|Listed||December 14, 1992|
|Description||A living fossil with a narrowly elongate shell with 5.5 to 6 whorls.|
|Habitat||Free-flowing cool spring alcoves.|
|Food||Plant debris or diatoms.|
|Reproduction||Lays eggs on the bottom of large rivers, probably early in the growing season.|
|Threats||Water quality degradation; New Zealand mudsnail.|
The Idaho springsnail is a relict of the Pleistocene Lake Idaho and is considered a "living fossil." It has a narrowly elongate shell reaching a length of 0.1-0.2 in (5-7 mm). This species is observed to have 5.5 to six whorls. The calcareous portion of the shell lacks a color pattern while the periostracus may or may not have a pattern. The aperture is holostomatous, without notches, canals, siphonal grooves, or denticulations. The foot is strong, mobile, truncate anteriorly and retractile. It bares lateral auriculate lobes and a mucous groove across the anterior edge; it is rounded and has a posterior pedal gland. The snail moves generally by gliding. The head bears filiform tentacles; the eyes are usually lateral at the outer bases of the tentacles. Body coloration is usually grayish-black. The species has also been classified as Pyrgulopsis idahoensis.
This species is restricted to a diet of diatoms and plant debris which grazes along mud surfaces, rocky surfaces and macrophytes.
The Idaho springsnail is found only in permanent, flowing waters of the mainstem Snake River. This snail is not found in any of the Snake River tributaries or marginal springs. It occurs on mud or sand associated with gravel to boulder-size sub-stratum. This species often attaches itself to vegetation such as common associate Potamogeton, in riffles.
In addition to the Idaho springsnail, the Snake River and its tributaries provide essential habitat to sensitive native species such as the Shortface lanx or giant Columbia River limpet, the Shoshone sculpin, the Bliss Rapids snail, the Snake River physa snail, the Banbury Spring lanx, and the Utah Valvata snail. These areas contain some of the last mainstem Snake River habitats with the full range of native molluscan species present, and represent a unique aquatic community.
Fossil records of the Idaho springsnail indicate this species to have been distributed throughout much of southern Idaho. This species is currently distributed discontinuously in the mainstem Snake River from sites from C. J. Strike Reservoir and upstream to Bancroft Springs in Owyhee and Elmore Counties, Idaho.
The free-flowing, cool water environments required by this species have been impacted by and are vulnerable to continued adverse habitat modification and deteriorating water quality from hydroelectric development, peak-loading effects from existing hydroelectric project operations, water withdrawal and diversions, water pollution, and inadequate regulatory mechanisms.
Water quality degradation continues from increased water use and withdrawal, aggravated by recent drought-induced low flows. The 121-mi (195-km) stretch of the Snake River is impacted by agricultural return flows; runoff from between 500 and 600 dairies and feed lots; effluent from over 140 private, state, and Federal fish culture facilities; and point source (e.g. municipal sewage) discharge. The ultimate impact of these factors are increased nutrient loads and concentrations which adversely affect the lotic fauna. Nutrient loading contributes to dense blooms of free-living and attached filamentous algae, which the species cannot utilize. This algae will often cover rock surfaces, effectively displacing suitable snail habitats and food resources.
A more recent threat is the discovery of the New Zealand mudsnail in the middle Snake River. The eurytopic mudsnail is experiencing explosive growth in the river and shows a wide range of tolerance for water fluctuations, velocity, temperature and turbidity. The mudsnail species seems to prefer warmer, polluted waters over pristine cold spring environments.
Conservation and Recovery
The U. S. Fish and Wildlife Service published a Recovery Plan for the Idaho springsnail and other endangered mollusks in the Snake River Basin in 1992. The conservation of this endangered snail requires the protection of its surviving critical habitat in the mainstem Snake River from impoundment, diversion, pollution, and other threatening activities. Moreover, where possible, habitat quality must be improved if the Idaho springsnail and other endangered species are to recover. Its populations should be monitored, and research undertaken into its biology and habitat needs.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
Snake River Basin Fish and Wildlife Office
1387 South Vinnell Way, Suite 368
Boise, Idaho 83709-1657
Telephone: (208) 378-5243
Fax: (208) 378-5262
U. S. Fish and Wildlife Service. 14 December 1992. "Endangered and Threatened Wildlife and Plants: Determination of Endangered or Threatened Status for Five Aquatic Snails in South Central Idaho." Federal Register 57 (240): 59244-59257.
U. S. Fish and Wildlife Service. 1995. "Snake River Aquatic Species Recovery Plan." Snake River Basin Office, Ecological Services, Boise, Idaho.