U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3041

 May 2008 Printed on recycled paper Printed on recycled paper

Sea ice plays an important role in the life of the 

Pacific walrus (Odobenus rosmarus divergens). U.S. 

Geological Survey (USGS) scientists are seeking to 

understand how losses of sea ice during summer 

over important foraging grounds in the Chukchi 

Sea will affect walruses. USGS scientists recently 

modified a remotely deployed satellite radio-tag that 

will aid in studying walrus foraging habitats and 

behaviors. Information from the tags will help USGS 

understand how walruses are responding to their 

changing environment.

Walruses and Their Environment

The Pacific walrus is a large pinniped, resident in the 

Bering and Chukchi Seas of Russia and Alaska, and is one of 

four marine mammal species managed by the U.S. Department 

of the Interior. Walruses feed on clams and a wide variety of 

other invertebrates from the seafloor. They rest between feeding 

trips on sea ice or land. Sea ice provides walruses with a resting 

platform, access to offshore feeding areas, and seclusion from 

humans and predators. The constant motion of sea ice transports 

resting walruses over widely dispersed prey patches. In winter, 

Pacific walruses live amid the dynamic sea ice in the Bering 

Sea. In spring, as the ice edge recedes northward and into 

the Chukchi Sea, most adult males shift to using land to rest 

between feeding trips, while adult females and young remain 

with the sea ice (Fay, 1974; 1985).

 Walruses can have a large effect on their prey and play 

an important role in the Arctic ecosystem by influencing the 

structure of benthic invertebrate communities. They can eat 

more than 50 clams during a single 7-minute dive to the seafloor 

and consume 35–50 kilograms (77–110 pounds) of food per 

day. Pregnant and nursing walruses consume even more food 

(Fay, 1985; Born and others, 2003). As walruses root along the 

seafloor in search of food, they plow through large quantities of 

sediment (Nelson and Johnson, 1987; Nelson and others, 1994). 

They remove large quantities of prey from the seafloor, affect 

the size structure of clam populations, mix bottom sediments 

while foraging, create new microhabitats from discarded shells, 

and generate food for seafloor scavengers from uneaten scraps 

of prey (Oliver and others, 1983). 

Pacific Walrus Response to Arctic Sea Ice Losses

Mother and juvenile Pacific walrus.
140°E 160°E 180° 160°W 140°W 120°W

70°N

60°N

0 100 200

Nautical Miles

0 200 400

Kilometers

Chukchi

Sea

Chukotka

Bering

Sea

Arctic

Ocean

Alaska

United States

of America

Russia

Although walruses are capable of deep diving (greater 

than 250 meters [Born and others, 2005]), they usually feed in 

waters less than 80 meters deep over the continental shelf where 

their prey are more abundant and easier to obtain than in deeper 

waters (Fay and Burns, 1988; Jay and others, 2001).

A Changing Sea Ice Environment

The extent of Arctic summer sea ice has decreased sharply 

over the past several decades (Stroeve and others, 2007). Sea 

ice is more frequently disappearing from the continental shelf 

of the Chukchi Sea during summer months. In 6 of the last 9 

years, the Chukchi Sea shelf was ice-free—with periods of no 

ice cover extending from 1 week to as much as 2.5 months. In 

contrast, there was always some ice over the Chukchi Sea shelf 

in all of the previous 20 years (1979–98) (passive microwave 

satellite imagery; Cavalieri and others, 1996 [2006]).

When the sea ice recedes over the deep ocean basin, 

walruses must either continue to haul out on the sea ice 

with little access to food, or abandon the sea ice and move 

to coastal areas where they can rest on land. During the 

record minimum sea ice extent in summer 2007 (National 

Snow and Ice Data Center, http://nsidc.org/news/press/2007_

seaiceminimum/20071001_pressrelease.html), the Chukchi Sea 

shelf contained little to no ice for about 80 days and several 

thousand walruses hauled out on previously unused shores 

of northwestern Alaska (Joel Garlich-Miller, U.S. Fish and 

Wildlife Service, oral commun., 2007).

During autumn 2007, tens of thousands female and young 

walruses began using resting areas along the northern coast of 

Chukotka, after sea ice was no longer available. There, a few 

thousand mortalities were reported, apparently from trampling 

due to disturbances that caused adults to stampede into the 

water (Anatoly Kochnev, ChukotTINRO, oral commun., 2007).

As more walruses haul out on land instead of sea ice, 

nearshore prey populations will be subjected to greater predation 

pressure. Today, it is unknown whether more concentrated 

foraging by walruses will change or deplete nearshore prey 

communities, or if walrus energetics will be affected if prey 

do become less abundant. A better understanding of walrus 

movement and foraging patterns is necessary to appreciate 

the ways in which decreasing availability of sea ice may 

affect walruses and the prey upon which they depend. This 

understanding will provide policy makers and regulatory agencies 

with information needed to address emerging issues related to 

climate change, such as new transoceanic shipping opportunities 

and increased resource development in the Arctic.

EXPLANATION

In summer, a major segment of the 

Pacific walrus population, especially 

females and their young, ranges 

in waters across the continental 

shelf of the Chukchi Sea (light blue 

shades). By September 2007, the sea 

ice (upper right) was far north of the 

continental shelf and over the deep 

Arctic Basin. Historically, the annual 

sea ice minimum edge (yellow line) 

occurred over the continental shelf.

DEPTH, in meters

Less than 20

20 - 40

40 - 80

80 - 160

160 - 200

Deep water

Base Map: September 2007 sea ice extent from NASA passive microwave imagery (12.5 kilometer resolution) 

processed by University of Bremen. Historical sea ice edge derived from median sea ice extent from 1979–2000 

National Snow and Ice Data Center. Bathymetry from International Bathymetric Chart of the Arctic Ocean.
Base map: 25 July 2007 ice extent. Source of sea ice extent and bathymetry data same as described 

in previous sea ice map.

180° 170°W 160°W 150°W

75°N

70°N

0 50 100

Nautical Miles

0 100 200

Kilometers

Chukchi

Sea

Chukotka

Russia

Alaska

United States

of America

To begin to understand where walruses go when the ice 

edge retreats off the continental shelf and over deep waters 

of the Arctic Basin, USGS researchers attached satellite 

radio-tags to walruses in the eastern Chukchi Sea. To avoid 

the difficult task of capturing walruses on sea ice, USGS 

developed a tagging system that uses a crossbow to deploy the 

radio-tags (Jay and others, 2006). Radio-tags were attached to 

nine walruses offshore of Barrow, Alaska, in June–July 2007, 

while the ice edge was still over the continental shelf. The 

tracking data showed that walruses rested on remnant ice floes 

that remained over the shallow waters of the eastern Chukchi 

Sea as the main ice edge retreated over deeper water. These 

observations suggest that walruses will exploit sparse ice to 

maintain access to preferred foraging areas over the continental 

shelf.

Pacific walrus with satellite radio-tag.

EXPLANATION

Seven walruses tracked with satellite 

radio-tags during June–July of 2007 

remained over the continental shelf, 

far south of the pack ice.

Barrow

 

First 25 July

Location Location

(late June - 

early July 

at ice edge)

Insights from Tracking Walrus with Satellite Tags
160°W

57°N

56°N

0 10 20

Nautical Miles

New Satellite Radio-Tags Identify Walrus Foraging 

Behaviors and Distribution

USGS researchers developed a new satellite radio-tag to 

record when walruses were feeding or not feeding. Data from 

these tags will allow researchers to identify foraging areas and 

compare activity budgets of walruses foraging from shore in 

ice-free conditions and walruses foraging from ice in offshore 

habitats. A prototype of the foraging-tag was deployed on a 

male walrus in the southeastern Bering Sea in September 2007, 

Nelson, C.H., and Johnson, K.R., 1987, Whales and walruses as 

tillers of the sea floor: Scientific American, v. 256, p. 112–117.

Nelson, C.H., Phillips, R.L., McRea, J., Jr., Barber, J.H., Jr., 

McLaughlin, M.W., and Chin, J.L., 1994, Gray whale and 

Pacific walrus benthic feeding grounds and sea floor interaction 

in the Chukchi Sea: U.S. Geological Survey, Menlo Park, 

California, Technical report for minerals management service/IA 

No. 14157, OCS Study MMS 93-0042, 51 p. 

Oliver, J.S., Slattery, P.N., O’Connor, E.F., and Lowry, L.F., 1983, 

Walrus, Odobenus rosmarus, feeding in the Bering Sea—A 

benthic perspective: Fishery Bulletin, no. 81, p. 501–512.

Stroeve, J., Holland, M.M., Meier, W., Scambos, T., and 

Serreze, M., 2007, Arctic sea ice decline—Faster than 

forecast: Geophysical Research Letters, v. 34, L09501, 

doi:09510.01029/02007GL029703.

References Cited

Born, E.W., Acquarone, M., Knutsen, L.O., and Toudal, L., 2005, 

Homing behaviour in an Atlantic walrus (Odobenus rosmarus 

rosmarus): Aquatic Mammals, v. 31, no. 1, p.23–33.

Born, E.W., Rysgaard, S., Ehlmé, G., Sejr, M., Acquarone, 

M., and Levermann, N., 2003, Underwater observations of 

foraging free-living Atlantic walruses (Odobenus rosmarus 

rosmarus) and estimates of their food consumption: Polar 

Biology, v. 26, no. 5, p. 348–357.

Cavalieri, D., Parkinson, C., Gloersen, P., and Zwally, H.J., 1996 

[updated 2006], Sea ice concentrations from Nimbus-7 SMMR 

and DMSP SSM/I passive microwave data: Boulder, Colo., 

National Snow and Ice Data Center, digital media, http://nsidc.

org/data/nsidc-0051.html

Fay, F.H., 1974, The role of ice in the ecology of marine 

mammals of the Bering Sea, in Hood, D.W., and Kelley, E.J., 

eds., Oceanography of the Bering Sea: Fairbanks, University 

of Alaska, Institute of Marine Science, Occasional Publication 

No. 2, p. 383.

Fay, F.H., 1985, Odobenus rosmarus. The American Society of 

Mammalogists.

Fay, F.H., and Burns, J.J., 1988, Maximal feeding depth of 

walruses: Arctic, v. 41, no. 3, p. 239–240.

Jay, C.V., Farley, S.D., and Garner, G.W., 2001, Summer diving 

behavior of male walruses in Bristol Bay, Alaska: Marine 

Mammal Science, v. 17, no. 3, p. 617–631.

Jay, C.V., Heide-Jørgensen, M.P., Fischbach, A.S., Jensen, M.V., 

Tessler, D.F., and Jensen, A.V., 2006, Comparison of remotely 

deployed satellite radio transmitters on walruses: Marine 

Mammal Science, v. 22, p. 226–236.

USGS, Alaska Science Center

4210 University Drive

Anchorage, Alaska 995083

(907) 786-7000 – http://alaska.usgs.gov

For more information: 

and yielded a continuous chronology of hourly foraging status 

for almost 2 weeks. The movement patterns and habitats used 

by this walrus were consistent with findings from previous 

studies of walruses in this region. The foraging-tag promises to 

be an important tool for identifying when and where walruses 

forage under different sea ice conditions. This information will 

be critical for managing the expansion of offshore resource 

development activities and for understanding the consequences 

of summer sea ice loss due to climate change. 

EXPLANATION

An 8-day foraging trip of an adult male 

walrus in the southeastern Bering 

Sea, tracked with the new satellite 

radio-tag. The walrus left the haulout 

and traveled more than 25 nautical 

miles to the northwest and foraged in 

waters 50 to 100 meters deep.

 Foraging

 Not Foraging

Base map: NOAA Chart No. 16011

 Soundings in fathoms

Chadwick V. Jay and Anthony S. Fischbach

Edited by Debra Grillo

Graphic Design by Bill Gibbs