Application of Genetic Pedigree to Inform on Habitat Use in Re-Establishing Stocks Above High Head Reservoirs

Construction of large dams in the upper Willamette River Basin of Oregon in the 1950s and 1960s blocked passage to adult spring Chinook and resulted in the loss of almost half of the most highly productive spawning and rearing habitat in the basin.  In the McKenzie River basin, construction of Cougar Dam on the South Fork McKenzie River in 1963 blocked access to 40 km of the high quality habitat.  Efforts to reintroduce spring Chinook into areas upstream of dams increased after adoption of the Willamette Biological Opinion in 2008.  Initial reintroductions in the South Fork McKenzie began with hatchery Chinook, but a fish trap at Cougar Dam competed in 2010 now allows naturally produced Chinook to be passed upstream. 

A genetic pedigree study was initiated to evaluate the reproductive success and total lifetime fitness of reintroduced Chinook, to determine the parentage of natural origin returns to the Cougar Dam fish trap, and to evaluate the relative success of alternative reintroduction strategies.  Tissues have been collected since 2007 from each adult released upstream of the dam.  In a preliminary study of emigrating juvenile Chinook captured upstream of Cougar Reservoir, over 95% of the fish were positively identified to family origin indicating the high power of molecular pedigree using a set of 12 highly variable microsatellites.  These results indicate that individual-based genetic identification methods can be used to inform studies on patterns in migratory behavior among cohorts sampled as juveniles from different habitats (above reservoir, reservoir, below reservoir) or as adults during ocean rearing and at return to the natal river.  In the South Fork McKenzie we collected tissues of juvenile spring Chinook just upstream of the reservoir and downstream of the dam, and we collected tissues of returning adults at the Cougar fish trap.  Preliminary findings indicate co-migration for some siblings, while other siblings vary in their migration timing by as much as 6 months. Ancillary evidence indicated extreme variance in the apparent numbers of offspring produced from different males.  Success at achieving these objectives will be increased by rigorous tissue-sampling of all potential parents combined with strategic non-lethal sampling of fish encompassing all habitats and seasons of interest.