Genetic monitoring of steelhead in the Klickitat River to estimate productivity, straying, and migration timing

Salmonids with complex life history variation present challenges for conservation management, but genetic approaches alongside fisheries monitoring can address questions regarding viability of natural populations. We genotyped adult (n=3,108) and juvenile (n=2,624) samples of anadromous Oncorhynchus mykiss that were collected in the Klickitat River, WA, USA at traps in the lower drainage to examine tributary level productivity, straying from outside sources and variation in adult migration timing. Genetic assignment of steelhead from this system indicated that the majority were produced within or near tributaries of the middle Klickitat River (juvenile mean = 72.8%; adult mean = 87.3%). Analyses with parentage-based tagging identified that most hatchery-origin adults were assigned to the Skamania Hatchery (80.8%) as expected since this has been the release stock for decades within the Klickitat River drainage. Hatchery-origin adults were also identified from programs operating outside the Klickitat River, which were primarily strays from Snake River hatcheries. Most natural-origin steelhead were assigned to the Klickitat River, but there were also natural-origin fish identified as strays from other regions of the Columbia River (22.3% of natural returns). We also examined genes known to be associated with migration timing in adult steelhead observed at the trap and observed a strong relationship between migration date and alleles for early and late migration, but individual outliers were detected across seasons. Our results indicate that genetic variation of steelhead in the Klickitat River has been influenced by hatchery programs as well as natural-origin straying from other sub-basins, but genetic diversity remains high throughout the sub-basin, and both early and late migration alleles are maintained. The genetic diversity present in Klickitat River steelhead may enable this Endangered Species Act listed (threatened) species to better adapt to stochastic environmental conditions compared to less diverse populations.Funding provided by: Bonneville Power AdministrationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100015704Award Number: 1995-06303