Technical Thematic Report No. 10. - Northern caribou population trends in Canada
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Northern caribou population trends in Canada
Canadian Biodiversity: Ecosystem Status and Trends 2010
Technical Thematic Report No. 10
Published by the Canadian Councils of Resource Ministers
Library and Archives Canada Cataloguing in Publication
Northern caribou population trends in Canada.
Issued also in French under title:
Tendances des populations de caribou des zones septentrionales du Canada.
Electronic monograph in PDF format.
Cat. no.: En14-43/10-2011E-PDF
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This report should be cited as:
Gunn, A., Russell, D. and Eamer, J. 2011. Northern caribou population trends in Canada. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 10. Canadian Councils of Resource Ministers. Ottawa, ON. iv + 71 p.
© Her Majesty the Queen in Right of Canada, 2011
Aussi disponible en français
The Canadian Councils of Resource Ministers developed a Biodiversity Outcomes FrameworkFootnote1 in 2006 to focus conservation and restoration actions under the Canadian Biodiversity Strategy.Footnote2 Canadian Biodiversity: Ecosystem Status and Trends 2010Footnote3 was a first report under this framework. It assesses progress towards the framework's goal of "Healthy and Diverse Ecosystems" and the two desired conservation outcomes: i) productive, resilient, diverse ecosystems with the capacity to recover and adapt; and ii) damaged ecosystems restored.
The 22 recurring key findings that are presented in Canadian Biodiversity: Ecosystem Status and Trends 2010 emerged from synthesis and analysis of technical reports prepared as part of this project. Over 500 experts participated in the writing and review of these foundation documents. This report, Northern caribou population trends in Canada, is one of several reports prepared on the status and trends of national cross-cutting themes. It has been prepared and reviewed by experts in the field of study and reflects the views of its authors.
This report builds on research and monitoring conducted and synthesized by participants in the CircumArctic Rangifer Monitoring and Assessment (CARMA) Network (CARMA, 2010b). We would like to thank those participants who so willingly shared their information and their time. CARMA is a network of researchers, managers, and community people who share information on the status of the world's wild Rangifer (reindeer and caribou) populations and how they are affected by stressors such as climate change and industrial development.
We also thank the reviewers of this report, who were from agencies, boards, and councils with management authority for northern caribou. This report went through two reviews; comments and additional information received from 17 reviewers were invaluable. Any errors or omissions remaining are the responsibility of the authors. This report was produced with the support of the ESTR Secretariat, Environment Canada, with graphics and design by the authors and by Kelly Badger and Jodi Frisk (Environment Canada).
Ecological Classification System – Ecozones+
A slightly modified version of the Terrestrial Ecozones of Canada, described in the National Ecological Framework for Canada,Footnote4 provided the ecosystem-based units for all reports related to this project. Modifications from the original framework include: adjustments to terrestrial boundaries to reflect improvements from ground-truthing exercises; the combination of three Arctic ecozones into one; the use of two ecoprovinces – Western Interior Basin and Newfoundland Boreal; the addition of nine marine ecosystem-based units; and, the addition of the Great Lakes as a unit. This modified classification system is referred to as "ecozones+" throughout these reports to avoid confusion with the more familiar "ecozones" of the original framework.Footnote5 In this report the three Arctic ecozones of the original framework (Southern Arctic, Northern Arctic, and Arctic Cordillera) are referenced in descriptions of herd ranges for greater clarity.
Ecological classification framework for the Ecosystem Status and Trends Report for Canada.
Long Description for Ecozones+ map of Canada
This map of Canada shows the ecological classification framework for the Ecosystem Status and Trends Report, named “ecozones+”. This map shows the distribution of 15 terrestrial ecozones+ (Atlantic Maritime; Newfoundland Boreal; Taiga Shield; Mixedwood Plains; Boreal Shield; Hudson Plains; Prairies; Boreal Plains; Montane Cordillera; Western Interior Basin; Pacific Maritime; Boreal Cordillera; Taiga Cordillera; Taiga Plains; Arctic), two large lake ecozones+ (Great Lakes; Lake Winnipeg), and nine marine ecozones+ (North Coast and Hecate Strait; West Coast Vancouver Island; Strait of Georgia; Gulf of Maine and Scotian Shelf; Estuary and Gulf of St. Lawrence; Newfoundland and Labrador Shelves; Hudson Bay, James Bay and Fox Basin; Canadian Arctic Archipelago; Beaufort Sea).
Historically, caribou were found in all Canadian provinces and territories – they are currently present in seven provinces and the three territories (Figure 1). Northern caribou, as reported on in this assessment (Figure 2), include migratory tundra caribou of three sub-species and the non-migratory Peary caribou (Rangifer tarandus pearyi) that are found on the islands of the Canadian Arctic Archipelago (Banfield, 1961; Rothfels and Russell, 2005). The three sub-species included in migratory tundra caribou are: 1) barren-ground caribou (Rangifer tarandus groenlandicus), ranging east of the Mackenzie River; 2) Grant's caribou (R. t. granti), ranging west of the Mackenzie River; and, 3) certain herds of woodland caribou (R. t. caribou): the two large herds in Ungava and two small herds that calve along the south coast of Hudson Bay (Campbell, 1995; Abraham and Thompson, 1998). We follow Bergerud et al. (2008) in referring to the Ungava caribou as migratory tundra caribou based on their ecological strategies for calving. Migratory tundra caribou occur in eight provinces and territories, although they currently occupy an area that is smaller than their historical distribution. Migratory tundra caribou are undergoing an assessment, starting in late 2011, by COSEWIC, the Committee for the Status of Endangered Wildlife in Canada. COSEWIC has assessed Peary caribou as Endangered and the Dolphin and Union Herd is listed as Special Concern (Government of Canada, 2011). In 2011, Peary caribou were listed under Schedule 1 of the federal Species At Risk Act (Government of Canada, 2011).
Figure 1. Current distribution and status designations of Rangifer in North America.
Migratory tundra populations (this includes barren-ground, Grant's, and some herds of boreal woodland caribou) as well as Peary and Dolphin and Union populations marked on this map are covered in this paper. See Environment Canada (2011) for an update of the current distribution of boreal caribou.
Source: adapted from Hummel and Ray (2008). Map reprinted with permission from Dundurn Press Ltd. © 2008.
Long Description for Figure 1
This map shows current distribution and status designations of Rangifer in North America. The Peary population in the northern Arctic is designated as endangered. Migratory Tundra, Alaska, and Newfoundland populations are ranked as not at risk or not assessed. Northern mountain and Dolphin Union populations' status is of Special Concern. Southern mountain and Boreal populations are ranked as threatened. An overlain line shows the historical southern extent of distribution, which runs from mid-British Columbia south into the United States, back north around the prairies, east across the Great Lakes region, ending in the east coast of Maine.
Figure 2. Northern caribou subspecies and groupings.
All caribou belong to the species Rangifer tarandus.
See text for sources.
Long Description for Figure 2
This hierarchical chart shows northern caribou subspecies and groupings. Northern Caribou are made up of Peary, Barren ground, Grant's, and Woodland subspecies. Groupings include Peary caribou (comprised of the Peary subspecies), Dolphin and Union herd (comprised of Peary and barren-ground, subspecies), and Migratory tundra caribou (comprised of Barren ground, Grant's and Woodland subspecies).
Northern caribou are found, at least in some seasons, in all the northern ecozones+: Arctic, Taiga Shield, Taiga Plains, Taiga Cordillera, and Hudson Plains, as well as in the western part of the mid-latitude Boreal Shield Ecozone+. Only Peary caribou and Hudson Plains forest-tundra caribou have annual ranges within or primarily within a single ecozone+; the barren-ground herds and the migratory tundra woodland caribou herds of Quebec and Labrador calve and summer in one ecozone+ and winter in one or two other ecozones+. The major and best known migratory tundra herds (Porcupine, Cape Bathurst, Bluenose-West, Bluenose-East, Bathurst, Qamanirjuaq, Beverly, Leaf River, and George River) calve within the Southern Arctic. Campbell et al. (2010) mapped the cumulative distribution of the Qamanirjuaq Herd based on locations of satellite-collared cows from 1993 to 2008. The herd's southern distribution coincides with the northern boundaries of the Boreal Shield and the Hudson Plains ecozones+.
The Ahiak Herd is included in this discussion as a major herd, based on the likely number of caribou and the size of the annual range (Gunn et al. 2000b). The herd was not the focus of much management effort until 2006. The resulting gaps in information have led to uncertainty about the Ahiak Herd's relationship to other herds, especially to the Beverly Herd (Gunn et al. In Press; Nagy et al. 2011). In this report, while we acknowledge these differing interpretations, we refer to the Ahiak as a discrete herd until all the evidence additional to the broad-scale analysis of satellite-collar locations undertaken by Nagy et al. (2011) has been comprehensively reviewed.
Also within the Southern Arctic are the herds on the large islands of Hudson Bay (Southampton, Coats, and Mansell islands). The Northern Arctic includes the northeast Nunavut mainland, where the Wager Bay, Lorillard, Melville Peninsula, and several smaller herds calve. Peary caribou and the Dolphin and Union Herd on Victoria Island also calve in the Northern Arctic.
The objective of this report is to summarize information on trends in numbers, distribution, and habitat of northern caribou. As noted in the Preface, this report forms a part of the background material for the 2010 assessment of status and trends of Canada's ecosystems, undertaken by the Canadian Councils of Resource Ministers (Federal, Provincial and Territorial Governments of Canada, 2010). The target audience for this report is resource managers and organizations and individuals with an interest in status and trends of northern caribou.
A key finding of the 2010 assessment of Canada's ecosystems was that the assessment had been hindered by the shortage of consistent, long-term, standardized, and accessible ecological monitoring results for Canada (Federal, Provincial and Territorial Governments of Canada, 2010). While there are better data for caribou than for many other species and ecosystem aspects, the experience of the authors in preparing this report supports this general key finding.
The level of monitoring and research on northern caribou varies considerably among herds and their ranges. Survey methods have changed over time and vary from region to region and the level of detail in reporting estimates varies widely. These factors make assessment of broader trends difficult.
Accessibility of survey results is also uneven. The most useful records were reports containing data sets and methodology, either published as agency reports and made available on the internet or published through scientific journals. Much of the data on caribou herds, however, remain in draft or unpublished reports that are difficult to acquire and not archived. Some survey results are only available in file records, media releases, unreferenced websites, or through personal communications. Older herd population estimates have often been repeated in newer publications, often without information on variance or methodology. As the older reports are often difficult to acquire, this is leading to a loss of information from earlier surveys. Some older estimates have been revised based on improved understanding of herd distributions or to make older estimates more comparable with recent survey results. This is a potential source of confusion as it can lead to conflicting population estimates being reported in documents and websites.
In producing this report, data on herd status and trends were compiled through literature searches and consultation with regional caribou experts. Data presented in this report are compiled and annotated, along with references and graphical presentations, and are available in a spreadsheet.
What is happening?
Caribou numbers typically rise and fall over a timescale of decades, but the information to measure population trends, especially trends before the 1970s, is more qualitative than quantitative. Aboriginal elders recall periods of abundance and scarcity. Other indicators of past caribou abundance and distribution include traditional place names (Legat et al. 2002). Highs and lows in historic abundance since the 1800s have been reconstructed from the frequency of hoof scars on spruce roots, at least for the Bathurst and George River herds (Payette et al. 2004; Zalatan et al. 2006). Current ranges and trends are presented in Figure 3, based on information summarized in this report.
Figure 3. Ranges and recent trends of northern caribou populations in Canada.
The time spans used to assess the recent trends vary, depending on survey data available. This map has been updated from the version published in Canadian Biodiversity: Ecosystem Status and Trends 2010 (Federal, Provincial and Territorial Governments of Canada, 2010).
Long Description for Figure 3
This map shows ranges and recent trends of northern caribou populations in Canada. Increasing populations include Teshekpuukk, Central Arctic, Porcupine, and Bluenose east. Decreasing populations include Bathurst, Ahiak (preliminary data), Qamanirjuaq (unknown/under study), Beverly, Pen Islands, George River, Leaf River (unknown/under study), northern and southern Baffin Islands, and Peary. Populations that are stable at mid to high population sizes that are stable include western Arctic, Southampton Island, and Cape Churchill while the Cape Bathurst, Bluenose west, and Dolphin and Union (unknown/under study) populations are stable at low population sizes.
On the mainland, caribou numbers were low from the 1950s until the 1970s, when the major herds began to increase (Kelsall, 1968 and this report). The increases continued into the 1980s for the major mainland herds, as well as for the Dolphin and Union Herd on Victoria Island. All eight major mainland caribou herds from the Western Arctic east to Hudson Bay have declined since their peak abundance in the mid-1980s to mid-1990s (the exact timing depends on the herd). The herds currently considered to be still in decline are the Bathurst, Beverly, Leaf River, and George River. After a calving ground photographic census in 2008, which was the first census since 1994, the trend for the Qamanirjuaq Herd was determined to be a statistically insignificant decline. The Porcupine Herd increased in numbers in the 2010 census from the previous census in 2001; the Cape Bathurst and Bluenose-West herds have stabilized at low numbers between 2006 and 2009, following a period of sharp declines; the 2010 census of the Bluenose-East Herd showed that the herd has increased since 2006. Since the mid-1980s, the George River Herd declined, based on the census results for 2010. The neighbouring Leaf River Herd, which increased from the mid-1980s at least until the most recent census (2001), is now considered to be declining based on information on demographic rates. The status of the Ahiak and several herds on the northeast mainland (Wager Bay, Lorillard, Melville Peninsula, and other smaller herds on Boothia Peninsula and Simpson Peninsula), Baffin Island, and the smaller islands in Hudson Bay are currently unknown. The exception is the Southampton Island Herd whose abundance is tracked during aerial surveys at relatively regular intervals. By 2007, the herd had declined to half the peak size estimated in 1997. The Dolphin and Union Herd likely declined between 1997 and 2008 after increasing during the 1970s and into the mid-1990s. In the Hudson Plains Ecozone+, the small Cape Churchill Herd appears stable while the Pen Islands Herd may be in decline. On Baffin Island, a recent compilation of reports and local knowledge indicates that caribou numbers are at a low in the cycle of abundance. See herd-specific assessments, on page 28, for further details and references for the trends summarized here.
The trends in abundance are based on one indicator – the number of caribou in the herd, estimated either through calving-ground or post-calving counts (Gunn and Russell, 2008). In a few herds, such as the Bathurst and George River herds, the trends in total numbers are supported by measured trends in demographic indicators such as adult or calf survival. In other herds, especially the Beverly Herd, monitoring of herd size was infrequent and supporting data on demographic rates were not collected.
The rates of increase and decrease of individual herds vary greatly, as can be seen when the rates of change for herds are plotted for periods when they were increasing (after 1970) and periods when they were decreasing (generally after the 1990s) (Figure 4). The herds with the greatest rates of increase were the Southampton and Bathurst, while the Bluenose-West and Porcupine herds showed the lowest rates of increase among herds for which there are sufficient data. During the decline phase, the Cape Bathurst Herd had the greatest rate of decline, although, with only a few breeding females on the Beverly traditional calving grounds in recent surveys, the rate of decline of the Beverly Herd may have been greater. Data are insufficient for the Beverly Herd to calculate this rate.
Figure 4. The exponential rate of increase and decline of major tundra-dwelling caribou herds in Canada.
The chart shows the annual rate of change during increase and decline phases, based on conversion of the population estimates to natural logarithms. The years used vary among herds depending on when herds were increasing and decreasing and when population estimates were made. For the Porcupine Herd, where a change in trend direction was detected in the 2010 survey, the rate of increase is the average of 0.033 (1972-1989) and 0.035 (2001-2010).
Source: rates based on population estimates that are shown and referenced in the herd-specific assessment section starting on page 28.
Long Description for Figure 4
This chart shows the exponential rate of increase and decline of major tundra-dwelling caribou herds in Canada. The increase and decrease of individual herds vary greatly. The herds with the greatest rates of increase were the Southampton and Bathurst, while the Bluenose-West and Porcupine herds showed the lowest rates of increase among herds for which there are sufficient data. Cape Bathurst, George River, and Bathurst show the greatest rates of decrease, while Qamanirjuaq and Porcupine show the lowest rates of decrease.
Trends in a herd distributions will change through time; shifts in distribution, however, are not well documented and are uncertain. Information from aerial surveys and satellite-collared individuals generally has not been analyzed to describe trends in distribution. Migratory tundra caribou characteristically shift their winter distribution among years and winter ranges often overlap between neighbouring herds (Schmelzer and Otto, 2003; Bergerud et al. 2008). Additionally, as herd abundance rises and falls, distribution – especially winter distribution – can shift (Bergerud et al. 2008). Maps of historical distribution (Banfield, 1961) and winter distribution since the 1970s, at least for the Beverly, Qamanirjuaq, and Bathurst herds (Gunn et al. 2001; BQCMB, 2004), hint at a contraction in the southern boundary of the winter distribution in northern Manitoba, Saskatchewan, and Alberta. During the 1996 to 2010 decline of the Bathurst Herd, the winter distribution of the satellite-collared cows showed a trend towards wintering further north of the 60th parallel (Gunn et al. 2011b).
Trends for Peary caribou are generally more difficult to define, given the infrequency of surveys (COSEWIC, 2004). The overall trend of Peary caribou between 1961 and 2010 is a decline. For Peary caribou on the larger southern islands of the Northern Arctic, declines recorded in the 1990s have not been reversed. On Prince of Wales and Somerset islands, there is no evidence for recovery following the collapse of the population between 1980 and 1995 – almost no caribou were found during 2004 surveys. Peary caribou on Banks and northwest Victoria Island are monitored relatively frequently. Abundance declined sharply in the 1980s and into the 1990s; low numbers have persisted. Further north, on the Queen Elizabeth Islands, there has been an overall decline since 1961, especially on the western Queen Elizabeth Islands (Miller et al. 2005). Those islands include the more frequently surveyed Bathurst Island, where caribou declined from 1961 to 1974. From the late 1970s into the early 1990s, Peary caribou on Bathurst Island recovered to the 1961 levels and then three consecutive severe winters triggered a collapse in numbers, followed by some recovery. See the section on Peary caribou, starting on page 40, for further details and references for the trends summarized here.
Why is it happening?
The current declining trends for some mainland caribou herds, as well as the recent declining trends with current indications of stabilization or recovery for other herds, are likely a reflection of natural cycles in caribou abundance accentuated by the cumulative effects of increasing human presence on the caribou ranges. More conjectural is to what degree climate warming and attendant broad-scale habitat changes are factors in the natural cycles.
The causes of declines are complex, with the roles of the various contributing factors changing as the declines continue. Caribou are similar to other northern herbivorous mammals (voles, lemmings, and hares) in that their abundance is cyclic (Morneau and Payette, 2000; Gunn, 2003; Zalatan et al. 2006) and, overall, the cycles are likely driven by climate interacting with forage availability, predation, and pathogens. Weather tends to have a decadal pattern, influenced by major patterns, such as the Arctic oscillation, switching between negative and positive phases (Bonsal and Shabbar, 2011). Winter temperatures and snowfall patterns, the most affected weather factors, interact with forage growth and availability. Winter conditions and forage availability influence caribou condition, which determines birth rates and calf survival (Couturier et al. 2009a; Couturier et al. 2009b). Trends in annual calf survival and fecundity also play a role in changing herd abundance.
Weather also interacts with parasites, such as warble flies, whose activity depends on summer weather. Weather affects the transmission of internal parasites, which in turn influences forage intake as caribou alter their feeding sites to try to reduce their exposure to the parasites (Van der Wal et al. 2000). Predation and harvest by humans have a pivotal role in declines as even small annual reductions in adult female survival strongly influence population trends (Gaillard et al. 1998).
Combining population estimate data on Canadian herd numbers since 1970 and scaling herd size relative to maximum estimates for each herd indicates that, on average, northern caribou numbers in Canada have increased from lows around 1975 to a peak around 1995, followed by a decline with some indication of a recent levelling off or reversal of the decline (Figure 5). The timing and magnitude of the changes vary.
Figure 5. The relative size of tundra-dwelling wild Rangifer herds (Canada).
The line represents the six-year running average. Other symbols represent individual herds. Relative population size is calculated as the population estimate for the year as a proportion of the maximum recorded estimate. Note that the maximum recorded estimate is not necessarily the peak population over this timeframe, as surveys usually did not cover the entire period and were not conducted every year.
Source: based on data that are shown and referenced in Figure 7 to Figure 14 and Figure 16 to Figure 18
Long Description for Figure 5
This scatter-plot graph shows the relative size of tundra-dwelling wild Rangifer herds for Canada from 1970 to 2010. An overlain line shows the six year running average for the period, which ranges from a relative population size of approximately 0.3 to 0.8. On average, northern caribou numbers in Canada have increased from lows around 1975 to a peak around 1995, followed by a decline with some indication of a recent levelling off or reversal of the decline.
On the High Arctic islands, weather is an overwhelming influence as periodic severe winters trigger large-scale mortality and reduction in productivity (Miller and Gunn, 2003; Harding, 2004). Although the signals of climate warming are strong in the High Arctic (Zhang et al. 2011), relating those trends in weather to changes in Peary caribou abundance is uncertain, partly because of high annual variability in climate and infrequent monitoring for most Peary caribou. The other reason is that harvest and predation also affect Peary caribou abundance.
Muskox trends in abundance tend to differ from Peary caribou, although this is area specific. Muskox increases relative to Peary caribou decreases have raised the question of competition. The role of intra- or inter-specific competition for forage is conjectural as diet and habitat selection differ considerably between caribou and muskoxen (Gunn and Dragon, 2002). On Banks Island, however, there was overlap in the use of some plants, such as willow, by Peary caribou and muskoxen (Larter and Nagy, 2004), which suggests that a competitive relationship could occur. Less emphasis has been placed on determining whether the increasing muskox abundance supported increased wolf numbers which, in turn, could increase predation rates on Peary caribou (Gunn and Dragon, 2002). Even less attention has been given to studying the relationship between caribou and muskoxen and their parasites. Hughes et al. (2009), however, discussed levels of intestinal nematode worms and warble flies in muskoxen and caribou for the Dolphin and Union Caribou Herd.
The cumulative effects of increasing human presence on caribou ranges (number of people as well as non-renewable resource exploration and extraction and infrastructure development) are largely unknown. However, tools are being developed to examine how responses of the individual caribou can be scaled up to measure population-level effects (Gunn et al. 2011b). Some recently constructed mine projects monitored effects on caribou. Changes in caribou distribution and time spent foraging were reported (Gartner Lee Limited, 2002). In response to large open-pit mines on the tundra summer range of the Bathurst Herd, caribou distribution was reduced in a 10 to 15 km zone of influence around the mines (Boulanger et al. 2004). Changes in the atmospheric transport of contaminants on individual caribou body burdens are monitored for some herds (Gamberg, 2009) and the results evaluated in relation to potential impacts on human health. These evaluations conclude that nutritional benefits of consuming caribou far outweigh any risks from the low levels of contaminants (Van Oostdam et al. 2005; Donaldson et al. 2010).
Why is it important?
Northern people and caribou are so inter-related that, without caribou, the Arctic would indeed be the barrens. Aboriginal people recognize the central role of caribou in tundra and taiga ecology and the inter-connection of caribou with the culture of many Aboriginal Peoples has parallels with the role of salmon on Canada's Pacific Coast.
Caribou are a numerically abundant, large-bodied herbivore in a relatively simple food web. Common species shape ecosystems by their sheer strength of numbers (Gaston and Fuller, 2008) which means that trends in their numbers are important in the structure and functioning of tundra and taiga ecosystems. At its simplest, the caribou role in the ecosystem is the net effect of forage removal, production of greenhouse gas, and return of nutrients through faecal pellets.
Based on energetics modelling (Russell et al. 2005), annually, a caribou:
- removes: 900 kg of forage (2.5 kg per day),
- produces: 20 kg of methane (55 gm per day), and
- returns to ecosystems: nutrients in the form of 270 kg of faecal pellets (30g x 25 times a day).
At the herd scale, annually, 170,000 to 350,000 caribou:
- remove: 153 to 315 million kg of forage,
- produce: 3.4 to 7 million kg of methane, and
- return to ecosystems: nutrients in the form of 46 to 94 million kg of faecal pellets spread over the herd's annual range (150 to 300 kg/km2).
As caribou travel and rest on frozen waterways, the nutrient return from faecal pellets is to aquatic as well as to terrestrial ecosystems.
The role of caribou in the ecosystem, however, is more intricate and complicated than the mere removal of forage, emission of gasses, and return of nutrients. The boreal and arctic food webs have relatively few links, which does not mean that they are simple systems – the links represent complex inter-relationships among the organisms. Northern ecosystems are nutrient-limited because so much carbon is inaccessible, with only a shallow active layer of the soil thawing each year. Caribou, through their forage intake and output (faecal pellets), have complex and cascading effects that are strongly patterned over time and space (Kielland et al. 2006). As well, caribou support a diverse group of other species, including external parasites such as blood-feeding mosquitoes. Mosquitoes, in turn, through the filter-feeding of their larvae, are a key element in nutrient cycling in aquatic systems. Further up the food webs, caribou support large-bodied and medium-sized predators and scavengers. Earlier debates about top-down (predator) or bottom-up (forage) regulation of caribou populations are now replaced by an appreciation of how nutrition and predation interact (Brown et al. 2007).
Relationships between plants and caribou include the plants' responses to caribou's highly selective foraging. Caribou are selective for individual plant species and forage for buds and young leaves to maximize nutritional value (White and Trudell, 1980; Russell et al. 1993). The gregarious and migratory behaviour of migratory tundra caribou forces their role in ecosystem structure and functioning to be strongly scale dependent (Griffith et al. 2002). As caribou convert plant tissue into body mass and faecal pellets, their local foraging movements and seasonal migrations lead to a redistribution of nutrients within and across ecozones+. In the taiga ecozones+, the effects of caribou herbivory lag by a season as caribou are foraging during winter when most plant growth and nutrient cycling is quiescent due to sub-zero temperatures. Over the timescale of decades, caribou winter ranges expand and contract and the herds cycle from high to low abundance. Abundance can vary three-fold, with cascading effects on plants and nutrient cycling as the plant communities shift from one state to another. Succession of plant communities as a response to intensity of foraging includes, for example, lichen-dominated communities shifting to moss, and moss communities shifting to grass (Van der Wal, 2006).
Nitrogen is a limiting factor for plant growth. Caribou summer grazing can increase the rate of soil nitrogen cycling, 1) through influencing the amount of plant litter, which changes the soil microclimate for decomposition and mineralization processes; and 2) by adding soluble nitrogen from faecal pellets and urine (Olofsson et al. 2004). The changes vary with season and time and with the intensity of grazing (Kielland et al. 2006).
Caribou are often a frequent item in the diet of predators and scavengers, although predator dependence will vary with accessibility, as wolves, grizzly bears, and wolverine will feed on alternate prey and on other food in the absence of caribou. In the Southern Arctic in the mid-1990s, the Bathurst Herd of 350,000 caribou was estimated to support some 1,000 wolves (Cluff, 2004, pers. comm.) and about 450 grizzly bears (based on an estimated minimum density of 3.5 bears per thousand square kilometres: Gau and Veitch, No Date).
Wolves will use caribou at the rate of just under one caribou every 10 days (Hayes and Russell, 2000). On the Bathurst Herd's spring to fall ranges, grizzly bears were effective predators and caribou made up 10 to 93% of their diet, depending on the season (Gau et al. 2002). An adult male needs about 8 kg of caribou meat daily to fulfil its daily energy requirement during normal activity (Walker et al. 2006). Although this evidence points to carnivores being effective predators on caribou, the overall effect of predation in regulating caribou population dynamics is complex and incompletely understood. Krebs et al. (2003) suggest that the Northern Arctic ecosystem is driven less by predation and more by variance in weather.
Caribou have provided the basis of the cultures of people in the Arctic for thousands of years (Gordon, 2005) and still play a central role in their lives. A measure of the importance is the annual harvest, which, in Nunavut (1996 to 2001) averaged 24,522 caribou (Priest and Usher, 2004). In the Northwest Territories, Dene, Inuvialuit, and Métis from almost all communities currently hunt the migratory herds. The minimum annual harvest in the Northwest Territories is about 11,000 caribou (Department of Environment and Natural Resources, 2006).
A study commissioned by the Beverly and Qamanirjuaq Caribou Management Board determined the total net annual economic value of the Beverly and Qamanirjuaq caribou harvest (meat, hides, and antlers) to be $19.9 million, based on an estimated harvest by all communities for the 2005/06 hunting season of approximately 14,000 caribou (InterGroup Consultants Ltd., 2008). This study calculated regional net values per caribou varying from about $1,050 to $1,720 by taking into account differences in production costs (including travel costs) and replacement costs (for high grade beef). The authors also concluded that, above and beyond this direct value, the herds are integral to the maintenance and transfer of knowledge, skills, and culture for people throughout the herds' ranges.
- Footnote 1
Environment Canada. 2006. Biodiversity outcomes framework for Canada. Canadian Councils of Resource Ministers. Ottawa, ON. 8 p.
- Footnote 2
Federal-Provincial-Territorial Biodiversity Working Group. 1995. Canadian biodiversity strategy: Canada's response to the Convention on Biological Diversity. Environment Canada, Biodiversity Convention Office. Ottawa, ON. 86 p.
- Footnote 3
Federal, Provincial and Territorial Governments of Canada. 2010. Canadian biodiversity: ecosystem status and trends 2010. Canadian Councils of Resource Ministers. Ottawa, ON. vi + 142 p.
- Footnote 4
Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch. Ottawa/Hull, ON. 125 p. Report and national map at 1:7 500 000 scale.
- Footnote 5
Rankin, R., Austin, M. and Rice, J. 2011. Ecological classification system for the ecosystem status and trends report. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 1. Canadian Councils of Resource Ministers. Ottawa, ON.
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