The cohabitation of Chinook salmon (Oncorhynchus tshawytscha) with trout populations in two important recreational fishing rivers in southern Chile

A study was carried out on two important recreational fishing rivers in southern Chile, the Petrohué and the Puelo, to assess the population structure of the salmonid species inhabiting both rivers. Five river sectors were surveyed on four dates between April 2016 and February 2017. In the Petrohué River, 2400 fish were sampled (42.9% rainbow trout Oncorhynchus mykiss; 23.8% brown trout Salmo trutta, and 33.3% Chinook salmon Oncorhynchus tshawytscha), while in the Puelo River, 1972 fish were examined (51.6% rainbow trout; 30.4% brown trout and 18% Chinook salmon). Fry and fingerling stages accounted for the highest proportion of fish collected by electrofishing. In the Petrohué and Puelo rivers, rainbow trout fry and fingerlings represented 96.3 and 99.2% of the fish sampled, respectively; 96.8 and 97.1% in the case of brown trout, while for Chinook salmon, parr and pre-smolts represented 97% of the fish examined in the Petrohué River and 98.3% in the Puelo River. Rainbow and brown trout shared the same habitats and food items in both rivers, and the two oldest trout recorded 5+ and 6+years. Parr and pre-smolt Chinook salmon were present mainly in the winter and spring seasons and were aged 1+ and 2+, respectively. There were no differences in the food items recorded from the juvenile fish sampled in both rivers. The mature, returning adult Chinook salmon aged between 1.5+ and 1.6+ years were devoid of food and were recorded over the autumn season with the highest abundance in the Petrohué River. The study did not identify any adverse competition or negative interactions among the three main salmonid species sharing the same habitat.