Identifying appropriate units for conservation requires knowledge of evolutionary
patterns and risks of managing at different geographical and genetic scales. I examined
genetic diversity at different geographical scales among 11,400 rainbow trout
(Oncorhynchus mykiss) from 243 locations in 13 major river basins throughout much of
their range and among coho salmon (O. kisutch) from 31 watersheds in Oregon,
Washington, and northern California. I also developed a model of genetic vulnerability of
managed populations that links sources of potential technological hazards, protective
mechanisms and responses, and potential losses, using artificial propagation of Pacific
salmon as an example. Across the range of rainbow trout, allozyme differences between
inland and coastal populations were more localized than previously acknowledged. In
contrast, evolutionary continuity was most related to stability and persistence of major
river systems, such as upper Sacramento, Klamath, and Columbia rivers. Isolated, pluvial
lake basins that contained divergent groups of redband trout (rainbow trout with
plesiomorphic characteristics associated with cutthroat trout, O. clarki) were sources of
evolutionary diversity within large river systems. Human effects on genetic organization
occurred in local breeding populations to regional metapopulations. In coho salmon,
regional differences in mitochondrial DNA existed among fish from Puget Sound,
Columbia River, northern Oregon coastal streams, and southern coastal streams.
Differences within regions lacked obvious geographical patterns but were most likely due
to recent fish translocations and genetic drift. In the Umatilla River, Oregon, significant
genetic differences were detected among rainbow trout, but temporal differences at sites
were as great as differences among sites within tributaries. In 10 of 12 locations, rainbow
trout became more similar to anadromous hatchery fish. Although small breeding sizes
suggested a role for genetic drift, episodic gene flow from hatchery fish most likely
explained temporal genetic changes. Program-specific genetic risk assessment of a large
artificial propagation program in the Columbia River revealed that artificial
supplementation would result in fewer hatchery-reared fish returning to the wild than were
taken from the wild for brood stock, that proximate safeguards for reducing vulnerability
were not available and appropriate, but that use of genetic reserves strengthened the
program
