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COSEWIC Assessment and Update Status Report on the Nooksack dace in Canada

Technical Summary

Rhinichthys cataractae ssp.

Nooksack dace

naseux de la Nooksack

Range of Occurrence in Canada: Fraser Valley, British Columbia

Extent and Area Information

Extent of occurrence (EO) km2
Calculated by GIS adaptation of maps from McPhail 1997 and Mongillo and Hallock 1997; changed to incorporate Brunette River watershed.
630 km2
Specify trend in EOUnknown
Are there extreme fluctuations in EO?No
Area of occupancy (AO) km2
calculated from measurements of riffle area in 4 occupied watersheds (Pearson 2004; unpubl. data)
based on overlaid grid of cell size one km2, total AO is the number of occupied squares that are intersected by the rivers
< 0.03 km2

14 km2
Specify trend in AO
Trend in last 10 years
Are there extreme fluctuations in AO?No
Number of known or inferred current locations4
Specify trend in #Unknown
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)3 years
Number of mature individuals (based on known populations)
(These may be overestimates as some juveniles may have been included in the survey)
Pepin Creek   Unadjusted - 4400   Adjusted - 800
Bertrand Creek   Unadjusted - 5700   Adjusted - 5700
Fishtrap Creek   Unadjusted - 3900   Adjusted - 300
Brunette River   Unadjusted - 38 300   Adjusted - Not Available
Total population trendDecline
% 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
Specify trend in number of populationsUnknown
Are there extreme fluctuations in number of populations?No
List populations with number of mature individuals in each:
   Bertrand Creek: <5700
   Pepin Creek: <800
   Fishtrap Creek: <1000
   Brunette River: Unknown

Threats (actual or imminent, to populations or habitats)

Physical destruction of riffle habitat (e.g. dredging, channelization)
Lack of water in late summer due to ground and surface water extraction and impermeable urban areas.
Riffle loss to beaver ponding.
Sediment accumulation in riffles caused by bank erosion, gravel mining and/or urban storm drains.

Rescue Effect (immigration from an outside source)

Status of outside population(s)?
Washington State: S3
Is immigration known or possible?Yes
Would immigrants be adapted to survive in Canada?Yes
Is there sufficient habitat for immigrants in Canada?No (assumed to be at capacity)
Is rescue from outside populations likely?No

Quantitative Analysis


Existing Status

Nature Conservancy Ranks (NatureServe 2006)
   Global – G3
      US – N3
      Canada – N1
      U.S: WA – S3
      Canada: BC – S1
Province: BC – Red
American Fisheries Society: Threatened
COSEWIC: Endangered 1996, 2000, 2007
SARA: Endangered, Schedule 1

Status and Reasons for Designation

Alpha–numeric code:
B1ab(iii,v) + B2ab(iii,v)
Reasons for designation:
The species is considered a habitat specialist dependent on stream riffles with loose, small-grained substrates. This small fish is a representative of the Chehalis fauna, and considered to be a distinct subspecies of the longnose dace. It is known in Canada from only four locations in southwestern BC where its area of occupancy is severely limited, and subject to ongoing physical destruction of riffle habitat by urban, industrial, and agricultural practices (e.g. dredging, channelization). Streams where the species is found are also impacted by lack of water in late summer due to ground and surface water extraction. Other activities have led to sediment accumulation in riffles caused by bank erosion resulting from gravel mining and/or runoff from urban storm drains, leading to further degradation of water quality and habitat.

Applicability of Criteria

Criterion A (Declining Total Population):
Not applicable – decline rates are unknown.
Criterion B (Small Distribution, and Decline or Fluctuation):
Meets Endangered B1ab(iii,v) + 2ab(iii,v).  The EO is less than 1000 km2, and the AO < 1 km2. The species is known to exist at only 4 locations, populations are fragmented and there is continuing decline in the extent and quality of habitat and number of individuals.
Criterion C (Small Total Population Size and Decline):
Not applicable, number of mature individuals is unknown.
Criterion D (Very Small Population or Restricted Distribution):
Meets threatened D2, AO, < 20 km2, and known from only 4 locations.
Criterion E (Quantitative Analysis):
Not applicable.