Cooperative Fish and Wildlife Research Units Program: Utah
Education, Research and Technical Assistance for Managing Our Natural Resources

Bonneville cutthroat trout (BVCT) are a sub-species of cutthroat trout, endemic to the Bonneville Basin, currently restricted to 33% of their historical range, and listed as a State of Utah Tier I protected species (Conservation Agreement) in an effort to avoid listing under the ESA. Currently, negative interactions with non-native fishes present one of the greatest threats to BVCT. Furthermore, an estimated 50% (1,356 km) of suitable habitat in the Bear River GMU alone is unoccupied (UDWR 2004). The Logan River, Utah, supports one of the largest remaining meta-populations of BVCT across their range; however, as elsewhere, native BVCT are threatened by negative interactions with non-native, invasive brown trout in the lower elevation portions of the river and in some tributaries, including Righthand Fork. Righthand Fork offers great potential for BVCT restoration as well as an opportunity to better inform BVCT restoration efforts. Historically, BVCT would have been abundant and dense in this tributary and would have used this area extensively for spawning and rearing. Currently this tributary is dominated by high densities of invasive brown trout, likely due to its close proximity to historical stocking areas in the lower river and more moderate hydro-geomorphic conditions; densities of brown trout here may exceed 3000/km. In the Logan River and in many mountain streams, the native and endemic trout (e.g., cutthroat trout) occupy upper reaches of a watershed in potentially high densities, while an exotic trout typically dominates the lower reaches of these streams. Although they are superior competitors, these exotic trout have not invaded further upstream despite the absence of physical barriers to movement or physical attributes that exceed their physiological tolerance. Under the concept of biotic resistance, the invasion success of introduced species is determined or controlled by “strong” interactions with native species and is a function of the density of native species. In theory, when densities of native fishes are adequately high, non-natives cannot successfully establish or dominate. In this proposal, we seek funds to 1) aid in the removal of brown trout and the restoration of native BVCT in Righthand Fork, a tributary to the Logan River, Utah, and 2) test the concept of biotic resistance using a large-scale, manipulative field study .