Northwestern Alaska Research Articles

Mixed-stock Inconnu Stenodus leucichthys habitat use in an Arctic estuarine delta complex

Inconnu Stenodus leucichthys is a large, long-lived piscivorous whitefish found in the Arctic and subarctic waters of Alaska. In the Kotzebue region of northwestern Alaska, Inconnu is one of the most important fishes harvested for subsistence purposes. With ongoing climate change, it is important to understand how a changing environment will affect Inconnu habitat use. This study described the habitat use of Inconnu in the Hotham Inlet/Selawik Lake complex from 2010 to 2012. Data collection consisted of surgically implanting acoustic telemetry tags in 80 fish from both rivers in 2010 and 2011 (n = 320), and deploying a fixed array of 20 Vemco VR2W acoustic receiving stations affixed with archival tags throughout the study area. Inconnu were detected at water temperatures and salinities ranging from −1.39 to 23.51 °C and 0 to 31.3 psu, respectively, and there was no detection of stock-specific or temporal trends in habitat use. Fish occupied colder water temperatures (−0.5 to 0.5 °C) during winter and primarily occupied the upper (15 °C) and lower (0 °C) ends of the temperature spectrum during summer. Although Inconnu occupied the entire range of salinities available during summer and winter months, they generally occupied waters of 5 to 20 psu. By providing a more thorough account of Inconnu habitat use, our results contribute baseline data for future comparisons to evaluate effects from climate-induced changes to Inconnu sustainability.

Avian influenza virus antibodies in Pacific Coast Red Knots (Calidris canutus roselaari).

Prevalence of avian influenza virus (AIV) antibodies in the western Atlantic subspecies of Red Knot (Calidris canutus rufa) is among the highest for any shorebird. To assess whether the frequency of detection of AIV antibodies is high for the species in general or restricted only to C. c. rufa, we sampled the northeastern Pacific Coast subspecies of Red Knot (Calidris canutus roselaari) breeding in northwestern Alaska. Antibodies were detected in 90% of adults and none of the chicks sampled. Viral shedding was not detected in adults or chicks. These results suggest a predisposition of Red Knots to AIV infection. High antibody titers to subtypes H3 and H4 were detected, whereas low to intermediate antibody levels were found for subtypes H10 and H11. These four subtypes have previously been detected in shorebirds at Delaware Bay (at the border of New Jersey and Delaware) and in waterfowl along the Pacific Coast of North America.

Variations in soil carbon dioxide efflux across a thaw slump chronosequence in northwestern Alaska

Warming of the arctic landscape results in permafrost thaw, which causes ground subsidence or thermokarst. Thermokarst formation on hillslopes leads to the formation of thermal erosion features that dramatically alter soil properties and likely affect soil carbon emissions, but such features have received little study in this regard. In order to assess the magnitude and persistence of altered emissions, we use a space-for-time substitution (thaw slump chronosequence) to quantify and compare peak growing season soil carbon dioxide (CO2) fluxes from undisturbed tundra, active, and stabilized thermal erosion features over two seasons. Measurements of soil temperature and moisture, soil organic matter, and bulk density are used to evaluate the factors controlling soil CO2 emissions from each of the three chronosequence stages. Soil CO2 efflux from the active slump is consistently less than half that observed in the undisturbed tundra or stabilized slump (1.8 versus 5.2 g CO2−C m−2 d−1 in 2011; 0.9 versus 3.2 g CO2−C m−2 d−1 in 2012), despite soil temperatures on the floor of the active slump that are 10–15 °C warmer than the tundra and stabilized slump. Environmental factors such as soil temperature and moisture do not exert a strong control on CO2 efflux, rather, local soil physical and chemical properties such as soil organic matter and bulk density, are strongly and inversely related among these chronosequence stages (r2 = 0.97), and explain ∼50% of the variation in soil CO2 efflux. Thus, despite profound soil warming and rapid exposure of buried carbon in the active slump, the low organic matter content, lack of stable vegetation, and large increases in the bulk densities in the uppermost portion of active slump soils (up to ∼2.2 g−1 cm−3) appear to limit CO2 efflux from the active slump. Future studies should assess seasonal fluxes across these features and determine whether soil CO2 fluxes from active features with high organic content are similarly low.

Sea Ice Crossing by Migrating Caribou, <em>Rangifer tarandus</em>, in Northwestern Alaska

Long movements across sea ice by Caribou (Rangifer tarandus) in Alaska are relatively uncommon and are not well documented. With rapidly diminishing sea ice cover in arctic waters, these movements may cease altogether. On 26 May 2012, a Caribou crossed a long span (57 km) of sea ice off the coast of Alaska. The cow successfully crossed after traveling 66 km on the sea ice and eventually reached the calving grounds. The highly dynamic nature of sea ice, which is driven by oceanic currents and wind during spring break-up, presents inherent hazards different from lake ice. Based on three years of Global Positioning System (GPS) radio-collar data, Caribou routinely crossed long expanses (30 km) of ice covering the brackish Selawik Lake and shorter stretches (<13 km) on Inland Lake during their spring migration north. There was also a single crossing on the ice covering Selawik Lake during the fall migration south to the wintering grounds that took place in early November 2010. Five GPS-collared Caribou crossed the short frozen span (14 km) of Kotzebue Sound between Cape Krusenstern National Monument and the Baldwin Peninsula in the fall of 2011.

Total Environment of Change: Impacts of Climate Change and Social Transitions on Subsistence Fisheries in Northwest Alaska

Arctic ecosystems are undergoing rapid changes as a result of global climate change, with significant implications for the livelihoods of Arctic peoples. In this paper, based on ethnographic research conducted with the Inupiaq communities of Noatak and Selawik in northwestern Alaska, we detail prominent environmental changes observed over the past twenty to thirty years and their impacts on subsistence-based lifestyles. However, we suggest that it is ultimately insufficient to try to understand how Arctic communities are experiencing and responding to climate change in isolation from other stressors. During interviews and participant observation documenting local observations of climatic and related environmental shifts and impacts to subsistence fishing practices, we find the inseparability of environmental, social, economic, cultural, and political realms for community residents. Many of our informants, who live in a mixed economy based on various forms of income and widespread subsistence harvesting of fish and game, perceive and experience climate change as embedded among numerous other factors affecting subsistence patterns and practices. Changing lifestyles, decreasing interest by younger generations in pursuing subsistence livelihoods, and economic challenges are greatly affecting contemporary subsistence patterns and practices in rural Alaska. Observations of climate change are perceived, experienced, and articulated to researchers through a broader lens of these linked lifestyle and cultural shifts. Therefore, we argue that to properly assess and understand the impacts of climate change on the subsistence practices in Arctic communities, we must also consider the total environment of change that is dramatically shaping the relationship between people, communities, and their surrounding environments.

Hematology, Plasma Chemistry, and Bacteriology of Wild Tundra Swans (Cygnus columbianus) in Alaska

Blood and cloacal swabs were collected from 100 (66 female, 34 male) wild Tundra Swans (Cygnus columbianus) molting in northwestern Alaska, USA, 25-28 July 2008, to establish hematologic and serum chemistry reference values and to isolate enteric Salmonella spp. and Escherichia coli O157:H7. Plasma biochemistry and hematology values did not vary significantly by sex or age. Tundra swans had high levels of creatine kinase, lactate dehydrogenase, amylase, and alkaline phosphatase compared with some other avian species (values were up to 7 times greater), possibly indicating capture myopathy. However, concentrations were much lower (up to 8 times lower) than in other waterfowl exposed to similar or more intensive capture methods. White blood cell count and hematocrit values were similar to other waterfowl species, and enteric Salmonella spp. and E. coli O157:H7 were not present among birds sampled. Our data provide the first biochemical, hematologic, and bacteriologic reference values for wild Tundra Swans.

Walrus areas of use in the Chukchi Sea during sparse sea ice cover

The Pacific walrus Odobenus rosmarus divergens feeds on benthic invertebrates on the con- tinental shelf of the Chukchi and Bering Seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase further in fre- quency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea from June to November of 2008 to 2011, years when sea ice was sparse over the conti- nental shelf in comparison to historical records. The earlier and more extensive sea ice retreat in June to September, and delayed freeze-up of sea ice in Octo- ber to November, created conditions for walruses to arrive earlier and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf from September to October caused walruses to forage in nearshore areas instead of offshore areas as in the past. Walruses did not frequent the deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occu- pied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and south- western Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently de - pauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.

Thermokarst lakes expand and drain laterally as permafrost degrades

In Arctic regions, thermokarst lakes form and expand from thawing permafrost or melting of ice. However, as lakes expand they have a tendency to drain laterally. Jones et al. surveyed the extent of thermokarst lakes in the continuous permafrost zone in the Cape Espenberg lowland of northwestern Alaska's Seward Peninsula using high‐resolution remote sensing imagery during 1950–1951, 1978, and 2006–2007. They found that most thermokarst lakes have been expanding at an average rate of 0.3 meter per year as permafrost degrades, with rates relatively stable over the 56‐year observation period. When viewed from above, a ring of expansion along most lake margins was visible; however, several ver y large lakes drained laterally during this observation period as the expanding lakes encountered a topographic drainage gradient. The authors report that this pattern of particularly large lakes being more prone to drainage resulted in more land area gain than land area loss since 1950 and may represent a carbon sink as these drained basins begin to accumulate peat.

Modeling influences on winter distribution of caribou in northwestern Alaska through use of satellite telemetry

I hypothesize that the distribution of barren-ground caribou (Rangifer tarandus granti) is affected by multiple, interrelated factors. These factors include, but are not limited to, terrain and snow characteristics as well as predation pressure and habitat. To test this hypothesis, I attributed caribou locations derived from satellite telemetry over a 6 year period with terrain (elevation, slope, aspect, and ruggedness), habitat characteristics, and moose density - potentially an index of wolf predation pressure. These locations were compared to random locations, attributed using the same data layers, using logistic regression techniques to develop resource selection functions (RSFs). I found that caribou moved significantly less during mid-winter than early- or late-winter and that cows moved significantly more in April than bulls due to their earlier departure on their spring migration. Distribution was different between cows and bulls. Terrain variables were important factors but were scale-dependent. Cows avoided forested areas, highlighting the importance of tundra habitats, and selected for dwarf shrub, with relatively high lichen cover, and sedge habitat types. Bulls selected for dryas, coniferous forest and dwarf shrub habitats but against lowland sedge, upland shrub and burned tundra. Cow distribution was negatively correlated with moose density at the scale of the Seward Peninsula. My results support the hypothesis that caribou distribution during winter in northwest Alaska is affected by multiple, interrelated factors. These results may be useful for researchers to track and/or model changes in future patterns of range use over winter.

Leadership in mixed-sex groups of muskoxen during the snow-free season

In social ungulates particular individuals or cohorts, such as adult females, can lead or initiate foraging movements. We use muskoxen (Ovibos moschatus) as a model system to test hypotheses regarding the sex and age class of leaders and the potential costs of leadership in 3 different behavioral contexts: activity initiation, foraging-bout movements, and spontaneous group movements. We conducted research on approximately 160 muskoxen at Cape Krusenstern National Monument adjacent to the coast of the Chuckchi Sea in northwestern Alaska. We observed free-ranging, mixed-sex groups of muskoxen from the ground during 5 June–22 September 2002. Adult females emerged as leaders in all 3 contexts, and other group members were more likely to follow adult females than adult males during initiations of activity. Half of successful initiations by adult males included aggressive behavior toward females. Males took a more active role during rut (the mating season) by provoking females to initiate group activity and by actively manipulating spontaneous movements led by females through herding and blocking activities. Leaders incurred no obvious costs in terms of lost foraging time. Costs and benefits of leadership can be subtle and difficult to measure in the field and can include foraging and reproductive trade-offs and increased risk of predation.

Trophic cascades and future harmful algal blooms within ice-free Arctic Seas north of Bering Strait: A simulation analysis

Within larger ice-free regions of the western Arctic Seas, subject to ongoing trophic cascades induced by past overfishing, as well as to possible future eutrophication of the drainage basins of the Yukon and Mackenzie Rivers, prior very toxic harmful algal blooms (HABs) – first associated with ∼100 human deaths near Sitka, Alaska in 1799 – may soon expand. Blooms of calcareous coccolithophores in the Bering Sea during 1997–1998 were non-toxic harbingers of the subsequent increments of other non-siliceous phytoplankton. But, now saxitoxic dinoflagellates, e.g. Alexandrium tamarense, were instead found by us within the adjacent downstream Chukchi Sea during SBI cruises of 2002 and 2003. A previous complex, coupled biophysical model had been validated earlier by ship-board observations from the Chukchi/Beaufort Seas during the summer of 2002. With inclusion of phosphorus as another chemical state variable to modulate additional competition by recently observed nitrogen-fixers, we now explore here the possible consequences of altered composition of dominant phytoplankton functional groups [diatoms, microflagellates, prymnesiophyte Phaeocystis colonies, coccolithophores, diazotrophs, and dinoflagellates] in relation to increases of the toxic A. tamarense, responding to relaxation of grazing pressure by herbivores north of Bering Strait as part of a continuing trophic cascade. Model formulation was guided by validation observations obtained during 2002–2004 from: cruises of the SBI, CHINARE, and CASES programs; moored arrays in Bering Strait; other RUSALCA cruises around Wrangel Island; and SBI helicopter surveys of the shelf-break regions of the Arctic basin. Our year-long model scenarios during 2002–2003 indicate that post bloom silica-limitation of diatoms, after smaller simulated spring grazing losses, led to subsequent competitive advantages in summer for the coccolithophores, dinoflagellates, and diazotrophs. Immediate top-down control is exerted by imposed grazing pressures of the model’s herbivores and bottom-up control is also effected by light-, nitrate-, ammonium-, silicate-, and phosphate-modulated competition among the six functional groups of the simulated phytoplankton community. Similar to the history of the southern North Sea adjacent to the Rhine River, possible farming of northwestern Alaska and Canada, in conjunction with other human activities of ice retreat and overfishing, may lead to future exacerbations of poisonous phytoplankton. These potential killers include both toxic dinoflagellate and diazotroph HABs, deadly to terrestrial and marine mammals, as well as those of prymnesiophytes, some of which have already foamed beaches, while others have killed fishes of European waters.

Expanding Alaska–Canada Rail

Recent changes in global markets have raised the value of mineral resources in northwestern Canada and Alaska. The development of these resources depends on the economics of rail infrastructure expansion. Transportation decision makers need revenue and cost assessments to plan investment in rail infrastructure. A tool based on a geographic information system was developed for mineral resource evaluation and visualization. The tool incorporated expert-augmented mineral resource data for more than 22,000 occurrences in the region. The tool included the proposed Alaska–Canada Rail Link, which would connect Alaska rail to the lower 48 states. Users selected locations of known mineral occurrences near actual or proposed rail routes and used statistical mineral deposit models to estimate resource sizes and extractable value over time by combining current or user-entered commodity prices with multimodal revenue freight volumes and optimally routed transportation costs. The tool translated the revenue scenario into likely carbon dioxide emissions according to the transport of mineral concentrates to regional and international destinations. Users could select and visualize multimodal transportation networks to understand and minimize mobile-source carbon emissions as part of their scenarios. Statistical estimates of mine capital expenditure and operating costs were also calculated according to type. The tool calculated the gross metal value of a mineral occurrence with statistical deposit models. This index was linked to the positive regional economic impact associated with the developed resource in terms of jobs, taxes and royalties, and resupply. This information helped decision makers close the loop on infrastructure investment assessments.

Linkages between large-scale climate patterns and the dynamics of Arctic caribou populations

Recent research has linked climate warming to global declines in caribou and reindeer (both Rangifer tarandus) populations. We hypothesize large-scale climate patterns are a contributing factor explaining why these declines are not universal. To test our hypothesis for such relationships among Alaska caribou herds, we calculated the population growth rate and percent change of four arctic herds using existing population estimates, and explored associations with indices of the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO). The AO, which more strongly affects eastern Alaska, was negatively associated with the population trends of the Porcupine Caribou Herd and Central Arctic Herd, the easternmost of the herds. We hypothesize that either increased snowfall or suboptimal growing conditions for summer forage plants could explain this negative relationship. Intensity of the PDO, which has greatest effects in western Alaska, was negatively associated with the growth rate of the Teshekpuk Caribou Herd in northwestern Alaska, but the Western Arctic Herd in western Alaska displayed the opposite trend. We suggest that the contrasting patterns of association relate to the spatial variability of the effects of the PDO on western and northwestern Alaska. Although predation and winter range quality have often been considered the primary causes of population variation, our results show that large-scale climate patterns may play an important role in caribou population dynamics in arctic Alaska. Our findings reveal that climate warming has not acted uniformly to reduce caribou populations globally. Further research should focus on the relative importance of mechanisms by which climate indices influence caribou population dynamics.

Iceberg discharge to the Chukchi shelf during the Younger Dryas

The extent of glaciation in northwestern Alaska, the source of sediment supply to the Chukchi shelf and slope, and the movement of sea ice and icebergs across the shelf during the last glacial maximum (LGM) remain poorly constrained. Here we present geophysical and geological data from the outer Chukchi margin that reveal a regionally extensive, heavily ice-scoured surface ∼ 5–8 m below the modern seafloor. Radiocarbon dating of this discrete event yields age estimates between 10,600 and 11,900 14C yr BP, indicating the discharge event occurred during the Younger Dryas. Based on mineralogy of the ice-rafted debris, the icebergs appear to be sourced from the northwestern Alaskan margin, which places important constraints on the ice extent in northern Alaska during the LGM as well as existing circulation models for the region.

Percentage of Fecal Moss in Arctic Ungulates as an Indicator of Wintering Area Quality

Abstract: I investigated local and regional differences in percent moss in the feces of muskoxen (Ovibos moschatus) and reindeer or caribou (Rangifer tarandus) in northwestern Alaska, USA, and related fecal moss to forage availability, snow conditions, animal density, and terrain ruggedness on wintering areas. Reindeer are a partially domesticated form of Rangifer tarandus originating from Europe and Asia and differ physiologically and ecologically from caribou. Percent moss in feces of muskoxen differed locally among individual wintering areas. Because of the large local variation in moss content of muskox feces, regional differences between the 2 study areas were difficult to resolve. Percent of moss in the feces of reindeer–caribou did not differ between wintering areas within the same study area but did differ between study areas. On muskox wintering areas, fecal moss correlated negatively with graminoid cover and snow hardness and positively with moss cover and muskox density, but fecal moss did not correlate with snow depth or terrain ruggedness. On reindeer–caribou wintering areas, fecal moss correlated positively with moss availability but not with lichen cover or snow depth or hardness. Because muskox groups in Alaska are isolated from each other in winter, even groups wintering on neighboring hills may face different foraging availability and might, therefore, exhibit differences in growth or productivity. Reindeer–caribou are more mobile than muskoxen in winter, and fecal samples may not be representative of vegetative and snow conditions at the wintering area where I collected them. I conclude that managers can use fecal moss as an indicator of overgrazed ranges, severe snow conditions, or crowded conditions on muskox wintering areas, but that the association between fecal moss and range conditions has to be drawn with caution for the more mobile reindeer–caribou.

A Reconsideration of Purported Holocene Bison Bones from Northern Alaska

While bison were the most abundant large mammals in Eastern Beringia for most of the last 100 000 years, their range declined drastically at the end of the Pleistocene and through the Holocene. Research into the nature of Holocene human interactions with bison suffers from scarcity of faunal remains from most archaeological sites and poor chronological control of paleontological specimens over broad areas of Eastern Beringia. We examined the dating, context, and identification of purported bison bones spatially associated with two late prehistoric archaeological sites in northern Alaska to contribute to a better understanding of bison biogeography and the possible role of these large mammals in prehistoric economies. We confirmed the presence of two bison bones from the 17th century Kangiguksuk archaeological site (49-XBM-012) in northwestern Alaska, but radiocarbon dates older than 30 000 14C years BP for both bones demonstrate that those bison were not hunted by the site occupants. From the Lakeside site (49-KIR-275) in the central Brooks Range, a bone reported to be bison and dated to about 2400 14C years BP was shown through DNA sequencing to be moose ( Alces alces ). We point to a large set of dated bison specimens from Alaska’s Arctic Slope that suggests bison were locally extinct in north-central and northwestern Alaska by the beginning of the Holocene and were subsequently unavailable to human hunters in that region.

Response of Overwintering Caribou to Burned Habitat in Northwest Alaska

Caribou (Rangifer tarandus granti) use lichens, when available, as primary forage on their winter range. In boreal forest habitats, wildland fires effectively destroy lichens, and overwintering caribou are known to avoid burned areas for decades while lichen communities regenerate. However, little has been published about caribou response to burned habitat in tundra ecosystems. To assess the relationship between winter caribou distribution and burned areas, we instrumented Western Arctic Herd caribou with satellite telemetry collars and evaluated their locations in relation to recent burns of known age (? 55 years old) across northwestern Alaska. We analyzed caribou distribution for different habitat types (tundra and boreal forest), age categories of burns, and possible edge effects. We also reanalyzed the data, limiting available habitat to a uniform traveling distance (5658 m) from daily satellite locations. Using selection indices that compared caribou use of burns and buffers to their availability, we found that caribou strongly selected against burned areas within the tundra ecosystem. Recent burns were selected against at both large (range-wide) and intermediate (5658 m) spatial scales. Caribou particularly selected against 26- to 55-year-old burns and the interior (core) portions of all burns. We found that caribou were more likely to select burned areas in the late fall and early spring than midwinter. Increased fires in northwestern Alaska could decrease the availability and quality of winter habitat available to the herd over the short term (up to 55 years), potentially influencing herd population dynamics and reducing sustainable harvest levels. We recommend that fire managers consider caribou midwinter range condition and extent: however, management that achieves a mosaic pattern of fire history may benefit a wide array of species, including caribou. A better understanding of the current regional fire regime and the distribution of available winter range will be required before practicable management recommendations can be developed for this herd.

Decrease of lichens in Arctic ecosystems: the role of wildfire, caribou, reindeer, competition and climate in north-western Alaska

We review and present a synthesis of the existing research dealing with changing Arctic tundra ecosystems, in relation to caribou and reindeer winter ranges. Whereas pan-Arctic studies have documented the effects on tundra vegetation from simulated climate change, we draw upon recent long-term regional studies in Alaska that have documented the actual, on-the-ground effects. Our review reveals signs of marked change in Arctic tundra ecosystems. Factors known to be affecting these changes include wildfire, disturbance by caribou and reindeer, differential growth responses of vascular plants and lichens, and associated competition under climate warming scenarios. These factors are interrelated, and, we posit, unidirectional: that is, they are all implicated in the significant reduction of terricolous lichen ground cover and biomass during recent decades. Lichens constitute the primary winter forage for large, migratory caribou and reindeer herds, which in turn are a critical subsistence resource for rural residents in Alaska. Thus, declines in these lichens are a major concern for rural people who harvest caribou and reindeer for subsistence, as well as for sport hunters, reindeer herders, wildlife enthusiasts and land managers. We believe a more widely distributed and better integrated research programme is warranted to quantify the magnitude and extent of the decline in lichen communities across the Arctic.

Drinking Water in Northwestern Alaska: Using or Not Using Centralized Water Systems in Two Rural Communities

Over the last 100 years, there have been major changes in the way Inupiaq villages in Alaska have procured fresh water for drinking and other human uses. Since the 1960s, major funding has been provided by local, state, and federal agencies to install centralized water systems in these villages. These systems have arrived with great expectations, and yet many of them have a myriad of problems due to harsh weather conditions, low winter temperatures, and permafrost. Other obstacles to success of the water systems arise from local preference for traditional water resources. On the Seward Peninsula, some villages rely heavily on centralized water systems, while others continue to rely more heavily on traditional water sources. We demonstrate in this paper that local variables, including different environmental factors and a sense of agency in the modernization process, affect local choices about whether or not to use the centralized water systems. We conclude that local, culturally specific ideas about health and acceptable drinking water quality must be taken into account for these projects to be successful.

Diet of wolverines (Gulo gulo) in the western Brooks Range, Alaska

Migratory caribou herds are an important component of the North American tundra. We investigated the wolverine (Gulo gulo) diet in the migratory range of the Western Arctic Caribou Herd in north-western Alaska. Within this area, caribou are absent or occur at low densities for large parts of the year, and thus show a strong seasonality in abundance. Analyses of stomach and colon contents suggested that wolverines primarily consumed caribou during the winter, and that the dietary dependence was related more to caribou mortality than to caribou abundance in the area. We also found indications that wolverines may switch between moose and caribou during periods of low caribou abundance, but that such a switch did not affect wolverine body condition. Our results thus support previous observations that wolverines primarily consume ungulates. However, a better knowledge of how alternative food sources are utilized will be necessary to predict the dietary and demographic responses of wolverines to variations in caribou abundance. We also suggest that further efforts should be made to investigate the effects of other ungulate-dependent predators on wolverine feeding ecology, because such predators may function both as competitors and as suppliers of carrion for scavenging.