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COSEWIC Assessment and Status Report on the "Eastslope" Sculpin (St. Mary and Milk River population) Cottus sp. in Canada

Technical Summary

Cottus sp.

“Eastslope” Sculpin
St Mary and Milk River Populations
Chabot du versant est
Populations des rivières St. Mary et Milk

Range of Occurrence in Canada: Alberta

Extent and Area Information

Extent of occurrence (EO)?
[see text , calculated from Figure 4]
< 2600 km2
Trend in EO?
Are there extreme fluctuations in EO?
Area of occupancy (AO)?
(Stream lengths of 80 km (St. Mary River) and 220 km (Milk river), maximum stream width is 0.02 km and sculpins do not utilize all areas of either river, see Distribution section of report)
<6 km2
Trend in AO?
Are there extreme fluctuations in AO)?
Minor but not extreme
Number of known or inferred current locations? (see Tables 1, 2)
Trend in # locations?
Are there extreme fluctuations in # locations?
Uncertain, but appears likely in response to wet/dry cycles
Number of historic locations from which designatable units have been extirpated?
Possibly 2
Trend in area, extent or quality or quality of habitat?

Population Information

Generation time (average age of parents in the population)?
2-3 yr.
Number of mature individuals?
Total population trend?
% decline over the last/next 10 years or 3 generations?
Are there extreme fluctuations in number of mature individuals?
Unknown, but some indication that this has been the case in response to wet - dry cycles
Is the total population severely fragmented?
Trend in number of populations?
Are there extreme fluctuations in number of populations?
List populations with number of mature individuals in each

Threats (actual or imminent threats to populations or habitats)

Restricted range, total area of occupancy constrained to an» 80 km stretch of the St. Mary and 220 km of the Milk River systems of Alberta (but < 1 km wide at widest section).

  • Habitat loss and degradation resulting from loss of water flow due to impoundments, diversions and water removal, as well as frequent periods of drought which may become more pronounced due to global climate change


Rescue Effect (immigration from an outside source): Moderate (St. Mary River only)

Status of the outside population(s)?
USA (see below)
Is immigration known or possible? (see sections on Distribution and Limiting Factors)
Possible from upper St. Mary River in the US
Would immigrants be adapted to survive in Canada?
Is there sufficient habitat for immigrants here?

Quantitative Analysis

Not Applicable


Existing Status

The entity "Eastslope" sculpin is not listed separately by the Association for Biodiversity Information. The Columbia sculpin, Cottus hubbsi and the mottled sculpin, Cottus bairdii , are listed as follows:

Columbia sculpin, Cottus hubbsi

NatureServe Ranks (NatureServe 2004)

Global -



US - N?
Canada - N?


US - Oregon S4
Canada - BC S3

Provincial Rank -

blue (British Columbia Conservation Data Centre 2000)

Wild Species 2000 -

not listed (Canadian Endangered Species Council 2001)


Special Concern 2000 (COSEWIC 2004)

Mottled Sculpin, Cottus bairdii

NatureServe Ranks (NatureServe 2004)

Global -



US - N5
Canada - N5


US - AL - S2, AR - SE1, CO - S4, DE - S1, GA - S4, ID - S5, IL - S2, IA - S4, IA - S2, KY - S4, MD - S3S4, MI - S5, MN - S?, MS - S4?, MO - S4, MT - S5, NN - S1, NV - S?, NJ - SR, NM - S1?, NY - S4, NC - S5, OH - S?, OR - S4?, PA - S5, TN - S5, UT - S4, VT - S2, VA - S4, WA - S3, WV - S5, WI - S4, WY - S5
Canada - AB - S1, BC - S3, MB - S5, NF/LA - S3S4, ON - S5, QC - S5

Provincial Rank -

BC blue (British Columbia Conservation Data Centre 2000)

Wild Species 2000 -

(Canadian Endangered Species Council 2001)

National -


Provincial -

BC - 3, AB - 6, MB - 4, ON - 4, QC - 4


Threatened (May 2005)

Status and Reasons for Designation

Status: Threatened
Alpha-numeric code: D2

Reasons for Designation: This species has a very restricted area of occurrence in the St. Mary and Milk rivers in Canada where it has been impacted by habitat loss and degradation from water diversion, conditions that have been exacerbated in recent years by drought.


Applicability of Criteria

Criterion A (Declining Total Population):
Not Applicable - no evidence to support overall declining population trends. However, because of the limited distribution, loss of some habitat, existing and potential threats (e.g., drought, water removal, possible dam construction on the Milk River), the species might possibly qualify as threatened under A4c.

Criterion B (Small Distribution, and Decline or Fluctuation):
Not applicable – the extent of occurrence (2600 km2) is less than 5000 km2, the area of occupancy (6 km2) is less than 500 km2, there are fewer than 5 locations, and there is evidence of decline in AO, quantity and quality of habitat and number of populations, but the rate is of decline is not known. There is some indication that populations may fluctuate in response to periodic drought conditions, however the magnitude of such fluctuations is unknown.

Criterion C (Small Total Population Size and Decline):
Not Applicable - Population size and trends not known, but no doubt exceed 1000 mature individuals (there is no quantitative estimate), however there is no evidence of overall decline although increases and decreases are known for various areas.

Criterion D (Very Small Population or Restricted Distribution):
Meets the criterion for Threatened D2, i.e., restricted distribution, known only from 3 locations and the area of occupancy is less than 6 km2. The species is prone to the effects of agricultural practices that alter stream flows for irrigation and to drought conditions resulting from global warming.

Criterion E (Quantitative Analysis):
Not Applicable – data not available.