Discovery of out-of-basin introgression in Pettit Lake Sockeye Salmon: management implications for native genetics

Population level biodiversity is critical for preventing extinction in endangered populations. Oncorhynchus nerka in the Snake River Basin have exhibited diversity losses as populations have become extirpated and federally listed as endangered. Efforts to restore O. nerka in the Snake River Basin have focused on preserving local populations, however, there has been no detection of native O. nerka in Pettit Lake. Pettit Lake O. nerka were reintroduced from a non-native kokanee stock originating from Lake Whatcom, WA, and a Sockeye Salmon population was established from Redfish Lake captive broodstock releases. However, recent genetic analyses detected an unexpected signal in Pettit Lake. This study examines genetic variation of Pettit Lake O. nerka in comparison to possible source populations. We used a single nucleotide polymorphism panel developed for Columbia River Basin O. nerka stock identification to determine the origin of Pettit Lake O. nerka . We found that Pettit Lake supports a population resulting from introgression between non-native kokanee and Redfish Lake Sockeye Salmon. Overlap of spawn timing has allowed mixing of these two shoal spawning populations and led to a gradual decrease of the previously predominant non-native kokanee genetic signature. While propensity and timing of emigration seems to remain unaffected by hybridization, the introgressed population displayed longer travel times and later arrival to dams when compared to native Sockeye Salmon in the region. The long-term survival of this Evolutionary Significant Unit is dependent on native diversity thus, O. nerka conservation management must monitor out-of-basin genetics and introgression in the recovery area.