U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3131

November 2012 Printed on recycled paper

2012

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1975 1980 1985 1990 1995 2000 2005 2010 2015

Year

Minimum sea ice extent (106 km2

)

Female polar bear with two dependent young 

feeding on a seal.

Female walrus with her calf resting among 

unconsolidated ice floes.

Changing Arctic Ecosystems

Polar Bear and Walrus Response to the Rapid Decline in Arctic Sea Ice

The Arctic is warming faster than other 

regions of the world due to positive climate 

feedbacks associated with loss of snow and 

ice. One highly visible consequence has been 

a rapid decline in Arctic sea ice over the past 3 

decades—a decline projected to continue and 

result in ice-free summers likely as soon as 

2030. The polar bear (Ursus maritimus) and the 

Pacific walrus (Odobenus rosmarus divergens) 

are dependent on sea ice over the continental 

shelves of the Arctic Ocean’s marginal seas. The 

continental shelves are shallow regions with high 

biological productivity, supporting abundant 

marine life within the water column and on the 

sea floor. Polar bears use sea ice as a platform for 

hunting ice seals; walruses use sea ice as a resting 

platform between dives to forage for clams 

and other bottom-dwelling invertebrates. How 

have sea ice changes affected polar bears and 

walruses? How will anticipated changes affect 

them in the future? 

Summer sea ice in the Arctic is melting at an alarming rate. Arctic sea ice extent (shown 

in pink in the map insets) declined to an all-time low on September 16, 2012. Data courtesy 

of the National Snow and Ice Data Center; maps courtesy of University of Illinois.

Through the Changing Arctic Ecosystems 

(CAE) initiative, the U.S. Geological Survey 

(USGS) strives to inform key resource 

management decisions by better understanding 

how wildlife populations of special interest 

to the Department of the Interior (DOI) are 

responding to rapid physical changes in the 

Arctic (Geiselman and others, 2012). The CAE 

initiative includes research themes spanning 

ice-dependent marine and terrestrial ecosystems 

of the north—the sea ice, and the broad 

zones on land underlain by continuous and discontinuous permafrost. This 

theme focuses on the sea-ice dominated environment and will produce new 

information about polar bears and walruses to better inform policy decisions. 

The DOI listed the polar bear as threatened under the Endangered Species 

Act in 2008, and a listing decision on the Pacific walrus will be made in 2017. 

Understanding how climate warming affects the pelagic and benthic food webs 

that support polar bears and walruses is paramount to successful conservation 

of these species. CAE will produce information useful to decisionmakers 

managing oil and gas exploration and development in the Chukchi and 

Beaufort Seas, and for addressing challenges posed by increased shipping and 

other economic opportunities 

in a more accessible Arctic. 

USGS has led research 

on polar bears and walruses 

for the DOI for many years, 

and the CAE initiative is 

supporting new integrated 

studies that target critical 

data gaps. Here, we introduce 

the conceptual framework for 

the sea ice-dependent marine 

mammal research 

theme and highlight our 

goals and early findings.
All-season walrus outcome

All-season

abundance

stressors

All-season

suitable ice

extent

Suitable ice

extent

(from winter

submodel)

Suitable ice

extent

(from spring

submodel)

Suitable ice

extent

(summer/fall)

Abundance

stressors

(summer/fall)

Abundance

stressors

(from spring

submodel)

Abundance

stressors

(from winter

submodel)

Total

mortality

Body

condition

Disease

and

parasites

Energy

expenditure

Shelf ice

availabilty

Predation and

associated

mortality

Benthic prey

abundance

Oil spills Crowding

Crowding and

disturbance

Haul-out

disturbance

Human-caused

direct mortality

Resource

utilization

Ice-free

months

Bering Sea

ice cover

Chukchi Sea

ice cover

Climate change

on benthos

Incidental

take

Subsistence

harvest

Human

settlements

Ship and

air traffic

Season: Summer / Fall (July - November)

Intermediate

calculations

Inputs Season

summaries

Outputs

Walruses hauled out near Point Lay, Alaska, September 2010. For video footage, see http://

gallery.usgs.gov/videos/307

Theme 1 - Marine Ecosystem

The Pacific walrus population winters 

in the Bering Sea. In spring, females and 

their young migrate with the sea ice as 

it retreats northward and then spend the 

summer over the continental shelf of the 

Chukchi Sea. The loss of sea ice habitat 

in the Chukchi Sea is believed to be one 

of the greatest influences on future Pacific 

walrus population dynamics. In recent 

years, sea ice receded northward beyond 

the edge of the continental shelf, causing 

walruses to haul out in large aggregations 

on the shores of Alaska and Russia. 

While onshore, young walruses are 

susceptible to mortality from stampeding 

events. In addition, hauling out on 

shore is likely to constrain foraging to 

nearshore areas, which could become 

depleted of benthic prey. We are focusing 

our studies on understanding how 

changes in the use of habitat by walruses 

affect their energetics and ultimately the 

dynamics of their population. 

CAE uses Bayesian Network 

models as a framework for 

projecting the status of wildlife 

populations in the 21st century 

under various scenarios of ice 

change. This type of model defines 

the primary relationships between 

stressors and the population based 

on a wide range of knowledge 

sources, including empirical data 

and professional judgment from 

scientists and traditional ecological 

knowledge from local residents. 

Model inputs can be varied to 

determine associated output 

sensitivity. This sensitivity analysis 

quantifies important uncertainties in 

the forecasts. CAE uses the network 

models to identify important 

knowledge gaps and prioritize future 

research and modeling efforts. 

For polar bears and walruses, key 

data gaps include assessment of 

habitat quality and how changes in 

habitat affect animal energetics and 

health or condition, and ultimately, 

population dynamics.

Pacific Walrus Response to Sea Ice Loss

Schematic of a portion of the Bayesian Network model used to forecast the status of the Pacific 

walrus under a range of sea-ice conditions (Jay and others, 2011). A similar type of model was 

used to forecast the status of polar bear populations (Amstrup and others, 2008, 2010).

Modeling Framework for Forecasting Future Status of Polar Bears and Walruses
Russia Alaska

Barrow

Walrus foraging hotspots in the Chukchi 

Sea during August, 2008-2011. Data from 

walruses tagged with satellite-linked 

transmitters. From Jay and others (2012).

Polar Bear Response to Sea Ice Loss

We are studying walruses in captive facilities to gain 

additional empirical data on bioenergetics. Here, 

Shawn Noren (University of California, Santa Cruz) 

and Holley Muraco (Six Flags Discovery Kingdom) 

take ultrasound measurement of Siku, an adult female, 

housed at Six Flags Discovery Kingdom, California.

Theme 1 - Marine Ecosystem

Pacific walruses spend the majority of 

their time in water and are extremely difficult 

to study using standard methods involving 

animal captures. Various complementary 

approaches and creative techniques are required 

to understand how sea-ice change is affecting 

walruses. USGS has developed a satellite 

transmitter that can be remotely attached to 

adult walruses using a crossbow. Transmitters 

deployed on walruses in the Chukchi Sea over 

the past several years have provided 

data to identify important seasonal 

movements and foraging areas. 

Information from tagged animals 

helps us quantify changes in activity 

patterns associated with foraging 

from shore resulting from the 

reduced availability of offshore sea ice.

We have developed a 

bioenergetics model for female 

walruses that allows us to estimate 

their food requirements during 

critical life history stages (for 

example, early growth, pregnancy, 

and lactation). This model helps us 

understand how changes in activity 

patterns and associated changes in 

energy expenditure due to loss of sea 

ice may affect reproductive success 

and survival.

Polar bears live across the circumpolar Arctic among 19 

recognized populations. The Chukchi Sea and the Southern 

Beaufort (SB) Sea populations occur in Alaska, and are 

shared with Russia and Canada. In this region of the Arctic, 

the sea ice melts and drifts away from the coast during 

the late summer and fall, and polar bears have historically 

remained with the ice during this period. Like walruses, 

the concern for polar bears is how they will cope when the 

ice that normally provides a foraging and travel platform 

over the continental shelf is absent for a longer period 

each year. 

The USGS has been studying the SB population since the 

1980s, and long-term data on this population have provided a 

baseline for understanding their response to current and

future sea ice changes. During spring we capture and remotely

biopsy dart polar bears on the sea ice as part of a markrecapture program to estimate abundance and characterize 

population vital rates. We deploy satellite transmitters 

on some captured bears to further understand movements, 

behavior and habitat use. Information to quantify their health, 

body condition, and diet is also collected. This wide array 

of information about polar bears provides insights into 

the ecological mechanisms responsible for changes in the 

population and informs our understanding of potential 

population response to future environmental change.

Polar bears are strong swimmers. Using data from polar bears with satellite 

telemetry collars, we have described long-distance swimming events by 

Southern Beaufort Sea polar bears during recent years of extensive open water 

(Pagano and others, 2012).

Pacific Walrus Response to Sea Ice Loss (continued)

To strengthen our understanding of walrus population dynamics, we are 

developing methods to estimate the age structure of walrus groups that hauledout onshore and on the ice. We also are looking for signatures of life history 

events, such as the ages of weaning and first reproduction in walrus teeth, 

which have annual growth rings. Because teeth have been routinely collected 

from harvested walruses in the past, we may have the ability to quantify how 

these vital rate parameters have varied over time, providing valuable empirical 

information on population dynamics.
Authors: K. Oakley , M. Whalen, D. Douglas, M. Udevitz, T. Atwood, 

and C. Jay

For more information:

U.S. Geological Survey, 4210 University Drive, Anchorage, AK 99508

http://alaska.usgs.gov

Publishing support provided by the U.S. Geological Survey

Tacoma Publishing Service Center

With more extensive and earlier sea-ice melt, more polar bears are choosing to move 

onshore when the ice recedes. We are studying the abundance, distribution, and diet of 

onshore bears to understand the significance of this behavior for the SB population. A unique 

feature in the SB region is the presence of subsistence-harvested bowhead whale remains 

that are annually deposited by local communities in three consistent locations along Alaska’s 

northern coast. These sites regularly attract many polar bears. We have established barbed 

wire corrals at two of the sites to collect hair samples from bears that visit the whale remains. 

The samples are used to determine a genetic identity for each bear and an isotopic signature 

of their diet, allowing us to determine how many individuals are using the whale remains, 

and how important the consumption of the remains is to the population.

The extensive and prolonged retreat of summer and autumn sea ice has resulted in polar

bears having to travel greater distances to reach foraging and denning habitat. The energetic 

cost of long-distance travel, particularly swimming, is believed to contribute to declines in 

body condition and survival. We are evaluating how movement strategies, such as swimming,

affect polar bear energetics. By using satellite telemetry collars equipped with sensors that 

measure acceleration forces, we will be able to examine the energetic costs of locomotion 

and better understand the effects that projected sea-ice declines will have on polar bear energetics.

Polar bear cub crawls under a strand of 

barbed wire at the bowhead whale bonepile 

in Barrow, Alaska, leaving behind a tuft of 

hair that provides a genetic fingerprint and 

isotopic signature of diet.

Polar bear on a barrier 

island. Polar bears that 

stay on the north slope 

of Alaska are spending 

on average 34 days on 

land in contrast to 9 

days in prior decades.

Application of Emerging Technologies

CAE is developing and using new approaches and technologies 

to advance our understanding of a changing Arctic. In this research 

theme, we are applying new satellite telemetry technologies as 

described above. In addition, we are using Next Generation DNA 

sequencing technology and classical genomics techniques to 

develop biological markers of gene expression that can identify 

the effects of environmental stressors on immune system function. 

This information will help us understand how environmental change 

influences physiological processes and, ultimately, population health.

Publications

Amstrup, S.C., DeWeaver, E.T., Douglas, D.C., Marcot, B.G., Durner, 

G.M., Bitz, C.M., and Bailey, D.A., 2010, Greenhouse gas mitigation 

can reduce sea-ice loss and increase polar bear persistence: Nature, 

v. 468, no. 7326, p. 955-960.

Amstrup, S.C., Marcot, B.G., and Douglas, D.C., 2008, A Bayesian 

network modeling approach to forecasting the 21st century worldwide 

status of polar bears in DeWeaver, E.T., Bitz, C.M., and Tremblay, 

L.-Bruno, eds., Artic sea ice decline—Observations, projections, 

mechanisms, and implications: Washington DC, American Geophysical 

Union, Geophysical Monograph Series, v. 180, p. 213-268.

Douglas, D.C., 2010, Arctic sea ice decline: Projected changes in timing 

and extent of sea ice in the Bering and Chukchi Seas: U.S. Geological 

Survey Open-File Report 2010-1176, 32 p.

Durner, G.M., Whiteman, J.P., Harlow, H.J., Amstrup, S.C., Regehr, E.V., 

and M. Ben-David, M., 2011, Consequences of long-distance swimming 

and travel over deep-water ice for a female polar bear during a year of 

extreme sea ice retreat: Polar Biology, v. 34, p. 975-984, doi:10.1007/

s00300-010-0953-2.

Fischbach, A.S., Monson, D.H., and Jay, C.V., 2009, Enumeration of 

Pacific walrus carcasses on beaches of the Chukchi Sea in Alaska 

following a mortality event, September 2009: U.S. Geological Survey 

Open-File Report 2009-1291, 10 p.

Geiselman, Joy, DeGange, Tony, Oakley, Karen, Derksen, Dirk, and 

Whalen, Mary, 2012, Changing Arctic ecosystems—Research to 

understand and project changes in marine and terrestrial ecosystems of 

the Arctic: U.S. Geological Survey Fact Sheet 2011-3136, 4 p.

Jay, C.V., and Fischbach, A.S., 2008, Pacific walrus response to Arctic sea 

ice losses: U.S. Geological Survey Fact Sheet 2008-3041, 4 p.

Jay, C.V., Fischbach, A.S., and Kochnev, A.A., 2012, Walrus areas of use in 

the Chukchi Sea during sparse sea ice cover: Marine Ecology Progress 

Series, m 10057, doi:10.3354/meps10057.

Jay, C.V., Marcot, B.G., and Douglas, D.C., 2011, Projected status of 

the Pacific walrus (Odobenus rosmarus divergens) in the twenty-first 

century: Polar Biology, v. 34, p. 1065-1084.

Noren, S.R., Udevitz, M.S., and Jay, C.V., 2012, Bioenergetics model for 

estimating food requirements of female Pacific walruses (Odobenus 

rosmarus divergens): Marine Ecology Progress Series, v. 460, p. 261-

275.

Pagano, A.M., Durner, G.M., Amstrup, S.C., Simac, K.S., and York, G.S., 

2012, Long-distance swimming by polar bears (Ursus maritimus) of the 

southern Beaufort Sea during years of extensive open water: Canadian 

Journal of Zoology, v. 90, p. 663-676.

.............................................................................

Polar Bear Response to Sea-Ice Loss (continued)

Theme 1 - Marine Ecosystem