BC Conservation Data Centre: Conservation Status Report
Oncorhynchus clarkii lewisi
Cutthroat Trout, lewisi subspecies
| Scientific Name: | Oncorhynchus clarkii lewisi |
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| English Name: | Cutthroat Trout, lewisi subspecies |
| English Name Synonyms: |
Westslope Cutthroat Trout
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| Provincial Status Summary | |
| Status: | S2S3 |
| Date Status Assigned: | April 29, 2018 |
| Date Last Reviewed: | March 29, 2018 |
| Reasons: | Declining population with wide-spread significant threats. |
| Range | |
| Range Extent: | F = 20,000-200,000 square km |
| Range Extent Estimate (km2): | 85,183 |
| Range Extent Comments: | COSEWIC 2016q |
| Area of Occupancy (km2): | G = 501-2,500 |
| Area of Occupancy Estimate (km2): | 6,824 |
| Area of Occupancy Comments: | COSEWIC 2016q |
| Occurrences & Population | |
| Number of Occurrences: | E = > 300 |
| Comments: | Approximately 928 locations (could be as high as 1319 if waterbodies where at least one occurrence of westslope cutthroat trout are included). COSEWICq 2016 |
| Number of Occurrences with Good Viability / Ecological Integrity: | BF = 1 to >125 |
| Comments: | Some of the subpopulations appear to be stable; however, it is inferred that the number of locations and subpopulations have declined, due to hybridization with Rainbow Trout and ongoing development that impacts available habitat (COSEWIC 2016q). |
| Number of Occurrences Appropriately Protected & Managed: | BE = 1 to >40 |
| Comments: | There are EOs within Provincial and National Parks, however fishing is allowed within these areas. There are also locations where only a portion of the stream is allowed within the protected area. In the East Kootenays, only 16% of the land base is protected; 9% is private ownership, while 75% is open to resource exploration and extraction (COSEWIC 2016q). |
| Population Size: | FG = 10,000 - 1,000,000 individuals |
| Comments: | Numbers of fish per stream are naturally lower than other freshwater salmonids on the order of magnitude of tens to hundreds per stream (Trotter 1987 in Costello and Rubidge 2003). Using the Alberta estimate of 100 fish/stream (12 fish/km) provides a conservative estimate of 92,800 fish (COSEWIC 2016q). Esimates range from 30-45 fish/km in the East Kootenays; 1000 fish in the Upper Bull River; and 3000 fish in the upper Fording River (COSEWIC 2016q). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | A = Very high |
| Comments: | The main habitat threats include mining, logging, agriculture, hydroelectric development and urbanization. Direct threats come from heavy angling pressure, which is increasing as access increases. Hybridization, particularly with brook and rainbow trout is also a concern with pure populations becoming restricted to isolated headwater streams. This is cited as one of the primary factors of decline in the US (reviewed in Costello and Rubidge 2003). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | FG = Decline of <30% to relatively stable |
| Comments: | Many populations are stable, while others are projected to decline due to due to hybridization with introduced trout, loss of habitat from development, increased temperatures resulting from climate change and overfishing (COSEWIC 2016q). |
| Long-Term Trend: | DF = Decline of 10-70% |
| Comments: | "Dramatic" declines are indicated for this subspecies (Costello and Rubidge 2003). In the Upper Kootenay watershed, many subpopulations have been adversely impacted by hybridization with introduced rainbow rout (hybridization occurring in 78% of the 23 streams tested); the Lodgepole Creek population has likely become a hybrid swarm (COSEWIC 2016q). Creel and snorkel surveys indicate the population is stable in certain systems; however, available habitat is likely decreasing, with subpopulations being concentrated into isolated headwater streams (COSEWIC 2016q). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Subpopulations are generally small; age of maturity ranges from 4-8 years; mean fecundity ranges from 227-459 depending on size ranges; species prefer cold water (COSEWIC 2016q). |
| Environmental Specificity: | B=Narrow. Specialist or community with key requirements common. |
| Comments: | This species inhabits cold waters and lakes; warming water temperatures due to climate change will reduce the amount of habitat available (COSEWIC 2016q). |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | |
| Inventory Needs: | Abundance, especially of mature individuals. |
| Stewardship | |
| Protection: | |
| Management: | |
| Version | |
| Author: | P. Woodruff and L.R. Ramsay |
| Date: | April 13, 2018 |
| References | |
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COSEWIC. 2016j. COSEWIC assessment and status report on the Westslope Cutthroat Trout Oncorhynchus clarkii lewisi, Saskatchewan-Nelson River populations and Pacific populations,in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xvi + 83 pp. |
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COSEWIC. 2006q. COSEWIC assessment and update status report on the westslope cutthroat trout Oncoryhnchus clarkii lewisi (British Columbia population and Alberta population) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 67pp.
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Costello, A. and E. Rubidge. 2003b (draft). COSEWIC status report on cutthroat trout (Oncorhynchus spp.). Prepared for Committee on the Status of Endangered Wildlife in Canada. 68 pp.
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Hagen, J. and J.T.A. Baxter. 2009. 2008 westslope cutthroat trout population abundance monitoring of classified waters in the East Kootenay region of British Columbia. Prepared for BC Ministry of Environment, Fisheries Program, East Kootenay Region, Cranbrook, BC.
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McPhail, J.D. 2007. The freshwater fishes of British Columbia. The University of Alberta Press, Edmonton, Alberta.
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Oliver, G.G. 2009. Towards a westslope cutthroat trout management plan for the province of British Columbia. Prepared for BC Ministry of Environment, Victoria, BC.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2018. Conservation Status Report: Oncorhynchus clarkii lewisi. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jan 24, 2025).