The Aquatic Wildlife of Warm Springs Natural Area
The Muddy River Aquatic Assemblage encompasses the Muddy River. It is characterized by shrubby vegetation composed primarily of tamarisk and honey mesquite growing along a highly incised streambank. Water temperatures range between 80°-90° F on the WSNA. Exotic fishes such as tilapia, mollies, and mosquito fish are ubiquitous. While many aquatic animal species occur throughout the aquatic assemblages, a few reach maximum prevalence within this assemblage. Two native fishes and two aquatic invertebrates of concern primarily occur in this assemblage.
Virgin River chub
The Muddy River population of Virgin River chub has a high potential for being listed as an endangered species. It has been declining throughout the Muddy River since the 1960s.
Chub decline has been attributed to changes in water and substrate quality, channelization, introduced fishes, and parasites. Since its extirpation in the Warm Springs area in about 1997, this species has not been able to recolonize these streams due to a diversion dam near Warm Springs Road. The Virgin River chub averages 8-10 inches in length. It prefers deep streams with swift water. Dietary preferences of larval and juvenile chub consist primarily of aquatic insects. Adult chub feed on both insects and algae. Management of Virgin River chub on WSNA requires reestablishing connectivity with the core population that occur downstream, eliminating introduced fishes, and restoring floodplain vegetation.
Moapa speckled dace
(Rhinichthys osculus moapae)
Moapa speckled dace populations are known to fluctuate greatly. The Moapa speckled dace averages three inches in length and typically lives for three years. The speckled dace is a close relative of the Moapa dace and has similar habitat requirements but prefers the cooler water temperatures below the Warm Springs area. Because of this thermal barrier, the two species are not competitive. Larval speckled dace are primarily plankton feeders, while the adults feed primarily on both aquatic insects and algae. Speckled dace prefer the lower horizon of shallow, cobble riffles. They likely face similar threats from deterioration in water quality, introduction of non-native fish, and parasites.
The only published collection of the Moapa skater (Rhagovelia becki) was by Polhemus (1973) who described the species and by Huillet (1998). Several surveys since have not recorded the species (Albrecht et al. 2008, Stevens Ecological Consulting 2004, Sada and Herbst 1999), but R. choneutes was commonly observed in the Warm Springs area, suggesting either local extirpation or misidentification of R. becki (Sada and Herbst 1999).
The Warm Springs crawling water beetle (Haliplus eremicus) was collected originally on the LDS Recreational Property as well as from Arizona (Wells 1989) and subsequently from the Muddy River on the LDS property (Huillet 1998). Current collection records include California and Utah within its range (R. Baumann, personal communication, April 2009). WS AQUATIC ASSEMBLAGE
The Warm Springs Aquatic Assemblage is considered irreplaceable and the most important assemblage in the upper Muddy River ecoregional portfolio (Provencher and Andress 2004). This assemblage includes the thermal springs and tributaries which constitute the headwaters of the Muddy River. The endangered Moapa dace (Moapa coriacea) and the Moapa White River springfish (Crenichthys baileyi moapae) are native thermophiles dependent upon the warm springs and streams for survival. The Moapa pebblesnail (Pyrgulopsis avernalis) isan endemic snail species found in the headwaters of the upper Muddy River. Additionally, three thermophilic aquatic insects are endemic to the Muddy River headwaters, namely, the Moapa naucorid (Limnocoris moapensis), Moapa riffle beetle (Microcylloepus moapus), and Moapa Warm Springs riffle beetle (Stenelmis moapa) (Parker et al. 1997). All seven species are identified by the Nevada Natural Heritage Program as at-risk. Other rare species within this assemblage that occur on the WSNA and other locations in Nevada include the Western naucorid (Ambrysus mormon), Pahranagat naucorid (Pelocoris biimpressus shoshone) (Parker et al. 1997), and Moapa Valley pyrg (Pyrgulopsis carinifera) (Albrecht et al. 2008). The latter two species are also listed as “at-risk” by the Nevada Natural Heritage Program.
The overall condition of the Warm Springs Aquatic Assemblage is considered “poor” due to water withdrawals, entrenchment, and exotic species (Provencher et al. 2005). Past and ongoing stream restoration has improved conditions, but until the Moapa dace population has rebounded, restoration efforts will continue. On the WSNA, stream reaches and spring heads have been identified and prioritized by the Biological Advisory Committee for restoration. The Lower Pederson has been rechanneled, and the system is currently being improved for dace habitat by installing drift stations and augmenting natural revegetation. Of the nine upper Muddy Valley stream segments identified for restoration by Provencher et al. (2005), four reside almost exclusively on the WSNA, and one other is shared with the Moapa Valley National Wildlife Refuge. The remaining reach segments would not be considered part of the Warm Springs Aquatic Assemblage but rather the Muddy River Aquatic Assemblage.
Species for Management Consideration
Moapa dace (Moapa coriacea)*
Moapa White River springfish (Crenichthys baileyi
Moapa naucorid (Limnocoris moapensis)*
Moapa riffle beetle (Microcylloepus moapus)
Moapa pebblesnail (Pyrgulopsis avernalis)*
Moapa Warm Springs riffle beetle (Stenelmis moapa)*
Grated tryonia (Tryonia clathrata)*
Moapa Valley pyrg (Pyrgulopsis carinifera)
Western naucorid (Ambrysus mormon)
Pahranagat naucorid (Pelocoris biimpressus shoshone)
* Recovery Plan for the Rare Aquatic Species of the
Muddy River Ecosystem (USFWS 1996)
Other Rare Aquatic Species
Moapa White River springfish (Crenichthys baileyi moapae)As the most abundant native fish on WSNA and the entire upper Muddy River, the Moapa White River springfish is the least threatened. The springfish is able to tolerate high water temperatures and low dissolved oxygen making the thermal springs and streams on WSNA ideal habitat. The upper Muddy River is the source population for those downstream. The Moapa White River springfish is commonly 1.5-2.0 inches in length and typically lives three years. Springfish reproduce year-round, with peak reproduction occurring in the spring when food sources, such as algae and aquatic insects are most readily available. Protecting existing thermaland flow qualities of the upper Muddy River springs and reaches, and controlling introduced fishes is important for this species.
Several aquatic invertebrates identified for management consideration are known to reach their maximum prevalence in the Warm Springs Aquatic Assemblage. The Recovery Plan for the Rare Aquatic Species of the Muddy River Ecosystem (1996) recognizes two snails and two insects as species of concern. They are all endemic to the Muddy River and known to occur on WSNA. The Clark County Multiple Species Habitat Conservation Plan (2000) identifies one additional snail and two additional aquatic insects as high priority species for evaluation. An aquatic invertebrate survey performed on WSNA by Albrecht et al. (2008) identified three additional rare insect species. The Nevada Natural Heritage Program adds another aquatic insect purported as occurring on WSNA on their watch list.
The Amargosa naucorid (Pelocoris shoshone amargosus) may have mistakenly been thought as occurring in the Muddy River due to referenced use of the common name “Amargosa naucorid.” Parker et al. (1997) lists P. shoshone as occurring in thermal springs of the upper Muddy River, but no mention is made of the subspecies. The Recovery Plan for the Rare Aquatic Species of the Muddy River Ecosystem (USFWS 1996) identifies Pelocoris shoshone shoshone as a species of concern on their recovery list but applies the common name as Amargosa naucorid. Huillet (1998) did not sample Pelocoris shoshone but listed Pelocoris biimpressus shoshone indicating taxonomic confusion among literature citing Pelocoris in the Muddy River.
Pelocoris biimpressus shoshone was also encountered by Sada and Herbst (1999). Albrecht et al. (2008) listed a sampled naucorid as Pelocoris biimpressus (?shoshone) suggesting uncertainty as to the identification at the subspecies level. It is apparent that all variations are the same species – hereafter referred to as the Pahranagat naucorid(Pelocoris biimpressus shoshone).
Aquatic Invertebrate Recovery
The general belief is that restoring stream habitat for Moapa dace will be beneficial for all aquatic invertebrates. Competition theory suggests niche separation will occur across the breadth of existing niches. Single species management can easily favor one group of species over another. Due to the diversity of rare aquatic species in the upper Muddy River, aquatic invertebrate sampling will be implemented for all stream restoration projects. Restoration projects will also give due consideration to habitat heterogeneity in design and implementation.
Stream restoration efforts require provisions for the full suite of endemic and rare aquatic macroinvertebrates at WSNA. Because the different species prefer different flow velocities, water depths, substrates, vegetation, coarse particulate organic matter, and bank structure, it is imperative to maintain a diversity of aquatic habitat parameters throughout the stream reaches. Sada and Herbst (1999) recommend maximizing habitat diversity to benefit the entire community. Focusing restoration work solely on fishes may negatively impact aquatic invertebrates. Community stability, resistance, and resilience are positively related to species diversity
The occurrence of rare aquatic invertebrates throughout the headwaters of the Muddy River within the Warm Springs Aquatic Assemblage indicates broad distribution with the exception of the Pahranagat naucorid which was only sampled in 3 of 11 headwater reaches (Albrecht et al. 2008). It was located in the Apcar, South Fork, and middle main stem reaches. Previous sampling by Sada & Herbst (1999) did not encounter it in the South Fork but did locate it in the Plummer and Pederson streams. They noted a habitat preference for slow backwater with fine substrates and sparse vegetation. Huillet (1998) mentioned the naucorid as commonly collected. The distribution of this species appears greater than what was sampled by Albrecht et al. (2008) and is likely an artifact of sample methodology.