Early development and diets of non-native juvenile Chinook Salmon (Oncorhynchus tshawytscha) in an invaded river of Patagonia, southern South America

Abstract

Chinook salmon (Oncorhynchus tshawytscha) have established populations in both the Atlantic and Pacific basins of southern South America. Yet, basic biological information about these salmon population is absent. Here, we documented relative densities, body size, condition and diet composition of juvenile Chinook Salmon from the Futaleufú River, Argentina. We sampled Chinook Salmon juvenile and environmental variables including daily river discharge, water temperature, electrical conductance, dissolved oxygen and total dissolved solids. We assessed individual variation in the diet of juvenile salmon over time. We estimated the incubation time before fry emergence to be around 101 days under a mean water temperature of 7.5°C. Salmon fry emerged during the Austral Winter (July-August) in off-channel habitats near the redds. Juvenile salmon were between 3.8 and 12.1 cm in length (TL) and their highest body condition occurred early during the Austral summer (December). Juvenile salmon abundances were positively associated with water temperature, but not flow. Diet analyses revealed a specialist feeding behaviour based on food pulses that included both aquatic and terrestrial insects; piscivory was not detected. Juvenile salmon co-occurred with native fishes suggesting a potential for interspecific interference. Our findings provide baseline information for the future management of non-native Chinook Salmon populations in the Southern Hemisphere and elsewhere.