| Summary: | Prior to their extirpation around 1900 CE, Lake Ontario hosted the world's largest freshwater Atlantic salmon (Salmo salar) fishery. Due to their early disappearance, questions remained about fundamental aspects of the species’ biology, such as whether they belonged to sea-run (anadromous) or freshwater resident (potamodromous) ecotypes. Recent isotopic analyses have demonstrated that the complex of Atlantic salmon populations spawning in tributaries emptying along Lake Ontario's northern shores were potamodromous. However, no evidence has yet been gathered for Atlantic salmon migratory behaviour from Lake Ontario's southeastern region, where historical observations suggest both anadromous and potamodromous populations may have spawned. Here, we provide the first results for isotopic analyses of bone collagen from seven fish bones from archaeological sites (c. 1427 to 1600 CE) identified as Atlantic salmon through ancient DNA and zooarchaeological analyses. The results of the isotopic analyses confirm that at least some of the salmon spawning in tributaries emptying into Lake Ontario's southeastern shores were also potamodromous. Although further analyses are needed, this suggests anadromy may have been completely absent in Lake Ontario's complex of Atlantic salmon populations in recent centuries.
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