmon. Chinook salmon distribution was mainly explained by the occurrence of flood plains. Brown trout distribution was highly related to the presence of woody debris, while small puyen and brook trout showed no preferences for any environment. These results provide little evidence for habitat competition between Chinook salmon and the other native and non-native fish species. In contrast, species habitat preferences are likely shaping the current fish distribution.