An assessment of headwater isolation as a conservation strategy for cutthroat trout in the Absaroka Mountains of Wyoming

Isolation of native cutthroat trout (Oncorhynchus clarki) populations in he adwater tributaries (by means of human-made barriers that prevent upstream movement of exotic Salmonidae) has been used (as an approach) to preserve e xtant populations from hybridization and competition. We evaluated this con servation strategy for Yellowstone cutthroat trout (O. c. bouvieri) in the Absaroka Mountains of northwestern Wyoming. We surveyed four existing popul ations to assess the potential for isolating Yellowstone cutthroat trout po pulations in 23 individual headwater tributary streams. It appeared that 21 of the populations would be large enough to minimize demographic risks of extinction, but only seven populations may be large enough (effective popul ation size > 500) to lower the risk of extinction due to genetic limitation s. Additionally, there is high potential for unpredictable environmental ev ents to cause severe reductions in population size or local extinctions of Yellowstone cutthroat trout populations above barriers due to the unstable flow and habitat conditions. Isolation of Yellowstone cutthroat trout popul ations in headwater tributaries upstream from barriers appears to have a lo w probability of preserving sustainable populations of Yellowstone cut-thro at trout in the Absaroka Mountains in the long term.