A Population Review of Rocky Mountain Bighorn Sheep in the Kootenay Region Photo B. Phillips Prepared for: BC Ministry of Forests, Lands and Natural Resource Operations Kootenay Region April 2013 Prepared by: Patrick Stent 1 , Kim G. Poole 2 , Ian Adams 3 , and Garth Mowat 1 1 BC Ministry of Forests, Lands and Natural Resource Operations, Suite 401, 333 Victoria St., Nelson, BC V1L 4K3 [email protected]; [email protected]2 Aurora Wildlife Research, 1918 Shannon Point Rd., Nelson, BC V1L 6K1 [email protected]3 Vast Resource Solutions, P.O. Box 538, 4500 Mennie Rd., Cranbrook, BC V1C 4J1 [email protected]
Transcript
A Population Review of Rocky Mountain Bighorn Sheep
in the Kootenay Region
Photo B. Phillips
Prepared for:
BC Ministry of Forests, Lands and Natural Resource Operations
Kootenay Region
April 2013
Prepared by:
Patrick Stent1, Kim G. Poole2, Ian Adams3, and Garth Mowat1
1 BC Ministry of Forests, Lands and Natural Resource Operations, Suite 401, 333 Victoria St., Nelson, BC V1L 4K3 [email protected]; [email protected]
2 Aurora Wildlife Research, 1918 Shannon Point Rd., Nelson, BC V1L 6K1 [email protected] 3 Vast Resource Solutions, P.O. Box 538, 4500 Mennie Rd., Cranbrook, BC V1C 4J1
Transplants and die-offs............................................................................................................................ 5
Population estimates ................................................................................................................................ 5
Harvest data .............................................................................................................................................. 8
Survey data ......................................................................................................................................... 11
Population trends ............................................................................................................................... 13
Age and sex structure ............................................................................................................................. 16
Harvest data ............................................................................................................................................ 22
Population trends .................................................................................................................................... 36
Literature cited............................................................................................................................................ 47
Rocky Mountain bighorn sheep (Ovis canadensis canadensis) are an important big game species in the
Kootenay Region of British Columbia (BC). In BC, the majority (80%) of native Rocky Mountain bighorn
sheep are located along the Rocky Mountains from Kickinghorse River south to the US border
(Shackleton 1999, Demarchi et al. 2000). In the Kootenay Region, introduced herds reside in the South
Salmo and Deer Park areas, located in the West Kootenay outside of historic bighorn sheep range. Other
introduced herds are located in the Thompson-Nicola Region at Spences Bridge and Chase, within
historic California bighorn sheep (O. c. californiana) range.
Bighorn sheep (both subspecies combined) are Blue-listed in BC (provincial conservation status ranking
S3 – special concern, vulnerable to extirpation or extinction – reviewed May 2010; B.C. Conservation
Data Centre 2012). Reasons given for this listing are that despite a provincially stable population, there
have been substantial localized declines in the past, and sheep continue to lose good quality habitat
(especially winter range) to various types of land conversion and to forest encroachment. Sheep are also
vulnerable to stress and stress-related diseases, and diseases introduced from domestic sheep
(Schommer and Woolever 2008) and outbreaks in this region during the 1980s caused major population
declines in some herds (Davidson 1994).
Two ecotypes of Rocky Mountain bighorn sheep exist in the Kootenay Region, sheep that winter at low
elevation and sheep that winter at high elevation. Sheep that winter at low elevation escape deep snow
at higher elevations by using grassland or open forested habitats on flat or southerly aspects associated
with rocky escape terrain. Sheep that winter at high elevation use mid- to high-elevation grassland
habitats on windswept, southerly facing slopes again associated with escape terrain. For accounts of the
status and biology of Rocky Mountain bighorn sheep in BC, refer to Shackleton (1999) and Demarchi et
al. (2000).
The Ministry of Forests, Lands and Natural Resource Operations (MFLNRO: formally Ministry of
Environment) manages wildlife in the region through 40 Management Units (MU), only 10 of which
support hunted sheep populations (Fig. 1). Sheep are also assigned herd names based on groupings (Fig.
2). Guide-outfitter territories exist throughout the majority of the Kootenay Region; however sheep
quotas are only offered to guides operating in the East Kootenay.
A recent survey showed bighorn sheep are the highest valued species for guide-outfitters in the
Kootenays and other regions where bighorn sheep are hunted (MFLNRO unpublished data). The average
price of a guided bighorn sheep hunt in the Kootenays was $30,000 in 2009, while the revenue
generated from hunting license and tag sales was over $352,000 provincially and $74,000 for hunts in
the Kootenay Region. Viewing bighorn sheep also provides economic value, particularly in Radium Hot
Springs, BC, which offers viewing tours during the fall rut.
Since 1999-2000, 1 Special Sheep Permit has been auctioned off annually (except for 2009-10, and the
bidder withdrew in 2008-09). By agreement, 85% of the auctioned funds are returned to the Habitat
Conservation Trust Foundation (HCTF) to be used on wildlife conservation projects in the Province. In
addition to the auctioned permit, a Limited Entry Hunting permit (LEH; lottery) is also drawn. Since
1999-2000, a total of 14 bighorn sheep have been harvested in the Kootenay Region under the Special
Kootenay Region bighorn sheep population review
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Sheep Permit (8 auctioned and 6 LEH). A total of $1.3 million have been raised since 1999-2000 (S. West,
HCTF, pers. comm.)
Figure 1. Bighorn sheep Management Units and broad sub-populations and for the Kootenay Region of British Columbia. Note Southern Rockies in the legend = South Rockies-Flathead.
Kootenay Region bighorn sheep population review
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Figure 2. Bighorn sheep herds within the Kootenay Region of British Columbia.
Previous sheep hunting seasons in the East Kootenay included a 7/8 curl or 8 year old ram season prior
to 1976 and a resident LEH ewe season between 1985 and 2001. Currently, only full-curl rams are
Kootenay Region bighorn sheep population review
4
hunted in the Kootenays. A quota system regulates non-resident (guided) harvest, while current
resident hunting seasons include general open seasons (GOS) in the East Kootenay. Limited Entry
Hunting seasons exist for the 2 West Kootenay MUs that support sheep and for 2 herds in the East
Kootenay (Phillips Creek and Mt. Assiniboine Park). Accurate sheep harvest numbers exist in the
Kootenay Region as all sheep harvested must be submitted and tagged by an inspector. Non-hunter kills
are also inspected if Conservation Officers have time. Annual hunter questionnaires also provide
valuable information regarding hunter success and effort, which can be used to infer population trends
over time.
At the request of the BC MFLNRO, Kootenay Region, we were tasked to review current and historic
population information about bighorn sheep in the Kootenay Region. This report has the following
objectives:
1. Critically review all population data for bighorn sheep in the Kootenay Region and summarize historic and current population size, population density, and population trajectory information, drawing on all available sources of information;
2. Summarize information on vital rates such as reproduction and mortality and present these measures across time;
3. Summarize hunter harvest, effort and success data, comparing harvest numbers and population estimates; and
4. Summarize data for management, herd or ecological units, as appropriate.
This review will provide wildlife and habitat managers with an up to date summary of population status
and also to demonstrate to other interested readers the current level of population knowledge for the
species.
Kootenay Region setting
The Kootenay Region covers the southeast corner of BC, extending from Kinbasket Lake to the US
border, and from west of Arrow Lakes and Lake Revelstoke to the Alberta border (Fig. 1). Four parallel
mountain ranges run northwest across the region. The Monashee and Selkirk ranges define the West
Kootenay sub-region, and the Purcell and Rocky Mountain ranges delineate the East Kootenay sub-
region. Large lakes and reservoirs are scattered throughout the region. In general, the West Kootenay is
warmer and wetter than the East Kootenay. These climatic differences are reflected by different
vegetation. Both the east and west have Interior Cedar Hemlock, Engelmann Spruce Subalpine Fir and
Alpine Tundra Biogeoclimatic Zones, but the east also has dry forest types, including Ponderosa Pine,
Interior Douglas Fir, Western Larch and Montane Spruce (Meidinger and Pojar 1991).
The Kootenay Region had extensive forest loss in the late 1800s and early 1900s due to large fires and
land clearing for settlements and agriculture (MFR 2006). Since the 1950s, forest succession, changes in
timber harvest practices, and aggressive fire suppression has resulted in greater forest cover. In
particular, the relative proportion of open range, open forest and closed forest in the East Kootenay
Trench has changed significantly over time. In the late 1880s early explorers reported extensive areas of
closed forest, but by the 1920s and 1930s, there was open range throughout most low elevation areas
(Pitt 1982). This created an abundance of new forage and, in response, domestic livestock and wildlife
Kootenay Region bighorn sheep population review
5
populations grew and expanded in distribution. Recent efforts have attempted to re-establish areas of
open range/open forest throughout the East Kootenay Trench and dry ecosystems of the West Kootenay
caribou (Rangifer tarandus) and mountain goat (Oreamnos americanus) (Poole 2006, Poole 2007,
Mowat and Kuzyk 2009). There are a wide range of predators as well, including grizzly bears (Ursus
arctos), black bears (U. americanus), wolves (Canis lupus), coyotes (C. latrans) and cougar (Puma
concolor) (Mowat 2007).
National and provincial parks occur throughout the Kootenays, some supporting sheep populations, with
the largest area of parks occurring in the northern East Kootenay (Fig. 1). Hunting is permitted in most
but not all provincial parks (including protected areas, recreation areas, and conservancies) but is
prohibited in national parks. A significant area of year-round sheep range in the Elk Valley (MU 4-23)
overlaps with Teck Coal properties; due to safety related issues, hunting is prohibited in active mine
sites (L. Amos, Teck Coal, pers. comm.).
Methods
Transplants and die-offs
We reviewed MFLNRO reports and files (Davidson 1994; I. Teske, MFLNRO, unpublished data) relating to
all sheep transplants and die-off's that have occurred in the Kootenay Region since the early 1980s. We
present transplant and die-off data first as many of the population changes relate to these events.
We used the definition by Blood (2001) to define a Successful transplant as a “population [that] has
grown substantially and persisted for at least 10 years”. We refined the definition to include Somewhat
successful, defined as “stable to minor population growth over a period of 4- 10 years”, and Not
successful, defined as “remnant population has not grown; introduced animals did not survive or left
release area”.
Population estimates
Aerial bighorn sheep survey data were obtained from MFLNRO files, mostly spreadsheets (I. Teske, BC
MFLNRO, unpublished data) and a limited number of reports (e.g., Teske and Forbes 2002, Stent 2011,
Phillips and Stent 2012, Poole 2013). Information describing survey methods from 1965 to 1999 was not
available. The spreadsheets provided no indication of survey area size, time spent on survey, or whether
a sightability correction factor was applied to the counts. A conditions field was added that ranked
surveys as ‘Good’, ‘Fair’ or ‘Poor’. We examined the data to remove incidental sightings and retain
formal surveys. Surveys between 2000 and 2011 were conducted by MFLNRO and the Columbia Basin
Fish & Wildlife Compensation Program. Ground survey totals between 2000 and 2011 for the Radium-
Stoddart herd in MU 4-25 (and possibly 4-35) were provided by Parks Canada.
Kootenay Region bighorn sheep population review
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For all surveys, records within 7 days were considered to be 1 survey. Surveys were given a discrete
code based on year, consecutive survey number and month of survey. This rule was especially important
in collating data from 1965 to 1999 where no indication was available to discern among discrete survey
efforts. In instances where records within 7 days of the previous record continued for up to 1 month
with the same pilot and observers and in the same general area, these were also considered to be a
single survey. At other times, there was clear duplication of survey effort of the same location within a
few weeks. Counts were summed for each discrete survey. Occasionally, more than 1 discrete survey
was recorded for each MU or sheep herd within 1 year. These records were double-checked and the
counts summed where appropriate (for example within MU 4-25, discrete surveys may have occurred
within 1 calendar year at both Radium-Stoddart and Columbia Lake). In instances where duplication of
survey effort was apparent (e.g., the same herd was surveyed twice within the calendar year), the
highest count value was taken.
We assumed that most sheep surveys were conducted using a total count (Teske and Forbes 2002), and
used the following survey methodology (adapted from Poole 2013). Surveys were conducted by
helicopter, generally a Bell 206B or 206L, and used a pilot, navigator/recorder, and 2 rear-seat
observers. Surveys covered all known or suspected sheep habitats, and were generally conducted in
mid- to late winter. Most surveys used contour flight lines, ensuring that census zone coverage was
complete. Prior to the mid-1990s, flight lines and animal locations were mapped on hard-copy maps;
subsequently hand-held GPS unit were used. Where possible, sheep were classified to Level 4
classification (RISC 2002), which consisted of lambs, ewes, and Class I, Class II, Class III, and Class IV
rams. Snow cover (%), oblique vegetation cover (%), activity code (resting or active), and broad habitat
class were available for most surveys from 2008 to 2012, but not for earlier surveys. Study area (census
zone) and time spent on survey were generally not available.
No surveys observe all sheep present within an area and the degree of sightability varies greatly
depending upon animal behaviour, snow conditions, terrain and vegetation, and other factors.
Documented sightability from various subspecies of bighorn sheep has ranged from 0.33–0.86 (Neal et
al. 1993, Bodie et al. 1995, Cubberley 2008, Poole 2013). To obtain a population estimate, sightability
can be applied based on sighting of marked animals (Teske and Forbes 2002, Poole 2013), application of
a logistic model (Bodie et al. 1995, Unsworth et al. 1998), or gut feeling. No sightability correction factor
was provided for most surveys reported here prior to 2009. A sightability of 0.75-0.85 had been
assumed during surveys carried out by BC MFLNRO up to about 2008 based on 4 tests conducted with
marked animals in the East Kootenay (sightability data not provided; Teske and Forbes 2002). Surveys of
a GPS-collared population in the Elk Valley in 2010 and 2011 found 0.82 and 0.77 sightability,
respectively (Poole 2013). Application of the Idaho model (Unsworth et al. 1998) during surveys of 4
large (>100 sheep) populations in the south Okanagan determined sightability ranged from 0.63 to 0.78
(Reid 2011). Modelled sightability from 8 East Kootenay herds surveyed in spring 2012 ranges from 0.67
to 0.83 (Phillips and Stent 2012). We clarify that some results are presented on raw counts, and some on
population estimates, incorporating sightability-corrected data (assumed or modelled).
We summarized most data at the herd, MU, or MU groupings levels (termed here sub-population; see
below), depending largely upon sample size and how data were recorded, as well as at the East
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Kootenay level. A significant component of the population review was analysis of existing harvest data,
which are summarized only at the MU level. The 2 West Kootenay MUs supporting smaller bighorn
sheep populations (4-08 and 4-15) were analysed separately where possible. Low sample sizes in some
areas required amalgamating years or areas to produce meaningful trends. Kill location data were also
used to infer changes in population distribution and harvest over time. We produced 90% fixed kernel
polygons (using 20% href) of kill locations for each decade since 1980 using “Home Range Tools” in
ArcGIS (version 9.3).
It is ideal to manage sheep at the herd level, however databases and samples sizes did not always allow
for management at this level. Most but not all MUs can be considered as a single sheep sub-population.
Some herds cross MU boundaries – sheep occupying the Wigwam, Mount Broadwood and Lizard Range
along the MU 4-02–4-22 boundary are an example. It was often convenient to group MUs into local
associations of populations (termed sub-populations) for descriptive purposes. We describe these sub-
populations as:
South Rockies-Flathead (MUs 4-01 & 4-02);
Upper Kootenay (MUs 4-21, 4-22 & 4-24);
Upper Columbia (MUs 4-25 & 4-35);
Elk Valley (MU 4-23);
West Kootenay (MUs 4-08 & 4-15).
In the West Kootenay, the Syringa bighorn sheep population estimate was based on ground counts prior
to 2011 (G. Mowat, MFLNRO, unpublished data), and an aerial survey in January 2011 (Stent 2011).
Estimates for the MU 4-08 Salmo-Creston herd were based on ground counts at the sheep feeding
station and represent minimum counts for this herd. A small amount of sheep sign was observed in the
South Salmo drainage during 2011 December mule deer surveys (P. Stent, personal observation),
suggesting a small number of animals may winter away from the feeding station.
We analysed composition data (lamb and ram ratios) from MFLNRO data (I. Teske, MFLNRO,
unpublished data) by summing sheep observations from mid to late winter (January – April) aerial and
ground surveys within population units. We calculated binomial confidence intervals (95%) using the
formula in Zar (1996: 525) for all population ratios. Lamb ratios are described as the number of lambs
per 100 ewes; ram ratios as the number of Class I to IV rams per 100 ewes. Yearling and 2-year-old rams
(Class I) are usually in nursery bands and are difficult to consistently distinguish from adult females (RISC
2002); thus a degree of bias is likely present in most counts. These surveys usually focused on 1 or more
sheep herds within the population units and the herd(s) surveyed differed among surveys. We excluded
composition data for surveys where there was <30 sheep as the sample for the population unit;
however, samples of <30 sheep were summed among units to show composition trends for the entire
East Kootenay. Published sources of ratio data were used where possible (primarily since 2008).
Lamb ratios were plotted against a winter severity index and the number of problem cougar kills to see
if these variables were correlated with late-winter lamb ratios. Winter severity index (T. Szkorupa,
MFLNRO, unpublished data; modified from Baccante and Woods 2008) was calculated using mean daily
Kootenay Region bighorn sheep population review
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air temperature by month (TEMP – °C) and total monthly snowfall (SNOW – cm) measured at the
Cranbrook airport between November and April using the following formula:
((TEMP if <0°C)/3) × (SNOW (cm))
The index was calculated monthly and summed for each winter.
Harvest data
We obtained sheep harvest data from Compulsory Inspections (CI) and voluntary hunter questionnaires.
All sheep harvested in the Kootenay Region require inspection by a designate of the provincial
government. Hunter questionnaires are mailed to a sample of hunters at the end of each hunting season
to determine the number of days hunted and whether the hunt was successful. Data are summarized by
residents and non-residents and by MU. Compulsory inspections likely provide more accurate harvest
numbers than hunter questionnaires as they are mandatory for all successful sheep hunters, while
hunter questionnaires are voluntary and produce estimates rather than total count. These 2 sources of
data were used to infer changes in harvest, hunter success (proportion of hunters that were successful),
and catch per unit effort (days per kill). Together these metrics can be used to produce an index of
population trend over time.
Age estimates were available for 63% of compulsory inspected sheep and were used to assess age
distribution of harvested sheep. Mean age of harvested rams and the proportion of 7+ year old rams in
the harvest were considered as an indication of harvest pressure, since the greater the pressure the
lower the overall age of harvested rams (Coltman et al. 2003, Hengeveld and Festa-Bianchet 2011).
Nearly all age estimates (95%) were based on horn annuli counts (Elbroch 2006), while 5% were
calculated using tooth sectioning. Hence, age distribution data presented are based on horn annuli
counts, which are less accurate than tooth sectioning (Turner 1977). Examination of 83 cases of
matching horn and teeth ages indicated a significant relationship that explained little of the variance (r2
= 0.12, P = 0.0008), largely due to 6 samples with teeth ages 11-17 years with corresponding horn ages
of 4-8 years. Restricting ages from both methods to ≥4 years of age (since it is highly unlikely that any
ram <4 years of age cold attain full curl; Festa-Bianchet 1989) and ≤11 years of age (likely limits of
accurate horn aging) did nothing to improve the relationship (r2 = 0.12, P = 0.0009).
Harvest rates for each sub-population were calculated by dividing the reported number of sheep
harvested in each time period by the population estimate for that time period (e.g., rams per 100 sheep,
expressed as a percentage). Rates were divided by sex where ewe harvests had occurred. We present
harvest data by MUs and all East Kootenay populations combined.
Note that we often present data with 3 or 5-year running average trend lines. We used 5-year trend
lines when sample sizes were low and 3-year trends with more robust sample sizes. For ratios, we
calculated trends as the average ratio among yearly values, and not the 5-year sum of the numerator
(lambs or rams) over the 5-year sum of the denominator (ewes).
Kootenay Region bighorn sheep population review
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Results
Transplants
Bighorn sheep transplants in the Kootenay Region have been conducted since the early 1980s, with the
majority of transplants occurring in the mid-to-late 1980s (Davidson 1994; Table 1). A total of 364 sheep
were transplanted between 1982 and 2009. The main objective in the 1980s was to aid in population
recovery from die-offs that occurred in the early 1980s (Davidson 1994, Blood 2001). Transplants that
occurred in 1990s and 2000s were to augment populations believed to be declining from harsh winters
and/or predation. The source of animals for transplants were primarily the Radium, Stoddart Creek,
Columbia Lake, and more recently Golden herds (MUs 4-25, 4-35), with most sheep going to various
destinations south of Canal Flats (Table 1). Two groups of sheep were moved to Syringa Provincial Park
in the West Kootenay in the 1980s to establish the Deer Park herd. The South Salmo herd was a natural
northern expansion of a herd from the Hall Mountain area of Washington State, established through
introductions in 1972 and 1982 (Shackleton 1999, Shepherd and Base 2010). Neither of these West
Kootenay herds is within areas known to have been formerly occupied by bighorn sheep, and the South
Salmo herd depends on supplemental feed in winter (Shackleton 1999, Demarchi et al. 2000). In
addition, about 35 Rocky Mountain bighorn sheep have been moved from the Kootenay region to the
United States for reintroductions (Shackleton 1999).
The success of the transplants has varied (Table 1). Of the 20 transplants where success was evaluated,
9 (45%) were deemed successful, 5 (25%) were somewhat successful, and 6 (30%) were not successful.
Mean number of sheep moved in unsuccessful transplants (12.7 sheep) tended to be smaller than mean
number of sheep moved in somewhat successful or successful transplants (19.4). However the
difference was not significant (t-test, t = 2.1, 18 df, P = 0.16).
Die-offs
The most significant bighorn sheep die-off to occur in the Kootenays was during the early 1980s in the
southeast portion of the region (Table 2; Davidson 1994). The die-off was believed to be a result of acute
pneumonia, which was passed from domestic sheep to wild sheep in the Maguire Creek drainage in MU
4-02 between 1979 and 1981. Elevated stress levels as a result of poor range condition, and severe
winter and spring conditions could have also been contributing factors in the die-offs. The die-off
affected the South Rockies-Flathead herds first, reducing populations by approximately 60%, then
spread to the Upper Kootenay herds, which experienced population declines of approximately 25%
(Davidson 1994). The 1981–1983 die-off reduced populations from approximately 2,100 to 1,500 sheep
(Davidson 1994). The outbreak did not affect sheep herds located at Phillips Creek, north of Columbia
Lake, and the Elk Valley. The die-off was believed to have reached the Bull River herd in MU 4-22 but
had less impact on this herd. Much work was conducted in 1980s to restore bighorn sheep populations
post die-off, with resulting regional population estimates of 2,380 sheep in 1988 (Davidson 1994).
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10
A less significant die-off occurred in 1980 as a result of a soremouth (contagious ecthyma) outbreak in
the Wigwam Flats area (Davidson 1994). Contagious ecthyma is a viral disease of sheep and goats (wild
and domestic) caused by infection with the parapoxvirus or orf virus. It is spread by direct contact with
scabs on infected animals. The lamb component of this population was severely affected by the disease,
with lamb ratios reduced to 10:100 ewes in the winter of 1980-81. Sore mouth occurs sporadically in
most bighorn sheep herds occupying the Rocky Mountain Trench. It has never been documented in
bighorn sheep occupying the Elk Valley. Soremouth was observed in the Radium herd as recently as
2005.
Table 1: Summary of bighorn sheep transplants and success in the Kootenay Region of British Columbia, 1982-2009 (Hatter and Blower 1996; Blood 2001; MFLNRO data).
Year Source MU Destination MU Number Success1
1982 Wigwam 4-02 Bull River 4-22 16 Not
1984 Columbia Lake 4-25 Elko
4-02 28 Somewhat
Maguire Creek 7 Successful
1985 Columbia Lake 4-25 Tulip/Syringa Creek 4-15 20 Somewhat
Maguire Creek 4-02
10 Successful
1986 Columbia Lake 4-25
Elko 11 Somewhat
Wildhorse 4-21 5 Not
Stoddart Creek 4-25 Wigwam 4-02 47 Successful
1987 Stoddart Creek 4-25 Syringa Creek 4-15 18 Successful
1987 Columbia Lake 4-25
Wildhorse 4-21
12 Not
Lakit Lake 11 Not
Mause Creek 4-22 17 Unknown
1989 Radium
4-25
Wigwam 4-02 20 Successful
1989 Stoddart Creek
Maguire Creek 4-02 19 Successful
1992 Ram Creek 4-21 22 Successful
1993 Ewin Ridge 4-23 Bingay Creek 4-23 7 Somewhat
Radium 4-25 Ram Creek 4-21 27 Successful
1994 Radium 4-25 Ewin Ridge 4-23 10 Successful
2005 Radium 4-25 Wasa Creek 4-21 25 Somewhat
2007 Golden 4-35 Whiteswan Lake area 4-25 19 Not
2009 Golden 4-35 Grundy Creek 4-21 13 Not
Total 364
1 Successful: population has grown substantially and persisted for at least 10 years; Somewhat successful: stable to minor
population growth over a period of 4- 10 years; and Not successful: remnant population has not grown; introduced animals did
not survive or left release area.
Kootenay Region bighorn sheep population review
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Table 2: Summary of bighorn sheep die-off is the East Kootenay Region of British Columbia, 1980-1983 (Davidson 1994). There have been no known die-offs since 1983.
Mgmt. unit Herd Year Estimate before Die-off
Estimate after Die-off
Cause
4-02 Wigwam 1980-81 Decline in lamb ratios Soremouth
4-02 Maguire 1981 80 14 Pneumonia
4-02 Wigwam 1982 450 140 Pneumonia
4-21 Wild Horse, Estella, Premier, Marmalade
1982 315 209 Pneumonia
4-21/4-24 Van Nostrand 1983 70 45 Pneumonia
4-25 Whiteswan 1983 70 35 Pneumonia
Population estimates
Movements
Evaluation of herd and MU estimates hinges in part on the degree of movement among herds.
Movement of transplanted sheep are common (I. Teske, MFLNRO, pers. comm.). Only 3 studies in the
East Kootenay followed collared sheep for any period of time. No dispersals or movement between
winter ranges was reported in 33 ewes fitted with VHF collars from 1997-99 at Columbia Lake, Bull River,
and Mount Broadwood herds (Kinley 2007). Dibb et al. (2008) did not detect any dispersal or
interchange between the Radium herd and other herds; however, the study design (9-10 animals of
both sexes collared for 4 years but only between January-March to November-December) did not lend
itself to this kind of detection. J. Krebs (MFLNRO, pers. comm.) noted that during the 1990s some sheep
from the Golden population mixed with the Radium-Stoddart herd on summer range in the Kindersley
area, some 80 km distant. Finally, no movements by sheep outside of the study area were detected over
a 2.5 year study in the Elk Valley (n = 41 ewes and rams; Poole 2013). Fidelity to winter ranges in this
study was high (88%), and most movements among winter ranges involved distances of <10 km. Only 1
sheep, a 4-year-old ram, conducted extra-home range movements (38 km and 20 km one way); this
animal returned to its normal home range on both occasions.
Survey data
We identified 247 discrete surveys between 1965 and 2011 (Fig. 3). The number of surveys per year
reached a maximum of 13 in 1991 and 12 in 2008. The only years with no survey effort were 2004 and
2007. Overall, survey effort has declined slightly over the 46 year time period.
Kootenay Region bighorn sheep population review
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Figure 3: Number of discrete surveys by year in the Kootenay Region, 1965 to 2011. Dashed line is a 5 year moving average.
Over the past 45 years some herds and MUs were surveyed close to 30 times (Appendices 1 and 2).
Survey data showed a broad range of results between 1965 and 2012 at both the MU (Appendix 1) and
sheep herd (Appendix 2) level. We culled numerous count values that were obviously low as a result of
incomplete survey effort. Results like these reflect reduced or incomplete survey effort and not actual
changes in population size. The lack of documentation on survey effort confounds efforts to identify real
changes in population size. Ground counts were available for relatively few herds and MUs (Table 3). No
data were available to assess coverage or survey effort among counts.
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Kootenay Region bighorn sheep population review
13
Table 3: Total sheep counts of ground-based bighorn sheep surveys, totalled by Management Unit and Sheep Herd, between January and April in the Kootenay Region, British Columbia, 2001-2011. There are no records of ground-based surveys prior to 2001. Sheep Herds: BR: Bull River; CL: Columbia Lake; RS: Radium-Stoddart; SY: Syringa.
Year Management Unit Sheep Herd
4-22 4-251 4-15 BR CL RS2 SY
2001 58 50 58 50
2002
2003 162 162
2004
2005 150 150
2006 168 168
2007 217 217
2008 64 215 91 64 68 147 91
2009
2010
2011 127 127 1 Combined MoE/CBFWCP and Parks Canada data.
2 Parks Canada data
Population trends
The survey data show some general trends in numbers over time (Fig. 4). Most sub-populations
increased in numbers between the mid-1960s and early 1980s. Subsequent declines were observed in
some of the sub-populations, most notably the South Rockies-Flathead – likely related to the die-offs –
and less so in the Elk Valley and Upper Columbia. The Elk Valley population appeared to decline during
the early 1980s concurrent with die-offs in other areas, despite no apparent die-off. Most sub-
populations peaked again in the early 1990s, with a decline in all but the Upper Kootenay sub-
population through the 1990s and prior to the very severe winter of 1996-97. No population estimates
are available between 1998 and 2000; however, although data to support this claim are poor, it is
probable that most sheep populations experienced additional declines due to the severe winter of 1996-
97. This trend was noted in other ungulate populations in the Kootenays (Robinson and Clarke 2007,
Mowat and Kuzyk 2009). We suspect the sheep population as a whole reached a 30-year low in the late
1990s, and likely increased during a series of mild winters through much of the 2000s. Estimates
increased through to the late 2000s, with the greatest increase within the Elk Valley sheep population.
The most recent population estimates for sheep within the Kootenay Region suggest approximately
2,150 sheep are present (Table 4). Dated or incomplete estimates (i.e., no associated variance) occur for
a few populations, most notably the Flathead (MU 4-01)
Kootenay Region bighorn sheep population review
14
Figure 4: Total survey counts (uncorrected for sightability) and trends (matching colours) for sub-
populations of Rocky Mountain bighorn sheep in the East Kootenay region, British Columbia, 1965-
2011. Data are from late-winter aerial surveys between January and April, expect for Upper Columbia
sub-population which includes Parks Canada ground count data (January – April) between 2001 and
2011. Trend lines are 5-year moving average. Grey shading approximates time period of die-offs in
South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations (Table 2). Heavy
vertical line indicates severe winter of 1996-1997.
0
100
200
300
400
500
600
700
800
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Tota
l Su
rvey
Co
un
t
South Rockies-Flathead Upper Kootenay Upper Columbia Elk Valley
Kootenay Region bighorn sheep population review
15
Table 4: Recent bighorn sheep population estimates for Kootenay populations. Underlined herd estimates are based on aerial survey counts corrected for incomplete sightability in the program AERIAL SURVEY or collar data (Elk Valley East). Red text denotes dated or unreliable estimates; brown text denotes ground counts. Lower 90% confidence intervals (CI) corrected upwards to minimum counts.
MU Herd Estimate 90% CI Date Source
4-01 Flathead 801 Unknown I. Teske, pers. comm.
4-02 Galtons 120 98-152 Feb 2012 Phillips and Stent 2012
4-02 Wigwam-Mt. Broadwood
215 158-283 Feb 2012 Phillips and Stent 2012
4-08 Salmo (LEH) 402,3
Mar 2012 I. Teske, unpubl. data
4-15 Syringa (LEH) 63 31-98 Jan 2011 Stent 2011
4-21 Premier-Diorite-Wild Horse
58 48-78 Mar 2012 Phillips and Stent 2012
4-21 Marmalade-Sharktooth
118 79-161 Mar 2012 Phillips and Stent 2012
4-22 Elko/Lizard 302 Unknown I. Teske, pers. comm.
4-22 Bull River 147 100-266 Mar 2012 Phillips and Stent 2012
4-23 Elk Valley West 87 69-108 Apr 2012 Phillips and Stent 2012
4-23 Elk Valley East 840 731-10314 Feb 2010 Poole 2103
4-23 Elk Valley East 750 655-9284 Feb 2011 Poole 2013
4-24 Whiteswan/Nine Mile 63 46-83 Mar 2012 Phillips and Stent 2012
4-25 Columbia Lake 151 101-240 Mar 2012 Phillips and Stent 2012
4-25 Windermere/Radium 1272 Apr 2011 Phillips and Stent 2012
4-25 Mt Assiniboine (LEH) 855 Mar 2009 I. Teske, unpubl. data
4-35 Golden (not hunted) 202 Apr 2012 Phillips and Stent 2012
Total 2154 1767-27796
1 Based on information from outfitters; survey scheduled for 2013.
2 Ground counts (no sightability correction).
3 Salmo sheep maximum ground counts at feeder of 37 in Jan 2011 and 29 in Mar 2012 (I. Teske, unpubl. data).
4 Elk Valley East surveys of the core collar study areas extrapolated to include areas not surveyed in 2010 and 2011; confidence
intervals increased proportionately. 5 Mt. Assiniboine count of 64, with estimate of 85 based on 0.75 sightability (I. Teske, unpubl. data).
6 Confidence intervals for total assume raw counts or estimates for surveys without associated variance.
Kootenay Region bighorn sheep population review
16
Age and sex structure
Lamb ratios
Lamb ratios within the Kootenay Region showed a slow decline from the late 1970s to the past 5 years,
with the greatest drop in the late 1990s (Fig. 5). Lamb ratios were highest between the mid-1970s and
1998 ( x = 45 ± 8.2 [SD] lambs:100 ewes, n = 24 years), and lower since 1999 ( x = 30 ± 7.8 lambs:100
ewes, n = 11 years). Trends varied among some of the 4 sub-populations (Figs. 6-9), with a strong dip in
the South Rockies-Flathead during the early 1980s (likely related to the pneumonia die-off) followed by
a rebound into the early 1990s (Fig. 6). Lamb ratios in the Elk Valley West herds largely mirrored those of
the Elk Valley East herds (Fig. 9). Lamb ratios for specific MUs with sufficiently large sample sizes are
presented in Appendix 3.
Figure 5: East Kootenay bighorn sheep lamb ratios (±95% CI), 1976–2012, relative to indices of winter severity (WSI) and cougar predation. Lamb ratio trend is 3-year running average. The winter severity index is based on monthly snowfall and temperature data recorded at the Cranbrook airport; 1997 = winter 1996-97. Annual problem cougar kills was multiplied by 5 to facilitate viewing on the primary Y-axis. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
100
200
300
400
500
600
0
10
20
30
40
50
60
70
80
Win
ter
Seve
rity
Ind
ex
Lam
bs:
10
0 E
we
s /
Co
uga
r C
on
tro
l Kil
ls (
x5)
Lambs:100 Ewes WSI Problem Cougar Kills
Kootenay Region bighorn sheep population review
17
Figure 6. Lamb ratios (±95% CI) within the South Rockies-Flathead, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
Figure 7. Lamb ratios (±95% CI) within the Upper Kootenay, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
10
20
30
40
50
60
70
80
Lam
bs:
100
Ewes
South Rockies-Flathead
Lambs: 100 Ewes
0
10
20
30
40
50
60
70
80
Lam
bs:
100
Ewes
Upper Kootenay
Lambs:100 Ewes
Kootenay Region bighorn sheep population review
18
Figure 8. Lamb ratios (±95% CI) within the Upper Columbia, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
Figure 9. Lamb ratios (±95% CI) within the Elk Valley, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
10
20
30
40
50
60
70
80
90
100
Lam
bs:
10
0 E
we
s
Upper Columbia
Lambs:100 Ewes
0
10
20
30
40
50
60
70
80
90
100
Lam
bs:
10
0 E
we
s
Elk Valley
Elk Valley East Lamb Ratio Elk Valley West Lamb Ratio
Kootenay Region bighorn sheep population review
19
Lamb ratio data for the entire East Kootenay were plotted against indices for winter severity and cougar
abundance (Fig. 5). Lamb ratios in 1997 (49:100 ewes) were not markedly lower than previous years,
despite the high winter severity in 1996-97; however, the ratio was calculated from only 2 MUs (4-25
and 4-35) and relatively low sample size (n = 57 ewes). Problem cougar kills peaked following the severe
winter, suggesting cougar populations were high after most ungulate populations had suffered a
significant die-off. Linear regressions showed a weak (and counter-intuitive) positive relationship
between lamb ratios and winter severity (y = 0.034 + 33.4; r2 = 0.14, P = 0.03); a 1 year lag provided no
better fit to the data (y = –0.004 + 40.7; r2 = 0.002, P = 0.80). Using the sum of snowfall alone as a
severity index resulted in no fit to the lamb ratio data (y = 0.031 + 38.3; r2 = 0.02, P = 0.46). We found no
relationship between lamb ratios and the cougar abundance index, either for the current year (y = –
0.076 + 41.1; r2 = 0.01, P = 0.57) or for a 1 year lag (y = –0.141 + 41.7; r2 = 0.03, P = 0.30).
Ram ratios
Within the East Kootenay as a whole, survey data suggest low ram ratios in the 1970s, and an increasing
trend through to the mid-1980s (Fig. 10). Ram ratios generally peaked in the late 1980s to mid-1990s
and then declined slightly to average 52 rams:100 ewes since 1999 (SD = 8.8, n = 11). Ram ratios have
remained relatively stable over time in the South Rockies-Flathead (Fig. 11) and Upper Kootenay (Fig.
12), but in the Upper Columbia and Elk Valley generally rose and declined (Figs. 13, 14). Wide confidence
intervals and extremely high ratios (>100 rams:100 ewes) suggest incomplete surveys in some years.
Ram ratios for specific MUs with sufficiently large sample sizes are presented in Appendix 4.
Figure 10: East Kootenay bighorn sheep ram ratios (±95% CI), 1976–2012. Ram ratio trend is 3-year running average. Data originate from winter aerial surveys. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
10
20
30
40
50
60
70
80
90
100
Ram
s:10
0 Ew
es
Rams:100 Ewes
Kootenay Region bighorn sheep population review
20
Figure 11. Ram ratios (±95% CI) within the South Rockies-Flathead, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
Figure 12. Ram ratios (±95% CI) within the Upper Kootenay (1976–2012); trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
10
20
30
40
50
60
70
80
90
100
Ram
s:10
0 Ew
es
South Rockies-Flathead
Rams: 100 Ewes
0
10
20
30
40
50
60
70
80
90
100
Ram
s:10
0 Ew
es
Upper Kootenay
Rams:100 Ewes
Kootenay Region bighorn sheep population review
21
Figure 13. Ram ratios (±95% CI) within the Upper Columbia, 1976–2012; trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
Figure 14. Ram ratios (±95% CI) within the Elk Valley (1976–2012); trend is 5-year running average. Grey shading approximates time period of die-offs in South Rockies-Flathead (Wigwam) and Upper Kootenay (Whiteswan) sub-populations. Heavy vertical line indicates severe winter of 1996-1997.
0
10
20
30
40
50
60
70
80
90
100
Ram
s:10
0 Ew
es
Upper ColumbiaRams: 100 Ewes
0
20
40
60
80
100
120
Ram
s:10
0 Ew
es
Elk Valley
Elk Valley East Ram Ratio Elk Valley West Ram Ratio
Kootenay Region bighorn sheep population review
22
Harvest data
Hunter numbers
The number of resident sheep hunters peaked in the early 1990s when the greatest numbers of ewe
tags were allocated (Fig. 15). Ewes were not hunted after 2002 and the number of resident hunters
dropped to levels that were similar to before ewes were hunted. The unusually low number of resident
hunters in 2004 appears to be a data error, as most calculations associated with this year result in
patterns that are significantly out of sync with adjacent years. Regardless of 2004, resident hunter
numbers increased during the latter half of the 2000s. The number of non-resident hunters increased
steadily in the East Kootenay during the late 1980s and early 1990s, stabilized through to the early
2000s, and varied widely but trended higher during the past decade (Fig. 15). Total number of resident
hunter days peaked in the late 1980s to early 1990s at just below 5,000 days, concurrent with the
greatest ewe allocations (Fig. 16). After a dip in the mid-2000s, the number of resident days increased to
roughly 3,500-4,000 days in the past few years. Number of non-resident days has increased slowly since
the mid-1980s, with levels approximately 10% of those of residents. Resident male sheep hunting
opportunity has averaged below 400 hunters over the last 30 years and has only exceeded that long-
term average once in the early 1980s and in 2009 and 2010. While no long-term trend in resident
hunting opportunity is apparent, non-resident sheep hunting opportunity has increased throughout the
period from the early 1980s to the early 2000s and appears to have levelled off since then.
Kootenay Region bighorn sheep population review
23
Figure 15: Number of resident and non-resident sheep hunters in the East Kootenay, 1976-2010. Data originate from voluntary hunter questionnaires. Trend lines are 3-year running averages. Numbers of ewe allocations were removed from the total number of resident hunters to better approximate numbers of ram hunters (most ewe allocations during 1989-93; Fig. 16). Grey shading depicts the period of ewe harvest, with the darkest grey the period of most numerous tag allocations (200-340 annually) and harvest (19-44 annually). Unknown numbers of ewe tags were allocated during 1997-2002, but the annual harvest during that period was 0-2 ewes.
0
10
20
30
40
50
60
0
100
200
300
400
500
600
No
n-r
esi
de
nt
hu
nte
rs
Re
sid
en
t h
un
ters
Residents Non-residents
Kootenay Region bighorn sheep population review
24
Figure 16. Total number of resident and non-resident sheep hunter days in the East Kootenay, 1976-2010. Data originate from voluntary hunter questionnaires, and did not separate out days for rams and ewes. Trend lines are 3-year running averages. Grey shading depicts period of ewe harvest, with the darkest grey the period of most numerous tag allocations (200-340 annually) and harvest (19-44 annually). Unknown numbers of ewe tags were allocated during 1997-2002, but the annual harvest during that period was 0-2 ewes.
Harvest numbers
Ewe Harvest
Ewe tags were issued to resident hunters via the LEH system between 1985 and 2002. It is unclear why
ewe harvests were implemented at this time in the East Kootenay, but it may have been a desire to
maintain sheep numbers within the limits of the carrying capacity of their winter range (Demarchi et al.
2000). Ewe permits were allocated to the Upper Columbia, Upper Kootenay and Elk Valley population
units (MUs 4-21, 4-22, 4-23, and 4-25), with the highest harvest occurring in the 2 former units between
1989 and 1992, at approximately 35–45 ewes annually (Fig. 17).
0
50
100
150
200
250
300
350
400
450
500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
No
n-r
esi
de
nt
hu
nte
r d
ays
Re
sid
en
t h
un
ter
day
sResidents Non-residents
Kootenay Region bighorn sheep population review
25
Figure 17: Bighorn ewe harvest for East Kootenay Management Units, 1985-2002. Data originate from compulsory inspections. Numbers of authorizations for 1997-2002 were unavailable. Ewes have not been hunted since 2002 in the Kootenay Region.
Ram harvests
Ram harvest numbers peaked during the late 1980s to mid-1990s, reached low values in the late 1990s
(non-residents) and early 2000s (residents) and have generally increased from these lows (Figs. 18, 19).
Within these trends, the split in the overall sheep harvest between residents and non-residents has
shifted, with non-residents taking roughly 20% of the ram harvest from the mid-1970s to the late 1990s,
to roughly 35-40% since 2000. Harvest numbers in MU 4-02 in 1982 and 1983 and to a less extent in the
Upper Kootenay sub-population during 1983-85 were likely affected by the die-off in the early 1980s
(Table 2; Fig. 19). A greater proportion of the region's recent ram harvest comes from the South Rockies-
Flathead and Elk Valley sub-populations, while the proportion of rams from the Upper Kootenay sub-
population has declined (Fig. 19). Harvest in the Upper Kootenay and Upper Columbia sub-populations
peaked in the early-to-mid 1990s. In recent years most of the harvest has come from MUs 4-23, 4-02, 4-
25, 4-22, and to a lesser extent 4-01 (Fig. 20). A very small proportion of the region's ram harvest came
st4-21 4-22 4-23 4-25 Number of LEH Authorizations
Kootenay Region bighorn sheep population review
26
Figure 18: Ram harvest for resident and non-resident (guided) bighorn sheep hunters in the East Kootenay, 1976-2010. Data originate from voluntary hunter questionnaires. Trend lines are 3-year running averages.
Figure 19: Bighorn sheep ram harvest by Kootenay Region sub-populations, 1976-2010. Data originated from compulsory inspection reports.
0
2
4
6
8
10
12
14
16
18
20
0
10
20
30
40
50
60
No
n-r
esi
de
nt
ram
har
vest
Re
sid
en
t ra
m h
arve
st
Residents Non-residents
0
10
20
30
40
50
60
70
80
Ram
Har
vest
South Rockies-Flathead Upper Kootenay Upper Columbia Elk Valley West Kootenay
Kootenay Region bighorn sheep population review
27
Figure 20. Bighorn sheep ram harvest by Kootenay Region management unit, 1976-2010. Data originated from compulsory inspection reports.
Hunter success
Here we define hunter success as the proportion of hunters who successfully killed a sheep. Within the
East Kootenay, hunter success of non-residents has always been on average 4–5 times higher than
success of residents (Fig. 21), but resident and non-resident hunter success was not correlated (r2 = 0.05,
P = 0.11). Non-resident success averaged 32% (SD = 11.0, n = 30 yrs) when summed across all years,
while resident success averaged 7% (SD = 2.3, n = 35 yrs). Resident hunter success has generally trended
in the 4–8% range, with a trend of increasing success during the first half of the 2000s, and declining
since 2005. The spike in resident hunter success in 2004 (14%) resulted from a drop by about half in the
number of resident hunters recorded in the database; although unverified these data appear suspect.
Non-resident hunter success has climbed steadily since the mid-1990s (Fig. 21). Hunter questionnaire
0
10
20
30
40
50
60
Ram
Har
vest
402 421 423 425
0
2
4
6
8
10
12
14
16
18
Ram
Har
vest
401 422 424 435
Kootenay Region bighorn sheep population review
28
results didn’t separate ewe hunters from ram hunters, therefore, we are unable to show hunter success
trends split between sexes. Hunting of ewes peaked between the late 1980s and late 1990s, and was
effectively non-existent after 1996 (Fig. 17).
Figure 21: Hunter success (ewe and ram harvest combined) for resident and non-resident (guided) bighorn sheep hunters in the East Kootenay, 1976-2010. Data originate from voluntary hunter questionnaires. Trend lines are 3-year running averages. Grey shading depicts period of ewe harvest, with the darkest grey the period of most numerous tag allocations (200-340 annually) and harvest (19-44 annually). Unknown numbers of ewe tags were allocated during 1997-2002, but the annual harvest during that period was 0-2 ewes.
Hunter success differed somewhat among MUs, although small annual harvest numbers in some areas
limited interpretation (Appendix 5). Resident hunter success was stable or trended slightly lower in most
MUs in recent years. During the past decade non-residents hunter success increased in MUs 4-02, 4-22,
and 4-25, and declined in MUs 4-21 (low samples size), 4-23 and 4-24.
Hunter success and the mean number of days hunted per kill (catch per unit effort; CPUE) were
correlated for residents (r2 = –0.57, P < 0.0001) and non-residents (r2 = –0.72, P < 0.0001). Resident
hunters averaged roughly 4 times more days per kill than non-residents (113 ± 8.2 [SD] days, n = 35
0
10
20
30
40
50
60
0
2
4
6
8
10
12
14
No
n-r
esi
de
nt
hu
nte
r su
cce
ss (
%)
Re
sid
en
t h
un
ter
succ
ess
(%
)
Residents Non-residents
Kootenay Region bighorn sheep population review
29
years, versus 32 ± 8.2 days, n = 30 years, respectively). Resident hunter effort per kill did not
differentiate rams and ewe when ewe tags were being allocated; hence hunter success is likely only a
useful index of population trend after 1996.
Ram harvest distribution
Distribution of ram kills appears to have expanded to the east in the South Rockies-Flathead (Fig. 22),
which is partially the result of ram harvest increasing in the Flathead River (MU 4-01) in recent years
(Fig. 20). Harvest data show fewer kills in MU 4-21 in the 2000s and distribution appears to have
restricted to the south in this unit (Fig. 22). Kill distribution has changed very little in the Elk Valley.
There is less continuity in kill distribution in the Upper Columbia, which could be attributed to fewer tags
issued to the Mt. Assiniboine Park in the past decade.
Kootenay Region bighorn sheep population review
30
Figure 22: Isopleths (90%) for fixed kernel polygons fit to resident and non-resident (guided) bighorn sheep harvest locations over approximately 10-year time periods, 1981-2010. Data originate from compulsory inspection reports. Colours diamonds represent hunter kills from 1981–90 (black), 1991–2000 (light blue) and 2001–10 (yellow). Points appearing west of the Kootenay and Columbia Rivers reflect spatial errors in the dataset.
Kootenay Region bighorn sheep population review
31
Age of harvested rams
The majority of rams harvested in the full-curl season (62%) were aged 6-8 years old (Fig. 23). Trend
lines suggest younger rams were harvested in the South Rockies-Flathead and older rams were
harvested in the Elk Valley. Mean age of harvested rams varied over time, but generally increased
between the late 1970s and 2000s (Fig. 24). Mean age of harvested rams for the East Kootenays
combined during 2001-10 was 7.8 years (±1.79 SD). In the past decade, non-residents and residents
have harvested rams of the same age (7.8 ± 1.70 yrs and 7.7 ± 1.83 yrs, respectively; years 2001-10).
A greater proportion of 7+ year old rams were harvested in MU 4-23 (Elk Valley; 74%), compared with
other MUs (4-02: 63%; 4-22: 67%; 4-25: 63%). Non-resident hunters harvested a greater proportion of
7+ year old rams (48%) than residents (42%). The proportion of 7+ year old rams in the East Kootenay
harvest increased in the 1970s and early 1980s, stabilized, and increased again in the mid-1990s to peak
in the early 2000s, and subsequently declined. The proportion of 7+ year old rams increased within the
East Kootenay, from a mean of 49% during the latter half of the 1970s, to 72% years during the most
recent 5 years (Fig. 25).
Figure 23: Age distribution of bighorn rams harvested from East Kootenay, 1976-2010. Data originate from compulsory inspections, and are based on horn annuli. Trend lines (line colour matched to sub-population) were fitted with 6th order polynomials.
-5
0
5
10
15
20
25
30
3 4 5 6 7 8 9 10 11 12 13
Pro
po
rtio
n (%
) of
har
vest
ed
ram
s
Age (yrs)
South Rockies (n=246) Upper Kootenay (n=379) Upper Columbia (n=298) Elk Valley (n=335)
Kootenay Region bighorn sheep population review
32
Figure 24. Mean age (± SD) of harvested bighorn sheep rams by Management Unit and for the East Kootenay combined, 1976-2010. Data originate from compulsory inspection reports. Rams were aged by counting horn annuli.
Figure 25: Proportion of 7+ year old rams in bighorn sheep harvest by Management Unit and for the East Kootenay combined, 1976-2010. Data originate from compulsory inspection reports. Rams were aged by counting horn annuli.
Bighorn ram harvest rates (number of rams killed per population estimate) were highest in the East
Kootenay during the late 1980s and early 1990s, averaging 2.4–2.6% of the total population annually
(Table 5). Ewe harvest rates were also highest during this period (1.2–1.3%) when most ewe tags were
being issued (Fig. 17). Ram harvest rates were lowest during 1996-2000, which includes the severe
winter of 1996-97 (Table 5). There was no correlation between ram harvest rate and mean age among 5-
year time periods (r2 = –0.09, P = 0.47). Separating harvest rates by MU, in the past decade the smaller
populations in MUs 4-01 and 4-22 have had the highest harvest rates (2.9–4.3%), while most of the
larger populations were ≤2.0% (Appendices 6, 7). Harvest rate in the late 1980s and early 1990s was
lowest in MU 4-02, where the greatest die-off likely occurred (Table 2).
Table 5: Bighorn sheep annual harvest and harvest rates for all East Kootenay populations combined. Population estimates are based on late winter aerial surveys; harvest data originate from compulsory inspections and hunter questionnaires.
Time Period Ram Annual
Harvest Ewe Annual
Harvest
Annual Ram Harvest Rate
(%)
Annual Ewe Harvest Rate
(%)
Annual Combined
Harvest Rate (%)
1986-1990 51 25 2.6 1.3 3.9
1991-1995 49 25 2.4 1.2 3.6
1996-2000 27 2 1.5 0.1 1.6
2001-2005 31 0 1.7 0.0 1.7
2006-2010 42 0 1.9 0.0 1.9
Using only the most recent survey data (Table 4) and average annual ram harvest numbers over the past
5 years (2006-10), calculated harvest rates were as follows:
South Rockies-Flathead (MUs 4-01 & 4-02) –2.5%;
Upper Kootenay (MUs 4-21, 4-22 & 4-24) – 2.6%;
Upper Columbia (MUs 4-25 & 4-35) – 2.5%;
Elk Valley (MU 4-23) – 1.2%.
Thus harvest rates on all sub-populations were relatively even at 2.5–2.6%, with the exception of a much
lower rate for the Elk Valley.
Non-hunting mortality
Non-hunting sources of mortality for Kootenay sheep populations are poorly documented. Two major
collaring programs have been conducted in the East Kootenay in the past 15 years that have contributed
mortality data. Nine mortalities were detected from 33 ewes fitted with VHF collars from 1997-99 at
Columbia Lake, Bull River, and Mount Broadwood herds (Kinley 2007). Of the 7 cases where cause of
Kootenay Region bighorn sheep population review
34
death was known, 4 were cougar kills, 2 from avalanche, and 1 from drowning. Eleven mortalities were
detected during a 2009-2011 GPS collaring study of 50 ewes and rams in the Elk Valley East population
near the Teck Coal mines (Poole 2013). Six mortalities (5 ewes, 1 ram) were attributed to unknown
natural causes, 1 ram to grizzly bear mortality, 1 ewe to wolf mortality, and 2 rams to starvation. Only 1
human-related mortality occurred, related to a suspected vehicle strike on a mine assess road, but 6 of
the mortalities occurred on mine properties.
Vehicle-sheep collisions on Kootenay highways resulted in an average of 6.9 sheep accidents
(presumably killed) annually between 1988 and 2007 (Fig. 26). Of these, 6 collisions per year occurred in
the East Kootenay and 1 collision per year occurred in the West Kootenay (Sielecki 2010). The data
suggest an increasing trend in accidents since the early 1990s in the East Kootenay, and relatively stable
numbers in the West Kootenay (Fig. 26), however, effort to monitor road kills and reporting may have
increased over time, confounding this as a reliable index. The greatest numbers and rate (accidents per
km per year) occurred on Highway 3 from Elko to the Alberta border. Sheep were also killed along
Highways 93 and 95 in the Upper Columbia Valley, with the highest rates near Golden and south of
Radium. Most West Kootenay collisions occurred on the Highway 3 in the Kootenay Pass west of
Creston.
Figure 26. Number of vehicle-sheep accidents annually in the East and West Kootenays, 1988–2007 (Sielecki 2010).
Parks Canada provided additional mortality data from the Radium herd, which showed 10-17 sheep
killed annually (Fig. 27), matching totals from the East Kootenay summaries (Fig. 26). This suggests that
provincial (Ministry of Transportation and Infrastructure) counts are a significant under-representation
of the actual mortalities. A significant jump in mortalities was recorded between 2010 and 2011.
Additional non-hunting mortalities of the Radium herd as quantified by Parks Canada for 1998-2011
included 8 mortalities as a result of disease or poor health, 16 predations, 1 poached, and 18 railway
mortalities , compared with a total of 143 highway-related mortalities (S. Wrazej, Parks Canada,
unpublished data).
Figure 27. Number of highway-related mortalities of bighorn sheep from the Radium, BC, herd, as reported to Parks Canada, 1998-2011 (S. Wrazej, Parks Canada, unpublished data).
Survival rates
Survival rates have been calculated from collaring studies conducted in the East Kootenay over the past
15 years. Seasonal (winter or summer) estimates of annual ewe survivorship among the 3 herds
(Columbia Lake, Bull River and Mt. Broadwood / Wigwam Flats) in an East Kootenay Trench study ranged
from 0.81 to 0.90 (5 of 6 season-areas had 0.88–0.90 survival rates) during 1997-2001, with little
difference among herds because of sample size (n = 10–12; Boulanger 2007). In the recent Elk Valley
study, average annual survival rates were 0.83 (90% CI 0.72–0.92) and 0.87 (0.77–0.97) for ewes and
rams, respectively (Poole 2013). Annual survival rates of both sexes combined during the more severe
winter of 2010-11 (0.78; 0.66–0.90) were lower than during the previous winter (0.93; 0.85–0.99), but
the difference was not significant (X2 = 2.3, 1 df, P > 0.05).
Kootenay Region bighorn sheep population review
36
Discussion
Population trends
Numerous aerial and ground-based surveys have been conducted for bighorn sheep in the Kootenay
Region over the past decades. Limited documentation has resulted in poor understanding of past survey
methodology, coverage and effort, all of which can influence numbers of sheep observed and
interpretation of the databases. Although difficult to determine, most surveys would have resulted in
minimum counts that, without correction, would result in a negative bias to the population estimate.
Positive bias may occur due to double-counting or overlap in adjacent census areas, but this is likely
more rare. Application of a set (e.g., 0.80) sightability correction to survey counts results in an unknown
bias to the data, but presumably would have less impact on trends. These earlier surveys do likely
provide reasonable broad-scale trends in populations over time at the sub-population scale (Fig. 4).
Empirical estimates of survey sightability have only recently been conducted (Poole 2013), as have
surveys enabling sightability correction using logistic models (Reid 2011, Stent 2011, Phillips and Stent
2012, Poole 2013). These recent surveys utilizing sightability corrections have likely produced the most
robust and realistic estimates. With the possible exception of the more open Elk Valley, we conclude
that the use of a set correction factor (0.75–0.85) may have underestimated earlier population
estimates in other herds.
Based on a limited number of collared individuals, there is little evidence of large-scale movements by
sheep between adjacent herds in the East Kootenay. Some movements can be expected (DeCesare and
Pletscher 2006, Dibb 2008); however, the class of individual most likely to move long distances – young
males (Geist 1971, DeCesare and Pletscher 2006) – was lightly represented in the collared samples.
Transplanted sheep have a greater tendency to move long distances after release, but these are not
indicative of established populations. Our conclusion is that among year changes in population
estimates within individual herds likely reflects actual changes in population or changes in sightability
from year to year, and not broad-scale shifts in animals among herds.
Surveys suggest lower populations of bighorn sheep in the early to mid-1980s – likely related to die-offs
in some areas – increases through to the mid-1990s, decreases both before and after the severe winter
of 1996-97, and subsequent slow increases through to the late 2000s (Fig. 4). Our data compilation
suggests most East Kootenay bighorn sheep populations have stabilized or declined recently, with the
exception of the Elk Valley population, which continues to trend higher (Phillips and Stent 2012, Poole
2013). Through the 2000s sheep numbers appear to have declined in the Upper Columbia, Upper
Kootenay, and Elk Valley West populations (Phillips and Stent 2012). We suspect the population
estimate for the South Rockies-Flathead is conservative as harvest and hunter success data have
exceeded 1980-1996 levels and remained high over the past decade despite a high apparent harvest
rate.
Data are too sparse to draw conclusions about sheep survival over time (from collaring studies) but
female and male survival rates (0.88–0.93 during most years; 0.78 during a more severe winter)
appeared to be similar to slightly lower than those measured elsewhere. Jorgenson et al. (1997) found
that in the absence of major predation or disease, adult ewes exhibited high survival rates up to 95%
Kootenay Region bighorn sheep population review
37
until approximately 7 years of age, but that survival of adult rams generally was lower, averaging 90%
yearly (Festa-Bianchet 1989). However, Geist (1971) observed 96% survival for rams 2–7 years old.
Lamb ratios
Concurrent with these changes in population size was a relatively steady decline in lamb ratios from the
late 1970s (~50 lambs/100 ewes) to the past 5-6 years (~30 lambs:100 ewes; Fig. 5). Lamb ratios
appeared to drop slightly in the early 1980s – likely related to die-offs – and more so in the late 1990s –
possibly as a result of the lingering effects of severe winters. Ewe harvests concentrated during 1989-92
did not appear to have a significant effect on resulting lamb ratios (e.g., density-dependent response),
likely because the maximum annual harvest (<45 ewes) was such a small proportion of the overall
population (<2% of total population) for a short period of time (4 years of highest harvest). Bighorn ewe
seasons have been used to push populations below carrying capacity to improve population productivity
and minimize risk of die-offs, but target harvest rates were 5% (Jorgenson et al. 1993). Maintaining
lower density sheep populations can also maximize horn growth in 4-5 year old rams (Jorgenson et al.
1993).
Changes in lamb ratios over time could be caused by a number of factors, including weather-mediated
changes to vegetation quality and availability, inter or intra-specific competition, and predation (Festa-
Bianchet et al. 1997, Portier et al. 1998, Shackleton et al. 1999). To explain the data the key factor or
factors must be acting across the region and take into account the increase in numbers in the Elk Valley.
Lamb:ewe ratios during 1999 and 2000 were lower than normal, and this lag of 2-3 years following the
severe winter of 1996-97 may be due to the high and declining cougar population during that period.
Survival of lambs at high population densities can be lower because small lambs may experience higher
mortality than large lambs (Festa-Bianchet et al. 1997, Feder et al. 2008). At high population densities,
there are greater numbers of small lambs and these animals are at greater risk of winter mortality. Elk
calf ratios in the East Kootenay were also lower during the mid-1990s to late 2000s compared with the
late 1970s and 1980s (Szkorupa and Mowat 2010), suggesting that some factor(s) could have been
driving trends in both species. Analyses conducted by Szkorupa and Mowat (2010) suggest snowfall,
harvest and predation may have interactively or additively affected elk calf ratios in the East Kootenay
over time, but none of the individual variables explained ratios directly.
Although lamb:ewe ratios are commonly used as indicators of bighorn sheep population vigour,
classification counts by themselves do not index population change, and an independent estimate of
population size is required to safely interpret classification results (Festa-Bianchet 1992, McCullough
1994). Age ratios (lambs:100 ewes) may not be ideal for population monitoring because they are
influenced by multiple contributing vital rates (Caughley 1974, McCullough 1994). Lamb numbers at the
time of survey are the product of the age specific fecundity of adult females (which is itself the product
of pregnancy rate and fetal survival) and lamb survival to the time of survey, whereas the number of
ewes is affected by the age-specific survival rates of adults since the birth pulse (DeCesare et al. 2012).
Notwithstanding the above discussion, Demarchi et al. (2000) suggested that providing ewe mortality
remains <10%, a bighorn sheep population requires an overwinter lamb:ewe ratio of approximately
30:100 to remain stable. With the exception of 2002 and 2003, all years since 1999 have found lamb
ratios close to or below 30 lambs:100 ewes(Fig. 5). This occurred during a period of slow growth to slow
Kootenay Region bighorn sheep population review
38
decline in most sub-populations and more rapid growth in the Elk Valley. The lowest lamb ratios have
occurred since the mid-2000s, concurrent with a stabilization or decline in all sub-populations except for
the Elk Valley. Lamb ratios were extremely variable among herds surveyed in 2012, ranging from 11
lambs:100 ewes in the Whiteswan/Nine Mile herds to 47 lambs:100 ewes in the Elk Valley West herd
(overall x = 29 lambs:100 ewes; Phillips and Stent 2012).
Ram ratios
Within the East Kootenay ram:ewe ratios generally peaked during the early to late 1990s and have
averaged lower in recent years (Fig. 10). The initial low ram ratios from the late 1970s were likely a
result of high hunting mortality in the early 1960s (Davidson 1994). Declines in ratios over the past 15
years could suggest higher harvest rates on ram populations; however, the mean age of harvested rams
and the proportion of 7+ year old rams in the harvest over the past several decades in most populations
has been general stable or increasing (Figs. 24, 25). It is not clear whether increasing proportions of 7+
year old rams in the harvest represents lighter harvest pressure (i.e., rams are living longer), or slower
horn growth (i.e., density dependence has resulted in rams attaining full curl status at an older age;
Jorgenson et al. 1993).
It is more difficult to infer trends in ram ratios at the sub-population scale because of the imprecision as
a result of small sample sizes. Ram data from aerial and ground surveys are also prone to sampling error
as rams often segregate from large ewe and lamb groups and may be underrepresented in samples
taken outside the rut period. Furthermore, yearling rams can also be misclassified as ewes (Festa-
Bianchet 1992), which would also bias ram (and lamb) ratios low. However, given mainly consistent
coverage and effort, and presumably relatively constant classification errors, the surveys likely provide a
reasonable indication of trends in ram ratios over time.
Limiting factors
Shackleton et al. (1999) suggested that bighorn sheep populations are regulated through density-
dependent feedback on fecundity and on lamb survival, and that density dependence is only influential
at intermediate and high population levels. At high population levels relative to carrying capacity ewes
in poor condition during the rut tend to produce lambs that are born later, after the optimum period
(Festa-Bianchet 1988). During periods of nutritional stress (i.e., food limitation) the age of first
reproduction is postponed, and mature ewes favour their own survival over producing a lamb (Festa-
Bianchet and Jorgenson 1998).
Factors that could affect regional sheep populations include trends in weather, broad changes in
predator numbers, forage quality and quantity, and inter- or intra-specific competition. The factors that
affect sheep populations are complex and understanding the relationships requires controlled analyses.
In a retrospective analysis of elk population trends in Oregon, annual variation in pregnancy and
recruitment was most influenced by August precipitation, but long-term trends in recruitment were
most influenced by cougar densities (Johnson et al. 2013). Among Kootenay sheep sub-populations,
changes in estimated population size did not always correlate with changes in lamb or ram ratios, hunter
Kootenay Region bighorn sheep population review
39
success, or the cougar population index (Fig. 28). The severe winters in the mid- to late 1990s may have
affected population size (see below).
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Kootenay Region bighorn sheep population review
40
Figure 28. Trends in bighorn sheep estimated population size, lamb and ram ratios, ram harvest and resident hunter success among sub-populations, East Kootenay. Winter severity index (WSI) and problem cougar kills are relative indices. Grey shading approximates time period of pneumonia die-offs.
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Kootenay Region bighorn sheep population review
41
Winter severity is only one weather factor that can affect populations. In broad terms, winters during
portions of the 1990s were more severe than normal, with most winters during the 2000s being
relatively mild with low snowfall. The winter of 1996-97 (characterized by a 50-year record snowfall and
a delayed spring melt) likely directly caused higher rates of over-winter mortality, and could have
affected lamb production and survival for the subsequent year, although our analyses did not clearly
show that. Stelfox (1976) concluded that severe winters were accompanied by greater winter weight
loss, and increased lamb mortality. White et al. (2008) documented decreased counts and recruitment
of bighorn sheep in the year following the severe winter of 1997 in Yellowstone National Park. However,
winter severity had no effect on ewe or ram survival in Alberta populations (Jorgenson et al. 1997).
Similarly, winter severity, precipitation, and temperature were not significant in explaining variation in
elk recruitment (Johnson et al. 2013). Density did interact with weather variables to affect neonatal
sheep survival; spring and winter temperatures had a positive effect on neonatal survival only when
population density was high (Portier et al. 1998).
As noted above, in a bighorn sheep population in eastern Alberta, Portier et al. (1998) found that winter
lamb survival was not affected by winter weather, but that wet springs had a positive effect on neonatal
and winter survival of lambs, and warm springs increased lamb survival the following winter. These
factors may have acted on vegetation growth resulting in increased maternal nutrition and hence lamb
survival. A similar mechanism was suggested for Oregon elk whereby higher than normal August
precipitation enhances forage growth and quality, and hence nutritional resources of the females
(Johnson et al. 2013). The lack of effect of winter weather on lamb survival may have been a result of a
lack of exceptionally cold and long winters during the Alberta study, and the resulting Chinook winds
that melt snow at lower elevations and clear it from higher slopes (Portier et al. 1998). Population
density negatively affected lamb survival, with any effects of weather on lamb survival most evident at
high density, suggesting that density-dependence was the central limiting factor.
Berger (1991) suggested that predation pressure overrides increased nutrient demands during late
stages of pregnancy, such that increased predation risk may result in reduced ewe condition and smaller
birth-weight lambs. Cougar numbers were likely higher during the 1990s, subsequently declined, and
may have been trending upwards in recent years (Fig. 28). Again, no direct linkage with lamb
composition data was detected even with a 1 year lag in the analysis. Problem cougar kill numbers are
likely a very rough indication of population trend, and may not reflect a strong positive linear
relationship. For example, if cougar numbers are depressed due to a reduced prey base and more
readily come into conflict situations, conflicts would be higher when in fact numbers are lower.
Predation events by cougars, often only 1-2 individuals, can cause bighorn sheep population declines
(Ross et al. 1997, Festa-Bianchet et al. 2006).
No information on wolf numbers was collected for this review; however, a review of carnivore data up
to 2004 suggested wolf numbers are increasing in both distribution and numbers throughout the
Kootenays (Mowat 2007). White et al. (2008) observed an increasing sheep population during a period
of increasing wolf numbers after re-introduction, concurrent with a 50% reduction in the number of elk.
No firm conclusions on black bear population trends are available, but grizzly bear numbers may have
increased in many parts of the region over the past 2-3 decades (Mowat 2007). Mortalities caused by
Kootenay Region bighorn sheep population review
42
bears have been documented in southern Alberta (Jokinen et al. 2007). Studies on collared sheep
suggest wolves and bears and especially cougars kill sheep in the East Kootenay, although sample sizes
were relatively small (Kinley 2007, Poole 2012). Coyotes may influence lamb survival (Festa-Bianchet
1988, Bleich 1999) on winter range in low-elevation wintering populations in the East Kootenays; no
data on trends in coyote numbers in the Kootenays are available.
Ewes may reduce maternal care against their own mass gain when resources are scarce through intra-
and inter-specific competition, resulting in decreased over-winter lamb survival (Festa-Bianchet and
Jorgenson 1998). There is uncertainty about the role of inter-specific competition on forage resources
for sheep. Elk numbers within the southern East Kootenay trench and the Elk Valley were likely high
during the 1980s, declined and bottomed out during the mid- to late 1990s, and have subsequently
increased through to the late 2000s (Szkorupa and Mowat 2010), concurrent with declines in sheep
lamb:ewe ratios. The elk population in the Elk Valley in 2013 was estimated at 2,772 animals (90% CI
2,682–2,862; P. Stent, MFLNRO, unpubl. data). Stelfox (1976) observed in the National Parks that wolves
did not prevent sheep and elk from exceeding range carrying capacities, and that elk were the major
competitor for winter range forage. Recent data from the Elk Valley suggest the majority of the winter
ranges sampled have pronounced overlap in habitat use between bighorn sheep and elk, with bighorn
sheep pellet group abundance typically subordinate to elk; several of the winter ranges were considered
slightly or moderately at risk from a range condition perspective (Smyth 2012).
Trends in habitat quality are difficult to quantify because of limited long-term monitoring. We are not
aware of significant areas of sheep habitat that are currently unoccupied. Between 1952 and 1990,
Gayton (1997) estimated that forest ingrowth and encroachment converted an average of 3,000 ha per
year of grassland and treed grassland habitats to open forest or closed forest habitats within the Interior
Douglas Fir and Ponderosa Pine biogeoclimatic zones. This would have resulted in a significant loss of
available forage in low elevation winter range for bighorn sheep in the East Kootenay. Trench
restoration efforts continue to reverse this loss; although a relatively small the treatment area was
to bighorn sheep habitat quality and quantity include housing development, off-road vehicle use and
invasive noxious weeds. The extent to which these factors have combined to reduce habitat quality and,
potentially, carrying capacity for bighorn sheep is unknown.
Mortality resulting from collisions with vehicles is undoubtedly under-reported, and may be affecting
some populations – notably the Radium herd (>5% of this herd is killed annually on Highway 93/95) and
along Highway 3 between Elko and the Alberta border.
Domestic sheep and goats can carry pathogens that may cause fatal respiratory disease or pneumonia in
wild sheep if direct contact occurs between these species (see Schommer and Woolever 2008, Wild
Sheep Working Group 2012). Effective separation of domestics and wild sheep should be the primary
management goal of agencies responsible for wild sheep. In BC, there is very limited, if any, Crown Land
grazing of domestic sheep within bighorn sheep ranges. The highest risk of contact is on private
properties managed for domestics that are adjacent to bighorn sheep habitat. The provincial
government has formed a working group that manages a Wild/Domestic Sheep Separation Program
which has received sporadic funding from non-governmental sources for measures such as education,
Kootenay Region bighorn sheep population review
43
outreach, risk assessments and to deliver site-specific mitigation activities on private lands such as
conservation covenants and fencing. To date, there are no enforceable legislative measures to promote
separation of domestics and wild sheep; however one Regional District did draft a bylaw with a
requirement for mitigation in areas of high risk of contact. With the interest in local food production,
increased domestic sheep or goat production on private land does increase the risk of disease
transmission to wild sheep.
Harvest trends
The ram harvest was lower during the late 1990s and early 2000s, and increased in the 2000s (Fig. 18).
During this period the harvest by non-resident hunters increased more rapidly than residents, such that
the proportion of the harvest taken by non-residents nearly doubled to 35-40%. Hunter success for non-
residents also doubled from about 20% or less in the late 1990s to 40% in the late 2000s, and for
resident hunters has remained relatively stable over time at the regional scale (with a possible dip in the
late 1990s to early 2000s; Fig. 21). Mean age of harvested rams and the proportion of 7+ year old rams
in the harvest have remained high or decreased slightly in most sub-populations (Figs. 24, 25). Ram age
in the Upper Columbia (primarily MU 4-25) may have dipped in the past 5 years; however, hunter
success has generally remained high.
The lack of correlation between estimated age using horn annuli compared with presumably more
accurate tooth aging does little to instill confidence in the former technique, leading us to question use
of mean age over time as an index to harvest pressure on populations. Given that older rams appear to
be more difficult to accurately age (in part because of heavily worn horn tips in older males; Hengeveld
and Festa-Bianchet 2011), use of the proportion of 7+ year old rams in the harvest may be a more
robust indicator of trend. We caution that at higher harvest pressure an increasing trend in harvest age
may indicate that males harvested over the later part of the time series required more years to reach
legal horn size, possibly because of selection for individuals with slower horn growth (Coltman et al.
2003, Hengeveld and Festa-Bianchet 2011) or a general decline in carrying capacity.
Although harvest rate calculations should be considered approximate considering the uncertainty in past
population estimates, the overall rate between 1986 and 2012 was 2.1% and most sub-populations were
in the 2.5% range. As of 2007, harvest rates of rams among North American jurisdictions responsible for
managing bighorn and desert sheep averaged 2.5% (range 1.3–3.5%; Wild Sheep Foundation
Professional Biologists Meeting Attendees 2008). Management Units 4-01 and 4-22 may have had
harvest rates in the 4.0% range over the past 5 years. Management Unit 4-01 may be influenced by
shared populations across the Alberta border, thus the population during the harvest season may be
larger than the population during mid to late winter when surveys typically occur. The harvest rate for
MU 4-25 has been consistently high over time (3.0–3.8% among 5-year intervals); coupled with declining
ram ratios, these data may signal excessive harvest. Genetic consequences were observed in an Alberta
population with a harvest rate of ~35% of legal rams or about 5 to 8% of all rams (Festa-Bianchet 1986).
The harvest rate of 3–4% in parts of the East Kootenay likely translates to upwards of 10% of all rams. A
full curl harvest restriction as is in place in the Kootenay Region should presumably be self-sustaining to
avoid over-harvest, and may have less population consequences compared with four-fifths curl
restrictions such as present in some Alberta populations (Coltman et al. 2003). A four-fifths curl
Kootenay Region bighorn sheep population review
44
restriction allows younger rams to be legally harvested compared with a full curl restriction, allowing
fewer prime rams to remain in the population and participate in breeding (Coltman et al. 2003).
The ewe harvest in the late 1980s and early 1990s had limited impact on population size and likely did
little to induce any density-dependent reaction to reduced sheep numbers. The rationale behind the
ewe harvest was poorly documented.
Aerial survey sightability
Results from recent surveys in the Elk Valley indicate collar-derived and model-derived sightability
estimates were similar, with <3% correction difference between methods (Poole 2013). Within the
Kootenays, a wide range of sightability can be encountered. Using the sightability model in the West
Kootenay, Stent (2011) estimated a 0.49 sightability rate, while in the Elk Valley sightability ranging
between 0.74–0.82 was calculated (both collar and model derived; Poole 2013). Modelled sightability
estimates from winter 2012 surveys throughout the East Kootenay ranged from 0.67 to 0.83 (Phillips
and Stent 2012), and among 4 large (>100 sheep) and adjacent populations in the south Okanagan
ranged from 0.63 to 0.78 (Reid 2011). Surveys in the Elk Valley conducted in 2010 and 2011 in almost
identical areas indicated a decrease in sightability of 0.05 (6%) between years. The variation in
sightability among these surveys strongly suggests that survey-specific sightability should be calculated
for all sheep surveys. However, the main variable influencing sightability in these surveys was habitat
type, which is roughly correlated to canopy closure. If retrospective analyses of data are required,
sightability in open habitat may be in the 0.75–0.85 range, in open forest perhaps 0.65–0.75, and in
closed forest 0.50–0.65.
Conclusions
The broad declines in lamb and ram ratios and increases in mean harvested ram ages suggest one or
more general factors are operating to limit sheep numbers in the region. However, the differences in
population trend, especially since the recent population lows of the mid-1990s, suggest there are herd-
specific differences in the strength of limiting factors. Generally, we expect forage quality, and to a
lesser extent quantity, to limit population density and we expect major negative pressures on
population growth at high densities. We expect juveniles and males to respond more strongly to forage
limits than adult females and, similarly, that periods of severe weather also affect female survival less
than juveniles and males. Indeed, periods of food shortage or severe weather both can result in major
shifts in age structure favouring adult females, such that increasing populations typically show
increasing ratios of juveniles and males and vice versa. Predation may have modest impacts on density
and even less on growth, though it may reduce the impact of food shortages or severe weather because
predators typically kill young or adult males, which are the same cohorts that are most impacted by food
shortages. Predation may also influence population trend as observed for elk recruitment (Johnson et al.
2013). Finally, weather can signal major short-term reductions in survival but does not often influence
forage or carrying capacity in any permanent way. The main effect of annual weather patterns is to
synchronize populations to similar population trajectories over broad areas of similar weather densities.
The above observations come from detailed long-term studies of ungulates, including 2 sheep
Kootenay Region bighorn sheep population review
45
populations, and detailed reviews of the literature, and can help us understand and inform predictions
stemming from these data (Owen-Smith 2010).
The Upper Columbia population unit has significant road mortality of all ages and may hence be less
food limited than other populations. However, lamb ratios are currently as low as other units and ram
ratios have recently declined to the lowest levels observed in the region (Fig. 28). Hunter-killed ram ages
are also currently lower than the rest of the region while hunter success appears to have largely
increased during the last decade. Survey data suggest a stable population during most of the last decade
and a substantive decline in the last several years (Figs. 4, 28). Younger ram age suggests higher food per
individual ram than in other populations or, higher male mortality than other units. Low lamb ratios
suggest low food per capita female or higher predation than previous decades. Low ram ratios suggest
high mortality or low food per capita for males. Rams may be killed at higher rates on the highway than
other cohorts.
The other sheep populations in the region show a pattern of low lamb recruitment and low male ratios
but roughly stable population size, hunter success, male age and harvest. The Elk Valley East population
has increased despite these low ratios and declining hunter success since the mid-2000s (Fig. 28). Low
lamb and ram ratios are likely a result of low lamb recruitment and low male survival. Juveniles and
adult males are more affected by food shortages than adult females hence this data suggest that sheep
populations are currently food limited and that hunter harvest is not strongly related to the current
population limiting factors. The general decline in grasslands in the region due to in-growth is one
possible explanation for the above observations.
The Elk Valley sheep population has certainly increased over the last decade and, in this case ram ages
and ratios are the highest in the region. Lamb ratios are also similar to or higher than currently found
elsewhere. Road mortalities are not unusual in this population but are unlikely high enough to influence
food limitation to any degree given how large the population is compared to the number of mortalities.
Hunter success and kills have been roughly stable for several decades while ram age is slightly higher
than in other units. This portion of the region may have an increasing trend in habitat supply because
the coal mines in the Elk Valley have a large total footprint and are currently re-claiming alienated
habitat to legume and grass dominated grasslands. The sheep population is likely responding to this
trend in habitat supply. Data from this unit also suggest that ram harvest is not strongly related to
current population trend or limiting factors because the Elk Valley has the lowest harvest rate in the
region. However the low harvest rate may be due to lower access in this part of the sheep distribution.
Adult ram abundance is related to population growth at the time the rams are born and to more recent
limiting factors that affect adult male survival. Hence the lack of relationship between current
population trend and ram abundance or harvest includes a delayed relationship between population
trend and ram abundance. This delay may be many years given that rams are not recruited into the
hunted population until at least 4 years of age. This 4-8 year delay largely de-couples present population
trend and ram abundance.
These descriptive data do little to help understand limiting factors because limiting factors often act in
synergy and show complex relationships with density or population growth (Owen-Smith 2010, Johnson
et al. 2013). A model-based analysis that considers key hypotheses regarding limiting factors
Kootenay Region bighorn sheep population review
46
simultaneously may help to better understand the limiting process (e.g., Johnson et al. 2013). The 4 key
questions that are important to sheep managers in this region are:
1. Are sheep populations predominantly food limited at the present time and does this pre-dispose
those populations that are to disease outbreaks?
2. Alternatively, is predation a significant limiting factor and how does it influence trend?
3. Is ram abundance and hunter harvest related to population trend?
4. Is hunter harvest related to food limitation, i.e. do male sheep reach full curl at a younger age if
populations are maintained below carrying capacity by the hunting of female sheep?
5. Does the full curl regulation cause genetic selection for rams with small horns?
The available data suggest most Kootenay sheep populations are food limited and have been so for
perhaps 10 years based on trends in male abundance, or longer based on trends in juvenile abundance.
Mild weather over the past decade has allowed some populations to increase despite low juvenile
recruitment which pre-disposes these populations to decline during a severe winter. Increased predator
populations over the past 2–3 decades may also be influencing recruitment. We do not know if the
current high numbers of sheep pre-dispose them to disease out-breaks but parasite loads were higher
during severe winters in Soay sheep (Ovis aries) in Hirta Island (Owen-Smith 2010).
The data presented here do not show an obvious relationship between ram harvest and population
abundance despite similar open hunting regulations during much of this period. It is possible that ram
harvest is related to population trend 3-6 years previously nearer to when the rams were born but this
very long lag would require detailed analysis to test and may be obliterated by weather or predation.
We do not know if males reach full curl at younger ages at lower population density but this has been
observed elsewhere (Jorgenson et al. 1993).
Recommendations
1. Conduct further analyses to examine which factors influence trends in sheep populations in the
Kootenays, including disease risk. A retrospective analysis, similar to the approach taken by
Johnson et al. (2013) for Oregon elk, could be conducted.
2. Since surveys are generally conducted during February to April each year, limited information
has been collected on determining causes and timing of lamb mortality. Surveys or studies at
different times of the year could provide information on neonatal survival and causes of lamb
mortality.
3. To improve accuracy of age and sex ratio data, composition surveys could also be conducted
during the November rut when rams are more integrated with ewe groups and less likely to be
underrepresented in samples.
4. To provide more robust population estimates, surveyors should at minimum collect the required
parameters for the sightability model during surveys (Bodie et al. 1995): activity (moving or not
moving) and broad habitat type when first observed. Although not current parameters in the
model, we also suggest recording estimated percent snow cover in the general area and percent
Kootenay Region bighorn sheep population review
47
vegetation cover (perhaps best described as screening cover) around the first animal seen in the
group (Unsworth et al. 1998) in case the original model is modified to incorporate these
parameters. Population size and sightability correction can be estimated using the Idaho sheep
model in program AERIAL SURVEY (Unsworth et al. 1998).
5. Conduct additional sightability trials using the Idaho Sheep model in habitats with dense cover
to build on data collected by Poole (2013) to further evaluate accuracy of the sightability model.
6. Standardize survey reporting to include documentation of census zone and effort (min/km2).
7. Test the accuracy of aging male sheep using horn annuli.
Acknowledgements
We thank S. Wrazej, Parks Canada Lake Louise, Yoho & Kootenay Field Unit, Radium, for supplying
highway mortality data. I. Teske, MFLNRO, kindly provided much of the background files for this review.
B. Phillips and H. Schwantje, MFLNRO, provided additional information. Thanks to I. Teske and H.
Schwantje for updating the die-offs and diseases sections of the review. J. Krebs provided helpful
comments on an earlier draft of this report.
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Appendix 1: Aerial-based bighorn sheep surveys (total counts) summed by Management Unit, between January and April in the Kootenay Region, British Columbia, 1965-2012. Data sources are described in Methods.
Year Management Unit
4-01 4-02 4-21 4-22 4-23 4-24 4-25 4-35 4-08 4-15
1965 106 93 24 33
1966 128 30 54 23 76
1967 179 113 14
1968 176 85 41
1969 194 49 15 108
1970 47 114
1971 39 161
1972 199 28 22
1973 259 51 228 16 28
1974 57 13 13
1975 307 74 14 189 47
1976 254 34 210 32
1977 157
1978 235 62 152 51
1979 233 133 167 87
1980 335 125 36 164 31
1981 423 98 420 75
1982 79 260 137 35 195
1983 127 115 11 358 37 178
1984 93 120 15 146 178
1985 72 61 314 162
1986 102 55 15 221
1987 115 84 280 6
1988 40 251 6
1989 231 99 90
1990 30 272 240 89 193 22 239 47
1991 26 261 204 29 224 33 229
1992 287
1993 160 211 90 100
1994 15 135 90
1995 112
1996 71
1997 120
1998 253 94
1999 149
2000 78 124 45
2001 154 104 95 59 199
2002 454 294
2003 176 308
2004
2005 245 445 65
2006 36 119
Kootenay Region bighorn sheep population review
53
Year Management Unit
4-01 4-02 4-21 4-22 4-23 4-24 4-25 4-35 4-08 4-15
2007
2008 216 152 132 508 114
2009
2010 85 140 626 67 2011 481 31
2012 256 127 100 691 46 101
1 4-23 west side only.
Appendix 2: Total sheep counts of aerial-based bighorn sheep surveys, totalled by herd, between January and April in the Kootenay Region, British Columbia, 1965-2012. BR: Bull River; CL: Columbia Lake; EE: Elk Valley East side; EW: Elk Valley West side; FL: Flathead; GA: Galton; GO: Golden; ML: Marmalade Basin; MA: Mt. Assiniboine; PE: Premier-Estella; RS: Radium-Stoddart; SA: Salmo; SY: Syringa; WS: Whiteswan; WW: Wigwam-Mt. Broadwood; WH: Wildhorse.
Year Sheep Herd
BR CL EE EW FL GA GO ML MA PE RS SA SY WS WW WH
1965 33 93 24 106
1966 22 54 30 54 23 130
1967 14 113 179
1968 19 85 41 167
1969 15 108 15 49 179
1970 114 13 47 135
1971 155 29 10 75
1972 22 23 42 28 157
1973 28 177 51 21 51 16 238
1974 13 18 35 57
1975 14 47 160 29 58 74 249
1976 32 161 49 34 254
1977 119 38
1978 51 104 48 18 62 217
1979 87 110 57 24 20 113 209
1980 18 31 155 55 41 84 21 298
1981 75 89 19 79 423
1982 35 195 79 46 91 254
1983 11 106 231 127 115 102 127
1984 15 54 103 43 15 31 89 130 78
1985 130 39 14 61 162 58
1986 15 165 56 55 102
1987 35 196 84 26 6 164
1988 108 143 5 40 6
1989 87 29 58 99 176
1990 59 117 154 39 30 59 54 175 122 29 243
1991 21 101 166 58 26 76 43 132 131 43 185 20
1992 100 55 25 91 189
1993 90 85 126 100 160
1994 75 135 24 90
1995 112
Kootenay Region bighorn sheep population review
54
Year Sheep Herd
BR CL EE EW FL GA GO ML MA PE RS SA SY WS WW WH
1996 65 50 71
1997 120
1998 142 94
1999 149
2000 124 45 36 25 45 17
2001 60 81 27 41 26 118 85 162 11
2002 81 323 131 51 162
2003 308 176
2004
2005 376 69 97 65 161
2006 67 102 31 5
2007
2008 132 68 412 96 33 57 47 48 162 216
2009 92 64
2010 140 626 33 27 73
2011 481 31
2012 100 101 69 98 20 79 127 46 158 48
Kootenay Region bighorn sheep population review
55
Appendix 3: Bighorn sheep lamb ratios (±95% confidence intervals) for selected Management Units. Trend line is a 5-year running average. Data originate from aerial surveys.
Lamb ratios (95% confidence intervals) for Management Unit 4-02.
Lamb ratios (95% confidence intervals) for Management Unit 4-21.
Lamb ratios (95% confidence intervals) for Management Unit 4-25.
0
10
20
30
40
50
60
70
80
90
Lam
bs:
10
0 E
we
s
Lambs:100 Ewes Lamb Ratio Trend (5 year running average)
MU 4-21
MU 4-25
MU 4-02
Kootenay Region bighorn sheep population review
56
Appendix 4: Bighorn sheep rams ratios (±95% confidence intervals) for selected Management Units. Trend line is a 5-year running average. Data originate from aerial surveys.
Bighorn sheep ram ratios (95% confidence intervals) for Management Unit 4-02.
Bighorn sheep ram ratios (95% confidence intervals) for Management Unit 4-21.
Bighorn sheep ram ratios (95% confidence intervals) for Management Unit 4-25.
0
10
20
30
40
50
60
70
80
90
Ram
s:1
00
Ew
es
Rams: 100 Ewes Ram Ratio Trend
0
20
40
60
80
100
120
Ram
s:1
00
Ew
es
Rams:100 Ewes Ram Ratio Trend
0
20
40
60
80
100
120
140
160
180
200
Ram
s:1
00
Ew
es
Rams: 100 Ewes Ram Ratio Trend
MU 4-02
MU 4-21
MU 4-25
Kootenay Region bighorn sheep population review
57
Appendix 5: Resident and non-resident (guided) hunter success by Management Unit, 1976-2010. Trend lines are 5-year running averages. Data originate from compulsory inspections and hunter survey reports.
Hunter success for Management Unit 4-02.
Hunter success for Management Unit 4-21.
Hunter success for Management Unit 4-22.
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
es
(%)
'4-02Resident Success Non-Resident Success
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
ess
(%)
'4-21Resident Success Non-Resident Success
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
ess
(%)
'4-22Resident Success Non-Resident Success
Kootenay Region bighorn sheep population review
58
Hunter success for Management Unit 4-24.
Hunter success for Management Unit 4-25.
Hunter success for Management Unit 4-23.
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
ess
(%)
'4-24Resident Success Non-Resident Success
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
30
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
ess
(%)
'4-25Resident Success Non-Resident Success
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
No
n-r
esi
de
nt
Hu
nte
r Su
cce
ss (%
)
Re
sid
en
t H
un
ter
Succ
ess
(%)
'4-23Resident Success Non-Resident Success
Kootenay Region bighorn sheep population review
59
Appendix 6: Bighorn sheep population estimates, annual harvest and harvest rates for East Kootenay Management Units with ewe hunting seasons, 1976-2010. Population estimates are based on late winter aerial surveys and harvest data originate from compulsory inspections and hunter questionnaires.
MU Time Period Ram
Annual Harvest
Ewe Annual Harvest
Annual Ram
Harvest Rate (%)
Annual Ewe Harvest Rate
(%)
Annual Combined
Harvest Rate (%)
421
1986-1990 7.4 6 2.4 2.0 4.4
1991-1995 7.6 9.2 2.6 3.1 5.6
1996-2000 2.8 0.4 1.0 0.1 1.1
2001-2005 1.4 0 1.0 0.0 1.0
2006-2010 1.6 0 1.0 0.0 1.0
422
1986-1990 4.2 1 2.2 0.5 2.7
1991-1995 6.6 4.4 3.2 2.1 5.4
1996-2000 2.6 0.6 1.4 0.3 1.7
2001-2005 3.8 0 2.9 0.0 2.9
2006-2010 7.6 0 4.3 0.0 4.3
423
1986-1990 13.6 6 2.6 1.1 3.7
1991-1995 8.8 4 1.8 0.8 2.6
1996-2000 7.6 0 1.4 0.0 1.4
2001-2005 11.2 0 2.0 0.0 2.0
2006-2010 10 0 1.4 0.0 1.4
424
1986-1990 3.4 11.8 3.9 11.9 15.8
1991-1995 4.2 7.4 3.6 6.3 10.0
1996-2000 2 0.8 2.0 0.8 2.8
2001-2005 2.4 0.6 3.1 0.8 3.9
2006-2010 1.8 0 1.3 0.0 1.3
Kootenay Region bighorn sheep population review
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Appendix 7: Bighorn sheep population estimates, annual harvest and harvest rates for East Kootenay Management Units without ewe seasons, 1976-2010. Population estimates are based on late winter aerial surveys and harvest data originate from compulsory inspections and hunter questionnaires.
MU Time Period Annual Ram Harvest Annual Ram Harvest
