Introduction and Background
This study concerns California and Rocky Mountain Bighorn Sheep population that are threatened by disease risks in British Columbia.
The close phylogenetic relation between Bighorn Sheep and domestic sheep allows genetic exchanges and transmission of diseases between these two species. Indeed, several infections can be transferred from one species to the other. However, domestic sheep have evolved across hundred of generations, developing resistance or tolerance to many of those infections while Bighorn Sheep are still sensitive to them. It has been acknowledged that occurrence of close contact between the two species often results in severe or even fatal contraction of infection by Bighorn Sheep, inducing some major declines in their population such as in 1999 in south Okanagan where the population loss reached 65%. However other stress factors also exist that reduce immunity of Bighorn Sheep.
Even if many of the Bighorn Sheep die-off have been followed by good recovery of the population size and distribution, it is clear that the disease transfer risk from domestic sheep remains a major limiting factor to the species. A program was proposed in the Okanagan following the decline of 1980 (BC Sheep Separation Program) and the actions it recommended were the same as two decades later during an international meeting in the same region. The BC Conservation Data Centre attests that efforts are currently done to reduce contact with domestic sheep.
Objectives
The objective of this report is to discuss appropriate management methods to reduce the risk of disease transfer between Bighorn Sheep and domestic sheep in the Southern Interior of British Columbia.
Methods
The first part of the report presents actions that have been implemented in the South Okanagan as a basis to assess suitable methods.
The second part of the report presents different potential strategies to mitigate the disease risk. This includes on one hand preventing actions such as collection of data and establishment of map concerning habitat of high Bighorn Sheep concentration and subsequently of high disease transfer risk, physical separation between the two species (keeping a distance or building fences) and vaccination. On the second hand, responsive actions are discussed such as shooting of infected Bighorn Sheep to avoid further contamination of their herd and treatment of the disease.
Results and Discussion
During the South Okanagan project, farms presenting elevated contact risks between Bighorn Sheep and domestic sheep were identified by the Ministry of Environment in 2004. Different solutions were found with farmers to mitigate the risk : displacement of domestic sheep and/or signature of Restrictive Covenant and/or building of new fences. The disadvantage of those actions were discussed. Identification of farms presenting a risk of contact has continued after 2004. Another success of the project was the resolutions taken by three levels of First Nation Government to reduce contact risks between the two species.
Two physical separation strategies are presented : establishment of a distance of at least 15 km between Bighorn sheep and domestic sheep or of the presence of a serious geographical boundary for the areas where domestic sheep graze free and building of a fence for other domestic sheep. Different designs are proposed but trial is still needed before approval for implementation. Neither vaccination nor treatment of infected Bighorn sheep result in recovery from the disease.
Several strategies include a system of funding. There is a risk that some farmers try to abuse this system.
The last part of the report focuses on a proposal based on Regional District of Okanagan-Similkameen Bylaw concerning new farms that will be created in areas that have been assessed to present a high risk of contact between Bighorn Sheep and domestic sheep.
Conclusion
The risk of disease transfer from domestic goat to Bighorn Sheep remains a major threat to Bighorn Sheep population. Several strategies to limit this risk have been tested but the more efficient ones appear to be preventative methods such as avoiding the presence of domestic sheep in high-risk areas or building of fences.
- Source Brian Harris, Helen Schwantje, Bert van Dalfsen. March 2011. Managing the Risk of Disease Transfer between Wild and Domestic Sheep in the Southern Interior of BC. Prepared by the Ministry of Environment, the Ministry of Natural Resource Operations, the Ministry of Agriculture. Available at : http://www.bcsheep.com/docs/2012/managing-wild-domestic-sheep.pdf [Accessed 03/2021].