Assessment of Springsnail Abundance at Ash Meadows National Wildlife Refuge

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USGS Nevada Water Science Center (NVWSC), in cooperation with the U.S. Fish and Wildlife Service (FWS), is performing a systematic field investigation designed to survey the status of springsnails and the condition of the springs in which they occur at Ash Meadows National Wildlife Refuge (AMNWR). 

Groundwater withdrawals and other anthropogenic alterations that reduce springflow negatively affect all wildlife, but especially obligate aquatic organisms with low vagility and limited distributions. At AMNWR, two species of springsnail went extinct in the 20th century due to habitat alteration at springs. AMNWR currently has 10 endemic species of springsnails, contributing to the one of the highest levels of endemism per unit area in the United States. As springsnails (Hydrobiidae) are characterized by extreme endemism, they represent a significant component of the biodiversity in southwestern deserts.

The mission of the FWS and the Endangered Species Act (ESA) is to protect such imperiled forms, necessitating the best available science to inform management decisions. In this region, FWS has been petitioned to investigate the status of springsnail abundance and distribution in an upcoming Species Status Assessment (SSA). The information from this project is crucial to this document, and the subsequent decisions that potentially afford protection under the ESA. 

NVWSC scientists collected detailed information on the abundance and habitat condition of 10 species of hydrobiid springsnails endemic to the Ash Meadows region. They used established and comparable methods to assess springsnail abundance, habitat condition, stressors acting on the habitat, and water quality parameters. Because springsnails are typically endemic to small geographic areas, the ability to compare this data to previous reports (e.g.; Sada 2017) affords an opportunity to provide a range-wide perspective on hydrobiid conservation. Broader implications of this research include:

USGS Nevada Water Science Center Scientists evaluating springsnails from a spring sample

USGS Nevada Water Science Center Scientists evaluating springsnails from a spring sample in Ash Meadows National Wildlife Refuge. 

(Public domain.)

  • The study will provide a better understanding of spring ecosystems useful to manage associated species, as AMNWR supports 26 endemic species, including many obligate aquatic taxa, e.g., Ash Meadows naucorid (Threatened), spring-loving centaury (Threatened), Warm Springs pupfish (Endangered), Ash Meadows Amargosa pupfish (Endangered), and Ash Meadows speckled dace (Endangered).
     
  • The collaborative aspects of this study will further promote partnerships among regional managers at USGS, FWS and BLM for future recovery actions.
     
  • This project builds upon recent work conducted on behalf of the FWS (Sada 2017) to characterize populations of 16 species of springsnail across the Great Basin. Conducting additional studies such as this one to supplement the work of Sada (2017) could eventually result in a near-complete assessment of springsnail species and localities across the region, with all data collected using the same methods to ensure comparability. 

Springsnail populations were assessed using methods described in Sada (2017). Initially, springsnails were identified to genus. While hydrobiids are superficially similar, the genera Tryonia and Pyrgulopsis can be distinguished by shell morphology after technical training, and will be classified for this study in situ. Habitat parameters measured in the field include stream width, depth, water velocity, vegetative cover on the banks and emergent from the stream, as well as the distributional extent of each genus downstream.

Springsnail abundance was quantified by catch per unit effort (CPUE) using the quadrat approach as follows:

  • At each site, five to 20 transect locations (depending on springbrook length) were identified. If width of the springbrook permits, springsnails were enumerated at each of three quadrat locations: channel center, near-bank left, and near-bank right.
     
  • At each quadrat location, a 10 cm x 10 cm wire-frame device was placed on the springbrook bed. The sediment and vegetation within the quadrat was roiled for three seconds, sweeping the springsnails into a sieve.
     
  • The springsnails were transferred from the sieve to a water-filled tray, where the number of each genus (Pyrgulopsis or Tryonia) were counted. After counting, the springsnails were returned to the spring as quickly as possible.
Table of springsnail species in Ash Meadows National Wildlife Refuge

Spring condition was assessed. The stressor observations were collected following the methods of Sada (2017), with modifications appropriate for FWS needs. Categories of potential stressors include water diversion, drought, invasive species and ungulates. Each stressor was assigned a numerical score based on stressor immediacy, intensity, percent habitat impacted and the anticipated response of the springsnails. 

Water quality parameters (temperature, dissolved oxygen concentration, pH and specific conductivity) were measured at the spring source. 

References Cited

Sada DW. 2017. Environmental and Biological Factors Influencing Great Basin and Surrounding Areas Springsnail (Gastropoda: Rissooidea) Abundance and Distribution. Report to U.S. Fish and Wildlife Service, Reno and Southern Nevada Fish and Wildlife Offices, Reno and Las Vegas, 675 pp.