Habitat-based variation in the trophic ecology of the world’s highest-altitude self-sustaining population of invasive rainbow trout

Rainbow trout (Oncorhynchus mykiss) have been widely introduced outside of their natural range and are one of the World’s most invasive species. Illegally introduced into the isolated, high-altitude (4520 m) Chungará catchment of northern Chile, rainbow trout have now been present in the system for ∼30 years and to our knowledge are the World’s highest known self-sustaining population. However, nothing is known about the status and impacts of these trout in the system. We analysed stomach contents and stable isotopes (δ13C, δ15N, δ34S) from liver and muscle to study the trophic ecology of rainbow trout from lake, river mouth and riverine habitats in the Chungará catchment to understand their basic ecology and to characterise their potential trophic interactions with native taxa. Both stomach contents and stable isotope values showed spatial differences in diet and habitat use, but also revealed that diet varied temporally within habitats. The trophic position of rainbow trout was similar in the three habitats examined and was constant over time, apart from the riverine population. Predation by rainbow trout had different potential effects across pelagic, benthic, and riverine habitats in the Chungará catchment, through the consumption of zooplankton, native amphipods, aquatic insects, and the endemic cypriniodontid fish Orestias chungarensis.