Blue-grey taildropper slug (Prophysaon coeruleum) COSEWIC assessment and status report: chapter 13

Technical Summary

Prophysaon coeruleum

Blue-grey Taildropper slug
Limace-prophyse bleu-gris

Range of Occurrence in Canada: Vancouver Island, British Columbia


Extent and Area Information

Extent of occurrence (EO)(km2)
Minimum polygon method from distribution records in Canada up to Aug 2004

About 150 km2


Specify trend in EO

Unknown


Are there extreme fluctuations in EO?

Unknown


Area of occupancy (AO)(km2)

< 5 km2


Specify trend in AO

Unknown


Are there extreme fluctuations in AO?

Unknown


Number of known or inferred current locations

5


Specify trend in #

Unknown


Are there extreme fluctuations in number of locations?

Unknown


Specify trend in area, extent or quality of habitat

Declining



Population Information

Generation time (average age of parents in the population)

Ca. 1 year


Number of mature individuals

Unknown


Total population trend

Unknown


% decline over the last/next 10 years or 3 generations

Unknown


Are there extreme fluctuations in number of mature individuals?

Unknown


Is the total population severely fragmented?

Yes


Specify trend in number of populations

Possibly declining due to habitat trends


Are there extreme fluctuations in number of populations?

Unlikely


List populations with number of mature individuals in each

1 severely fragmented population on southern Vancouver Island; number of individuals unknown; the degree of genetic exchange, if any, among slugs from the 5 known sites is unknown.



Threats (actual or imminent threats to populations or habitats)

  • Habitat loss and fragmentation primarily due to urban expansion;
  • habitat degradation by human activities and by invasion of introduced plants and animals;
  • competition with introduced gastropods; predation by native and introduced species, especially in small habitat patches


Rescue Effect (immigration from an outside source)

Status of outside population(s)?

USA:
Common in southern Oregon, rare elsewhere. Considered a sensitive species in Washington State. Designations: S3 (Oregon); To be assessed in Washington State


Is immigration known or possible?

Unlikely


Would immigrants be adapted to survive in Canada?

Possibly


Is there sufficient habitat for immigrants in Canada?

Possibly


Is rescue from outside populations likely?

No



Quantitative Analysis

Insufficient data


Current Status

British Columbia: S1, Red-listed

COSEWIC: Endangered (April 2006)


Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: B1ab(iii)+2ab(iii)

Reasons for Designation: This species has a very small extent of occurrence (~ 150 km2) and area of occupancy (< 5 km2), and a continuing decline is projected in quality of habitat. It is found in remnant patches of older forest with a deciduous component. It is currently known from only 5 locations on southern Vancouver Island. Threats at these locations include heavy recreational use and the impacts of introduced plants and animals, including introduced invasive slugs and snails.


Applicability of Criteria

Criterion A (Declining Total Population):
No information available to apply this criterion: Current and past population sizes are unknown; the species was first documented in Canada in 2002, and only 14 live specimens have been found.

Criterion B (Small Distribution, and Decline or Fluctuation):
Endangered B1ab(iii)+2ab(iii). Extent of Occurrence is ~ 150 km2 and Area of Occupancy is < 5 km2; species is known to exist at only 5 locations; species occurs in forested habitats in the Coastal Douglas-fir Biogeoclimatic Zone where only ~ 5% of forested land-base is in protected areas - habitats outside protected areas are declining due to urban development and associated infrastructure and habitats in protected areas are often degraded by heavy recreational use and introduced plants and animals.

Criterion C (Small Total Population Size and Decline):
The number of mature individuals in the population is unknown; hence, this criterion cannot be applied.

Criterion D (Very Small Population or Restricted Distribution):
D2 applies for threatened because the species is known to exist at only 5 locations and the Area of Occupancy is less than 5 km2.

Criterion E (Quantitative Analysis):
Not applicable.

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