Effective population size (N e) is among the most important metrics in evolutionary biology. In natural populations, it is often difficult to collect adequate demographic data to calculate N e directly. Consequently, genetic methods to estimate N e have been developed. Two N e estimators based on sibship reconstruction using multilocus genotype data have been developed in recent years: sibship assignment and parentage analysis without parents. In this study, we evaluated the accuracy of sibship reconstruction using a large empirical dataset from five hatchery steelhead populations with known pedigrees and using 95 single nucleotide polymorphism (SNP) markers. We challenged the software COLONY with 2,599,961 known relationships and demonstrated that reconstruction of full‐sib and unrelated pairs was greater than 95% and 99% accurate, respectively. However, reconstruction of half‐sib pairs was poor (<5% accurate). Despite poor half‐sib reconstruction, both estimators provided accurate estimates of the effective number of breeders (N b) when sample sizes were near or greater than the true N b and when assuming a monogamous mating system. We further demonstrated that both methods provide roughly equivalent estimates of N b. Our results indicate that sibship reconstruction and current SNP panels provide promise for estimating N b in steelhead populations in the region.

FishGen is a final repository for Pacific salmon Oncorhynchus spp. and steelhead O. mykiss genetic data generated as part of the genetic stock identification and parentage‐based tagging projects in the Columbia River basin and throughout the Pacific Coast of North America. Resource Data, Inc., developed this web‐based, GIS‐interfaced software, which is freely available to the public, with funding from the Pacific Coastal Salmon Recovery Fund and Bonneville Power Administration. FishGen currently houses genetic stock identification baselines for both Chinook Salmon O. tshawytscha and steelhead in the Columbia and Snake river basins, as well as hatchery, parentage‐based, tagging baselines for both species in the Snake River basin. Because it has a user‐friendly interface and protocol for submitting and storing standardized genetic and sample metadata, it is an excellent tool for supporting genetic research and monitoring projects throughout the region.

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Mating systems and patterns in reproductive success of fishes play an important role in ecology and evolution. While information on the reproductive ecology of many anadromous salmonids (Oncorhynchus spp.) is well-detailed, there is less information for non-anadromous species including the Yellowstone Cutthroat Trout (O. clarkii bouvieri), a species of recreational angling importance and conservation concern. Here, we used data from a parentage-based tagging study to describe the mating system of Yellowstone Cutthroat Trout from a spawning tributary of the South Fork Snake River, Idaho, and identify predictors of relative reproductive success. We detected evidence of monogamy, polygyny, and polyandry and showed that reproductive success was best explained by arrival time at the spawning ground and total length. Specifically, the largest adults arrived earliest in the season and produced a disproportionate number of offspring. Lastly, we estimated the effective number of breeders (N) and effective population size (N) and showed that while Nb was lower than Ne, both are sufficiently high to suggest Yellowstone Cutthroat Trout in Burns Creek represent a genetically stable and diverse population.