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Steelhead, the anadromous form of Oncorhynchus mykiss, occupying the Columbia River Basin between the Wind (Washington) and Hood (Oregon) Rivers upstream to include the Yakima River are a part of the Inland Steelhead – Middle Columbia River ESU

Collection of data for population delineation largely from the YKFP

Genotype is string of numbers, two numbers per loci.

More loci for Naches vs. Roza

Ahtanum a SaSI stock?

Current project

1) Inferences about population dynamics (e.g., census size fluctuations or hatchery introgression) based on genetic data rely on accurately estimating the frequencies of alleles observed.

2) Several recent genetic studies have reported inconsistencies in allele frequency estimates taken from a single population at multiple time periods, with some temporal variation high enough in magnitude to cause erroneous conclusions about population differentiation

3) If allele frequency differences are observed between temporally replicated collections from the same location, possible explanations for the result are the population is experiencing genetic drift, there is gene flow from a differentiated stock, or the collection itself is not a valid population sample.

1)These results suggest that the Roza Dam collections are from a population of sufficient size to resist stochastic fluctuation in allele frequencies over time due to genetic drift or gene flow from a genetically differentiated stock is limited.

2)Stated differently, by grouping Roza Dam samples together, separate from other population collections, the amount of genetic variation attributed to among collection differences is the smallest observed value of 0.43%.

1) Roza Dam has excellent collection facilities, and could be used to collect steelhead for broodstock for the upper Yakima population. Yet, Roza Dam is located fairly far downstream of steelhead spawning areas, so it is important to determine if there are multiple populations upstream of Roza Dam. If a collection is composed of two or more separate populations, and the mixed collection is analyzed as if it were a single randomly mating population, the distribution of genotypes given the allele frequencies observed will not meet statistical expectations.

Population samples have expected distributions of genotypes based on allele frequencies.

1) We tested for HWE and LD in the five replicated collections from Roza Dam. The 2000 and 2001 Roza Dam collections were consistent with HWE expectations, and the 2003, 2005 and 2006 had slight deviations from equilibrium expectations. The LD results showed minimal correlations among alleles.

2) These results suggest that Roza Dam collections are not composed of a mixture of populations upstream of the dam and are consistent with the presence of a single steelhead population above Roza Dam. Therefore, if steelhead are collected for broodstock at Roza Dam, these collections would represent one spawning population from the upper Yakima.

Considerable attention recently has focused on the reproductive interactions between resident rainbow trout and steelhead. In some areas in the Pacific Northwest interbreeding between the two forms appears extensive (Araki et al. 2006)

The probability of each resident being derived from a baseline reference population is determined by comparing the genotype of each resident to baseline allele frequencies. Please note that a resident trout collection is not present in the baseline. An optimal reference genetic baseline contains all potential stock sources for an unknown sample. Since it is unknown whether the resident trout are a distinct stock, the individual assignment analysis should be interpreted as providing information about which steelhead stock present in the baseline is the most similar to each resident.

1) For each resident, the probability of its genotype being derived from each genetic baseline population is shown. Despite the genetic baseline including all major divisions of steelhead observed, resident trout samples were only assigned to the Naches River and Roza Dam populations.

2) These results suggest that the resident trout samples collected in the Teanaway River in 2006 are indistinguishable from the Naches River and Roza Dam steelhead, which is consistent with a high level of interbreeding between residents and steelhead.

1) Three qualitative pieces of evidence supporting the observed similarity between residents and steelhead are the alleles observed in the collections, the genic differentiation tests, and the AMOVA results.

2) Although our ability to make inferences about the genetic similarity between resident trout and Roza Dam steelhead is limited by the small resident trout sample size included in this study, the genetic data are consistent with the resident trout and steelhead being derived from the same population.

Adults returning or smolts emigrating