Science Advisory Report 2009/072

Recovery potential assessment for hotwater physa (Physella wrighti)

Summary

• Hotwater Physa is found within the hot springs complex of the Liard River Hot Springs Provincial Park. The snail is present in two hot springs pools known as the Alpha and Beta pools, the outlet of the Alpha pool (Alpha stream) and a warm-water swamp.
• Survey estimates of population size are likely biased low and the true population abundance potentially is in the tens of thousands.
• The semelparous life history strategy, short generation time and evidence from other freshwater snail species implies that the productivity is moderate to high.
• The species requires an aquatic environment that maintains a water temperature between 23-40ºC year round. The snails are found on substrates both above and below the water level. The preferred habitat is Chara sp. mats but they also are found on mats of green alga, woody debris (logs, bark, leaves), and soil/stream bed substrates.
• Factors affecting snail habitat represent the main threats to the hotwater physa population. Recreational activities pose the greatest present threat through habitat impacts and direct mortality to individual snails. Bathers in the hot springs pools may also contribute to population decline by exposing the snails to foreign substances such as soaps, lotions, and oils. The risk posed by recreational activities is considered moderate given that the population has persisted at least since 1973 when the Provincial Park opened.
• The introduction of invasive species to this endemic population is likely to have grave consequences and represents a high conservation risk.
• A collapse of the dam or weir structure in Alpha Pool would cause a change in the flow regime of the water entering the Alpha stream and on the water level of the Alpha pool. A flash flood of water could have a devastating effect on the snail population. Although a flash flood would cause a high impact, the likelihood of occurrence is considered to be low.
• Large scale changes to the water flow through the region would occur if the proposed Liard River Hydroelectric Project was initiated. The project would flood the entire hot springs complex with cooler water and therefore the impact of the threat is high. The likelihood of the threat depends on policy direction but presently the power proposals are dormant.
• Drilling activities during oil and gas exploration outside the park could potentially interfere with the underground thermal source. The source of the hot springs has not been clearly identified but it is believed to be located outside of the park boundaries. Drilling into the source water may affect the flow of hot water within the Park. Without knowledge of the boundaries of the thermal source the impact of drilling is considered to be high.
• Efforts to inform and educate park users of the ecological sensitivity of the area would help reduce the threats to habitat as well as the population of hotwater physa. This information could be in the form of better signage, interpretive programs, and greater monitoring by park staff at the pool.
• Assuming the intrinsic rate of growth r_m ranges from 0.2-0.5 per year and an equilibrium population size of 10,000 mature snails suggests a precautionary, sustainable removal rate of roughly 5-15% or 500-1500 animals per year.

Complete document (PDF, 147 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.