Ongoing restoration projects for the endangered Moapa dace, Moapa coriacea, & Virgin River chub, Gila seminuda, at the Moapa (Muddy) Warm Springs, Clark County, Nevada

Authors: David Syzdek, Michael Schwemm

Year: 2023

Abstract

The Moapa (Muddy) Warm Springs in Southern Nevada is a regional carbonate warm water spring complex that forms the headwaters of the Muddy (Moapa) River. These springs and associated streams are habitat for an endemic suite of thermophilic aquatic species that includes the federally endangered Moapa dace (Moapa coriacea) and a federally unprotected population of Virgin River chub (Gila seminuda). Currently, the Southern Nevada Water Authority (SNWA), US Fish and Wildlife Service (USFWS), Nevada Department of Wildlife (NDOW) and other stakeholders are undertaking recovery actions for the Moapa dace and its habitat. These include construction and removal of fish passage barriers, removal of invasive species and habitat restoration. To facilitate recovery of the Moapa dace and other native species, SNWA purchased the 1,218-acre Warm Springs Ranch in September 2007 and designated it the Warm Springs Natural Area for conservation and environmental stewardship purposes. In 2008, Moapa dace numbers suddenly declined to a record low of 459 individuals. Following this nadir, SNWA, NDOW and USFWS conducted stream restoration work and intensive habitat improvements to improve conditions for the Moapa dace. NDOW successfully treated the Upper Muddy River with rotenone to control the invasive and predatory blue tilapia (Oreochromis aureus). Furthermore, stream restoration and clearing of dense stands of fan palms (Washingtonia filifera) are facilitating the re-establishment of native riparian vegetation, providing prevention of future wildfires and continued improvement in Moapa dace numbers. Moapa dace numbers are generally stable at a significantly higher level than in previous years but have yet to reach recovery levels of 6,000 fish. Recent snorkel counts recorded 1,933 Moapa dace in February 2023, and 1,888 Moapa dace in August 2023. Surprisingly, 23 young of year Virgin River chub were also detected by snorkel count in August 2023, showing the first documented reproduction of this species in the Warm Springs Natural Area since 1994. Work continues to improve dace habitat, improve stream connectivity, and to monitor for invasive species. In 2019 and 2020, 88 Moapa dace were translocated into the South Fork. This population persists but has been declining. In 2021, 90 Moapa dace were transferred to the Lake Mead Fish Hatchery for a NDOW fish propagation program and 18 progeny of these fish were released back into the wild in June 2023.