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COSEWIC assessment and update status report on the Chiselmouth in Canada

Technical Summary

Acrocheilus alutaceus

Bouche coupante

British Columbia

Extent and Area Information

Extent of occurrence
<5000 km2


Likely stable, although several small lake populations deliberately extirpated

Fluctuations in extent of occurrence


Area of Occupancy

<500 km2 several hundred linear km of stream length; half a dozen lakes


Likely stable

Fluctuations in area of accupancy

Unknown, but unlikely

Number of extant locations

Present in at least 8 major drainages

Trend in # locations


Fluctuations in # locations


No. locations from which populations have been extirpated

Several (deliberate, but exact number unknown)

Habitat trend


Population Information

Generation time
4-6 years

Number of mature individuals in the Canadian population

10 000 – 30 000 (estimate)

Population trend


Fluctuations in number of mature individuals


Are populations fragmented?

Populations are relatively isolated from one another, but the exchange rate of individuals between pops. Is unknown

Populations and the number of mature individuals in each

(L = 2000-5000  M = 1000-2000
S = < 1000)

1) Blackwater/Nazko/Euchi niko L
2) Salmon/Muskeg S
3) Similkameen M
4) Okanagan L
5) Kettle L
6) Upper Chilcotin S
7) Nicola L
8) Shuswap M

Trend in number of populations

Likely stable

Fluctuations in number of populations

Probably not


- Cumulative impacts of agriculture, forestry, and livestock grazing may be impacting chiselmouth in some rivers (e.g. Okanagan, Nicola), and these impacts will likely get worse in the near future. 
- Populations in some lakes may be subject to extermination as competitors of game fish species.

Rescue Effect: Low for most pops.

Does species exist elsewhere in Canada?


In the U.S.?

Yes – ID, NV, OR and WA

Status of the outside populations?

ID-S5, NV-S?, OR-S4, WA-S4

Is immigration known or possible?

Dams and natural barriers prevent most natural migration

Would immigrants be adapted to survive here?

For Columbia R. pops, likely; possibly not for Fraser basin pops.

Is there sufficient habitat for immigrants here?


Quantitative Analysis


Existing Status

CDC Ranks
– N5
National U.S. N5
Canada– N3
Regional U.S.  ID - S5, NV – S?, OR – S4, WA – S4
Canada  BC – S3, Provincial Listing Blue (Special Concern)

Status Designated May 2003
Not At Risk

Reasons for Status Designation
The Canadian distribution of this species is restricted to a few disjunct populations in south-central British columbia where they are found in low densities, but appear to be stable and are not subject to any known factors that could put them at risk.