Human: A recurring theme in wildlife and fisheries management over the centuries is that numerical abundance is not always a hedge against declines to the point of almost local extinctions. We only have to think of salmon, northern cod, bison etc. What determines persistence is rate of change not the size of the starting population. But numerical abundance carries the risk of over-confidence - 'there's still lots of caribou'. Another contribution to over confidence among users is that the caribou, being a cyclic in their abundance, have been low in number before and have come back. However, given changing environmental conditions, the past may not be a secure guide to the future.
The changes on the caribou ranges in the 1970s-2008 are an overall increase in numbers of people, and shifting socio-economic patterns such as wage-earning which influence harvest levels. The increase in number of people is reflected in the increasing size of communities (centralization) and seasonal and all-year road developments especially in NT. Caribou are adapted to environmental variability such as severe winters or increasing predation levels by changing their patterns of movements across a large-scale landscape. Human presence (roads, communities) is increasing, especially on the southern edges of the winter ranges. Aboriginal elders state that caribou have been displaced by such a human presence.
Mineral exploration activities boomed in the 1990s on range of Bathurst herd and 2003-2008 for the Beverly herd's calving and summer ranges. Also oil and gas exploration on winter ranges of Bluenose East and Bluenose West herds.
Pollution and contamination: Site-specific contamination occurs at abandoned mines and DEW line sites. The sites are a concern to local people who fear that the contaminants such as from tailings will affect wildlife such as caribou. The trend since the 1990s is to cleaning up those sites.
Atmospheric currents bring pollutants from distant sources and the pollutants are deposited on snow and vegetation. Arctic Haze is a persistent diffuse layer in the lower (2-5 km) layers of the atmosphere. It is a complex mixture of small particles and acidifying pollutants from natural sources such as forest fires and volcanoes as well industrial pollution. Long-distant transport of pollutants from industrial sources such as nitrogen oxides are increasing. The levels are low but as sulfur dioxide is decreasing since the mid 1990s, the potential importance of nitrous oxides for acidification is increasing. The Arctic Haze forms in winter and the particles are deposited in snow which as it melts carries the particles and pollutants into aquatic ecosystems. Particles on the snow surface contribute to earlier snow melting. Currently, the effects of the Arctic Haze on terrestrial ecosystems appears to be restricted to the locality of the industrial plants mostly in Russia.
The Canadian Northern Contaminants Program has been active in monitoring Persistent Organic Pollutants (POPs), heavy metals and radionucliotides for the last two decades. The following account is extracted from their second summary report.
Some 15 different caribou herds across Nunavut, the Northwest Territories, and the Yukon were monitored during the 1990s through two large monitoring programs. 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 to either caribou or human health. Some of the heavy metals, however, are found at elevated levels in caribou, though not to the same extent as found 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 are 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 the opposite geographical pattern, with the highest levels found in the Beverly herd and in Meta Incognita Peninsula caribou (which are 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 believe that 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 sources may be more important.
Forest fires: The importance of trends in forest fires to caribou is that their winter forage is dominated by fruticose lichens which are most abundant in older successional forests. The effect of forest fires on caribou abundance has been controversial but most studies do document that caribou tend to avoid recently burnt areas. The annual pattern of forest fires is episodic with years of high fire activity (1979, 1989, 1994, 1998 in the Taiga Shield ecozone during the period 1960-2007) interspersed by years of low fire activity.
Accelerated climate change: Climate is changing in different directions, at a different magnitude and at different times of the year. For example, in north-western North America, spring has been warming at a dramatic rate of the last few decades. In the central barrens, spring conditions have remained stable or slightly cooled, whereas autumn temperatures have warmed. East of Hudson Bay temperatures have remained the same or cooled over most of the year during this same period. The same diversity in temperature changes has been documented in Russia. What we do know is that climate has been changing and will likely continue to change and most dramatically in the north. Another factor that adds to the complexity to predicting impacts of climate change is that all herds have evolved and adapted to a unique suite of environmental factors within their range - 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 within a narrow intense summer growing season. Changes that result in more severe winter range conditions for example, would have a different effect on different herds. Further, at the population level, some herds have exhibited a high rate of increase, approaching 20% annually while others increase at rates of less than 5%, primarily reflecting higher adult female mortality rates. Changes that result in an increase in adult female mortality therefore would have a greater impact on those herds demonstrating a low rate of increase.
In North America there are four different subspecies of caribou occupying ranges close to the 49th parallel to the high arctic islands. Peary caribou populations of the arctic islands are classified as Endangered by COSEWIC as severe weather conditions, such as fall icings are suspected of resulting in large die-offs. At the other end of the scale many of the wide-spread woodland caribou populations are considered threatened and extensive habitat loss combined with harvest and predation are linked to their status, climate has not been implicated in regulating these populations. The Grant's caribou of Alaska and the migratory caribou occupying the tundra and northern taiga regions of Canada have shown a population cycle of approximately 40 years and the regulation of these subspecies have been governed more by large scale climate trends rather than annual weather or habitat disruption.
The challenge for biologists, managers and co-management boards, therefore is to assess the vulnerability of their herds keeping in mind all these factors, assessing not only what the impact might be on the herds but also what the impact will be on those communities that depend on the abundance of caribou. How will climate changes affect the movements and distribution of the herd, how will changes affect the ability of hunters to get on the land to be able to continue their traditional hunting practices Table 2 provides a very general treatment of climate impacts on caribou, their range and the communities that depend on them.