Genomic evidence of mainland-driven invasion without local establishment of pink salmon in Svalbard, Norway

Abstract Pink salmon ( Oncorhynchus gorbuscha ) has rapidly expanded throughout northern Europe, raising concern that continued warming may enable establishment even in high Arctic ecosystems. Svalbard has experienced increasing occurrences of pink salmon in recent years, yet it remains unclear whether these individuals reflect successful local reproduction or straying from mainland populations. We combined field surveys and population genomics to assess the origin and establishment potential of pink salmon on Svalbard. Five rivers around Isfjorden were surveyed in 2024 following observations of unusually high pink salmon abundance and suspected spawning in 2023. Despite extensive sampling of spawning substrates, no eggs or fry were detected. Because most Svalbard rivers freeze to the bed or dry out during winter, current environmental conditions are likely insufficient to support successful egg incubation and emergence . Genomic analyses of 24 adults captured in 2023, integrated with a 3RAD SNP reference dataset (6174 SNPs), revealed that Svalbard individuals retained genetic diversity within the observed range of the mainland populations but formed no distinct genetic cluster. Instead, they exhibited admixture and greatest affinity to sampling populations in the Varanger Fjord region, indicating recurrent long-distance dispersal from established invasion hotspots. Together, the absence of detected recruitment and the lack of a distinct Svalbard genetic cluster indicate that pink salmon in Svalbard currently represent a demographic and genetic sink sustained by recurrent immigration from mainland populations rather than a self-sustaining population. However, the genetic diversity of incoming strays suggests that, if future environmental change weakens current barriers to egg incubation and juvenile emergence, establishment may become increasingly possible.