Lake Erie watersnake COSEWIC assessment and status report: chapter 11
Technical Summary
Nerodia sipedon insularum
Lake Eriewatersnake – couleuvre d'eau du lac Érié
Range of Occurrence in Canada:
Ontario
Extent and Area Information
Extent of occurrence (EO) (km²)
188 km² Calculation based on data from King et al. (1997)
Specify trend in EO
Declined from historical records
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²)
24 km² Calculation based on data from King et al. (1997)
Specify trend in AO
Declining from historical records
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations
Current locations restricted to four islands in western Lake Erie
Specify trend in #
Declining, but may have stabilized
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
Declining quality and extent
Population Information
Generation time (average age of parents in the population)
6+ years
Number of mature individuals
Range 365-1665
Total population trend:
Declining from historic population
% decline over the last/next 10 years or 3 generations.
Unknown
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
Yes
Specify trend in number of populations
Declining (from 6 to 4 islands and also declined within islands)
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each:
- Ontario: 4 populations;
- Pelee Island ~410 (95% CI = 200-1500) individuals
- Middle Island ~ 50 individuals
- Hen Island < 15 individuals
- East Sister Island ~ 100 individuals
- Total mean population ~ 565
Threats (actual or imminent threats to populations or habitats)
- Loss of habitat due to shoreline and inland development and quarrying
- Increased rates of road mortality due to expanding tourism-based development (increased road construction and usage by human inhabitants)
- Increased predator populations with the increase in human activity (raccoons)
- Persecution by people
- Potential threat due to bioaccumulation of environmental contaminants (PCBs and other organochlorines)
- Small populations that are more susceptible to demographic and ecological stochasticity
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
USA:
- Listed as threatened under the Federal List of Endangered and Threatened Wildlife
- Listed as endangered by the state of Ohio and the Ohio Division of Parks and Recreation
Is immigration known or possible?
Known but infrequent
Would immigrants be adapted to survive in Canada?
Yes
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
Not likely to be important
Current Status
- COSEWIC: Endangered 1991, Endangered 2006
- Ontario: Endangered-regulated
- Ohio: Endangered
Status and Reasons for Designation
Status: Endangered
Alpha-numeric code: B 1 ab(iii,iii,v) + 2 ab(ii,iii,v). C2a(i)
Reasons for Designation: It has a small population, likely fewer than 1000 adults, confined to four small islands in western Lake Erie. Threats, which include loss of its shoreline habitats, mortality on roads, and destruction of hibernacula by quarries and construction, are increasing. Although persecution by people may be levelling off, it is still a significant threat to these snakes.
Applicability of Criteria
- Criterion A: (Declining Total Population): Not applicable
- Criterion B: (Small Distribution, and Decline or Fluctuation): The EO(B1) and AO(B2) are both well below the threshold for Endangered. There are only 4 known populations (a) and there is decline in b(ii,iii,v).
- Criterion C: (Small Total Population Size and Decline): Qualifies as Endangered (C2a(i))
- Criterion D: (Very Small Population or Restricted Distribution): Qualifies as Threatened (D1)
- Criterion E: (Quantitative Analysis): NA
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