Do conservation actions improve native fish populations? Differences between managed and unmanaged reaches of a desert river give insight

• DOI: 10.1093/najfmt/vqaf002
• Publication Date: 2025-04-01T18:42:14Z
• Authors: Skyler C Hedden; Brandon Albrecht; Ron J Rogers; Kevin Guadalupe; Melinda Bennion; Martin Schijf; Kody Callister; Christian Edwards; Kevin Wheeler; Erik Woodhouse; Rick Fridell; Steve Meismer

ABSTRACT Objective: Resource managers are tasked with conducting management actions to improve native communities and/or offset negative anthropogenic activities. However, measuring the effectiveness of conservation actions is difficult due to temporal variations, time lags, and a lack of control sites with which to examine change. Consequently, the effectiveness of conservation management actions often goes unmeasured, and at times managers can be uncertain of their efforts. In the Virgin River (Nevada, Arizona, and Utah), management actions have differed substantially between the upper and lower reaches of the river. The upper Virgin River has seen the construction of nonnative fish barriers, applications of rotenone to eradicate nonnatives, implementation of native fish stocking programs, and installation of pump-back systems to maintain stream temperatures within desirable tolerance ranges. In the lower Virgin River, efforts have largely been focused on collecting information for long-term data sets, with relatively minimal management actions taken. Methods: To examine differences in management outcomes, we evaluated native fish community structure and densities between the upper reach (six sites) and lower reach (six sites) of the Virgin River. Results: Our findings showed that the fish community structure differed considerably between the two reaches, largely driven by the eradication of nonnative fish from the upper Virgin River reach. When we examined native fish community structure, differences were less apparent but still existed, driven by three native species. Site-specific differences were evident between the upper and lower reaches; however, sites in the upper reach had similar fish communities, while spatial variability existed for sites in the lower reach. Conclusions: Although many factors can contribute to community change and there are associated difficulties in quantifying how each factor may contribute to change, our results suggest that conservation management actions likely had a positive impact on native fish communities. However, these actions may be more influential for certain species and may potentially supplement nearby populations that are not within management boundaries.