Speckled dace (Rhinichthys osculus) COSEWIC assessment and status report: chapter 11

Technical Summary

Rhinichthys osculus

speckled dace – naseux moucheté

Range of Occurrence in Canada:
British Columbia

Extent and Area Information

Extent of occurrence (EO) (km²).
Calculated from Figure 3 using best fit polygon : ~ 3000 km²
Specify trend in EO.
Decline is inferred from increasing frequency and severity of summer drought conditions. Possibly Declining - inferred
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²)
Based on total stream length of 245 km and mean wetted width of 30.5 m (estimated from sub-drainage areas and average water yields) :7.47 km²
Specify trend in AO
Decline is inferred from increasing frequency and severity of summer drought conditions : Possibly Declining - inferred
Are there extreme fluctuations in AO?
Low flow conditions in extremely dry summers or drought conditions may reduce adult habitat, particularly riffles (see Canadian Range). Possible
Number of known or inferred current locations
Kettle, West Kettle and Granby rivers : 3
Specify trend in # :
Stable
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat.
Decline is inferred from increasing frequency and severity of summer drought conditions. Declining

Population Information

Generation time (average age of parents in the population) :
2 or 3 years
Number of mature individuals :
Unknown
Total population trend:
Inferred from decrease in riffle habitat with worsening drought conditions. Declining - inferred
% 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?
If fragmentation occurs, it is not severe. 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:

Threats (actual or imminent threats to populations or habitats)

Decreasing summer low flows; the limited distribution, which can be impacted by a single large event; and cumulative habitat degradation including possible water quality issues related to industrial activity (forestry related), urbanization (sewage) and agricultural run-off, i.e., irrigation/water diversion in terms of changing run-off patterns and demand in relation to climate change leading to extended low-flow periods.

Rescue Effect (immigration from an outside source)

Status of outside population(s)?
USA: The Nature Conservancy – Global Rank G5; 4 ssp. listed under U.S. ESA; 12 ssp. ranked at risk by The Nature Conservancy
Is immigration known or possible?
Possible, from the part of population that resides in the 45 km of river above Cascade Falls that loops south into USA (EO = ~ 2 km²). Would depend on whether this area was impacted as well. Not possible from outside populations located below Cascade Falls.Possible but limited.
Would immigrants be adapted to
survive in Canada?
Yes
Is there sufficient habitat for
immigrants in Canada?
Appears limited
Is rescue from outside populations likely?
Cascade Falls is a 30.5 m high barrier to upstream movement. Not Likely. See above

Quantitative Analysis

Analysis has not been done. None

Existing Status

Nature Conservancy Rank (NatureServe 2005)

Global – G5

National:

  • U.S.: N5, PS under Endangered Species Act (several subspecies are threatened or endangered in the U.S). One subspecies (R. osculus reliquus) is extinct.
  • Canada: N1N2

Regional:

  • U.S.: AZ – S3S4, CA – S5, CO – S5, ID – S5, NN – S5, NV – S5, NM – S3, OR – S4, UT – S5, WA – S4
  • Canada: B.C. S1S2 (Province lists as Red)
Wild Species 2000 (Canadian Endangered Species Council 2001)
  • National: 6
  • Regional: BC – 3
COSEWIC  
  • Vulnerable (Special Concern) 1980
  • Endangered (2002)
  • Endangered (2006)

Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: B1+2ab(iii)

Reasons for Designation: The species is restricted to the Kettle River mainstem and two main tributaries in south-central British Columbia where it appears to be limited by the availability of suitable habitat. As this population is isolated above Cascade Falls, it cannot be rescued from downstream United States populations. The Kettle River is a flow-sensitive system that appears to be experiencing increasing frequency of drought conditions. The species is threatened by these reduced water flows and projected increasing water demands.

Applicability of Criteria

Criterion A: (Declining Total Population): Not Applicable – Decline is inferred, but the rate of decline is not known.

Criterion B: (Small Distribution, and Decline or Fluctuation): Meets Endangered under criteria B 1+2ab(iii) – The area of occupancy is 7.47 km², and exists at 3 locations with continuing decline observed or projected in the extent and quality of available habitat as a result of increases in water extraction and drought conditions.

Criterion C: (Small Total Population Size and Decline): Not Applicable – Number of mature individuals is not known.

Criterion D: (Very Small Population or Restricted Distribution): Meets Threatened D2 – Area of occupancy is 7.47 km² and is known from only 3 locations.

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

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