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Round Pigtoe (Pleurobema Sintoxia)

Technical Summary

Pleurobema sintoxia

Round Pigtoe
Pleurobème écarlate

Range of occurrence: Southwestern Ontario

Extent and Area Information

Extent of occurrence (EO) (km2)
By drawing polygons in Arcview, historical EO was 26 592 km2, the current EO is 12 360 km2
Lake St. Clair, Sydenham River, Middle Thames River, Lower Grand River ~12 400 km2
Specify trend in EODecline (~54%)
Are there extreme fluctuations in EO?No
Area of occupancy (AO) (km2)8 km2 in Lake St. Clair delta, 0.5 km reach of Bear Creek/North Sydenham River (~0.01 km2), 75 km of East Sydenham River (~2 km2), 0.5 km reach of Middle Thames River (~0.02 km2), 45 km reach of lower Grand River (~5 km2).  Total = ~15 km2.
Specify trend in AODecline
Are there extreme fluctuations in AO?No
Number of known of inferred locations5
Specify trend in #Decline
Are there extreme fluctuations in number  of locations?No
Specify trend in area, extent or quality of habitatDecline

Population Information

Generation time (average age of parents in the population)Unknown (estimate 10 years)
Number of mature individualsUnknown
Total population trendDeclining
% decline over the last/next 10 years or 3 generationsUnknown
Are there extreme fluctuations in number of mature individuals?No
Is the total population severely fragmented?Yes, no mixing between populations in different watersheds
Specify trend in number of populationsDecline
Are there extreme fluctuations in number  of populations?No
List each population and the number of mature individuals in each:Total population ~200 000 but # of mature individuals unknown

Threats (actual or imminent threats to populations or habitats)

- Zebra Mussels (invasive species).
- Habitat loss and degradation due to agricultural impacts (siltation, nutrient loading, loss of riparian vegetation), urbanization, and municipal and industrial pollution.

Rescue Effect (immigration from an outside source): None

Status of the outside population(s)?Largely stable
Is immigration known or possible?No
Would immigrants be adapted to survive in Canada?Likely (genetic testing required)
Is there sufficient habitat for immigrants here?No
Is rescue from outside populations likely?No

Quantitative Analysis


Status and Reasons for Designation

Alpha-numeric code:
A2ace; B2ab(i,ii,iii,iv)
Reason for designation:
Species limited to a small area of occupancy in the Lake St.Clair and three watersheds in southern Ontario with continuing declines in habitat area, extent and quality. Threats include urban, industrial and agricultural development and irreversible impacts from zebra mussels in Lake St. Clair, with potential threats from introduction of zebra mussels in impoundments in the Sydenham River.

Applicability of Criteria

Criterion A (Declining Total Population):
population size reduction estimated from 54% decline in extent of occurrence (and probably area of occupancy), continuing declines in quality and extent of habitat, and effects of introduced taxa (Endangered, A2a,c,e).
Criterion B (Small Distribution, and Decline or Fluctuation):
qualifies for threatened under B1 (Extent of Occurrence < 20 000 km2) but Endangered for the following criteria: species has a small area of occupancy (<15 km2), population is severely fragmented and there are continuing declines in: Extent of Occurrence; Area of Occupancy; area, extent and quality of habitat; number of locations (Endangered B2a,b(i-iv)).
Criterion C (Small Total Population Size and Decline):
number of mature individuals unknown.
Criterion D (Very Small Population or Restricted Distribution):
qualifies for Threatened under D2, small area of occupancy.
Criterion E (Quantitative Analysis):
unable to estimate probability of extinction.