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

Authors: David Syzdek, Michael Schwemm

Year: 2024

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 1,935 Moapa dace in February 2024, and 2,110 Moapa dace in August 2024. Twenty-three young of year Virgin River chub were detected by snorkel count in August 2023, showing the first documented reproduction of this species in the Warm Springs Natural Area since 1994. These fish have been detected in subsequent snorkel counts. 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 of the Muddy River. This population peaked at 268 in August 2021 but has been declining steadily and only 16 Moapa dace were found in this stream in August 2024. It is postulated that Moapa dace exited this stream reach to enter water with cooler water temperatures but were excluded from moving back into the reach by a fish passage barrier caused by a stream gage.