Evaluating Potential Refugia for the Endangered Mohave Tui Chub

Science Center Objects

The USGS Nevada Water Science Center (NVWSC), in partnership with the National Park Service (NPS), is evaluating and monitoring the basic water quality and sediment chemistry of two proposed refugia and three established habitats for the endangered Mohave Tui Chub over the course of the year. NVWSC will also compare and evaluate findings to U.S. Environmental Protection Agency screening levels and published tolerances to determine if sites are suitable for tui chub introduction.

The Mohave Tui Chub (Siphateles bicolor mohavensis, here abbreviated as MTC) is a member of the minnow family native to the Mojave River in California. The MTC was extirpated from the Mojave River by habitat degradation and hybridization and/or competition with the arroyo chub, introduced as a bait fish in the 1930s. By the early 1950s, the only remaining population of the MTC was found in MC Spring near Zzyzx (also referred to as Soda Springs), just inside the western border of Mojave National Preserve (MOJA)1. In 1970, the MTC was listed as endangered by the U.S. Fish and Wildlife Service (USFWS) and a Recovery Plan for the species was developed in 1984.

Mohave Tui Chub

Mohave Tui Chub (Credit: Joe Ferreira, California Department of Wildlife)

The Recovery Plan lists 14 attempts at establishing new populations made between 1939 and 1981, only one of which is still extant today. Inadequate water quality, limited water quantity, and floods are considered the primary reasons behind the large number of failures. In the 1950s, two new sub-populations of MTC were established at Zzyzx, within a few hundred meters of MC Spring: in Lake Tuendae (a spring-fed ornamental lake) and West Pond (an excavated pit, also referred to as Three Bats Pond). The West Pond population died off in 1985 due to elevated salinity.

According to the plan, the MTC can be delisted once it is reestablished in the Mojave River, an outcome that is viewed as impossible in the foreseeable future due to the continued presence of introduced fish species and changes in habitat. The plan also provides for downlisting of the MTC from “endangered” status to “threatened” status once six independent populations had been established in the vicinity of the broader Mojave River drainage.

Currently, five populations exist that meet the criteria of the Recovery Plan:

  • Lark Seep at China Lake Naval Weapons Center (established 1972),
  • Camp Cady Wildlife Area (established 1986),
  • Lewis Center for Educational Research in Apple Valley (established 2008),
  • Morning Star Mine pit lake on MOJA (established 2011), and
  • MC Spring and Lake Tuendae at Zzyzx.

One more population needs to be established to meet the down-listing requirements given in the Recovery Plan. Very few aquatic environments in Mojave River drainage are capable of sustaining a stable MTC population. Two potential refugia outside of the Mojave River flood plain with perennial sources of water have been identified within the boundaries of MOJA: Rainbow Wells Pond and West Pond. 

USGS scientist collecting water-quality samples from MC Spring, Mojave National Preserve, Nev.

USGS scientist collecting water-quality samples from MC Spring, Mojave National Preserve, Nev. (Public domain.)

To assess the habitat suitability of the two potential refugia for the MTC, water quality will be evaluated and monitored on a quarterly basis over the course of a year. Water quality will be monitored at a total of five sites:

  • two potential refugia (Rainbow Wells Pond and West Pond) and
  • three existing MTC habitats in MOJA (MC Spring, Lake Tuendae, and Morning Star Mine).

The other two existing MTC populations (Lark Seep and Lewis Center) will not be monitored due to budgetary constraints.

USGS scientist collecting water-quality data at Rainbow Wells Pond, Mojave National Preserve, Nev.

USGS scientist collecting water-quality data at Rainbow Wells Pond, Mojave National Preserve, Nev. (Public domain.)

Water and sediment samples will be collected and analyzed for:

  • Nutrients and major ions. Samples will be collected quarterly at the five ponds.
  • Field water-quality parameters. Depth profiles of temperature, pH, specific conductance, and dissolved oxygen will be collected quarterly at the five ponds.
  • Dissolved metals and cyanide. Quarterly samples will be collected at Rainbow Wells pond and Morning Star Mine (the two sites with prior mining activity). The samples will be analyzed for cyanide and 23 metals, including lead, zinc, arsenic, copper, aluminum, and mercury.
  • Volatile organic compounds (VOCs). One surface water sample will be taken from Rainbow Wells Pond to determine the presence and concentrations of VOCs, which can indicate contamination from gasoline, solvents, and other chemicals.
  • Hydrogen sulfide. Hydrogen sulfide samples will be collected quarterly from Rainbow Wells Pond, the only site where hydrogen sulfide has been observed. Spectrophotometer analysis in the field will provide accurate low concentration detections for the samples.

Water temperature will be monitored continuously at Rainbow Wells Pond and West Pond. The maximum temperatures and spawning season temperatures from these records will be compared to the temperature requirements of the MTC.

Sediment samples will be collected from Rainbow Wells Pond to assess whether metals contamination may have made the pond unsuitable habitat for the MTC. Samples will be analyzed by the laboratory for total metals (including lead, copper, and mercury). 

A Criterion Continuous Concentration will be calculated for copper concentrations in Rainbow Wells Pond that is protective of aquatic life using the EPA’s Biotic Ligand Model, a tool for the evaluation of the toxicity of metals that considers how water chemistry affects speciation and bioavailability.

 

 

References

1 Woo, D., and D. Hughson. 2003. Zzyzx mineral springs-cultural treasure and endangered species aquarium. George Wright Society Conference. San Diego, California.