Human-mediated habitat fragmentation in freshwater ecosystems can negatively impact genetic diversity, demography and life history of native biota, while disrupting the behaviour of species that are dependent on spatial connectivity to complete their life cycles. In the Alouette River system (British Columbia, Canada), dam construction in 1928 impacted passage of anadromous sockeye salmon (Oncorhynchus nerka), with the last records of migrants occurring in the 1930’s. Since that time, O. nerka persisted as a resident population in Alouette Reservoir until experimental water releases beginning in 2005 created conditions for migration; two years later, returning migrants were observed for the first time in ~70 years, raising important basic and applied questions regarding life history variation and population structure in this system. Here, we investigated the genetic distinctiveness and population history of Alouette Reservoir O. nerka using genome-wide SNP data (n=7,709 loci) collected for resident and migrant individuals, as well as for neighbouring anadromous sockeye salmon and resident kokanee populations within the Fraser River drainage (n=312 individuals). Bayesian clustering and principal components analyses based on neutral loci revealed five distinct clusters, largely associated with geography, and clearly demonstrated that Alouette Reservoir resident and migrant individuals are genetically distinct from other O. nerka populations in the Fraser River drainage. At a finer-level, there was no clear evidence for differentiation between Alouette Reservoir residents and migrants; although we detected eight high-confidence outlier loci, they all mapped to sex chromosomes suggesting that differences were likely due to uneven sex ratios rather than life history. Taken together, these data suggest that contemporary Alouette Reservoir O. nerka represents a landlocked sockeye salmon population, constituting the first reported instance of deep-water spawning behaviour associated with this life history form. This finding punctuates the need for re-assessment of conservation status and supports on-going fisheries management activities in Alouette Reservoir. 

7012_SNPs_neutral.vcf: genotypic data for 312 individuals at 7012 SNPs (neutral only) generated via RADseq

7709_SNPs_all.vcf: genotypic data for 312 individuals at 7709 SNPs (all) generated via RADseq

7709_Loci.fa: Fasta file containing sequences for 7,709 loci

7709_SNPs_mapped.txt: Loci and SNPs mapped to linkage groups

metadata.txt: individual metadata including sample identifiers, location, migratory form and sex (where known)