Long-Term Perspective of Native Fishes Within the Muddy River, Nevada

Authors: Harrison Mohn, Brandon Albrecht, Ronald Rogers, Ron Kegerries, David Syzdek

Year: 2018

Abstract

The Moapa (Muddy) River of southern Nevada once held a healthy assemblage of native species that included the Virgin River Chub Gila seminuda, Moapa Dace Moapa coriacea, Woundfin Plagopterus argentissimus, Moapa Speckled Dace Rhinichthys osculus moapae, Desert Sucker Catostomus clarkii, Flannelmouth Sucker Catostomus latipinnis, and Moapa White River Springfish Crenichthys baileyi moapae. By the 1960s only one native fish species, the Virgin River Chub, was captured below the Wells Siding Diversion, and sampling through the 1970s indicated that the fish assemblage in this section of river consisted predominantly of nonnative species. Above the Wells Siding Diversion, only the Virgin River Chub remains as a sustainable population, stocking of Moapa Speckled Dace is required to maintain the species, and the Moapa White River Springfish and the Moapa Dace are found only in the uppermost reaches of the river. We make comparisons of the present day fish community composition, relative abundance, and distribution to historical collections stemming from the 1960s and 1970s, which indicate an overall decline in the abundance and distribution of native fishes. Floods in the past 12 years have shown benefits for the chub population in years following flood events, while populations decrease again after a couple years post-flood. To date, PIT tagging data shows Virgin River Chub exhibit life spans of at least 6 years in the Muddy River, which perhaps allows the population as a whole to outlast difficult conditions between flood events. Further difficulties for native fish include connectivity issues due to diversion dams as well as summer temperatures that often remain above 30.0°C, which is above the optimal temperature for Virgin River Chub of 24°C (critical maximum temperatures between 28°C and 36°C). Nonnative species are a principle concern within the Muddy River at this time, but are being mitigated through the use of rotenone by the Nevada Department of Wildlife upstream of the Wells Siding Diversion. The Virgin River Chub holds no special protection within the Muddy River at this time, despite being the same endangered species that occurs in the Virgin River.