There and back again : an investigation of the biological and genetic consequences of a sockeye stocking program

Marine and freshwater fisheries have seen dramatic declines over the past century due largely to various direct and indirect anthropogenic factors. In tandem with addressing the initial causes leading to fish population decline, stocking initiatives have been increasingly employed for stock reintroduction and/or enhancement. One such program aimed at repatriating the anadromous sockeye salmon (Oncorhynchus nerka) in Skaha Lake, British Columbia has seen successful establishment over the past 15 years. However, substantial levels of hybridization with the freshwater resident ecotype of O. nerka, kokanee, have been detected in juvenile fish. While this hybridization could be a healthy source of genetic diversity, it could also lead towards the genetic swamping of either population, lowered reproductive success, and potentially even extirpation. Here, we aim to investigate the genetic and biological consequences of hybridization and introgression in this system. We examined a total of 786 individuals comprising both spawners and age-0 fish collected from 2008 – 2017. Each sample was genotyped at 32 single nucleotide polymorphisms and assigned to a sockeye, kokanee, or hybrid class. We selected individuals from all three classes to undergo otolith microchemistry analysis to determine their migratory life history. Across sampling years, we found a large majority of hybrids to be non-anadromous with a resident maternal parent and of an intermediate size in comparison with the purestocks. These results provide empirical support for the theorized mechanisms of hybridization and offer some prospective pathways for management in this system. Additionally, we have developed a generalized methodology to construct a panel of molecular markers to differentiate advanced introgression classes. Demonstrated with the test case of sockeye – kokanee hybridization, the resulting accuracy- and cost-optimized panel will assist in the continued time-series sampling of Skaha Lake to monitor this reintroduction program as it matures.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat