Population Structure and Genetic Divergence of Coastal Rainbow and Redband Trout in the Upper Klamath Basin

Freshwater-resident coastal rainbow trout Oncorhynchus mykiss irideus and the anadromous form of the subspecies, coastal steelhead (summer and winter runs), are present throughout the lower Klamath River–Trinity River system. Although coastal steelhead and other anadromous salmonids historically migrated into the Upper Klamath Basin (which encompasses the upper Klamath River and Upper Klamath Lake) and associated tributaries, the construction of Copco Dam in 1918 and Iron Gate Dam in 1962 stopped all upstream migration of fish past these barriers. In the Upper Klamath Lake basin, native Upper Klamath Lake redband trout O. mykiss newberrii are found along with coastal rainbow trout that were trapped above the dams or stocked from hatchery sources. However, relatively little is known about the genetic relationships among the O. mykiss populations within the Upper Klamath Basin. A population genetic analysis based on data from 17 variable microsatellite loci was conducted for samples collected in the Upper Klamath Basin, including rainbow trout and Upper Klamath Lake redband trout (presumably representative of the ancestral coastal and inland lineages) as well as samples of O. mykiss from neighboring inland lake basins. In addition, the Upper Klamath Basin samples were compared with data from O. mykiss populations below Iron Gate Dam. Results demonstrate the presence of distinct inland and coastal genetic lineages as well as divergent lineages represented by samples from the inland lake basins; these results have significant implications for future restoration of O. mykiss in the greater Klamath River–Trinity River system.