Wildlife Status Reports - Grizzly Bear (original) (raw)

POPULATION SIZE AND TRENDS

1. Alberta. - Assessing the population status and trend of grizzly bears is difficult when compared to most other vertebrate wildlife species. Inherently low population densities, winter inactivity and poor sightability make censusing scientifically challenging and expensive. It is estimated that there were approximately 6000 grizzly bears in Alberta in the 1800s (Herrero 1992). This estimate was based on an assumed density of at least one bear/100 km² across the 600 000 km² that constitutes Alberta (S. Herrero, pers. comm.). The accuracy of this historical estimate remains unsubstantiated.

The total estimated grizzly bear population in 2000 (excluding national parks) was 841. The Alberta Fish and Wildlife Grizzly Bear Management Plan (1990) estimated the total population of grizzly bears in Jasper, Banff and Waterton National Parks at 215 bears. National park representatives were asked to provide an up-to-date grizzly bear estimate for each park. There are an estimated 100-110 grizzly bears (all age classes) in Jasper National Park, which is based on data from their study in the late 1970s and the ongoing Foothills Model Forest grizzly bear study (W. Bradford, pers. comm.). The number of grizzly bears in Banff National Park is currently unknown, but a conservative estimate of 60 bears (males and females) is used for planning purposes (T. Hurd, pers. comm.). The most recent estimate from Waterton Lakes National Park is from a 1998 study of Waterton and surrounding area, which suggests approximately 15 bears in the park (Mowat et al. 1998). Therefore, the current grizzly bear population estimate for Alberta national parks is 175 to 185 bears. It should be noted that this number is very conservative and does not necessarily mean there has been a decrease in the number of grizzly bears in national parks.

The status of grizzly bear populations has fluctuated in this century with changes in the classification of the grizzly from its perceived image as a predator, to its official designation as "fur-bearer" in 1928. It was afforded further protection as a "big game animal" in 1929 (Alberta Fish and Wildlife Division 1990). Despite this, by the late 1940s, ranchers along the east front of the Rocky Mountains had reduced the grizzly population significantly in the foothills and mountain valleys (McCrory and Herrero 1982). Protection was still minimal in the 1950s and inadequate regulation of killing grizzlies by landowners, cattlemen and hunters, resulted in a further decline in grizzly bear numbers (Alberta Fish and Wildlife Division 1990). More protection was afforded in the 1960s, with more stringent hunting restrictions and surveys of hunter harvests. The Alberta population likely increased in the 1970s, but concerns of unsustainable mortality in the 1980s led the Alberta Fish and Wildlife Division to enact several management policies with the goal of increasing the provincial population outside of national parks to 1000 grizzlies (Alberta Fish and Wildlife Division 1990).

Figure 3. The location of current grizzly bear management areas (BMAs) in Alberta�s Natural Regions. A colour version of Alberta�s Natural Region map is available from Alberta Community Development (http://www.cd.gov.ab.ca/preserving/parks/anhic/index.asp.

Systematic records of grizzly bear occurrences, mortalities and translocations have been kept in Alberta since 1971. A detailed provincial grizzly bear management plan was published in 1990 and included the first estimates of populations for 21 Bear Management Areas (BMAs). These estimates were based on conservative extrapolations of baseline population densities from field research studies available as of approximately 1989 (Nagy and Russell 1978, Russell et al. 1979, Carr 1989, Nagy et al. 1989). Population densities of grizzly bears from field research projects were extrapolated to BMAs with similar ecological conditions and were then discounted based on objective measures of land surface disturbance (Pedocan Land Evaluation Ltd. 1984). The measured disturbance value was multiplied by two (= total disturbance value) to take into account the large home ranges and mobility of grizzly bears and the projection of disturbance effects beyond the physically disturbed areas (Alberta Fish and Wildlife Division 1990). Total surface disturbance values used for BMAs averaged 45%. The locations of current Alberta BMAs are shown in Figure 3.

In the case of BMAs 4A, 4B and 4C, in the mountains and foothills east and north of Banff and Jasper National Parks, the baseline population density estimate (Russell et al. 1979) was halved from 10 bears/1000 km² to 5 bears/1000 km² (Alberta Fish and Wildlife Division 1990). This was done to reflect the effects of past grizzly bear harvest.

Since 1988, Alberta Sustainable Resource Development has been making annual updates to the original grizzly bear population estimates within Bear Management Areas in the province. These estimates modify the previous year�s population estimate based on net translocations, estimated net immigration and net natural growth (Gunson 1996). Net natural growth is defined as allowable human-caused mortality at 6% per year minus known mortality (plus 25% unknown mortality). Six percent to 6.5% is considered to be the scientifically acceptable human-caused mortality rate above which mortality could cause a population decline (Harris 1986, Eastern Slopes Grizzly Bear Project 1998, McLellan et al. 1999).

Table 1 provides Alberta Sustainable Resource Development�s grizzly bear population estimates for BMAs and groups of BMAs on Alberta provincial lands from 1988 to 2000. Figure 4 illustrates trends in the total estimated grizzly bear population for Alberta provincial lands (excluding national parks) from 1988 to present. The population estimates provided in Table 1 and Figure 4 are affected mainly by known human-caused mortality. Table 2 provides annual records of the number of reported human-caused grizzly bear mortalities per Bear Management Area since 1972. Figure 5 illustrates trends in total reported human-caused mortality per year on Alberta provincial lands from 1972 to present.

Table 1. Number of grizzly bears estimated to occur in Alberta Bear Management Areas (BMAs), 1988 - 2000 (excluding national parks).

Figure 4. Estimated grizzly bear population on Alberta provincial land (excluding national parks) from 1988 - 2000.

Table 2. Total known mortality of grizzly bears by Alberta Bear management Area (BMA), 1972 to 1999.

Figure 5. Trends in reported human-caused mortality of grizzly bears in Alberta (1972-1999)

Based on the above Alberta Fish and Wildlife Division estimates, the total Alberta grizzly bear population has increased from 575 animals in 1988 to an estimated 841 in 2000 (excluding national parks). BMAs with large increases are REM (105%), 3B (+81%), 4A (+67%), 1 (+63%), 3A (+52%), 2B (+47%) and 4B (29%). With the exception of BMA 1, the largest estimated increases have occurred in northern Rocky Mountains and foothills regions. BMA 1 is found primarily in boreal mixedwood, northland and sub-arctic habitat in northwestern Alberta. The remainder areas (REM) supported the highest estimated increase in population (+105%). REM includes BMA 5 (Kananaskis Country), Peter Lougheed Park, WMU 410 (Bow Corridor), BMA 13 (central and southern agricultural fringe areas), BMA 16 (northeastern Alberta) and the White Goat, Siffleur and Ghost River Wilderness Areas.

Based on Alberta Sustainable Resource Development�s annual updates, BMAs with recorded decreases in grizzly bear numbers are 2A (-68%) and 6/7 (-31%). BMA 7 and 2A are considered to be secondary grizzly bear range in Alberta (Alberta Fish and Wildlife Division 1990). BMA 7 is located in the montane and foothills parkland of southwestern Alberta and comprises WMUs 300, 302, 304, 305, 306, 308, 310, 312 and 314. BMA 2A is found primarily in boreal mixedwood and lower foothills regions of northwest Alberta. BMA 6 is primary grizzly bear range and is located in the mountains of southwestern Alberta encompassing WMUs 400 and 402. It is contiguous with and lies west of the southern half of BMA 7.

Total known mortality records have been kept since 1972 (Table 2). Reported mortality rose steadily from 1972 and peaked in 1987. Mortality levels have decreased significantly in most BMAs since limited entry draws for grizzly bear hunting were extended province-wide in 1989.

Original (1988) population estimates calculated by Alberta Fish and Wildlife were based on conservative extrapolation from empirical research studies. Annual changes to the original estimates were based on known population biology of grizzly bears (Alberta Fish and Wildlife Division 1990). Nonetheless, there are several possible sources of error associated with the assumptions inherent in these estimates. The 25% unreported kill level used is at the low end of estimates from published papers (Banci 1991, McLellan et al. 1999). These and other possible scientific issues notwithstanding, it is the only systematic effort to assess the status of grizzly bear populations over large areas of the province.

There have been three recent population research efforts that have shed some light on current grizzly bear population status in Alberta. Gibeau and Herrero (1998) reported on an estimate of the density of grizzly bears in Banff National Park and Kananaskis Country (4000 km²) in the summer of 1996 using a DNA-based hair snagging approach (modified from Sherry 1996). A density estimate of 12 to 14 grizzly bears/1000 km² was calculated although it was made clear that data were too sparse to consider this estimate to be useful for management purposes. It is interesting to note that this estimate, although preliminary, is almost identical to the estimate of 12.2 to 14.5 grizzly bears per 1000/km² calculated by Carr (1989). It is slightly less than the value of 14.7 bears/1000 km² used by Alberta Fish and Wildlife Division (1990) for their original baseline population densities for the southern montane/subalpine/alpine.

A similar approach was used for a 5030 km² study area in the mountains, foothills and parkland of southwestern Alberta (Mowat et al. 1998). In this study a density of 14.7 grizzly bears/1000 km² was calculated, identical to the original estimate for this region by Alberta Fish and Wildlife Division (1990). These authors indicated that the calculated estimate could be high by approximately 10% because of bear movement in and out of the study area. If this were the case, the modified estimate would lie within the range reported by Gibeau and Herrero (1998). The study area of Mowat et al. (1998) is representative of much of BMA 6 and 7. At the time of the publication of their findings, Alberta Sustainable Resource Development was estimating a total of 31 grizzly bears in the 14 128 km² land area occupied by BMAs 6 and 7. This amounts to a 1998 density estimate of 2.2 grizzly bears/1000 km².; This is much lower than the empirical density findings of Mowat et al. (1998) and is indicative of the conservative nature of Alberta Sustainable Resource Development’s annual population update model. Based on the new findings by Mowat et al. (1998), Alberta Sustainable Resource Development increased their 1998 population estimate for BMAs 6/7 to 57 from 31 (Table 1).

During 1999 and 2000, another estimate of grizzly bear population density was initiated using hair capture and DNA fingerprinting techniques in the Yellowhead region (Stenhouse 2000, Stenhouse and Munro 2001). This 5352 km² study area consists of predominantly subalpine and upper boreal habitats and straddles provincial and national park lands. A density estimate of 14.9 bears/1000 km² was calculated. This estimate is almost three times the 5.0 bears/1000 km² used for the original (1987) population estimates by the Alberta Fish and Wildlife Division (1990) for this area. The provincial portion of Stenhouse�s (2000) study area encompasses the majority of provincial BMA 4B. As of 2000, Alberta Sustainable Resource Development estimated a total of 44 grizzly bears in the 6089 km² land area occupied by 4B. This amounts to a year 2000 density estimate of 7.2 grizzly bears/1000 km². This density is one-half of the minimum empirical density estimate reported by Stenhouse and Munro (2001), further supporting the conservative nature of Alberta Sustainable Resource Development�s estimates of population size.

The current population density estimates as calculated by Alberta Sustainable Resource Development for licence allocation purposes appear to be consistent with or less than recent empirical estimates using DNA-based hair snagging techniques. These findings could reflect overly conservative original (1988) population estimates and stable populations in these study areas. They could also reflect grizzly bear populations that are increasing at a greater rate than predicted by the annual updates conducted by Alberta Sustainable Resource Development. Since the techniques used to compare grizzly bear population densities between the late 1980s and late 1990s differ markedly, it is difficult to be certain of trends in populations. Continued DNA-based hair snagging projects offer the most accurate and cost-effective population estimates and as such should be continued over space and time to monitor trends in Alberta�s grizzly bear populations.

2. Other Areas. - Population densities of grizzly bears are influenced by regional biogeoclimatic conditions and latitude (Picton et al. 1986, Fuhr and Demarchi 1990). For example, moist, temperate regions with significant topographic variability have the inherent capacity to support more bears per unit of land area than Cold Taiga Plains that have limited food and cover. This is reflected in the wide range of population densities observed across Canada as well as within Alberta.

The status of grizzly bears in Canada was reviewed in 1990 (Banci 1990). Twelve grizzly bear zones were designated that maintain current bear populations. Population densities in these zones were as follows:

Alberta grizzly bear populations occur within four zones: the Taiga Plains, Cold Boreal Plains, Cool Moist Mountains, and Cool Dry Mountains. The Taiga Plains and Cold Boreal Plains roughly encompass BMAs 1, 2A, 2B, 3A, 3B, 13, and 16. The combined land area of these BMAs is 273 071 km². Alberta Sustainable Resource Development�s 2000 population estimate for this region is approximately 600 grizzly bears, yielding a density of 2.1 bears per 1000 km². This is similar to the densities of 2.7 to 3.3 per 1000 km² identified by Banci (1991) for the Taiga Plains and Cold Boreal Plains. The Cool Moist Mountains zone occupies the northern Rocky Mountains and upper foothills of Alberta. This zone includes BMAs 4A, 4B and 4C. Combined, these three BMAs occupy 22 340 km² and support a 2000 population estimate of 168 bears. This yields a density of 7.5 grizzly bears/1000 km² which is considerably lower than the average of 19.6/1000km² reported by Banci (1991). The Cool Dry Mountains zone occupies Alberta BMAs 5, 6 and 7 and Waterton Lakes National Park. Recent grizzly bear densities of 14.7/1000 km² are slightly lower than the 17.9/1000 km² reported by Banci (1991).

The Cool Moist and Cool Dry Mountain zones straddle the Continental Divide between Alberta and British Columbia. The Alberta side of the Rocky Mountains is generally drier because of regional rain-shadow effect. Topography is also generally less rugged on the Alberta side of the Rockies. As a result, habitat conditions for grizzly bears are generally more favorable within the British Columbia portions of the Cool Moist and Cool Dry Mountain zones. This largely explains the lower population densities reported for Alberta�s portion of these zones.

A similar east to west variability exists in grizzly bear population densities within the Northern Continental Divide Ecosystem of the northwestern United States. Reported population densities east of the Continental Divide (more typical of Alberta) of this ecosystem range from 2.3 to 10.1 bears/1000 km² (Aune and Kasworm 1989). Studies in habitats west of the Continental Divide (more typical of British Columbia) reported grizzly bear densities of from 20.4 to 25.0/1000 km² (Servheen 1981, Mace and Waller 1997). Grizzly bear populations in British Columbia , including those along the British Columbia/Alberta border, are considered to be stable for the most part, although populations in the dry interior appear to be declining (D. Fraser, pers. comm.).