Population genetics reveals bidirectional fish movement across the Continental Divide via an interbasin water transfer

Interbasin water transfers are becoming an increasingly common tool to
satisfy municipal and agricultural water demand, but their impacts on
movement and gene flow of aquatic organisms are poorly understood. The
Grand Ditch is an interbasin water transfer that diverts water from
tributaries of the upper Colorado River on the west side of the
Continental Divide to the upper Cache la Poudre River on the east side of
the Continental Divide. We used single nucleotide polymorphisms to
characterize population genetic structure in cutthroat trout (Oncorhynchus
clarkii) and determine if fish utilize the Grand Ditch as a movement
corridor. Samples were collected from two sites on the west side and three
sites on the east side of the Continental Divide. We identified two or
three genetic clusters, and relative migration rates and spatial
distributions of admixed individuals indicated that the Grand Ditch
facilitated bidirectional fish movement across the Continental Divide, a
major biogeographic barrier. Previous studies have demonstrated ecological
impacts of interbasin water transfers, but our study is one of the first
to use genetics to understand how interbasin water transfers affect
connectivity between previously isolated watersheds. We also discuss
implications on native trout management and balancing water demand and
biodiversity conservation.