Date of Award
Master of Natural Resources (MNR)
Native fish species such as Bonneville Cutthroat Trout (BCT) require cold, clear, well-connected streams for spawning and rearing as well as access to complimentary habitats. Increasing river temperatures and lower water flows may have allowed non-native Brown Trout (BNT) to migrate into higher elevation pristine streams. Additionally, anthropogenic actions such as stocking non-native Brown and Brook (BKT) and Rainbow Trout (RBT) for angling opportunities impact BCT. Invasion of these tributaries by non-native species may reduce or eliminate cutthroat trout by predation, competition, displacement, genetic suppression, and exclusion. A seven-fold increase in BNT numbers of 50 to 350 from 2017 to 2018 demonstrated the need for this research. The goal of this project was to assess the density and distribution of non-native BNT and BKT, conduct a complete mechanical removal of BNT and BKT, and reconstruct the history of the expansion of BNT and BKT in the Temple Fork and Spawn Creek tributaries of the Logan River, UT, USA. In order to meet this goal we used pre-existing sampling data, conducted removal efforts on Temple Fork and Spawn Creek, and analyzed historical data of when BNT and BKT first appeared in sampling efforts in these locations. Our sampled locations were 400m to 500m in length on Temple Fork from the confluence with Logan River and also on Spawn Creek. We identified all captured fish and BNT and BKT were removed. We observed a surprisingly high number of BNT (2,551) and BKT (566). We did not observe BNT above reach 9 on Temple Fork and reach 6 on Spawn Creek. We were encouraged to find high numbers of BCT though BNT numbers have been increasing as previously mentioned. We demonstrated by capturing 6 BNT that a permanent selective barrier at the confluence of the Logan River and Temple Fork was not be necessary to prevent the high numbers of brown trout from invading this tributary each fall to spawn. A second trapping effort with the picket weir may further help identify movements of BNT (Figure 11). While immigration of BNT into Temple Fork from the Logan River may contribute BNT in the lower reaches of Temple Fork, ultimately the establishment of a resident population of BNT and BKT threatens to overwhelm BCT. Further actions such as additional mechanical removal efforts every other or every third year and fishing regulation changes may be warranted to protect BCT from further invasion throughout this tributary, range-wide, and where native fish populations struggle from similar concerns.
Brunson, Clint, "Evaluating the Effect of the Removal of Non-Native Trout in Two High Elevation Tributary Streams in the Intermountain West" (2020). All Graduate Plan B and other Reports. 1471.
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