What Movements and Genetic Relationships Tell US about Connectivity of Habitat and Bull Trout Spawning Populations in the Jarbidge River, NV

Bull trout Salvelinus confluentus in the Jarbidge River of southern Idaho and northern Nevada are the southern-most population across the species’ range. This population has been isolated from other populations for over 100 years. Managers have recognized bull trout habitat use, population connectivity, and genetic information as important factors for guiding recovery actions in the Jarbidge River. To assist in this effort, we determined the distribution, relative population size, movements, and gene flow amongst populations of Jarbidge River bull trout. During 2006 and 2007, we electrofished about 40 km of the headwaters of the Jarbidge River basin per year, PIT-tagged 1,536 bull trout, and collected 237 tissue samples for genetic analysis. We also monitored the movements of PIT-tagged bull trout within the basin from 2006 through 2009 using six PIT-tag interrogation systems installed at strategic locations. For genetic analysis, we used a suite of 15 microsatellite loci to provide fine-scale information on genetic variation within and among the Jarbidge River bull trout populations. Our use of PIT-tag technology provided information about the patterns and timing of short-term movements of individual fish that could be correlated to spawning and other factors. Relying on a single method may have led us to false conclusions. For example, PIT-tagging suggested that there was considerable movement between a few panmictic spawning populations. Genetic analysis identified the spawning population that an individual fish originated from and that there was strong site fidelity with little mixing between the six spawning populations identified. Collectively, the results of both methods were complementary and indicated that considerable movements of fish occurred within and between tributaries and the mainstem river but fish largely returned to their natal tributaries to spawn. Combining the genetic and PIT-tag methods provided much insight into the habitat use and connectivity of the Jarbidge River bull trout populations.