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At least 523 records · Page 29Linked to original sources
USGS2008

Space and habitat use by black bears in the Elwha valley prior to dam removal

Dam removal and subsequent restoration of salmon to the Elwha River is expected to cause a shift in nutrient dynamics within the watershed. To document how this influx of nutrients and energy may affect black bear (Ursus americanus) ecology, we used radio-telemetry to record movements of 11 male and two female black bears in the Elwha Valley from 2002-06. Our objective was to collect baseline data on bear movements prior to dam removal. We calculated annual home ranges, described seasonal timing of den entry and emergence, and described seasonal patterns of distribution and habitat use. Adaptive kernel home ranges were larger formales (mean = 151.1 km2, SE = 21.4) than females (mean = 38.8 km2, SE = 13.0). Males ranged widely and frequently left the watershed during late summer. Further, they exhibited predictable and synchronous patterns of elevation change throughout each year. Bears entered their winter dens between 8 October and 15 December and emerged from dens between 10 March and 9 May. Male bears used low-elevation conifer and hardwood forests along the Elwha floodplain during spring, mid- to high-elevation forests and meadows during early summer, high-elevation forests, meadows and shrubs during late summer, and mid-elevation forests, shrubs and meadows during fall. Data acquired during this study provide important baseline information for comparison after dam removal, when bears may alter their late summer and fall movement and denning patterns to take advantage of energy-rich spawning salmon.

Northwest Science↗
USGS1987

Size and growth patterns of the Yellowstone grizzly bear

Weights and/or measurements of 151 grizzly bears ( Ursus arctos ) captured 261 times were recorded from 1975 to 1985. Males were consistently heavier than females within all age classes beginning at age 2. Mean weight for 65 captive males (5+ years old) was 192 kg and 135 kg for 63 adult females (5+ years old). Mean monthly weights by sex and age class indicated adults lost weight from den emergence through July, generally regaining emergence weight by August. Weaned yearlings lost weight July-Septmber, whereas unweaned yearlings gained weight during the same period. Sexual dimorphism in body measurements within age classes was apparent in cubs and became significant in all body measurements by age 3. Girth was the measurement most closely correlated with weight for both males and females. Adults feeding at garbage dumps weighted more than bears relying on natural food sources. Bears were smaller and weighed less in this study than during the period 1959-70, when major dumps were available as a food source. Mean annual weights of nondump females were highly correlated with annual habitat productivity indices for Yellowstone Park. Correlations between mean adult female weight an cub litter size ( r ) = 0.92) and mean age at 1st cub production ( r = -0.52) were apparent. In general, females with reliable high-energy foods tended to attain larger body sizes, mature at an earlier age, and have larger cub litters than females using relatively low-energy foods.

Book↗
USGS2013

Response of Yellowstone grizzly bears to changes in food resources: A synthesis. Final report to the Interagency Grizzly Bear Committee and Yellowstone Ecosystem Subcommittee

The Yellowstone grizzly bear ( Ursus arctos ) was listed as a threatened species in 1975 (Federal Register 40 FR:31734-31736). Since listing, recovery efforts have focused on increasing population size, improving habitat security, managing bear mortalities, and reducing bear-human conflicts. The Interagency Grizzly Bear Committee (IGBC; partnership of federal and state agencies responsible for grizzly bear recovery in the lower 48 states) and its Yellowstone Ecosystem Subcommitte (YES; federal, state, county, and tribal partners charged with recovery of grizzly bears in the Greater Yelowston Ecosystem [GYE]) tasked the Interagency Grizzly Bear Study Team to provide information and further research relevant to three concerns arising from the 9th Circuit Court of Appeals November 2011 decision: 1) the ability of grizzly bears as omnivores to find alternative foods to whitebark pine seeds; 2) literature to support their conclusions; and 3) the non-intuitive biological reality that impacts can occur to individuals without causing the overall population to decline. Specifically, the IGBC and YES requested a comprehensive synthesis of the current state of knowledge regarding whitebark pinbe decline and individual and population-level responses of grizzly bears to changing food resources in the GYE. This research was particularly relevant to grizzly bear conservation given changes in the population trajectory observed during the last decade.

Idaho, Montana, Wyoming↗
USGS2014

Use of isotopic sulfur to determine whitebark pine consumption by Yellowstone bears: a reassessment

Use of naturally occurring stable isotopes to estimate assimilated diet of bears is one of the single greatest breakthroughs in nutritional ecology during the past 20 years. Previous research in the Greater Yellowstone Ecosystem (GYE), USA, established a positive relationship between the stable isotope of sulfur (δ 34 S) and consumption of whitebark pine (Pinus albicaulis) seeds. That work combined a limited sample of hair, blood clots, and serum. Here we use a much larger sample to reassess those findings. We contrasted δ 34 S values in spring hair and serum with abundance of seeds of whitebark pine in samples collected from grizzly (Ursus arctos) and American black bears (U. americanus) in the GYE during 2000–2010. Although we found a positive relationship between δ 34 S values in spring hair and pine seed abundance for grizzly bears, the coefficients of determination were small ( R 2  ≤ 0.097); we failed to find a similar relationship with black bears. Values of δ 34 S in spring hair were larger in black bears and δ 34 S values in serum of grizzly bears were lowest in September and October, a time when we expect δ 34 S to peak if whitebark pine seeds were the sole source of high δ 34 S. The relationship between δ 34 S in bear tissue and the consumption of whitebark pine seeds, as originally reported, may not be as clean a method as proposed. Data we present here suggest other foods have high values of δ 34 S, and there is spatial heterogeneity affecting the δ 34 S values in whitebark pine, which must be addressed.

Yellowstone National Park↗
USGS2011

Development of a pan-Arctic monitoring plan for polar bears: Background paper

Polar bears (Ursus maritimus), by their very nature, and the extreme, remote environment in which they live, are inherently difficult to study and monitor. Monitoring polar bear populations is both arduous and costly and, to be effective, must be a long-term commitment. There are few jurisdictional governments and management boards with a mandate for polar bear research and management, and many have limited resources. Although population monitoring of polar bears has been a focus to some degree within most jurisdictions around the Arctic, of the 19 subpopulations recognised by the IUCN/Species Survival Commission Polar Bear Specialist Group (PBSG), adequate scientific trend data exist for only three of the subpopulations, fair trend data for five and poor or no trend data for the remaining 11 subpopulations (PBSG 2010a). There are especially critical knowledge gaps for the subpopulations in East Greenland, in the Russian Kara and Laptev seas, and in the Chukchi Sea, which is shared between Russia and the United States. The range covered by these subpopulations represents a third of the total area (approx. 23 million km2) of polar bears’ current range, and more than half if the Arctic Basin is included. If we use popular terms, we know close to nothing about polar bears in this portion of their range. As summer sea-ice extent, and to a lesser degree, spring-time extent, continues to retreat, outpacing model forecasts (Stroeve et al. 2007, Pedersen et al. 2009), polar bears face the challenge of adapting to rapidly changing habitats. There is a need to use current and synthesised information across the Arctic, and to develop new methods that will facilitate monitoring to generate new knowledge at a pan-Arctic scale. The circumpolar dimension can be lost when efforts are channelled into regional monitoring. Developing and implementing a plan that harmonises local, regional and global efforts will increase our power to detect and understand important trends for polar bears, with particular emphasis on how climate warming may differentially affect populations and habitats. Current knowledge is inadequate for a comprehensive understanding of the present and future impact of climate warming and its interaction with other stressors. The cumulative effects are unknown (Laidre et al. 2008). An integrated pan-Arctic research and monitoring plan will improve the ability to detect future trends, identify the most vulnerable subpopulations and guide effective conservation. There is a need to direct attention and resources where data are deficient to understand the mechanisms that drive trends, and to facilitate more effective and timely conservation response.

Report↗
USGS2003

Large carnivores, moose, and humans: A changing paradigm of predator management in the 21st century

We compare and contrast the evolution of human attitudes toward large carnivores between Europe and North America. In general, persecution of large carnivores began much earlier in Europe than North America. Likewise, conservation programs directed at restoration and recovery appeared in European history well before they did in North America. Together, the pattern suggests there has been an evolution in how humans perceive large predators. Our early ancestors were physically vulnerable to large carnivores and developed corresponding attitudes of respect, avoidance, and acceptance. As civilization evolved and man developed weapons, the balance shifted. Early civilizations, in particular those with pastoral ways, attempted to eliminate large carnivores as threats to life and property. Brown bears (Ursus arctos) and wolves (Canis lupus) were consequently extirpated from much of their range in Europe and in North America south of Canada. Efforts to protect brown bears began in the late 1880s in some European countries and population reintroductions and augmentations are ongoing. They are less controversial than in North America. On the other hand, there are no wolf introductions, as has occurred in North America, and Europeans have a more negative attitude towards wolves. Control of predators to enhance ungulate harvest varies. In Western Europe, landowners own the hunting rights to ungulates. In the formerly communistic Eastern European countries and North America, hunting rights are held in common, although this is changing in some Eastern European countries. Wolf control to increase harvests of moose (Alces alces) occurs in parts of North America and Russia; bear control for similar reasons only occurs in parts of North America. Surprisingly, bears and wolves are not controlled to increase ungulates where private landowners have the hunting rights in Europe, although wolves were originally exterminated from these areas. Both the inability of scientific research to adequately predict the effect of predator control on ungulate populations and a shift in public attitudes toward large carnivores have resulted in an accelerating number of challenges to predator management in places where it is still espoused. Utilitarian attitudes towards wildlife are declining in Western cultures and people now increasingly recognize the intrinsic value of wildlife, including large predators. In the future, agencies responsible for managing resident wildlife will face increased pressure to balance the needs of the hunting public with the desires of non-hunting publics. We suggest that in the next century we will witness a continued shift in how wildlife agencies manage both moose and large carnivores. More attention will be paid to maintaining and restoring intact ecosystems and less toward sustainable yield of meat.

Alces↗
USGS2007

Adapting to the reality of climate change at Glacier National Park, Montana, USA

The glaciers of Glacier National Park (GNP) are disappearing rapidly and likely will be gone by 2030. These alpine glaciers have been continuously present for approximately 7,000 years so their loss from GNP in another 25 years underscores the significance of current climate change. There are presently only 27 glaciers remaining of the 150 estimated to have existed when GNP was created in 1910. Mean annual temperature in GNP has increased 1.6°C during the past century, three times the global mean increase. The temperature increase has affected other parts of the mountain ecosystem, too. Snowpacks hold less water equivalent and melt 2+ weeks earlier in the spring. Forest growth rates have increased, alpine treelines have expanded upward and become denser, and subalpine meadows have been invaded by high elevation tree species. These latter responses can be mostly attributed to longer growing seasons and warmer temperatures. Ecosystem modeling of possible future changes in the GNP mountain environments suggest that increased tree growth rates and evapotranspiration will reduce soil moisture and streamflow. The drier forests, with more wood, will burn more frequently and with greater severity, leading to degradation in air quality and increased risk to people and infrastructure. Management of forest fires is an important issue in the arid western United States. In 2003, 13% of GNP’s 4,082 km 2 was burned in three large fires and numerous smaller fires. Managers can accomplish some of their goals, such as preserving threatened wildlife populations, by altering their management of fires. In 2003, intense efforts were successfully made to divert the fires away from valuable grizzly bear ( Ursus arctos horribilis ) habitat that contained huckleberry plants ( Vaccinium spp .) necessary to ensure bear survival through the winter.

Montana↗
USGS1980

The natural food habits of grizzly bears in Yellowstone National Park, 1973-74

The natural food habits of grizzly bears ( Ursus arctos horribilis Ord) in Yellowstone National Park were investigated in 1973-74 to identify the grizzly's energy sources and trophic level(s), nutrient use, and distribution. Food consumption was determined by scat analysis and field observations. Food quality and digestibility were estimated by chemical analysis. Grizzlies were distributed in 3 distinctive feeding economies: valley / plateau , a grass/rodent economy where grizzlies were intensive diggers; mountain , primarily a grass/springbeauty/root economy where grizzlies were casual diggers; and lake , primarily a fish/grass economy where grizzlies were fishers. The economies occurred in areas with fertile soils; distribution of bears within each was related to the occurrence of succulent plants. The feeding cycle in the valley/plateau and mountain economies followed plant phenology. Grizzlies fed primarily on meat before green-up and on succulent herbs afterwards; meat, corms, berries, and nuts became important during the postgrowing season. Succulent grasses and sedges with an importance value percentage of 78.5 were the most important food items consumed. Protein from animal tissue was more digestible than protein from plant tissue. Storage fats were more digestible than structural fats. Food energy and digestibility were directly related. Five principle nutrient materials (listed with their percentage digestibilities) contributed to total energy intake: protein from succulent herbs, 42.8; protein and fat from animal material, 78.1; fat and protein from pine nuts, 73.6; starch, 78.8; and sugar from berries and fruits, digestibility undetermined. Protein from succulent herbs, with a nutritive value percentage of 77.3, was the grizzlies' primary energy source. Because succulent, preflowering herbs had higher protein levels than dry, mature herbs, grizzly use of succulent herbs guaranteed them the highest source of herbaceous protein. Low protein digestibility of succulent herbs was compenstated for by high intake. Grizzlies were digestively flexible and maximized use of protein from plant and animal sources. They were adapted to the most constant and abundant sources of protein: succulent herbs and animal material from open, fertile grasslands. Competition among grizzlies for animal food during the pregrowing season may be regulatory for the grizzly population. The grizzly population level can be partially accounted for by the grizzlies' status as secondary consumers during pregreen-up periods and primary consumers during the growing and postgrowing seasons. The essential environmental requirement was the availability of fertile grasslands and herblands interspersed with cover and capable of maintaining artiodactyls, rodents, and abundant nutritious herbs as sources of food.

Yellowstone National Park↗
USGS1980

Movements of radio-instrumented grizzly bears within the Yellowstone area

Grizzly bear ( Ursus arctos horribilis ) movement patterns were studied with the aid of 18 radio-instrumented grizzly bears in 1975 and 1976. Five bears gave minimal information because of death, transmitter failure, or loss of transmitters. Seasonal home range information is presented for 13 bears. Two bears, trapped inside Yellowstone National Park, included areas outside of the park in their home ranges. Twelve bears trapped outside included parts of the park in their home ranges. Three females with young gave no indication of having smaller home ranges than other individuals. Movement patterns prior to denning and dates of denning varied among individual bears.

Yellowstone National Park↗
USGS1983

Possible relationships between trichinellosis and abnormal behavior in bears

Data compiled from parasite studies of grizzly bears ( Ursus arctos ) and black bears ( U. americanus ) in the Yellowstone and Glacier National Park populations and surrounding areas of Montana and Wyoming during 1969-79 are reviewed with reference to the possible influence of infection with the muscleworm Trichinella sp. on bear behavior. In grizzly bears, the high prevalence of this parasite (61% of 254 bears infected), the elevated larval concentrations in sensitive anatomical sites such as the tongue (average, 51 larvae per gram of tissue), and the chronic nature of bear infections as indicated by the tendency for highest infection rates to occur in older age classes (> 16 yrs.), suggest a potential behavior-modifying effect might exist. However, retrospective analysis of recent human attacks by 4 grizzlies and 2 black bears in the northern Rocky Mountain region failed to demonstrate a consistent connection between erratic conduct and levels of Trichinella larvae (trichinae) in bear tissues. Clinical similarities of trichinellosis in bears and humans are hypothesized, and possible behavioral effects of ursine trichinellosis are discussed.

Book chapter↗
USGS1995

Appraising status of the Yellowstone grizzly bear population by counting females with cubs-of-the-year

The grizzly bear ( Ursus arctos horriblilis ) in the lower United States was declared threatened in 1975 under the Endangered Species Act of 1973 (16 U.S.C. 15-31-1544). According to that Act, the U.S. Fish and Wildlife Service had to prepare a plan to recover populations to levels where the species could be conserved and delisted from its threatened status. The Recovery Plan (U.S. Fish and Wildlife Service 1993) uses counts of distinct females with cubs-of-the-year as a recovery parameter in several grizzly bear ecosystems. The total number of these females is assumed to be the minimum number with cubs born in the current year. To our knowledge, this technique, its methodology, and value as a population indicator have never been adequately explained or discussed. Thus, we describe the methodology and assess its potential for continued use in the Yellowstone ecosystem.

Wildlife Society Bulletin↗
USGS2004

Oak-black bear relationships in southeastern uplands

Bears ( Ursus americanus ) primarily occur in upland habitats in the Southeast because uplands were the last to be developed for agriculture and were more likely to become publicly owned. National parks and forests created in the early to mid-1900s served as sources to supply surrounding uplands with bears. Bears could not survive in southeastern uplands without oak mast. Bear reproductive and mortality rates in the region have been shown to be directly linked with acorn production. Masting is thought to be an adaptation by oaks to satiate predators during good acorn years, thus ensuring that the remainder will germinate. Acorn predator populations, however, cannot respond numerically to increased acorn production because the masting is episodic and synchronous. Consequently, bears have developed physiological, behavioral, and ecological adaptations to cope with such food shortages. Despite such adaptations, upland hardwood forests in the Southeast are of lower quality than they once were. The loss of the American chestnut ( Castanea dentata ), higrading, and soil degradation have markedly decreased the carrying capacity for bears and other wildlife. Other changes such as recent forest management practices, forest fragmentation, invasion by the gypsy moth ( Lymantria dispar ), and oak decline threaten to further degrade the capability of southeastern uplands to support bears.

Report↗
USGS1994

A demographic comparison of two black bear populations in the Interior Highlands of Arkansas

The Ozark and Ouachita mountain regions of western Arkansas, collectively known as the Interior Highlands, historically supported large numbers of black bears ( Ursus americanus ). Indiscriminate killing of bears by early settlers and subsequent habitat reductions due to extensive logging and changes in land use resulted in their decline (Smith et al. 1991). By the late 1940's, bears had been extirpated from both regions (Holder 1951). Between 1958 and 1968, Arkansa Game and Fish Commission (ACFC) Officials trapped 254 black bears in northern Minnesota and Manitoba, Canada and released them in the Interior Highlands (Rogers 1973, Smith et al. 1991d). Since then, bear numbers have dramatically increased, making the Arkansas reintroduction the most successful attempted for black bears (Smith et al. 1991). Hunts have been conducted each autumn or winter since 1980. Because little was known about bear demographics and sustainable harvest in the Interior Highlands, however, hunting regulations have been restrictive with 5-31 bears harvested/year (J.D. Clark, AGFC Annu. Harvest Rep., 1980-1988). Bears now range throughout the Ozark Mountains and Ouachita Mountains, but these regional populations are allopatric, separated by the Arkansas River Valley and Interstate 40 (J.D. Clark, unpubl. data). Past reintroduction strategies and harvest levels differed between the 2 regions, with more intensive restocking and hunting in the Ozark region. Habitat also differs with the Ozark Mountains primarily oak-hickory ( Quercus spp.- Carya spp.) upland forest compared to pine ( Pinus spp.) and mixed pine-hardwood forest in the Ouachita Mountais (Smith 1989). Because habitat quality has been shown to be the major factor affecting black bear productivity (Rogers 1976, Bunnell and Tait 1981, Elowe and Dodge 1989) and bear populations are susceptible to overharvest, our objectives were to: 1) estimate population growth and sustainable yield for populations in both regions and 2) determine whether different environmental conditions in the 2 regions resulted in differences in demographic parameters.

Arkansas↗
USGS2016

New challenges for grizzly bear management in Yellowstone National Park

A key factor contributing to the success of grizzly bear Ursus arctos conservation in the Greater Yellowstone Ecosystem has been the existence of a large protected area, Yellowstone National Park. We provide an overview of recovery efforts, how demographic parameters changed as the population increased, and how the bear management program in Yellowstone National Park has evolved to address new management challenges over time. Finally, using the management experiences in Yellowstone National Park, we present comparisons and perspectives regarding brown bear management in Shiretoko National Park.

Bulletin of the Shiretoko Museum↗
USGS2006

A model for autumn pelagic distribution of adult female polar bears in the Chukchi Seas, 1987-1994

We made predictions of polar bear (Ursus maritimus) autumn distribution in the Chukchi Sea with a Resource Selection Function (RSF) developed from 1198 satellite radio-collar locations on 124 adult female polar bears, 1987 – 1994. The RSF was created to assist in an aerial survey design for polar bears proposed by the U.S. Fish and Wildlife Service. The RSF was based on bathymetry and daily sea ice covariates extracted from passive microwave satellite imagery within the pelagic region > 25 km from shore. The RSF indicated that polar bears selected habitats with intermediate amounts (~50%) of ice cover in close proximity to higher ice concentrations, and over relatively shallow waters. The RSF showed good predictive abilities for the years of its construct, worked best in October, and was robust to inter-annual variability. When evaluated with recent (1997 – 2005) data, the RSF performed well for October and November but poorly in September. This loss of predictive abilities appeared to be related to recent changes in habitat due to longer melt seasons and younger sea ice, and testing the retrospective model with a small sample of recent polar bears locations from a limited region of the Chukchi Sea. Contemporary applications of this RSF must consider three factors that could limit its utility: 1) 2 different sea ice phenology; 2) distributions of males and sub-adults; and 3) occupancy in nearshore habitats.

Report↗
USGS1996

Mass and body-dimension relationships of polar bears in northern Alaska

Models developed from morphometric parameters are useful for estimating body mass (M) of captured wild ursids. The accuracy of those models, however, may depend on sex, season, and geographic location of the population. We tested the suitability of reported models to predict mass of polar bears ( Ursus maritimus ) captured in northern Alaska, but found that models developed for other populations performed poorly. Hence, we derived new models from field measurements of axillary girth (AG), straight-line body length (SLBL), condylobasal length (CL), and zygomatic width (ZW). Our equations accurately predicted body mass for polar bears captured during spring and autumn. The equation for spring-captured polar bears was M = 0.000078 * AG 1.6026 * SLBL 1.3579 (R 2 =0.97), while the equation for autumn-captured polar bears was M = 0.000250 * AG 1.4967 * SLBL 1.2468 (R 2 =0.97). Our results suggest that investigators should verify the accuracy of reported equations when applied to each situation and if necessary, develop models specific for the population in question.

Alaska↗
USGS1998

Satellite telemetry: A new tool for wildlife research and management

The U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game have cooperated since 1984 to develop and evaluate satellite telemetry as a means of overcoming the high costs and logistical problems of conventional VHF (very high frequency) radiotelemetry systems. Detailed locational and behavioral data on caribou ( Rangifer tarandus ), polar bears ( Ursus maritimus ), and other large mammals in Alaska have been obtained using the Argos Data Collection and Location System (DCLS). The Argos system, a cooperative project of the Centre National d'Études Spatiales of France, the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration, is designed to acquire environmental data on a routine basis from anywhere on earth. Transmitters weighing 1.6-2.0 kg and functioning approximately 12-18 months operated on a frequency of 401.650 MHz. Signals from the transmitters were received by Argos DCLS instruments aboard two Tiros-N weather satellites in sun-synchronous, nearpolar orbits. Data from the satellites were received at tracking stations, transferred to processing centers in Maryland and France, and made available to users via computer tape, printouts, or telephone links. During 1985 and 1986, more than 25,000 locations and an additional 28,000 sets of sensor data (transmitter temperature and short-term and long-term indices of animal activity) were acquired for caribou and polar bears. Locations were calculated from the Doppler shift in the transmitted signal as the satellite approached and then moved away from the transmitter. The mean locational error for transmitters at known locations (n - 1,265) was 829 m; 90% of the calculated locations were within 1,700 m of the true location. Caribou transmitters provided a mean of 3.1 (+5.0. SD) locations per day during 6h of daily operation, and polar bear transmitters provided 1.7 (+6.9SD) locations during 12h of operation every third day. During the first 6 months of operation, the UHF (ultra-high frequency) signal failed on three of 32 caribou transmitters and 10 of 36 polar bear transmitters. A geographic information system (GIS) incorporating other databases (e.g., land cover, elevation, slope, aspect, hydrology, ice distribution) was used to analyze and display detailed locational and behavioral data collected via satellite. Examples of GIS applications to research projects using satellite telemetry and examples of detailed movement patterns of caribou and polar bears are presented. This report includes documentation for computer software packages for processing Argos data and presents developments, as of March 1987, in transmitter design, data retrieval using a local user terminal, computer software, and sensor development and calibration.

Resource Publication↗
USGS1999

Comparison of aerial survey procedures for estimating polar bear density: Results of pilot studies in northern Alaska

The U.S. Marine Mammal Protection Act (MMPA) and International Agreement on the Conservation of Polar Bears mandate that boundaries and sizes of polar bear ( Ursus maritimus ) populations be known so they can be managed at optimum sustainable levels. However, data to estimate polar bear numbers for the Chukchi/Bering Sea and Beaufort Sea populations in Alaska are limited. We evaluated aerial line transect methodology for assessing the size of these Alaskan polar bear populations during pilot studies in spring 1987 and summer 1994. In April and May 1987 we flew 12.239 km of transect lines in the northern Bering, Chukchi, and western Beaufort seas. In June 1994 we flew 6.244 km of transect lines in a primary survey unit using a helicopter, and 5,701 km of transect lines in a secondary survey unit using a fixed-wing aircraft in the Beaufort Sea. We examined visibility bias in aerial transect surveys, double counts by independent observers, single-season mark-resight methods, the suitability of using polar bear sign to stratify the study area, and adaptive sampling methods. Fifteen polar bear groups were observed during the 1987 study. Probability of detecting bears decreased with increasing perpendicular distance from the transect line, and probability of detecting polar bear groups likely increased with increasing group size. We estimated population density in high density areas to be 446 km 2 /bear. In 1994, 15 polar bear groups were observed by independent front and rear seat observers on transect lines in the primary survey unit. Density estimates ranged from 284 km 2 /bear to 197 km 2 /bear depending on the model selected. Low polar bear numbers scattered over large areas of polar ice in 1987 indicated that spring is a poor time to conduct aerial surveys. Based on the 1994 survey we determined that ship-based helicopter or land-based fixed-wing aerial surveys conducted at the ice-edge in late summer-early fall may produce robust density estimates for polar bear populations in the Chukchi/Bering and Beaufort seas.

Conference Paper↗