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Effective management of Pacific salmon requires an accurate understanding of both population genetic diversity and structure. Spring Chinook Salmon Oncorhynchus tshawytscha from the upper Willamette River (UWR), Oregon, are listed as threatened under the U.S. Endangered Species Act, and although this evolutionarily significant unit is recognized to be distinct from other Columbia River stocks, genetic relationships among its constituent hatchery and wild populations remain obscure. We used genotypic data from 13 microsatellite loci to test whether hatchery populations of UWR spring Chinook Salmon are most similar to wild populations within the same subbasin, or whether hatchery populations from different subbasins are more similar to each other than to local wild populations. We also tested for differences between the genetic diversities of hatchery and wild populations, as measured through heterozygosity and allelic richness. Our results suggest that populations are weakly structured among subbasins and, in all cases, hatchery populations are genetically most similar to local wild populations. We also found heterozygosity to be higher (P = 0.009) in hatchery populations (median, 81.5%) than in wild populations (median, 75.2%), but observed no significant difference with respect to allelic richness (P = 0.406). We conclude that hatchery‐origin UWR spring Chinook Salmon represent genetically appropriate founder populations for ongoing reintroduction programs and recommend that the conservation and recovery of this stock proceed through management actions developed specifically for each subbasin. We further recommend that current restrictions on hatchery stock transfers among UWR subbasins be continued to preserve extant population genetic structure. Received January 8, 2014; accepted April 29, 2014 [ABSTRACT FROM AUTHOR]

Induced triploidy typically causes sterility in teleost fishes, and has therefore been proposed as a tool to manage genetic risks that farmed and hatchery-produced salmon pose to wild populations. Application of this technology for aquaculture has been challenged by inferior growth, survivorship and, in the case of free-ranging anadromous salmonids, relatively low numbers of adult returns. There is little information on whether or not triploidy affects the physiological development of juvenile salmonids in ways that impair their ability to grow, imprint on natal waters, survive, and return from the ocean as adults. In this study we pressure treated fertilized eggs to produce two cohorts of triploid hatchery steelhead trout (i.e., anadromous Oncorhynchus mykiss). We calculated survivorship through early life stages, and measured gill ATPase and plasma thyroxine (T4) for yearling triploids and their full-sibling diploid controls. We found no clear pattern of difference between diploid and triploid steelhead for the biomarkers of smoltification T4 or ATPase. After a year of freshwater rearing, we transferred 448 tagged treatment and control fish to a saltwater tank, and tracked their growth and survivorship for over 15 months. Diploids outperformed triploids in growth and, by the end of our study, survivorship of diploids (72%) was more than twice that of triploids (35%). Our findings suggest that inferior growth and survivorship of triploids in saltwater seriously challenge the application of this technology for free-ranging steelhead and, by extension, Pacific salmon. Additional research is needed to identify and offset the causal mechanisms underpinning triploid attrition during saltwater rearing. [ABSTRACT FROM AUTHOR]