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Technical Thematic Report No. 10. - Northern caribou population trends in Canada


Predation, parasites, disease

Although predation, diseases, and parasites are part of the ecology of migratory tundra caribou, they are listed here as threats because their role in trends in caribou abundance interacts with human activities. The interactions work in a number of ways at the individual and herd scales and include variables such as whether predation is additive or compensatory to harvesting. The major predators of migratory tundra caribou are wolves and grizzly bears, but wolverines, lynx, and eagles all take caribou as well. Wolves and grizzly bears are effective predators of caribou of all sex and age classes and caribou have evolved behavioural strategies such as spacing themselves across their landscapes to reduce the risk of predation (Bergerud et al. 2008).

Numbers of predators are infrequently monitored on the ranges of the various caribou herds. Some information is available for the ranges of the Bathurst and Beverly herds. During the 1990s, wolf den occupancy on the Bathurst summer range (Cluff, 2004, pers. comm.) and along the Thelon River in Thelon Game Sanctuary (Hall, 2005, pers. comm.) decreased. The latter is the Beverly Herd's calving and summer range. Wolves are heavily hunted on parts of the Beverly Herd's winter range (Cluff, 2004, pers. comm.) and the trend (based on export permits for pelts) was an increase in wolves harvested in the 1980s compared to the 1970s, which may suggest an increase in abundance of wolves over that period. More recent information has not been compiled. Although annual variability makes measuring trends uncertain, wolf abundance on the Bathurst range may have declined since the late 1990s (Adamczewski et al. 2009). The number of grizzly bears increased during the 1980s and 1990s on the summer and fall ranges of the Beverly and Bathurst herds (Mulders, 2009, pers. comm.).

Information on the status and trends of diseases and parasites in migratory tundra caribou is fragmentary among herds and over time. The lack of information is partly because parasites and diseases have not been considered as important as, for example, predators in caribou population dynamics – which may itself reflect the lack of information. On Southampton Island caribou abundance and condition are monitored and a recent high incidence of brucellosis in both sexes has been implicated in the herd's decline (Campbell, 2008, pers. comm.).

Through the CircumArctic Rangifer Monitoring and Assessment Network (CARMA) International Polar Year projects, the herd-specific statuses for several parasites have been, and continue to be, evaluated. The bacterium causing Johne's disease, known for causing chronic wasting and diarrhea in cattle, has been found in caribou from Greenland and was found at low levels in Bathurst and Bluenose-West caribou in 2008 (Orsel et al. 2008). No evidence of chronic wasting disease was found in Porcupine or Bathurst herds (CARMA, 2010b).

For a long time, appreciation lagged for the role of parasites and pathogens in caribou ecology. However, that is changing: for example, gastro-intestinal worms occur in almost all caribou (deBruyn et al. 2009) and, while the infections may not cause obvious symptoms, they are likely costly to the caribou (Gunn and Irvine, 2003). For Svalbard wild reindeer, infection by parasitic worms influenced fecundity and played a role in regulating caribou abundance (Albon et al. 2002). Trends in parasites are unknown but warming temperatures and the northward extension of some hosts raises concerns. An additional concern is that, on the caribou's southern ranges, the possibility of parasite-host switching occurs where caribou and other deer species overlap in time and space (deBruyn et al. 2009). Hosts exposed to novel parasites maybe more susceptible (Ball et al. 2001).

Several parasites link caribou with their predators because the parasite needs two hosts to complete its life-cycle. The implications of this parasite linkage between predator and prey are unknown for caribou, but are established for other species. For example, the hydatid tape-worm infection in moose may increase the vulnerability of moose to wolf predation. Wolves are the secondary host for this parasite (Joly and Messier, 2004). In caribou, Besnoitia tarandi is a single-celled parasite with a two-host life cycle; carnivores and biting flies have been respectively suggested as potential definitive hosts and vectors of besnoitiosis. Typically the parasite can cause areas of roughened skin, but its overall effect on caribou health is unknown (Ducrocq et al. 2009). The status of Besnoitia, assessed from caribou harvested in the fall from 2007 to 2009, was variable, with the Leaf River Herd having a higher percentage of infected caribou (77% of males and 57% of females) than in the George River, Bathurst, and Bluenose West herds (all in the range of 30 to 45%), and with the Porcupine Herd having an infection rate of only 8% (Ducrocq et al. 2009).

One parasite whose status is better known is the warble fly, which is widespread on the summer ranges of all herds, although considerably less common on the High Arctic islands. Caribou reduce their foraging time as they try to avoid the flies and, additionally, there are immune costs once nose-bot and warble flies have parasitized the caribou. Heavy infestations reduce calf growth, adult condition, and pregnancy rates (Weladji et al. 2003; Bergerud et al. 2008). Summer weather influences the activity of the adult flies (Russell et al. 1993) and, at least on the Bathurst Herd's summer range, summers have warmed. The trend between 1957 and 2009 is for an increase in the index of suitable weather and a longer season for warble fly harassment (Gunn and Poole, 2009; Witter, 2010).

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Harvest of caribou is part of people's relationship with caribou and harvesting is a rich source of information about caribou – their health, distribution, and ecology. However, in a changing world, and especially if the trends in abundance are in decline, even slowly, harvest can play a role in accelerating the decline (Adamczewski et al. 2009; Boulanger et al. 2011). The Cape Bathurst, Bluenose-West, and Bathurst herds were declining in the early 2000s; this decline was likely accelerated by a hunter harvest that remained substantial relative to the declining herd size. When harvests were curtailed, the declines halted (see herd section).

Changes that have occurred on caribou ranges since the 1970s include an overall increase in number of people and shifting socio-economic patterns (such as wage-earning) which may influence harvest levels. The human populations of the Arctic and the three taiga ecozones+ have all increased, the combined population almost doubling, from 59,390 people in 1971 to 107,213 people in 2006 (Figure 6). The increase in number of people is reflected in the increasing size of larger communities (centralization) (Environment Canada, 2009)and increased seasonal and all-year road developments, especially in the Northwest Territories and northern Saskatchewan, on the southern edges of the winter ranges in the taiga and boreal ecozones+ (BQCMB, 2011; Trottier, 2011, pers. comm.). Caribou are adapted to respond to environmental variability, such as severe winters or increasing predation levels, by changing their patterns of movement across a large-scale landscape (Gunn et al. 2011a).

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Figure 6. Human population levels in northern Canadian ecozones+, 1971 and 2006.


Source: census data from Statistics Canada compiled by ecozone+ (Environment Canada, 2009)

Long Description for Figure 6


This bar graph shows human population levels in northern Canadian ecozones+ for 1971 and 2006. A table of the results is provided below.
Taiga Cordillera368533
Taiga Plains20,91028,433
Taiga Shield26,16541,686

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The increasing number of people, a shift to wage-earning, and changing technologies for hunting (snowmobiles, ATVs, aircraft, winter roads, and rapid communications) have likely altered hunting effort and made finding and harvesting caribou more efficient. The relationship between hunting effort and harvest levels, however, is largely unknown and this limits understanding of the effects of hunting. Most of the understanding about the importance of measuring hunting effort is from a range of exploited species other than caribou (Ludwig, 2001). Schooling fish have parallels with gregarious caribou in relation to harvest vulnerability. For pelagic fisheries, constant yield harvests can lead to population collapses if harvesting effort is not directly related to local abundance (Mullon et al. 2005).

Understanding the effects of harvest is complicated as there are few measures of hunting effort and data on harvest levels are sporadic over time. Levels of, or trends in, wounding loss are unknown, although increased effort in management planning includes education and help from Aboriginal elders about respectful hunting practices (for example PCMB, 2009; Tlicho Government and Department of Environment and Natural Resources, Government of the Northwest Territories, 2011). Harvest levels at the community level vary; this is related to annual variability of the distribution of caribou on their seasonal ranges. In Canada's territories, most hunters are aboriginal and, under Canada's constitution and under land claims settlement acts, their hunting rights are protected. Generally, aboriginal hunters can harvest unlimited numbers of caribou unless there is a conservation issue. A second category of hunters is resident hunters. The trend is for fewer resident hunters in the Northwest Territories (Government of the Northwest Territories and NWT Biodiversity Team, 2010) as a result of restrictions following the decline of herds. The third category of hunters is under the heading "commercial", which can include both harvesting for commercial meat sales and guided, outfitted hunts by non-residents. The level of commercial harvesting has varied among herds. Commercial use has been progressively reduced as the herds have declined and currently there is no commercial harvesting of any Northwest Territories barren-ground caribou herd (Department of Environment and Natural Resources, 2006) and commercial harvesting has been sharply reduced in Nunavut (Coral Harbour, 2011; Dumond, 2011, pers. comm.).

In the late 1980s, the Government of the Northwest Territories recognized the importance of collecting harvest information and initiated the collection of caribou harvest data from hunters. This was a time when herds were at or approaching peak herd sizes. The Dogrib Harvest Study collected information on the Bathurst Herd during the period 1986 to 1993 and reported that annual harvests ranged from about 7,000 to 23,000 caribou (Boulanger and Gunn, 2007). When the harvest study ended it was not replaced – although information collected in the 2005/06 season from check stations and community hunts indicated a decline in aboriginal harvest to about 4,500 caribou (Boulanger and Gunn, 2007). In 2007, for the Bathurst Herd, the number of tags per resident hunter was reduced from five to two and the harvest was restricted to bulls; in 2010 the harvest was reduced to zero (Miltenberger, 2010).

There is information for other herds on subsistence harvest levels, collected through harvest studies established under land claims legislation (Usher and Wenzel, 1987). For example, the annual caribou harvest in Nunavut from 1996 to 2001 averaged 24,522 animals (Priest and Usher, 2004). Information on the western Northwest Territories herds (Cape Bathurst, Bluenose-West, and Bluenose-East) is available through the Gwich'in Harvest Study (GRRB, 2009) and Inuvialuit Harvest Study (Inuvialuit Renewable Resources Committee, 2003) for community caribou harvests from 1988 to 1997. Information for 1998 to 2005 is available through the Sahtu Harvest Study (SRRB, 2004; Bayha and Snortland, 2006). As an example of harvest trends drawn from these studies, harvest from the Bluenose-West Herd in the Sahtu decreased from 1,022 in 1999 to 270 caribou in 2005 (SRRB, 2007).

The Beverly and Qamanirjuaq Caribou Management Board also provides estimates of caribou harvests in the board's annual reports. The combined harvest of the two herds was estimated at 14,080 in 2005/06, 13,770 in 2006/07, and 13,225 caribou in 2007/08 (BQCMB, 2006; BQCMB, 2007a; BQCMB, 2008a). With a lack of harvest data, the decline of the Beverly Herd, and uncertainty around herd movements and harvest locations, there was not enough information to provide reliable estimates for 2008/09 or 2009/10 (BQCMB, 2009; BQCMB, 2010a). Recent information on distribution of satellite-collared caribou suggests that the communities may also be harvesting caribou from the Ahiak Herd whose winter distribution overlaps with the Beverly Herd's typical winter range. If this is the case, previous harvest estimates for the Beverly Herd are not reliable (BQCMB, 2009).

Monitoring harvest levels is also complicated by different political reporting systems. For example, for the Porcupine Caribou Herd, harvest monitoring is the responsibility of two countries, one state, two territories, and seven aboriginal governments or councils. As a consequence, harvest reporting is sporadic and if detailed surveys are initiated they are seldom continued. Over the last 20 years, a reasonable estimate of total harvest has only been reported for a three-year period (1992 to 1994) (PCMB, 2009). Because the Porcupine Herd had been declining since 1989 and had potentially declined further since the population estimate in 2001, the Porcupine Caribou Management Board, a co-management body that generates management recommendations for the herd in Canada, developed a harvest management plan with options for responding to periods of herd decline, stability, and growth (First Nation of the NaCho Nyäk Dun et al. 2010).

On Southampton Island, caribou have been commercially harvested since the 1990s to supply a local meat processing plant. Commercial harvest averaged 2,432 caribou from 1992 to 2003, with an increasing trend over that period, while domestic harvest was estimated in 2006 at about 1,500 caribou annually (Campbell, 2006). The commercial harvest was suspended after the 2009 harvest because the herd had declined (Coral Harbour, 2011; Dumond, 2011, pers. comm.).

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Along with increasing numbers of people on the caribou ranges, there are trends towards more exploration and resource development activity. Most notable are activities associated with mineral and hydrocarbon exploration and development. Caribou behavioural responses to human activities, especially those associated with industrial exploration and development, are quite well known (Wolfe et al. 2000; Stankowich, 2008). As the rate of human activities increases, however, our lack of understanding about the cumulative effects on caribou at the individual and the herd level becomes a more worrisome gap (Cameron et al. 2005). Limited progress has been made in measuring and managing these cumulative effects (Festa-Bianchet et al. 2011; Gunn et al. 2011a).

Mining and oil and gas exploration and development

Mining typically follows boom and bust cycles. Exploration activities for diamonds and uranium were widespread on the Bathurst Herd ranges in the 1990s and over the period 2003 to 2008 on the Beverly Herd's calving and summer ranges. Although the amount of activity can be partially tracked through land-use permits, not all activity is regulated through permits and cumulative effects are difficult to access (Gunn et al. 2011a).

Site-specific contamination occurs at abandoned mines, a concern to local people who fear that the contaminants (for example from tailings) will affect wildlife, including caribou (for example Macdonald et al. 2005). Abandoned mines in the Northwest Territories and northern Saskatchewan still require clean-up (BQCMB, 2008b) despite the trend toward increased efforts since the 1990s to clean up these abandoned sites.

Exploration for and mining of uranium has been the greatest concern in the past among communities that harvest Beverly caribou. Uranium exploration and development has occurred for decades on the Beverly winter range in northern Saskatchewan. Mineral exploration has been increasing over the past 10 years on the ranges of both the Beverly and Qamanirjuaq herds in the Northwest Territories and Nunavut (BQCMB, 2010b). As of May 2010, there were many active prospecting permits, mineral claims, and mineral leases on the Beverly and Qamanirjuaq traditional calving ground (BQCMB, 2010b). The level of camps and aircraft activity associated with those claims and leases is highly variable. Since 1996, four diamond mines have been built and are operational on the Bathurst Herd's summer range. Three of the diamond mines are large open-pit mines and their activities have reduced the occurrence of caribou in their vicinity over a greater distance than expected (Johnson et al. 2005). In mid-2011, three large open-pit mines were at the formal environmental assessment stage for the Bathurst, Beverly, and north Baffin caribou ranges (NIRB, 2011).

In the Western Arctic, increases in oil and gas exploration activities over the last 10 to 15 years are a concern for people on the winter range of the Bluenose-East and Bluenose-West herds. Further west, the range of the Porcupine Caribou Herd extends from northeast Alaska to west of the Mackenzie Delta. The US portion of the herd's core calving range is in the Arctic National Wildlife Refuge. Opening the Arctic National Wildlife Refuge to oil and gas development (a proposal that has been under consideration in the United States for several years) has the potential to constitute a major threat to the Porcupine Caribou Herd. The "1002" area on the Alaskan coastal plain contains both high potential for hydrocarbon deposits and sensitive habitat for the herd during the calving and post-calving periods (Griffith et al. 2002).

Roads and transmission lines

The trend is toward increased access to some caribou seasonal ranges, with additional proposed roads in the planning stages. Roads can create partial barriers to caribou movement and provide easy access, creating the potential for increased harvest levels, including from hunters from communities outside of the region (Wolfe et al. 2000). Restrictions on use of roads for harvesting are difficult to establish and enforce. The three examples below illustrate some issues and concerns regarding linear development on caribou ranges.

1. Beverly Herd

Potential impacts on Beverly caribou from construction and operation of the Athabasca seasonal road through winter range in northern Saskatchewan, as well as a proposal for upgrading to an all-weather road, have raised concerns with the Beverly and Qamanirjuaq Caribou Management Board and with the Athabasca Interim Advisory Panel that is charged with developing a land use plan for a 50 km wide corridor along the road (Athabasca Interim Advisory Panel, 2006; BQCMB, 2009). Expected impacts of the road on caribou include increased hunting pressure from unregulated hunters from southern Canada, as well as cumulative impacts from development of additional roads and trails.

2. Qamanirjuaq Herd

Feasibility studies were first proposed in 1999 for transmission lines and roads from northern Manitoba to communities on the west coast of Hudson Bay, as well as for hydro generation facilities just north of the Manitoba border. These proposed facilities are all located on the Qamanirjuaq Herd range. An all-weather road along the Hudson Bay coast could increase access and possibly affect caribou movements during spring migration, and along the herd's fall migration corridor in southern Nunavut and northern Manitoba (BQCMB, 2007b).

3. Porcupine Herd

The Dempster Highway connects Dawson City, Yukon to Inuvik, Northwest Territories, traversing the winter range of the Porcupine Herd. The Dempster is a challenge to managers because of the access it provides to hunters (PCMB, 2010). Historically, harvest success was linked to the distribution of the herd. Since the construction of the highway, hunters have had access to the herd in the Richardson Mountains, Eagle Plains, and Ogilvie Valley. As well as direct mortality from harvesting, there has been an ongoing concern that portions of the herd's winter range south and east of the highway may be lost if there is a disruption of the migration across the highway due to hunting. In the past, this potential threat was addressed by applying various no-hunting corridor widths along the highway and by completely closing the highway to hunting for one week during the peak of fall migration in the region (Environment Yukon, 2010b). Because implementation of the no-hunting corridors varied from formal regulations to voluntary restrictions, depending on the user group, the success of the corridors was mixed. Enforcement of the no-hunting corridor was halted in 2007 due to legal challenges (PCMB, 2008).

Hydroelectric development

The largest land conversion in the Quebec portion of the Taiga Shield Ecozone+ has been the flooding of land for hydroelectric development. Since the 1970s, about 2,000 km2 of lake area and about 11,000 km2 of land have been converted to reservoir for the La Grande development (Therrien et al. 2004). About 6,000 km2 of forest was lost due to conversion to reservoirs, roads, and other types of infrastructure (ESTR data analysis by F. Ahern based on Leckie et al. 2006), a trend that may continue with expansions and additional hydro projects planned (Hydro-Québec, 2011). In Newfoundland, caribou avoided a hydro-project during construction and operation (Mahoney and Schaefer, 2002).


The pattern of increasing access associated with development of caribou ranges is not restricted to terrestrial ecozones+. Shipping is increasing in Arctic passages, with the biggest increases in Hudson Strait and the Mackenzie Delta (Judson, 2010). There are implications of ice-breaking ships for caribou sea-ice crossings, especially in the fall, when changes to the timing and patterns of sea-ice formation could interrupt migration or increase the risks to caribou crossing the ice between Victoria Island and the mainland (Poole et al. 2010). Increased shipping also brings more people to the Arctic. Cruise ship stops and associated tours on land bring a new type of tourism – large groups wishing to observe wildlife in over a short time period. This has the potential for increased impacts on wildlife, a factor now being considered in park management planning (for example Wildlife Management Advisory Council (North Slope), 2006). Passages of cruise ships increased more than threefold between 1993 and 2007 (Judson, 2010).

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Atmospheric currents bring pollutants from distant sources and deposits them on snow and vegetation. Some of these pollutants are considered contaminants, as they can accumulate as they move up the food chain – including through the lichen-caribou-human food chain (Gamberg et al. 2005). In general, most contaminants are more of a concern for aquatic ecosystems (especially for marine mammals) than for terrestrial ecosystems (Gamberg et al. 2005). Other pollutants do not accumulate in the plants and animals but have other ecosystem impacts that may indirectly affect caribou. For example, arctic haze, a persistent, diffuse layer in the lower (2 to 5 km) layers of the atmosphere, is a complex mixture of small particles and acidifying pollutants from natural sources such as forest fires and volcanoes, as well from industrial pollution. It forms in winter and the particles are deposited in snow which, as it melts, carries the particles and pollutants into aquatic ecosystems. Dark particles on the snow surface contribute to earlier snow melt, a feedback mechanism known to accelerate global climate change (Rinke and Dethloff, 2008). Currently, the direct effects of arctic haze on terrestrial ecosystems appear to be restricted to the locality of industrial plants, mainly in Russia (AMAP, 2006).

The Canadian Northern Contaminants Program (NCP) has been active in monitoring persistent organic pollutants (POPs), heavy metals, and radionuclides for the last three decades. The following account is derived from the NCP summary report (Northern Contaminants Program, 2003), except where noted. Some 15 different caribou herds across Nunavut, the Northwest Territories, and the Yukon were monitored during the 1990s through two large monitoring programs; additional monitoring has been undertaken since then for some herds (Gamberg, 2009). Assessments of risk to human health from contaminants show that caribou is a safe and nutritious food choice across northern Canada (Donaldson et al. 2010).

Persistent organic pollutants such as DDT, PCBs, dioxins, and furans were found at only very low levels in caribou (often too low to be detected at all) and are not of concern for either caribou or human health (see also Gamberg et al. 2005).

Some heavy metals, however, are found at elevated levels in caribou, though not to the same extent as in some marine mammals. There are wide variations in the levels of metals from herd to herd, probably due to the variation of levels in the underlying geology. Cadmium levels tend to be higher in the kidneys and livers of the Beverly caribou in the Northwest Territories and Nunavut, compared to the levels in other herds. Natural sources of cadmium in the underlying rocks in the area are likely responsible. This cadmium accumulates in lichen, which is then eaten by the caribou. Mercury levels show no clear pattern (Gamberg et al. 2005), with the highest levels found in the Beverly Herd and in Meta Incognita Peninsula caribou (part of the South Baffin population). In the central and northeastern parts of northern Canada, levels of mercury in caribou follow the same geographic pattern as levels found in sediments. Scientists consider that much of this mercury has been transported from human-made sources in other parts of the world. An exception is mercury in caribou from the Yukon, where local geology may be a more important contributing factor.

Radioactivity levels became elevated in caribou during the 1960s from atmospheric nuclear weapons testing, with the highest concentrations of radiocesium found in the large caribou herds of central northern Canada. Levels declined steadily, with a temporary, and relatively small, increase from fallout following the Chernobyl reactor accident. Concentrations now are about ten times lower than in the 1960s and continue to decline (Macdonald et al. 2007).

New and emerging contaminants (contaminants that have recently been found to accumulate in ecosystems) are generally of more concern for aquatic environments – but, nonetheless, they are also a recommended focus for further monitoring and research in terrestrial ecosystems (Gamberg et al. 2005). An example of this class of contaminants is perfluorinated compounds (PFCs, used to make consumer goods like water-repellent coatings and fire-fighting foams), which are known to be widespread globally (Donaldson et al. 2010) and increasing in the Arctic (Ostertag et al. 2009). Caribou liver and meat accumulate PFCs and contribute to the intake of these contaminants by those northern residents who eat caribou frequently. Health risks associated with the current levels measured in people are considered to be very low (Ostertag et al. 2009; Donaldson et al. 2010).

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Forest fires

Forest fires are a long-standing part of caribou ecology but trends toward increasing size and severity of fires could change the relationship. The influence of forest fires on northern caribou ecology will vary among herds as the herds vary in the percentage of their annual range that extends below the tree-line. The tree-line dips south in the continental centre of Canada and then turns north toward the Atlantic coast. The George River Herd's annual range is 90% below the tree-line as the area of tundra is narrow. The other herds have between 57 and 79% of their annual range below the tree-line, while the Dolphin and Union and the northeastern mainland herds remain north of the tree-line year-round. Through the cycles of high and low abundance, the winter range shifts, expands, and contracts.

The northern caribou herds use the boreal forests mostly within the Taiga Plains and the Taiga Shield. Partly because of their dry continental climate, fuel types, and relative lack of suppression, fires in these ecozones+ tend to be relatively severe and large (Krezek-Hanes et al. 2011). The annual pattern of forest fires is episodic, with, for example, years of high fire activity (1979, 1989, 1994, 1998 in the Taiga Shield Ecozone+ during the period 1960 to 2007) interspersed with years of lower fire activity (Krezek-Hanes et al. 2011). This episodic pattern is related to variations in weather during the fire season, influenced both by decadal climate shifts caused by the Pacific decadal oscillation and by the trend toward warmer temperatures (Krezek-Hanes et al. 2011).

Average annual area burned by large fires has increased since the 1960s in Canada's taiga ecozones+ (Krezek-Hanes et al. 2011). Results from the Canadian Climate Centre General Circulation Model scenarios suggest a further increase in fire occurrence across Canada of 25% by 2030 and 75% by the end of the century, with the average area burned expected to approximately double from the beginning to the end of the 21st century (Wotton et al. 2010). The magnitude of the changes in fire regimes is projected to be greater at northern latitudes (Flannigan et al. 2005). Trends toward an increase in forest fire intensity and frequency will affect caribou winter range (Russell et al. 1993; Thomas, 1998) as caribou shift their distribution in response to the pattern of recently burnt areas, as well as in response to snow conditions (Thomas and Kiliaan, 1998; Joly et al. 2003; Barrier, 2011). An increase in forest fires may have additional, long-term effects on lichens. On the tundra-boreal forest ranges of the Western Arctic Caribou Herd in Alaska, lichens have decreased from the combined effects of forest fires, grazing, and possibly the warmer temperatures (Joly et al. 2009; Joly et al. 2010). As lichens decreased, shrubs and grasses increased – a trend also seen elsewhere in the Arctic (Cornelissen et al. 2001).

Two trends characterize the forested winter ranges of the migratory tundra caribou. First, the cumulative effect of forest fires is reducing the areas of mature to old forest, which is where the mats of lichens have reached maximum growth. Between 1990 and 2000, for example, forest fires on the winter range of the Bathurst Herd (including the area south of Great Slave Lake) reduced the area of forest by 30% (Chen et al. In Prep.[a]). Caribou moved through recently burnt areas but did not stay, as lichens, their main winter forage, are rare until about 40 to 60 years after a forest fire. Caribou avoided areas with a high density of burns and selected the older patches of forest with a ground cover of lichens and herbaceous forage, although caribou did use the habitats adjacent to the burn boundary and some caribou occupied habitats in early-succession stages more than expected (Barrier, 2011). On the Beverly winter range, lichen recovery was relatively slow and caribou did not make the highest use of forests until 150 to 250 years after fires (Thomas and Kiliaan, 1998). Caribou harvesters from communities on the Beverly winter range in southern Northwest Territories and northern Saskatchewan believe that loss of habitat due to forest fires on the winter range has resulted in decreased use of large areas by caribou and changes to migration routes (BQCMB, 2005; BQCMB, 2011).

The second trend is an overall contraction of the southern boundary of the forested winter ranges as herd abundance declines (and correspondingly, expansion when herds increase in numerical strength). This is best known through the work of Bergerud et al. (2008) for the George River Herd. However, it is also a recent trend for herds such as the Bathurst Herd (Gunn et al. 2011b).

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Climate change

Climate in the North has changed by different magnitudes and at different times of the year depending on location. For example, in northwestern North America, spring has been warming at a high rate over the last few decades. In the central and eastern barrens, spring conditions remained stable or cooled slightly for periods of several years within the same time frame. The overall trend since 1950 across the Canadian Arctic, however, is to annual average temperature increases, with strongest warming in the winter, spring, and summer months (Zhang et al. 2011). The same regional and seasonal diversity in temperature trends, with an underlying warming trend, has been documented in Russia. Climate models demonstrate that the climate will continue to change – and most conspicuously in the North (ACIA, 2005).

Broad-scale trends in patterns and amount of vegetation are related to these trends in climate. For example, the Southern Arctic showed a net increase in the Normalized Difference Vegetation Index (NDVI), an index of photosynthetic activity, of about 24% from 1985 to 2006 (Ahern et al. 2011). Studies relate increases in NDVI in the Arctic to increased growth of shrubs in many areas, accompanied by decreases in tundra vegetation (for example Hudson and Henry, 2009; Olthof and Pouliot, 2010). The global area of arctic tundra was estimated to have decreased about 20% between 1980 and 2000, based on trends in climate and on NDVI studies (Wang and Overland, 2004). However, predicting the changes is complicated as even within a single plant species there are considerable variations in responses to climate. For example, bud, flower, and leaf growth of arctic heather (Cassiope tetragona) responses to temperature and precipitation varied among sites and Arctic islands, based on decade-long chronologies (Rayback et al. 2011).

At the scale of individual herd ranges, for example the Bathurst Herd's calving grounds, shrub encroachment may have reduced the area of lichens. Lichen cover, as measured through remote sensing, decreased between 1990 and 2000 from 44 to 22% of the total calving ground area (Chen et al. In Prep.[b]). Other trends in vegetation that have been measured on the Bathurst Herd's summer range include a significant increasing trend in green biomass, based on NDVI satellite imagery (Chen et al. In Prep.[b]).

Annual variability in arctic climate is high – which means detecting trends can be difficult (Chen et al. In Prep.[a]). Additionally, it is difficult to attribute a single event such as an icing storm as being within the "normal" range or as an indication of a warming climate. Examples of this type of event occurred in the fall of 2003, when coastal areas from Alaska to Kugluktuk, Nunavut experienced icing conditions that forced caribou to move in search of accessible forage. Ice on the land formed a barrier between the caribou and their food (Nagy, 2007).

Another factor that adds to the complexity of predicting impacts of climate change is that all herds have evolved and adapted to a unique suite of environmental factors within their ranges – some herds cope with winter ranges characterized by deep, persistent snow, others enjoy mild winter conditions; some herds occupy excellent summer ranges with an abundance of fresh green vegetation; others have to replenish fat and protein reserves depleted over winter with vegetation that is limited by a brief, intense summer growing season. Changes that result in more severe winter range conditions, for example, would have different effects on different herds – even neighbouring herds. For example, under a warmer climate, the annual range for the Leaf River Herd may expand while that of the George River Herd may contract (Sharma et al. 2009).

Further, at the population level, some herds have exhibited a high rate of increase, over 15% annually, while others have increased at rates of less than 5% annually, primarily reflecting higher adult female mortality rates (Figure 4). Environmental changes that result in an increase in adult female mortality would have a greater impact on herds that demonstrate a low rate of increase.

Within the range of the Porcupine Herd, for example, the trends of climate change are marked. Spring strongly warmed over the last three decades. During late spring, after calving, this has resulted in early snowmelt and more food available for nursing mothers. As a consequence early calf survival had improved (Griffith et al. 2002). In early spring, however, when the herd is on migration, warmer weather has resulted in more freeze-thaw cycles as temperatures get above freezing during the day and below freezing at night. Specifically, the number of days during spring migration where the temperature rose above zero doubled during the population decrease phase (1989 to 2001) compared to the previous population increase phase of this herd (1975 to 1988) (Griffith et al. 2002). The greater difficulty in traveling and feeding through ice crusts would result in higher energetic costs and moving onto wind-blown ridges during migration would result in potential increased mortality from wolves, as wolves are at an advantage in shallow snow (Griffith et al. 2002).

Gaps in monitoring impede understanding of the effects of trends in a warming climate and this is accentuated by a lack of baseline information. For example, caribou avidly feed on mushrooms in late summer and mushrooms constitute a late-summer source of protein just after the insect harassment season and prior to the breeding season. But almost nothing is known about the timing and prevalence of the mushrooms. In northern Europe, the timing of the fruiting bodies of fungi (mushrooms) has changed. In Norway, with warmer temperatures and changes in summer rainfall extending the growing season, the average date of mushrooms fruiting in the fall was 13 days later in 2006 than in 1980 (Kauserud et al. 2008).

Table 1 provides a very general treatment of climate impacts on caribou, their ranges, and the communities that depend on them. The table is an updated version of a table contributed by the author (Russell) to Chapter 10 of the Arctic Climate Impact Assessment (ACIA, 2005).

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Table  1. Climate change impacts on migratory tundra caribou populations.
Climate change conditionImpact on habitatImpact on movementImpact on body conditionImpact on productivityManagement implications
Earlier snowmelt on coastal plain
  • Higher plant growth rate
  • Core calving grounds move further north
  • Less use of current calving grounds
  • Cows replenish protein reserves faster
    Higher calf growth rate
  • Higher probability of pregnancy
    Higher June calf survival
  • Need for flexibility in calving ground protection (adaptive management)
Warmer, drier summer
  • Earlier peak biomass
  • Plants harden earlier
  • Reduction in mosquito breeding sites
  • Increased parasitic (oestrid) fly harassment
  • Increased frequency of fires on winter range
  • Fewer "mushroom" years
  • Movement off of calving grounds earlier
  • More use of insect relief habitat in July
  • Avoidance of recently burned winter habitat
  • Increased harassment will lower fall body condition
  • Reduced probability of pregnancy
  • Protection of insect relief areas important
Warmer, wetter fall
  • More frequent icing conditions
  • Caribou abandon ranges with severe surface icing
  • Higher winter mortality
  • Earlier weaning
Warmer, wetter winters
  • Deeper denser snow
  • Icing conditions, especially in tundra and arctic islands
  • Increased dependence on low snow regions
  • Stay on winter range longer
  • Greater over winter weight loss
  • Higher incidence of extended lactation
  • Lower over winter mortality on calves
  • Need to consider protection of low snow regions (adaptive management)
Warmer springs
  • More freeze/thaw cycles during spring migration
  • Faster spring melt
  • Movement slowed and/or movement unto drier windswept ridges
  • Accelerated weight loss in spring
  • Higher wolf predation on cows and calves due to use of windswept ridges
  • Concern over timing and location of spring migration in relation to traditional harvesting areas

Overall effect: In very general terms: the calving range improves but with movement and reliance on more northern portions of the calving range; animals leave calving range earlier; cows and calves suffer reduced summer and fall body reserves due to increase in oestrid fly harassment; mosquito harassment may be reduced if summers drier; more frequent icing in fall, winter, and spring ranges, which depend on the location of these ranges; may have moderate to severe implications to body condition and survival.

Source: update of Chapter 10 of the Arctic Climate Impact Assessment (ACIA, 2005) by the author (Russell)

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