Banff Springs snail (Physella johnsoni) COSEWIC assessment and status report: chapter 13

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Technical Summary

Physella johnsoni

Range of Occurrence in Canada: Alberta

Demographic Information

Number of mature individuals in each population

Extent and Area Information

Quantitative Analysis

Threats (actual or imminent, to populations or habitats)

In order of certainty and severity (highest to lowest) the following threats have been identified (Table 2 and Limiting Factors and Threats) and occur naturally (N) or by humans through facility operations (FO) or other actions (Hu):

1. Thermal water flow stoppages (N)
2. Thermal water flow reductions / fluctuations (N and FO)
3. Thermal water flow redirections (N, FO)
4. Limited or low quality habitat (N, FO)
5. Soaking and swimming (Hu)
6. Population lows and genetic inbreeding (N)
7. Trampling and other local disturbances (Hu)
8. Limb-dipping (Hu)
9. Stochastic events (N)
10. Others (predation, competition, collecting, twitch-ups) (Hu, N)

Rescue Effect (immigration from an outside source): No

Current Status

COSEWIC: Threatened (April 1997)
COSEWIC: Endangered (May 2000)
COSEWIC: Endangered (April 2008)
Global Status: G1
Alberta Status: S1

Status and Reasons for Designation

Reasons for Designation: This is a Canadian endemic species with its distribution entirely within the upper reaches of fewer than 5 separate thermal springs locations in Banff National Park, Alberta. These springs comprise a single population, which makes it very susceptible to a catastrophic event. These short-lived animals undergo natural annual fluctuations of over two orders of magnitude. All thermal springs historically or currently occupied by this species have been impacted by human development. These snails are habitat specialists requiring a steady supply of warm thermal spring water containing a high concentration of dissolved minerals and a complex microbial community that provides food and habitat. The species and its habitat are currently protected from disturbance and destruction under Species at Risk Act and the Canada National Parks Act, but illegal activities such as soaking in thermal waters, which can crush snails and eggs and disturb habitat, are ongoing. The increase in frequency of springs drying due to climate change, which has been observed in the past decade, is believed to be an important threat to this species’ survival. However, the species is closely monitored by Parks Canada.

Applicability of Criteria

Criterion A (Decline in Total Number of Mature Individuals):
Does not apply. There is no current evidence that the population is declining or will decline over the next 10 years.

Criterion B (Small Distribution Range and Decline or Fluctuation):
Meets B1ac(iv)+2ac(iv) 1: EO = 0.177 km² (< 5000 km²) – Endangered 2: AO = 0.0006 km² (< 500 km²) – Endangered a: Population severely fragmented and found in 3 locations (< or = 5, Endangered), c(iv): Extreme fluctuations of numbers of individuals.

Criterion C (Small and Declining Number of Mature Individuals):
Does not apply. The number of individuals, most mature, varies annually (1 561–33 915) but the population overall has not declined.

Criterion D (Very Small Population or Restricted Distribution):
Meets D2 for Threatened. The species has a very restricted AO (5 km²), with 3 locations forming 1 population; it is a habitat specialist requiring geothermally regulated water, a high concentration of dissolved minerals and a complex microbial community. The population is of limited extent and prone to the effects of human activities or stochastic events within a very short time period.

Criterion E (Quantitative Analysis):
A quantitative analysis was done and the probability of extinction in the wild over the next 40 years (based on the 5 original locations) was zero. The probability of extirpation of individual sub-populations was higher: Lower Middle springs 27%, Cave 21%, Basin 4%, Upper Cave and Basin 3%, Lower Cave and Basin 29%.