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

Summer base flows for rivers are critical for maintaining water quality, healthy fish populations, and a functional aquatic ecosystem. Low summer base flows can increase water temperatures and reduce dissolved oxygen levels. These conditions can stress Brown Trout (Salmo trutta) energetically and thus result in lower angler catch. The goal of our study was to determine if low river flows and higher water temperatures influence angler catch rates of Brown Trout on the lower Logan River, Utah. We performed a creel survey on approximately 6.4 km (4 miles) of the lower Logan River from 1 April to 31 October 2019, during which we recorded angler effort and catch data to calculate mean monthly catch rates. We used continuous collection of stream temperature and flow from a river gage within the survey reach to calculate monthly means. Total angling effort for the survey period was 2,147 hours with 1,481 fish caught for an overall catch rate of 0.69 fish per hour (fph). June was the highest for angler catch rate (1.2 fph) as well as the highest discharge at 16 m³/s while also having the lowest average water temperature (9.6 °C). Our data from September demonstrated the lowest angler catch (0.41 fph) in addition to the lowest discharge (2.12 m³/s), and highest average water temperature (11.2°). Collectively these data demonstrate a positive correlation between high flow rates and angler catch rates (R2 = 0.37, p = 0.15), and a negative correlation between higher water temperatures and angler catch rates (R2 = 0.42, p = 0.12); however, time of year can be a confounding factor for angler behavior. This project is a collaboration of Trout Unlimited, the Utah Division of Wildlife Resources , the U.S. Forest Service Rocky Mountain Research Station, and Utah State University. Our data suggest that even on a higher-than-average runoff year, angler success is impacted by low summer base flows. Maintaining increased river flow during typical summer low-flow time periods could increase angler catch rates and, ultimately, even greater satisfaction with this potential Blue Ribbon fishery.