The ecological life history of the Bruneau Hot Springs Snail (Pyrgulopsis bruneauensis). Final report

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The Bruneau Hot Springs Snail (Pyrgulopsis bruneauensis) is an endemic, potentially endangered species inhabiting a complex of related hot springs near the Bruneau River south of Mountain Home, Idaho. The snail's habitat has been diminished considerably in recent years due to agriculture-related groundwater mining in the area. As a result, the snail has been proposed for listing as an endangered species (USDI 1985). Temperature appears to be the predominant factor influencing life history. Reproduction occurs year around at suitable temperatures (20–35 °C). Sexual maturity occurs in approximately 2 months, with maximum size reached at 4 months. Sex ratio was approximately 1:1. Snails are found in most current regimes available. They prefer warmer waters and are little affected directly by light siltation, although considerable habitat has been lost in recent years due sedimentation. The known population may have declined by 50% (100% locally at Indian Bathtub for example) based on comparisons with previous investigators' population estimates (Taylor 1982). Snails at different sites responded similarly to environmental factors such as water temperature. However, given the different characteristics of the sites (distance from spring source, physical structure, temperature, and flow regime), seasonal trends were different. Due to their different temperature regimes, the predominating factors affecting abundance varied among sites. Discharge measured in Hot Creek fluctuated seasonally and was the best predictor of snail abundance at site 1, while chlorophyll a/c ratios and temperature were the best predictors for sites 2 and 3, respectively. Within the temperature limits for survival, chlorophyll ratios were the best predictors of abundance for combined study site data. Reproduction was severely reduced at temperatures greater than 35 °C and less than 24 °C. Growth was reduced at cooler temperatures. Therefore sites having marginally lower temperature may provide suitable snail habitat only if they undergo seasonal warming, allowing sexual maturity and reproduction to occur.

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ELECTRONIC FILE - Zoology

[SWAP cites the THESIS, not this report?]