Western silvery minnow (Hybognathus argyritis) COSEWIC assessment and status report: chapter 11

Technical Summary

Hybognathus argyritis

Western silvery minnow – Méné d’argent de l’Ouest

Range of Occurrence in Canada:
Alberta


Extent and Area Information

Extent of occurrence (EO)(km²)(Estimated from a convex hull around the river stretch from the U.S. border to 1 km past the last distribution point upstream) :
1200 km²
Specify trend in EO :
Stable?
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²)(based on overlaid grid of cell size one km², total AO is the number of squares that are intersected by the river from the U.S. border to 1 km past the last distribution point upstream) :
244 km²
Area of occupancy (AO) (km²)(based on occupied riverine habitat assuming average river width of 60 m from the U.S. border to 1 km past the last distribution point upstream) :
13.4 km²
Specify trend in AO :
Fluctuates with water flow regimes
Are there extreme fluctuations in AO?
Yes – during drought conditions
Number of known or inferred current locations :
1 possibly 2
Specify trend in # :
Stable?
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat :
Fluctuates with water flow regimes

Population Information

Generation time (average age of parents in the population) :
3+
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?
Possibly – in drought conditions
Is the total population severely fragmented?
no
Specify trend in number of populations :
Stable
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each:Unknown

Threats (actual or imminent threats to populations or habitats)

Immediate
  1. Low flows and high water temperatures resulting from drought and surface water extractions
  2. Introduced exotic species
  3. Anoxia in overwintering habitat related to water diversions
Potential
  1. Surface and ground water extraction
  2. Low flows and high water temperatures resulting from drought exacerbated by climate change
  3. Dam and reservoir construction
  4. Livestock and agricultural uses of the floodplain
  5. Canal maintenance and drought
Rescue Effect (immigration from an outside source):
Limited
Status of outside population(s)?
USA: See current status below
Is immigration known or possible?
Possible under limited conditions
Would immigrants be adapted to survive in Canada?
yes
Is there sufficient habitat for immigrants in Canada?
yes
Is rescue from outside populations likely?
no

Quantitative Analysis

No data

Current Status

Nature Conservancy Ranks (NatureServe 2007) 
  • Global – G5 (Secure)
  • National
    • US – N4 (Secure)
    • Canada – N3N4 (May be at Risk)
  •  Regional
    • US
      • IL – S2 (Vulnerable),
      • IA – S1 (Critically Imperilled),
      • KS – S2,
      • MO – S2,
      • MT – S4S5 (Possibly Secure).
      • NE – S5 (Secure),
      • ND – SNR (Not Ranked),
      • SD – S5,
      • WY – S2.
    • Canada
      • AB – S1
Wild Species 2005 (Canadian Endangered Species Conservation Council 2006)
  • Canada – 2 (May Be At Risk)
  • Alberta – 1 (At Risk)
COSEWIC
  • Threatened 2001
  • Endangered 2008
SARA
  • Schedule 1 Part 3 – TH

Status and Reasons for Designation

Status: Endangered

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

Reasons for Designation: This small minnow species is restricted to the Milk River in Southern Alberta, a region characterized by drought conditions of increasing frequency and severity. While the future of flow regimes associated with the St. Mary’s diversion canal and proposed water storage projects are uncertain, consequences of these activities have the potential to significantly affect the survival of the species. Rescue effect from U.S. populations is not possible.

Applicability of Criteria

Criterion A (Declining Total Population): Not Applicable – no evidence of decline in the total number of mature individuals.

Criterion B (Small Distribution, and Decline or Fluctuation): Met criteria for Endangered B1ab(iii)+2ab(iii), as the EO (1200 km²) and AO (244 km²) are below threshold values, there is only one known location, and the area, extent and/or quality of habitat is impacted by water flow regimes resulting from water extraction for irrigation, and predicted increase in frequency and severity of drought conditions.

Criterion C (Small Total Population Size and Decline): Not Applicable – number of mature individuals is unknown and there is no evidence of decline in the number of mature individuals.

Criterion D (Very Small Population or Restricted Distribution): Met criteria for Threatened D2 – only one location.

Criterion E (Quantitative Analysis): Not Applicable – no data.

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