Grizzly bear (Ursus arctos) COSEWIC assessment and update update status report: chapter 2

2. Species information

2.1 Name, classification

Ursus arctos is widely known as the grizzly bear or the brown bear. Typically, Eurasian and coastal North American populations are called brown bears, whereas interior North American bears are referred to as grizzlies. Common names such as “Kodiak bear”, “Alaskan brown bear”, “silvertip”, and “barren-ground grizzly” are vernacular only and are misleading as to the geographic distribution, morphology, or habitat association of the species. Taxonomy is as follows:

Class:
Mammalia
Order:
Carnivora
Family:
Ursidae
Genus:
Ursus
Species:
arctos


Wide variation in phenotype across its broad distribution originally resulted in the description of more than 90 subspecies in North America (Merriam 1918). Refinement of taxonomic criteria later led to the widely accepted identification of 2 subspecies, U. a. middendorffi, from the Kodiak Island archipelago, and U. a. horribilis, from the remainder of North America (Rausch 1963). Subsequent reclassifications identified 3 (Kurtén 1973) or 7 (Hall 1984) North American subspecies.

Recent mitochondrial DNA sequence analysis of grizzly bears, however, disputes all of the historical North American classifications (Cronin et al. 1991; Waits et al. 1998). Four mtDNA lineage groups, or clades, have been distinguished in North America (Figure 1). Little congruity was noted between mtDNA phylogeny and the morphological variation used in previous subspecific categorization of grizzly bears, and the boundaries of each phylogeographic clade are not consistent with those of the currently accepted subspecies (Waits et al. 1998). However, Waits et al. (1998) argue against revision of the taxonomy of the grizzly bear based on the results from a single mtDNA region.

2.2 Description

Grizzly bears share the typical ursine body morph: large, muscular, and robust. Attributes that characterize members of the species include a prominent shoulder hump, concave facial profile, and long front claws (Figure 2). Considerable variation in physical appearance occurs among grizzly bears across their North American range. Pelage colour ranges from blonde through shades of brown to nearly black. Sexes are dimorphic, with males, on average, 1.8 times as heavy as females (Hilderbrand et al. 1999). Typical body mass for adult females ranges from 100 kg for interior populations to 200 kg for coastal bears (McLellan 1994). Adult males average 190 kg in interior populations, and 322 kg in coastal populations (McLellan 1994). Because body mass of bears increases greatly between spring and fall, then declines over winter, the season of capture strongly influences these data.


Figure 1. Four clades of grizzly/brown bears in North America defined by mtDNA sequence analysis

Figure 1. Four clades of grizzly/brown bears in North America defined by mtDNA sequence analysis.

Note zone of overlap at Arctic National Wildlife Refuge in northeastern Alaska (see text). From Waits et al. (1998).


Figure 2. Immobilized adult female grizzly bear (Ursus arctos) in northeastern British Columbia (BC)

Figure 2. Immobilized adult female grizzly bear (Ursus arctos) in northeastern British Columbia.

Note concave facial profile and long front claws. Photo by author.

2.3 Populations

Distinction of subpopulation units for grizzly bears in Canada is difficult. With the exception of a few isolated groups in southern BC, within their Canadian distribution (Figure 3), grizzly bears essentially occupy continuous habitat.


Figure 3. Current distribution of grizzly bears in Canada

Current distribution of grizzly bears in Canada.

Confirmed observations outside normally occupied range are identified by triangles.


McLoughlin et al. (In Press) used multivariate cluster analysis of telemetry data to distinguish 3 population units of grizzly bears in the central Canadian Arctic. Population ranges for female bears were exclusive, but male population ranges overlapped. However, bears of both sexes emigrated out of their original population unit; up to 35% of males could be expected to emigrate from their source unit per year. Furthermore, genetic interchange among population units was likely. McLoughlin et al. (In Press) concluded that exchange rates among population units prevented distinction of any of the 3 as independent demographic units, and that the grizzly bear population in the central Arctic should be managed as one continuous population, and contiguous with adjacent populations outside his study area. At present, man-made barriers to grizzly bear movement do not occur in the Arctic and bear movements and dispersal are not compromised as they are in particular southern situations.

Genetic criteria have been used to distinguish Evolutionarily Significant Units (ESUs) and Management Units (MUs; Moritz 1994). An ESU is a group that has been isolated from conspecifics long enough to have undergone meaningful genetic divergence (Ryder 1986). An MU is a group within which population dynamics are driven primarily by birth and death rather than by immigration and emigration; MUs are populations with significant differences in allelle distributions (Moritz 1994). However, both of these definitions are predicated upon geographic isolation of the units under consideration (Paetkau 1999).

Genetic analysis of grizzly bears from representative locations throughout the Canadian range does not support distinction of populations. Although 4 genetically defined groups, or clades, have been identified in North America (Figure 1), boundaries between clades are indistinct and have not been demarcated. Contact zones between clades cannot be ruled out; in fact, one has been identified in the Arctic National Wildlife Refuge (Waits et al. 1998). Intuitively, interchange of individuals among clades is to be expected because habitat between clade areas is essentially continuously occupied by grizzly bears, and the species is capable of and characterized by moderately high dispersal ability (LeFranc et al. 1987; Weaver et al. 1996; but see McLellan and Hovey 2001). At present, distinction of grizzly bear population units based on genetic criteria--with the exception of confirmation of genetic isolation--is not very useful to the evaluation of their status in Canada. Demographic data, including estimates of population size and trend, specific to individual clades are not complete enough to determine status of members of those clades. In addition, clade association has not yet been assigned for grizzly bears throughout much of their Canadian distribution, including most of British Columbia and the eastern Arctic (Waits et al. 1998), precluding definition of Canadian subpopulations on this basis.


2.3.1 Population Isolates in Southern British Columbia

Recent genetic investigations have determined that grizzly bears in the Southern Selkirk Mountains are isolated. This work is described in Section 2.3.2.

Grizzly bears in the North Cascade Mountains also occupy an insular habitat area. Connection to occupied bear habitat to the east and northeast is unlikely across a broad (70-160 km) unoccupied band, and has not been demonstrated except for a single translocated individual that returned (McLellan 1998; T. Hamilton, pers. commun.). Potential connectivity to occupied bear habitat to the northwest is impeded by a barrier consisting of the Fraser River, the Trans-Canada Highway, the Canadian Pacific and Canadian National railroads, and associated developments, and is also undocumented. Genetic confirmation of isolation in the North Cascades is not currently possible because of the paucity of samples from within the area.

The population within the North Cascades Grizzly Bear Population Unit (GBPU) was estimated to consist of <20 individuals (Province of British Columbia 1995) but may include up to 23 bears (North Cascades Grizzly Bear Recovery Team [NCGBRT] 2001). However, recent, unsuccessful efforts to detect bears within the area (M. Austin, K. Romain, pers. commun.) suggest that even these estimates may be high. The Canadian portion of the North Cascades could support a population of 44-64 bears (Province of British Columbia 1995). A provincial recovery plan is being developed for the North Cascades (NCGBRT 2001). Recovery plan components under consideration include access management, prevention of internal fracture zones, restoration of linkages to external population units, and population augmentation. This population unit is contiguous to the south with the North Cascades Grizzly Bear Recovery Zone in the U.S., which is isolated from any other U.S. grizzly population (USFWS 1993). The population in the U.S. portion of the North Cascades is believed to be <20 bears (W. Kasworm, pers. commun.), and may be as low as 5 bears (Servheen 1999a), and population augmentation is being considered. Recent efforts to detect bears using DNA extracted from barbed-wire hair snags have been largely unsuccessful; in 5304 trap nights between 1998 and 2000 spanning both sides of the border, a single female grizzly bear was detected, on the Canadian side (K. Romain, pers. commun.).

At least 6 other population isolates have been identified in southern BC (T. Hamilton and B. McLellan, pers. commun.). Three of these occur within GBPUs which have been recognized by the province as Threatened. The status of these population isolates is described in Section 6.3.

Grizzly bears in other parts of Canada may exist in virtual isolation, but this has not been confirmed through documented geographic or genetic isolation. The southern fringe of grizzly bear distribution consists of several peninsular extensions (Figure 4; Section 2.3.2). Where these peninsulas are constricted, bear movement is compromised. Actual status of some of these “peninsulas” is unknown, and connectivity along them may in fact be inhibited or lost. Examples include the Kettle-Granby, Valhalla, Central Monashee, and Yahk GBPUs in south-central to southeastern BC (Figure 11). Although complete population isolation has not yet been demonstrated, it is suspected by local authorities as a consequence of a combination of natural barriers and human development and activity zones (T. Hamilton, B. McLellan, pers. commun.; McLellan 1998), and each of these has been recognized by the Province of BC as a Threatened GBPU. In the southern Rocky Mountains of Alberta and BC, reduced genetic flow across the Trans-Canada Highway through Banff National Park, and across Highway 3 through the Crowsnest Pass, has been documented (M. Gibeau, M. Proctor, pers. commun.; Proctor et al. In Press).


Figure 4. Approximate current distribution of grizzly bears in southwestern Canada (after McLellan 1998)

Figure 4. Approximate current distribution of grizzly bears in southwestern Canada (after McLellan 1998).

Locations of North Cascades (N.C.) and South Selkirks (S.S.) population units are marked. Historic (ca. 1800) distribution included all mainland areas shown.


2.3.2 Southern Selkirk mountains population

Prepared by Michael Proctor and Ian Ross.

2.3.2.1 Introduction

In this section we discuss the recent documentation of the genetic and demographic isolation of grizzly bears inhabiting a region in the Southern Selkirk Mountains of southern British Columbia. These data and their interpretation are significant as they demonstrate one possible mechanism for the slow process of anthropogenic isolation and local extinction which threatens the long term survival of grizzly bears, particularly at the southern edge of their North American distribution. There is particular relevance in that newly isolated units (population islands) of grizzly bears have an elevated risk of local extirpation. Furthermore, habitat peninsulas have a greater risk of turning into islands.

Geographic population isolation has both genetic and demographic consequences. The genetic isolation of small populations leads to loss of genetic diversity through genetic drift and increased inbreeding. Reduced genetic variability should decrease the population’s ability to respond to future environmental changes because the breadth of genetic options has been reduced. In reality, a population’s response to reduced genetic variability may not be so simple. For example, the brown bears on Kodiak Island, Alaska, have extremely reduced (one-third) genetic variability relative to mainland populations (Paetkau et al. 1998a), yet they have survived and apparently thrived for tens of thousands of years. A similar finding among Newfoundland black bears (Paetkau et al. 1998a) suggests that genetic variability may not be an immediate threat to bear populations in North America. Demographic isolation, however, may be more relevant in the modern landscape where an isolated small population may require immigrants from a nearby source population to offset population declines induced by anthropogenic habitat degradation and mortality.

Grizzly bears, at the southern edge of their North American distribution in southern Canada, inhabit relatively narrow “habitat peninsulas” corresponding to mountain ranges (Figure 4; McLellan 1998). There is an elevated risk of population isolation within these peninsulas with the associated risk of local extirpation, particularly for small populations.

Michael Proctor’s PhD research has been investigating grizzly bear population fragmentation in southeastern British Columbia and southwestern Alberta. His very recent work has documented the existence of “habitat peninsulas” in the southern Selkirk and southern Purcell Mountains and the complete isolation of the grizzly bears in the southern Selkirk Mountains south of British Columbia Highway 3A. Proctor used 15 locus microsatellite genotypes and a log-likelihood population assignment test and related genetic distance measure (Paetkau et al. 1995; Paetkau et al. 1997; Paetkau et al. 1998b) to genetically characterize bears in specific geographic areas and to measure the migration patterns between these local populations.

2.3.2.2 Southern Selkirk grizzly bear population isolation

There are 3 types of genetic evidence, introduced here and discussed below, that suggest the grizzly bears in the southern Selkirk Mountains are genetically and demographically isolated from the adjacent grizzly populations in the region. One is the population assignment test that clusters individuals by their similar allele frequencies and compares that to their location (Paetkau et al. 1995; Waser and Strobeck 1999). Related to the assignment test is the genetic distance, DLR, that quantifies the genetic distance between 2 populations (Paetkau et al. 1997). The third test is the standard population genetic measure of heterozygosity. In this context, we used relative expected heterozygosity as an index of relative genetic variability (Nei and Roychoudury 1974).

2.3.2.3 Genetic samples and southern Selkirk population boundaries

Genetic samples were obtained from several sources. The BC Ministry of Environment provided hair samples from the 1996 Central Selkirk Grizzly Bear Survey covering 9866 km2. The US Fish &Wildlife Service (W. Kasworm) provided samples from bears handled within the Yaak River area in northwestern Montana and southeastern BC, and Idaho Fish and Game (W. Wakkinen) provided samples from bears handled in the southern Selkirks within the US. M. Proctor collected hair samples from the southern Selkirks and the southern and central Purcells within Canada. All samples were collected in the 1990s, and most (90%) were collected since 1996. Samples from handled bears were extracted from blood or hair collected during capture events and all others were non-intrusively collected using scent lures and barb wire corrals as detailed in Woods et al. (1999).

The set of 45 samples representing the southern Selkirk Mountain population came from an area of approximately 8000 km2 south of the BC Highway 3A transportation corridor which parallels the west arm of Kootenay Lake between Balfour and Nelson. The eastern boundary was the Kootenay River and Kootenay Lake valley containing the towns of Creston BC and Bonners Ferry, Idaho. The western boundary for sampling was BC Highway 6 between Nelson and Salmo. This population extends south into Idaho to the southern limit of occupied habitat within the Selkirk Mountains (W. Wakkinen, Idaho Dept. of Fish and Game, pers. commun.); some samples were contributed from Idaho.

Immediately to the west of the southern Selkirks is a small area (1440 km2) with very few grizzly bears (BC Wildlife Branch population estimate ~10 bears) that was not sampled. To the west of this area is an unoccupied zone south of Castlegar BC in the Trail BC area.

2.3.2.4 Evidence from the population assignment test

The assignment test uses allele frequencies from the populations to be compared. The likelihood of assignment to any population is the cumulative probability of occurrence of 30 alleles in this instance (15 loci/bear and 2 alleles/locus). Each bear is assigned to the population with the highest probability of assignment. Comparing 99 grizzly bears sampled from the Central Selkirk Mountains and 45 bears from the Southern Selkirk Mountains, Proctor found that all bears were assigned to the area of their capture (Figure 5). This result strongly suggests that of the sampled bears, there were no migrants between geographic areas and that all bears were captured in the area of their birth. The strong segregation of individuals corresponding to each geographic area (Figure 5) clearly separates the bears from the 2 populations based on their differing cumulative allele frequencies. The power of these results is enhanced by the relatively high percentage of bears that was sampled from each population. The 45 samples from the southern Selkirks represent approximately 40-55% of the entire (Canada plus US) estimated population of 97 (82-112) bears (extrapolated from Wielgus et al. 1994; BC Ministry of Environment estimate, G. Woods pers commun; W. Wakkinen, Idaho Dept. of Fish and Game, pers. commun.). The 99 samples from the central Selkirks represent approximately 40% of the estimated population in that area (256; Mowat and Strobeck 2000). Proctor also found a similar result when comparing the Southern Selkirk population to a sample of 22 bears from the Southern Purcell Mountains immediately to the east (Figure 6). The sample of 22 bears from the Purcells is small (but still >40% of estimated population: BC Wildlife Branch and W. Kasworm, pers commun.) but strongly suggests a separation of the 2 populations with no dispersal between the areas. The Southern Selkirk grizzly population appears to be completely isolated from the bears immediately to the north and east.

These assignment test results contrast sharply with comparisons of the Central Selkirk bears to the Northern Selkirk bears (Figure 7). Allele frequencies of these 2 areas are minimally separated with evidence of bears moving between areas. Bears in these 2 areas are clearly not genetically or demographically separate.


Figure 5. Map and population assignments of the Southern Selkirk (SS) and Central Selkirk (CS) Mountains grizzly bears

Figure 5. Map and population assignments of the Southern Selkirk (SS) and Central Selkirk (CS) Mountains grizzly bears.

 


Figure 6. Map and population assignments of the Southern Selkirk (SS) and Southern Purcell (SP) Mountains grizzly bears

Figure 6. Map and population assignments of the Southern Selkirk (SS) and Southern Purcell (SP) Mountains grizzly bears.

 


Figure 7. Map and population assignments of the Central Selkirk Mountains (CS) and the North Columbia Mountains west of the Columbia River (“West Slope”; WS) grizzly bears

Figure 7. Map and population assignments of the Central Selkirk Mountains (CS) and the North Columbia Mountains west of the Columbia River (“West Slope”; WS) grizzly bears.

 

2.3.2.5 Evidence from genetic distance

Genetic distance is related to migration and mutation rates, population sizes, genetic drift, and time (Hartl and Clark 1997). While an exact relationship between genetic distance and movement rates has not been established, progress on this topic has been made. Using the same microsatellite loci used by Proctor, Paetkau et al. (1999) found that population pairs of polar bears (U. maritimus) with a genetic distance (DLR ) greater than 3.5 had no observed inter-population migrants. This result indicates that a threshold of genetic distance may exist above which migration is extremely limited or non-existent. The DLR values found in Paetkau et al.’s (1999) polar bear population pairs ranged from 0 to 7.8 (Fst = 0.002-0.108). These polar bear populations are probably at equilibrium between mutation, migration, and genetic drift, and natural fractures are responsible for the observed population structure (Paetkau et al. 1999). Proctor measured the genetic distance (DLR) between the southern and Central Selkirk grizzly populations at 11.4 (Fst = 0.133), far greater than the 3.5 threshold for “no migration” suggested by Paetkau et al. (1999). Furthermore, the southern Selkirk system is unlikely in equilibrium and the genetic distance of 8.5 is a conservative estimate. While DLR is a relatively new genetic measure, Paetkau et al. (1997) found it correlated closely with more traditional genetic distance measures such as Nei’s standard measure, Ds.

2.3.2.6 Evidence from loss of genetic diversity

Figure 8 shows the average heterozygosities of 8 grizzly bear assemblages in adjacent geographic areas (Figure 9) within southern BC and Alberta. When comparing the heterozygosity of all 15 loci between the Southern Selkirks and the immediately adjacent Central Selkirks, Proctor found that the average heterozygosity of grizzly bears in the Southern Selkirk Mountains (Figure 8) is lower than expected (paired sample t-test p<0.05). These data suggest that this assemblage of bears has been genetically isolated for at least several generations. Loss of genetic diversity in small populations is dominantly mediated by genetic drift (Lacy 1987), a genetic random walk process driven by the small sub-sampling of alleles of breeding individuals between subsequent generations.

Using mean values for demographic parameters, Proctor estimated the time since isolation of the southern Selkirks grizzly bear population unit from the central Selkirk bears at 60 years. This calculation is a rough approximation based on several assumptions that are difficult to verify. Rather than being an exact documentation of time since isolation it provides a plausible framework for explaining the reduced heterozygosity displayed by the southern Selkirk grizzly bears. It assumes that the Central Selkirk and Southern Selkirk grizzly bears were connected in the past, had equal heterozygosities, and that the larger Central Selkirk population has not experienced a significant reduction in heterozygosity since isolation. It also assumes, probably incorrectly, that the isolation event was abrupt. Proctor also estimates grizzly generation time at 10 – 15 yrs (Allendorf and Servheen 1986; Craighead et al. 1995) and an effective population, Ne (number of breeders contributing to a subsequent generation), of 0.11 of the total population size (range = 0.04 - 0.19, Paetkau et al. 1998a).


Figure 8. Average heterozygosity in grizzly bear populations in southeastern BC and southwestern Alberta

Figure 8. Average heterozygosity in grizzly bear populations in southeastern BC and southwestern Alberta.

See Figure 9 for study area locations.


Figure 9. Location of study areas in southeastern BC and southwestern Alberta providing grizzly bear samples for evaluation of heterozygosity

Figure 9. Location of study areas in southeastern BC and southwestern Alberta providing grizzly bear samples for evaluation of heterozygosity.

Letter codes for areas are same as in Figure 8.


A further indicator of reduced genetic diversity is the unbiased probability of identity (PI). The PI value represents the probability that 2 individuals selected at random from within a population will have identical genotypes at all 15 loci. For the Southern Selkirks population unit, the PI was 1/822 000 000. By comparison, the PI for the Central Selkirks was 1/11 000 000 000 000, and for the Southern Purcells it was 1/2 000 000 000 000.

2.3.2.7 Grizzly bear habitat peninsulas in southern British Columbia

The isolation of the Southern Selkirk grizzly population from the Central Selkirks and the Southern Purcell grizzlies contrasts with the connectivity between the grizzlies in these same 2 mountain ranges just to the north. Results comparing the grizzlies in adjacent areas in the northern parts of the Selkirk and Purcell Mountain ranges suggest that bears are moving between the mountain ranges (Figure 10). These results suggest that the adjacent grizzly bear populations in the Southern Selkirk and Purcell Mountains are acting as two habitat peninsulas.

2.3.2.8 Discussion

Habitat fragmentation is considered to be a major threat to population, and ultimately species, persistence in modern conservation biology theory (Caughley and Gunn 1996). Habitat fragmentation, taken to an extreme, leads to population fragmentation. In the case of grizzly bears, particularly near the southern edge of their North American range, the peninsular nature of their currently occupied habitat makes them susceptible to anthropogenic population fragmentation resulting in habitat islands. These islands are at elevated risk of extirpation, particularly when there are fewer than 100 individuals in the island as is the case in the Southern Selkirks. This mechanism, coupled with human-induced habitat degradation and mortality, probably represents the major threat to long term grizzly bear persistence in southern Canada.

Proctor notes that there are two possible explanations for the lower heterozygosity and divergent allele frequencies of the southern Selkirk grizzlies. The Southern Selkirk population may be a remnant of a past separate population inhabiting land to the southwest of the west and south arms of Kootenay Lake, or the Southern Selkirks may be a recently pinched-off island that was previously connected to the northern populations through the central Selkirks. Proctor argues that the latter explanation is far more likely. He notes that the valley creating the fracture to the north is relatively narrow, holding the slow river-like west arm of Kootenay Lake. Until the recent past, Kootenay Lake had for centuries offered a landlocked salmon (Oncorhynchus nerka) run that spawned in many of its tributaries. At present this run is severely reduced, primarily kept alive in a controlled spawning channel. Other isolating mechanisms include a narrow strip of continuous human settlement lining the BC Highway 3A corridor. This highway is the modernization of an historic route that supported the development of the area’s fruit-growing industry starting in the early 1900s. Twenty to forty years ago, calls to the Wildlife Branch of the BC Ministry of Environment to deal with nuisance grizzly bears were relatively common. Since 1990, these calls have all but ceased (G. Woods, pers. commun.). Besides the riparian habitat exclusion mediated by these settlements, decades of fire suppression in the valley have reduced early seral stage habitats yielding an even-aged conifer forest of low quality as grizzly bear habitat.


Figure 10. Map and population assignments of the Central Selkirk (CS) and Central Purcell (CP) Mountains grizzly bears

Figure 10. Map and population assignments of the Central Selkirk (CS) and Central Purcell (CP) Mountains grizzly bears.


To the immediate east of the Southern Selkirk population unit is the continuation of BC Highway 3A along the south arm of Kootenay Lake, as well as the town of Creston and associated agricultural developments. To the west is a relatively developed landscape of towns and agriculture in the vicinity of Arrow Lake and the Columbia River. The Southern Selkirk grizzly population is functionally an island.

While it is difficult to prove that the Southern Selkirk and Central Selkirk grizzly bears were connected in the past, a review of developments of the past century provides ample evidence to support the fragmentation hypothesis. Conversely, if the west arm of Kootenay Lake in its historic natural state had the potential to fracture grizzly bear populations, then innumerable other fractures would exist within grizzly bear distribution and the bulk of the Canadian grizzly population could not be considered a contiguous unit.

Proctor also argues that it is the context of the small population size (97 animals; see above) and 10% effective population size that provides an explanation of the divergent log likelihood population assignments that demonstrate the separation of these two populations. Furthermore, the southern Selkirk grizzly population possibly went through a population bottleneck from excessive human-induced mortality in the early part of the 20th century, hastening the genetic drift process.

In essence, the grizzlies in the Southern Selkirks and adjacent connecting lands likely experienced heavy human-related mortality in the early 1900s by activities of miners and farmers. This was further exacerbated in the last few decades by an increasingly dense and continuous human settlement separating the two populations.

There is nothing particularly unusual about this population fracture in that the conditions that most likely created it exist in many areas throughout western North America and southern BC, including other areas presently and recently occupied by grizzly bears. The problem has risen to the acute stage when combined with the narrow peninsular nature of occupied habitat in the region.

Proctor et al. (In press) report on the fragmentation of grizzly bear populations on both sides of BC Highway 3 as it crosses the Rocky Mountains in the Crowsnest Pass. They demonstrate that the highway corridor, with approximately 7000 vehicles per day and non-continuous human development, has all but severed female grizzly movement and dispersal across the highway. They found evidence of male grizzly movement across the highway but argue that a greater-than-expected genetic distance across the highway corridor suggests limited and reduced male grizzly bear movement and gene flow.

2.3.2.9 Threats and population stability

Grizzly bear hunting was eliminated in the Southern Selkirks in 1995, but the last bear legally harvested was in 1991 (G. Woods, pers. commun.). Wielgus et al. (1994) reported that the Southern Selkirk population was tentatively stable, with threats to this condition being human-related mortalities. Recent research in the US (W. Wakkinen, Idaho Fish & Game, pers. commun.) reports that numbers may be on the rise as a result of progress in reducing human-caused mortalities. No recent research within Canada has been conducted. Canadian wildlife managers for the area are aware of the threat of human-related mortalities but feel the situation is stable at present (G. Woods, pers. commun.). However, an island population with an estimated 97 animals with an effective population of 5 to 20 is clearly at risk of extirpation in the long term.


Figure 11. Grizzly Bear Population Units in British Columbia

Figure 11. Grizzly Bear Population Units in British Columbia.

Map courtesy of BC Ministry of Water, Land and Air Protection. Labeled GBPUs are isolated (see text).

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