Hotwater physa (Physella wrighti) COSEWIC assessment and upate status report: chapter 11
Technical Summary
Physella wrighti
Hotwater Physa – Physe d’eau chaude
Range of Occurrence in Canada:
British Columbia
Demographic Information
Generation time (average age of parents in the population)
Unknown
Population trend and dynamics
Observed percentage of reduction in total number of mature individuals over the last 10 years.
Unknown
Projected percentage of reduction in total number of mature individuals over the next 10 years.
Unknown
Observed percentage reduction in total number of mature individuals over any 10 year period, over a time period including both the past and the future.
Unknown
Are the causes of the decline clearly reversible?
Are the causes of the decline clearly understood?
Are the causes of the decline clearly ceased?
Observed trend in number of populations
Stable
Are there extreme fluctuations in number of mature individuals?
Unknown
Are there extreme fluctuations in number of populations?
No
Number of mature individuals in each population
Values for different lengths of Alpha stream sampled
- 1,426 (Sep 1997)
- 5,186 (Aug 2000)
- 1,426 (Aug 2006)
Grand Total: Number of mature individuals in the total population unknown
Extent and Area Information
Estimated extent of occurrence (km²)
0.02 km² - 16,310 m², 2006 survey area measured using scale on park map
Observed trend in extent of occurrence
Stable
Are there extreme fluctuations in extent of occurrence?
No
Estimated area of occupancy (km²) using 1x1 km² grid
1 km² - Actual AO based on habitat occupied: ~ 4.6 m²
Inferred trend in area of occupancy
Stable
Are there extreme fluctuations in area of occupancy?
No
Is the total population severely fragmented?
No
Number of current locations
1
Trend in number of locations
Stable
Are there extreme fluctuations in number of locations?
No
Observed trend in area of habitat
Unknown
Quantitative Analysis
Not available
Threats (actual or imminent, to populations or habitats)
- Recreational use of the hotsprings continues
- The small population size and very limited geographic distribution makes this species extremely vulnerable to disturbance brought about by anthropogenic activities.
- Rapid temperature change could occur in Alpha Stream if the outflow from Alpha Pool were diverted, exposing species to potentially lethal ambient air temperature. This would be most likely to occur through stochastic events or through the actions of recreational users altering the dam or creating alternative outflows.
- Trampling caused by park users exploring Alpha Stream
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
Not applicable - Species is endemic to the Liard Hotsprings complex
Is immigration known or possible?
No
Would immigrants be adapted to survive in Canada?
Not applicable
Is there sufficient habitat for immigrants in Canada?
Not applicable
Is rescue from outside populations likely?
No
Current Status
COSEWIC: Endangered, April 2008
Status and Reasons for Designation
Status: Endangered
Alpha-numeric code: B1ac(iv)+2ac(iv)
Reasons for Designation: This small snail is an endemic species living only within the hotsprings complex located in Liard River Hotsprings Provincial Park in British Columbia. The population is small, numbering fewer than 10,000 individuals and occupies an extremely restricted habitat around the margins of two pools and an outlet stream. Population size is believed to fluctuate by at least an order of magnitude in this short-lived snail (~1 year lifespan). The species is a habitat specialist requiring geothermally regulated water and substrates near the water/air interface in areas of no current. The hotsprings complex has been in use by humans for over 200 years. The species has survived structural modification and maintenance of the pools, the introduction of foreign substances such as soaps and shampoos, and trampling. However, a single event such as abrupt changes in water flow, chemical contamination or introduction of exotic species, could significantly affect persistence of this snail.
Applicability of Criteria
- Criterion A: Not applicable. There is no evidence that the population is declining or will decline over the next 10 years.
- Criterion B: Meets B1: EO ~ 0.02 km² (< 5,000 km²) for Endangered, and B2: 1 km² (< 500 km²) for Endangered a: Number of locations, 1 (less than or equal to 5, Endangered), c(iv): extreme fluctuations in mature individuals observed annually in a species that is believed to have a lifespan of ~ 1 year.
- Criterion C: Not applicable. The number of individuals is most likely > 2,500 but < 10,000, but the number of mature individuals is not believed to be in decline at present nor is it projected to decline in the next 10 years.
- Criterion D: Meets D2 for Threatened because: AO 1 km² (< 20 km²), there is only 1 locality (less than or equal to 5), the species is an habitat specialist, the locality is heavily used by humans for recreation, and a single catastrophic event could eliminate the entire population.
- Criterion E: Does not apply; not available.
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