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BC Conservation Data Centre: Conservation Status Report

Ovis dalli dalli
Dall's Sheep


 
Scientific Name: Ovis dalli dalli
English Name: Dall's Sheep
   
Provincial Status Summary
Status: S3
Date Status Assigned: March 08, 2023
Date Last Reviewed: March 08, 2023
Reasons: Abundance of Dall's Sheep is low within a restricted range; however, much of the area is within Tatshenshini-Alsek Provincial Wilderness Park. There are potential threats associated with disease transmission from domestic sheep and goats and from climate change including events and heavy snowfall causing significant population declines and problems with lamb survival. Additionally there is growing evidence of climate change causing ecosystem changes in high elevation grasslands due to increased shrub growth and rising treelines. Population trends are considered stable to declining.
 
Range
Range Extent: E = 5,000-20,000 square km
Range Extent Estimate (km2): 9,768 square km
Range Extent Comments: Range extent is 9,768 square km using the herd map and subspecies classification outline in MOF (2022) and Jex (2022). The herds regarded as Ovis dalli dalli are the Tatshenshini, Mansfield, Primrose, Tutshi and Table herds (MOF 2022). The Atlin and Snowdown herds are regarded as admixed although predominately O.d.dalii. This range extent does not include the area delineated as "admixed" Thinhorn Sheep in Sims et al (2019), MOF (2022,) and Jex (2022) where there are sheep showing a mixture of genes from both Dall's and Stone Sheep subspecies.
Area of Occupancy (km2): G = 501-2,500
Area of Occupancy Estimate (km2): 5200 square km
Area of Occupancy Comments: Up to approximately 1,300 2x2 km grid cells contain occupied territory, with only about 600 cells containing areas that have moderate (1 sheep per 1.3 - 5 Sq Km) or plentiful (over 1 sheep per 1.3 Sq Km) abundances of sheep. Habitat model based on BEC and TRIM data for slope/aspect and elevation, validated with survey data for core ranges, habitat model developed for ungulate winter range protection (S. Sharpe, pers. comm. 2017).
 
Occurrences & Population
Number of Occurrences: AB = 1 - 20
Comments: NatureServe defines and separates element occurrences based on populations that exhibit specific migration patterns or management groups, not by distances. Ovis dalli dalli populations consist of the Tatshenshini, Mansfield, Primrose, Tutshi and Table herds (MOF 2022). The Atlin and Snowdown herds are regarded as admixed although predominately O.d.dalii.
Number of Occurrences with Good Viability / Ecological Integrity: Rank Factor not assessed
Number of Occurrences Appropriately Protected & Managed: B = 1 - 3
Comments: Tatshenshini-Alsek Provincial Wilderness Park and Atlin/Áa Tlein Téix_'i Provincial Park contain the majority of the Dall's Sheep in the province (Demarchi and Hartwig 2014; MOF 2022).
Population Size: C = 250 - 1,000 individuals
Comments: The most recent estimates (Jex 2022, MOF 2022) have between 700 and 1,300 Dall's Sheep in the province. Using a correction factor of 60 percent adults (Festa-Bianchet 2020) the estimate for mature individuals is 420-780. This population estimate does not include "admixed" Thinhorn sheep that contain both Dall's and Stone Sheep genes as outlined in MOF (2022) and Sims et al (2019).
 
Threats (to population, occurrences, or area affected)
Degree of Threat: B = High
Comments: Three generation time frame for the severity scoring is 21 years (Festa-Bianchet 2020). In the past, over harvesting and human activities (mining, forestry, etc.) affected Dall's Sheep (R. Marshall, pers. comm. to Sean Sharpe), but the annual local harvest is closely monitored and restricted to full-curl rams in British Columbia, and is not a conservation concern. An effective environmental assessment and mitigation process related to natural resource development can reduce development impacts. R. Marshall (pers. comm.) believes increased access and the resulting increased disturbance, as well as unregulated First Nations harvest are of potential concern. Fest-Bianchet (2020), Jex et al (2016), and MOF (2022) outline potential threats to Thinhorn Sheep, including this subspecies in detail. Climate change implications that result in increased frequency of icing events (making winter range forage inaccessible) and heavy snowfall events effect winter and lamb recruitment.
Of particular concern is catastrophic population collapse from exposure to disease transferred from domestic sheep and goats in proximity to wild sheep (WSWG 2012, MOF 2022). The risk of disease transmission from domestic sheep and goats is high where cross-valley migrations bring Dall's sheep in close proximity to domestic goats.
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: F = Decline of 10-30%
Comments: Population trend for this subspecies is listed as stable to declining in MOF (2022).
Long-Term Trend: G = Relatively Stable (<=10% change)
Comments: Population is thought to be relatively stable.
 
Other Factors
Intrinsic Vulnerability: BC=Moderately vulnerable to not intrinsically vulnerable.
Comments: The BC population is relatively isolated from other metapopulations. Dall's sheep have relatively low lambda potential rates of increase and low dispersal among metapopulations. There is a risk of disease and climate related events, specifically icing during winter (eliminating forage access) and heavy snowfall events due to proximity to coastal mountains (Bill Jex, pers. comm. to S. Sharpe 2017; Jex et al 2016).
Environmental Specificity: C=Moderate. Generalist or community with some key requirements scarce.
Comments: Dall's sheep have specific habitat requirements related to proximity to escape terrain and availability of alpine forage (Demarchi and Hartwig 2004).
Other Rank Considerations:
 
Information Gaps
Research Needs: Disease transmission and potential vaccine development to prevent transmission of disease from domestic sheep and goats; further research into Dall's and Stone's sheep sub-species status and description related to North-South clades at BC / Yukon border. Studies on the impact of climate change driven shrub growth and woody plant encroachment on high elevation grasslands is required.
Inventory Needs: Systematic absolute abundance inventories should be completed every 3 - 5 years to obtain a good understanding of Dall's Sheep numbers and trends in British Columbia (I. Hatter, pers. comm.; Bill Jex, pers. comm. to S. Sharpe 2017).
 
Stewardship
Protection: Effective separation of Dall's Sheep from domestic sheep and goats. Climate change is liable to make recruitment events more unpredictable, harvest regimes will need to take that into account (BIll Jex pers comm to D.Fraser 2023).
Management: Effective separation is defined as spatial or temporal separation between Thinhorn Sheep and domestic sheep or goats. Reducing the potential for association between those taxa and the likelihood of transmission of pathogenic organisms or parasites between species is critically important. Maintaining effective separation is presently the only meaningful tool available for minimizing pathogen transfer and the risk of respiratory disease.

Climate change is liable to make recruitment events more unpredictable, harvest regimes will need to take that into account (BIll Jex pers.comm to D.Fraser 2023)

Habitat management is a concern. Suppression of forest fires may result in a decline of suitable grassland habitat. The number, age, and sex of sheep harvested by First Nations hunters are unknown at present (R. Marshall 2017 pers. comm. to S. Sharpe). Conduct population dynamics studies to investigate current limiting factors on population growth, and impacts of climate related impacts of icing and heavy snowfall related mortality.
 
Version
Author: Fraser, D.F. (2023), S Sharpe and L. Ramsay (2017)
Date: March 08, 2023
 
References

Western Association of Fish and Wildlife Agencies (WAFWA) Wild Sheep Working Group (WSWG). 2020. Jurisdictional Wild Sheep Population, License, Harvest Demand Estimates, 1990-2019.
Aleuy, O. A., Ruckstuhl, K., Hoberg, E.P., et al. 2018. Diversity of gastrointestinal helminths in Dall's sheep and the negative association of the abomasal nematode,Marshallagia marshalli, with fitness indicators. PLoS ONE; 13(3): e0192825.
Bailey, J.J., and D.R. Klein. 1997. United States of America in D.M. Shackelton, ed. Wild Sheep and Goats and their Relatives. IUCN Publ. Cambridge, U.K. pp.307-315.
Banfield, A. W. F. 1974. The mammals of Canada. University of Toronto Press, Toronto, Canada. 438 pp.
Bill Jex. 2017. Pers. comm. BC Ministry of Forest Land Natural Resource Operations, Skeena Region, Sheep Biologist.
 
Blower, D. 1988. Wildlife distribution mapping, big game series, mountain sheep. Unpubl. map by B.C. Minist. Environ., Lands and Parks, Victoria, BC.
Cowan, I. McT. 1940. Distribution and variation in the native sheep of North America. Am. Mid. Nat. 24:505-580.
Demarchi, R.A., and C.L. Hartwig. 2004. Status of Thinhorn Sheep in British Columbia. B.C. Minist. Water, Land and Air Prot,.Biodiversity Branch, Victoria, BC. Wild. Bull. No. B-119.

Festa-Bianchet, M. 2020. Ovis dalli. The IUCN Red List of Threatened Species, 2020. Accessed March 2023. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T39250A22149895.en
Jex, B. A., J. B. Ayotte, V. C. Bleich, C. E. Brewer, D. L. Bruning, T. M. Hegel, N. C. Larter, R. A. Schwanke, H. M. Schwantje, and M. W. Wagner. 2016. Thinhorn sheep: conservation challenges and management strategies for the 21st Century. Wild Sheep Working Group, Western Association of Fish and Wildlife Agencies, Boise, Idaho, USA.
Jex, B.A. 2022. Population status and trends -Thinhorn Sheep in British Columbia. Wild Sheep Foundation. Presentation.
Ministry of Forests. 2022. [DRAFT] Stewardship Framework for Thinhorn Sheep (Ovis dalli) in British Columbia. Thinhorn Sheep Indigenous Perspectives and Thinhorn Sheep Management Teams. Prepared for the Fish and Wildlife Branch, British Columbia Ministry of Forests, Victoria, BC. 69 pp.
Nagorsen, D. 1990. The mammals of British Columbia: a taxonomic catalogue. Mem. No. 4. Royal B.C. Mus., Victoria. 140pp.
Shackleton, D.M. 1998. Ungulates of British Columbia. B.C. Prov. Mus. Handb. (in press).
Shackleton, D.M., ed. 1997. Wild sheep and goats and their relatives. IUCN, Gland, Switzerland. (Available from IUCN Publ. Serv. Unit, Cambridge CB2 0DL, U.K.). 390pp.
Shackleton, D.M., N. Barichello, A. Gunn, D.H. Hebert, and F. Harper. 1997. Canada. Pp. 296-302 in D.M. Shackleton, ed. Wild Sheep and Goats and their Relatives. IUCN Publ. Serv. Unit, Cambridge U.K.
Sim, Z., C.S. Davis, B. Jex, et al. 2019. Management implications of highly resolved hierarchical population genetic structure in thinhorn sheep. Conserv Genet 20, 185?201.
Worley, K, C. Strobeck, S. Arthur. 2004. Population genetic structure of North American thinhorn sheep (Ovis dalli). Molecular Ecology, 13:2545?2556.
Youngman, P. M. 1975. Mammals of the Yukon Territory. Publications in Zoology, No. 10., National Museums of Canada, Ottawa. 192 pp.
 

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. 2023. Conservation Status Report: Ovis dalli dalli. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Apr 24, 2024).