The Genetic Relationship between Anadromous and Resident Oncorhynchus mykiss at a Putative Barrier with Implications for Habitat Improvement

AbstractBig Bear Creek in the Potlatch River system, Idaho, contains an Endangered Species Act-listed wild population of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) that is the focus of extensive habitat restoration actions intended to increase population abundance. Both anadromous and resident O. mykiss populations occur in the Big Bear Creek drainage; however, anadromous individuals are known to spawn and rear only in the lower drainage, whereas putative resident fish occur in the headwaters. Big Bear Falls is a potential upstream migration barrier that is located between the two populations. Oncorhynchus mykiss of unknown origin are present within 1 km above the falls. We used analyses of genetic diversity, structure, and sibship reconstruction to determine whether Big Bear Falls limited the movement of steelhead to headwater areas. Known resident O. mykiss were sampled in headwater areas, known anadromous adults were sampled at a weir in the lower drainage, and juveniles of unknown life h...