Virgin River Long-Term Fish Community Monitoring

Authors: Ron Kegerries, Brandon Albrecht, Harrison Mohn, Ron Rogers, Aaron Ambos

Year: 2018

Abstract

From 1993 through 2017, BIO-WEST, Inc., with funding and support from various agencies, has monitored the lower Virgin River to assess the long-term fish community dynamics and the success of stocking efforts to establish and enhance Woundfin, Plagopterus argentissimus populations. Native fish relative abundance increased in the upper study reaches following flood events, while nonnative fish abundance declined during these post-flood periods. Reaches above the Bunkerville Diversion are still considered the source of all native fishes within the lower Virgin River. A historical comparison of both native and nonnative fish species captured in the lower Virgin River since 1998 shows species composition to be similar across years indicating that positive trends associated with flooding are short-lived. Long-term catch rate analysis for the lower Virgin River show that native fish abundance has not significantly changed, but nonnative fish abundance has declined significantly in the last two decades. A similar analysis of habitat shows little variation in habitat types, substrate, or cover present at sampling locations within the study area. This monitoring yields a long-term perspective to assess fish populations within the lower Virgin River by providing Virgin River Chub, Gila seminuda population estimates, and provide a holistic understanding of the fish community in anticipation of future nonnative fish species removal. Consistent data collection will continue to be important in monitoring the rare fishes of the lower Virgin River and update recovery goals, particularly given the growing water demand in the region.