Supplementary data from: A genetic assessment of natural barriers for isolating a proposed Greenback cutthroat trout reintroduction area

We used genetic techniques to evaluate a series of natural waterfalls for
their potential to serve as barriers to prevent nonnative salmonids from
entering a proposed reintroduction area for federally threatened Greenback
cutthroat trout Oncorhynchus clarkii stomias. Genetic samples
were collected from nonnative Brook Trout Salvelinus fontinalis at 11
sampling reaches above and below natural waterfalls (height: ~1-3 m under
baseflow conditions) along a 33-km segment of Colorado’s upper Cache la
Poudre River near the outflow of the proposed reintroduction area. To
evaluate whether upstream movement of Brook Trout is restricted by any of
these waterfalls, we characterized longitudinal trends in genetic
diversity along the river corridor and examined patterns of genetic
differentiation and population structure in relation to waterfall
locations using a panel of microsatellites. We found no evidence that the
waterfalls served as complete movement barriers for nonnative Brook Trout
based on genetic clustering analyses, estimates of population
differentiation, and longitudinal genetic patterns. Our multi-locus
assessment did not identify alleles restricted to downstream reaches, and
the river segment was genetically homogenized. This evaluation suggests
that the existing waterfalls do not fully prevent upstream movement by
nonnative Brook Trout, and thus barrier modification would be needed to
establish an isolated Greenback cutthroat trout population in the proposed
wilderness area.