Young-of-the-year Coho Salmon Oncorhynchus kisutch recruit in fresh waters of remote Patagonian fjords in southern Chile (51°S)

Salmonid invasions are currently recognized as one of the main threats to the conservation of freshwater ecosystems in Patagonia. Although a number of salmonid species have been introduced to Patagonia over the last century not all species have succeeded at establishing widespread and large populations. To date, there are no reports of established self-sustaining Coho Salmon (Oncorhynchus kisutch) populations in southern Chile despite propagule pressure from aquaculture. Here, we assessed the natal origin of young-of-the-year Coho Salmon collected from estuaries and lakes associated with remote Patagonian fjords (51°S) by examining their otolith microchemical composition. Low strontium concentrations along a line transect from the otolith edge to its core in fish collected in one lake are consistent with freshwater residence until the moment of capture. Fish caught in estuaries displayed instead, relatively high strontium concentrations only at the otolith edge. This pattern suggests very recent movement from freshwater down to the estuary. Our findings are consistent with the hypothesis that the juvenile Coho Salmon collected in estuaries originated in the local freshwater system (lake) and provide the first ever evidence of recruitment and probable establishment of self-sustaining Coho Salmon population in Patagonia.