Big Horn Sheep
South Thompson River California Bighorn Sheep
Current Status & Distribution
The South Thompson River California bighorn sheep herd has expanded rapidly from a founder population of a few animals that crossed the North Thompson River from Kamloops Lake in the late 1970s. The founder group, comprised of 2 ewes and 2 yearling rams, apparently made their way from Wheeler Mountain north of Kamloops Lake and crossed the North Thompson River into the Heffley Creek area in early May 1978.
By mid-June, the two females had settled on Mt. Paul. Later that year, a wild bighorn ram, thought to have wandered from the Chase Rocky Mountain bighorn herd 36 kilometres to the east, was captured while tryng to breed a captive ewe held at the Kamloops Wildlife Park.
This 5-year-old ram was immediately released onto the Kamloops Indian Reserve, where he was apparently successful in breeding the two resident ewes in the autumn of 1978, as each was accompanied by a lamb the following year.
Wildlife managers reported little increase in the now well established group between 1979 and 1981; therefore, to ensure the herd’s persistence and increase it’s genetic diversity, 6 animals from the Junction herd in Williams Lake were transplanted to the Harper Ranch area in 1985.
Since 1990, the population has increased dramatically. Currently, an estimated 250 individuals form three separate identified bands in the Mt. Paul, Harper Ranch and Lionhead areas. Lamb recruitment has consistently been high, averaging 47 lambs per 100 ewes in the 15-year period between 1987 and 2001 (Lemke et al., unpublished data).
As a general rule, an over-winter lamb:ewe ratio of 30 lambs per 100 ewes is the required minimum to maintain a population of bighorn sheep (Demarchi et al. 2000).
The herd’s range encompasses approximately 7,600 ha bordering the north side of the South Thompson River, north and east of Kamloops, including Mt. Paul, Mt. Peter and the south-facing slopes and bluffs eastward to Swain Creek and Lionshead.
BIGHORN SHEEP MANAGEMENT
Past & Present
Management of the South Thompson California bighorn sheep herd, to date, has been informal, and focussed primarily on population management, particularly over the past decade as the herd has expanded rapidly. In the absence of recreational hunting and in light of the vigorous growth of the herd, requests for bighorn sheep transplant stock from western United States and interprovincial jurisdictions have been granted in an effort to reduce/and or stabilize numbers and population growth.
The effective management of the South Thompson bighorn sheep population will involve surveying bighorn numbers and distibution, capturing and transplanting bighorns (if necessary), disease detection and control, and evaluating (and controlling, if necessary) predators.
TRANSPLANTING OF BIGHORN SHEEP
Following the initial transplant of 6 animals from the Junction herd in 1985, no further augmentation of the South Thompson herd has occurred. Indeed, excellent lamb survival and recruitment rates, vigorous health, no recreational harvest and apparently low predation rates have resulted in a rapidly expanding herd from which 85 bighorns have been removed since 1996 (Table 1). Additional removals from the South Thompson herd (Mt. Paul band) may be justified: The population is currently believed to be exceeding optimal levels on this habitat (estimated 100; optimal 40-50) (D. Jury, MWLAP, personal communication) and other jurisdictions are requesting stock, i.e. Okanagan.
Table 1. Number of animals, transplant location and year of removals from the South Thompson herd
Year Transplant Location # of Animals
1996 Washington 7
1997 Utah 11
1997 Seton Lake, BC 2
1998 Penticton Creek, BC 14
1999 Navada 18
2000 Washington 21
2004 Shorts Creek, BC 12
Mangement Action: Transplant bighorn sheep from the Mt. Paul band to other jurisdictions requesting augmentation or reintroduction of California bighorn sheep.
Strategy: Capture bighorn sheep, using one or more approved methods, including helicopter net gun, corral trapping and drop netting. Population levels and general herd health must be assessed by Ministry of Water, Land and Air Protection regional wildlife staff prior to approval of any and all transplant operations, to ensure that the population is capable of supporting the deficit. Transplants of bighorn sheep are usually comprised of females and young rams (although lambs approaching 1 year of age may be included). Mature rams are generally not selected as they are difficult to handle and tend to wander once released.