Document Type
Report
Publisher
Utah State University
Publication Date
11-25-2024
Keywords
restoration action, Bear Lake, native fishes, environmental resilience
First Page
1
Last Page
42
Abstract
Stream fragmentation due to the construction of dams, diversions, and road crossing culverts have limited the ability of native migratory fishes to access the distinct habitats required to complete their life history, contributing to widespread declines in abundance and distribution. The Bear Lake Cutthroat Trout (Oncorhynchus virginalis spp., recently reclassified from O. clarkii), represent a unique adfluvial life history variant, living in the lake and migrating up tributary streams to spawn. However, development of water resources and construction of roads in the valley surrounding Bear Lake reduced their ability to access their historic spawning grounds, leading to the near extirpation of the species from the lake by the 1950s. Recent efforts to reestablish connectivity between the lake and its tributaries has resulted in substantial increases in recruitment of wild Cutthroat Trout to the population, such that wild individuals accounted for the majority of the population in a recent annual lake monitoring survey. As such, further increasing connectivity to tributary streams may increase the production and resilience of the wild Cutthroat Trout population in Bear Lake.
North Eden Creek, on Bear Lake’s eastern shore, is home to a relict population of Bear Lake Cutthroat Trout that are isolated in the headwaters. Adfluvial Cutthroat Trout enter the stream during their spawning migration, but are blocked from ascending upstream of the intersection with North Cisco Road by an impassable culvert. Trout Unlimited and partners are planning to replace the culvert in Fall of 2025 to allow adfluvial spawners to access the additional spawning habitats upstream of the road crossing. To understand how this planned restoration action ultimately impacts the Cutthroat Trout population of North Eden Creek, we conducted a review of historical documents and data collection efforts, and designed and implemented a monitoring plan to assess the physical habitat, fish assemblage, and aquatic invertebrate community along an elevational gradient of North Eden Creek, including sites both below and above the culvert.
Cutthroat Trout and non-native Brook Trout (Salvelinus fontinalis) were the only two species of fish captured upstream of the culvert at North Cisco Road, while two additional native fishes (Utah Chub Gila atraria and speckled dace Rhinichthys osculus) were also captured downstream of the culvert. An additional native species (Utah Sucker Catostomus ardens) has also been observed downstream of the culvert in recent years, but was not captured in our samples. Brook Trout were found at all sites inhabited by Cutthroat Trout, and represent potential competitors for resources and predators of juvenile Cutthroat Trout. Importantly, fish were restricted to headwater habitats and to habitats downstream of the culvert, being absent throughout the middle and low elevation reaches upstream of the culvert.
Physical habitat conditions demonstrated clear elevational patterns along North Eden Creek. Riparian vegetation was most abundant in lower elevation sites both upstream and downstream of the culvert, and was very limited in middle and high elevation reaches. The low elevation sites maintaining riparian vegetation cover do not experience cattle grazing, while the upper and middle elevation reaches do. Undercut bank habitat was abundant in high elevation sites, but very limited in middle and low elevation sites. Gravel substrates were more abundant in high elevation sites, while cobble substrates were most available in low elevation sites, and middle elevation sites were dominated by silty substrates. Stream temperatures were highest in middle elevation reaches, where temperatures exceeded 7-day incipient lethal temperatures for at least part of the summer. Headwater and low elevation temperatures never exceeded this thermal limit, and were generally lower than in middle elevation sites, demonstrating complex, nonlinear thermal patterns along the length of the river.
Aquatic invertebrates were most abundant at the low and high elevation sites, and much less abundant in middle elevation reaches. Additionally, the proportional contribution of sensitive taxa (Ephemeroptera, Trichoptera, Plecoptera) was greatest in high and low elevation reaches, and lower in middle elevation reaches. Taken together, the physical habitat and aquatic invertebrate data suggest middle elevation reaches are suboptimal and even unsuitable at specific times of the year, thus limiting the distribution of both native and non-native trout. As such, while we expect reestablishing connectivity for adfluvial Cutthroat Trout to increase the availability of spawning habitat and the production of juvenile Cutthroat Trout, the middle elevation reaches of the stream are unlikely to support large increases in abundance of trout without further habitat restoration efforts.
We recommend repeating the monitoring surveys presented in this report, alongside additional efforts to monitor the abundance of spawning adfluvial trout entering the stream each year to assess the population level response of Cutthroat Trout to the planned culvert replacement. We provide a description of the monitoring protocol in an appendix. If surveys are repeated every 1-3 years, managers and stakeholders will be able to determine the effects of culvert replacement and any subsequent habitat restoration efforts on both the adfluvial and resident populations of Cutthroat Trout in North Eden Creek.
Recommended Citation
Walsworth, T.E., Coleman, T., DeRito, J., Budy, P. 2024. Establishing a Baseline to Assess Impact of Restoration Actions Reconnecting Bear Lake Tributaries to Increase Resilience and Abundance of Native Fishes. Progress Report to the Utah Division of Forestry, Fire, and State Lands and the Janet Quinney Lawson Institute for Land, Water, and Air at Utah State University.
