Editing Walrus (section)

==Ecology==
[[File:Лежка моржей на острове Нортбрук.jpg|thumb|right|A herd of walruses on [[Northbrook Island]], [[Franz Josef Land]], Russia]]

===Range and habitat===
The majority of the population of the Pacific walrus spends its summers north of the [[Bering Strait]] in the [[Chukchi Sea]] of the Arctic Ocean along the northern coast of eastern [[Siberia]], around [[Wrangel Island]], in the [[Beaufort Sea]] along the northern shore of [[Alaska]] south to [[Unimak Island]],<ref name="Izembek National Wildlife Report Sept 2015">{{cite web|title=Izembek National Wildlife Report Sept 2015|url=http://www.aleutianseast.org/vertical/Sites/%7BEBDABE05-9D39-4ED4-98D4-908383A7714A%7D/uploads/Izembek_National_Wildlife_Refuge_Report_Sept_2015.pdf|publisher=USFWS|access-date=26 March 2017|archive-date=30 December 2016|archive-url=https://web.archive.org/web/20161230181745/http://www.aleutianseast.org/vertical/Sites/%7BEBDABE05-9D39-4ED4-98D4-908383A7714A%7D/uploads/Izembek_National_Wildlife_Refuge_Report_Sept_2015.pdf|url-status=dead}}</ref> and in the waters between those locations. Smaller numbers of males summer in the [[Gulf of Anadyr]] on the southern coast of the Siberian [[Chukchi Peninsula]], and in Bristol Bay off the southern coast of Alaska, west of the [[Alaska Peninsula]]. In the spring and fall, walruses congregate throughout the Bering Strait, reaching from the western coast of Alaska to the Gulf of Anadyr. They winter over in the [[Bering Sea]] along the eastern coast of Siberia south to the northern part of the [[Kamchatka Peninsula]], and along the southern coast of Alaska.<ref name="Fay85"/> A 28,000-year-old fossil walrus was dredged up from the bottom of [[San Francisco Bay]], indicating that Pacific walruses ranged that far south during the [[Wisconsin glaciation|last Ice Age]].<ref>{{cite journal| vauthors = Dyke AS |year = 1999|title = The Late Wisconsinan and Holocene record of walrus (''Odobenus rosmarus'') from North America: A review with new data from Arctic and Atlantic Canada|journal = Arctic|volume = 52|issue = 2|pages = 160–181|doi=10.14430/arctic920|doi-access = free}}</ref>
[[File:Herd of Pacific walrus resting.png|thumb|Herd resting on a beach, Alaska.]]
Commercial harvesting reduced the population of the Pacific walrus to between 50,000 and 100,000 in the 1950s–1960s. Limits on commercial hunting allowed the population to increase to a peak in the 1970s-1980s, but subsequently, walrus numbers have again declined. Early aerial censuses of Pacific walrus conducted at five-year intervals between 1975 and 1985 estimated populations of above 220,000 in each of the three surveys.<ref>{{cite book | vauthors = Estes JA, Gol'tsev VN |title=Soviet American Cooperative Research on Marine Mammals | volume = 1 ''Pinnipeds'' |date=1984 |publisher=NOAA, Technical Report, NMFS 12 |pages=67–76 |chapter=Abundance and distribution of the Pacific walrus (''Odobenus rosmarus divergens''): results of the first Soviet American joint aerial survey, autumn 1975.}}</ref><ref>{{cite journal | vauthors = Estes JA, Gilbert JR |title=Evaluation of an aerial survey of Pacific walruses (''Odobenus rosmarus divergens''). |journal=Journal of the Fisheries Research Board of Canada |volume=35 |issue=8 |pages=1130–1140 |date=1978|doi=10.1139/f78-178 }}</ref><ref>{{cite book | vauthors = Gol'tsev VN |title=Aerial surveys of Pacific walruses in the Soviet sector during fall 1975 |date=1976 |publisher=Procedural Report TINRO |location=Magadan}}</ref><ref>{{cite book | vauthors = Johnson A, Burns J, Dusenberry W, Jones R |title=Aerial survey of Pacific walruses, 1980. |date=1982 |publisher=U.S. Fish and Wildlife Service, Marine Mammals Management |location=Anchorage, Alaska}}</ref><ref>{{cite book | vauthors = Fedoseev GA | veditors = Rodin VE, Perlov AS, Berzin AA, Gavrilov GM, Shevchenko AI, Fadeev NS, Kucheriavenko EB |title=Marine Mammals of the Far East |date=1984 |publisher=TINRO |location=Vladivostok |pages=73–85 |chapter=Present status of the population of walruses (''Odobenus rosmarus'') in the eastern Arctic and Bering Sea}}</ref><ref>{{cite book | vauthors = Gilbert JR |title=Aerial survey of Pacific walruses in the Chukchi Sea, 1985 |date=1986 |publisher=Mimeo Report}}</ref><ref>{{cite journal | vauthors = Gilbert JR |title=Aerial census of Pacific walruses in the Chukchi Sea, 1985 |journal=Marine Mammal Science |date=1989 |volume=5 |issue=1 |pages=17–28|doi=10.1111/j.1748-7692.1989.tb00211.x |bibcode=1989MMamS...5...17G }}</ref><ref>{{cite journal | vauthors = Gilbert JR |title=''Errata'': Correction to the variance of products, estimates of Pacific walrus populations |journal=Marine Mammal Science |date=1989 |volume=5 |pages=411–412|doi=10.1111/j.1748-7692.1989.tb00356.x }}</ref><ref>{{cite book | vauthors = Fedoseev GA, Razlivalov EV |title=The distribution and abundance of walruses in the eastern Arctic and Bering Sea in autumn 1985 |date=1986 |publisher=VNIRO |location=Magadan}}</ref>

In 2006, the population of the Pacific walrus was estimated to be around 129,000 on the basis of an aerial census combined with satellite tracking.<ref>{{cite journal|vauthors= Speckman SG, Chernook VI, Burn DM, Udevitz MS, Kochnev AA, Vasilev A, Jay CV, Lisovsky A, Fischbach AS, Benter RB|display-authors=etal|year=2010|title=Results and evaluation of a survey to estimate Pacific walrus population size, 2006|journal=Marine Mammal Science|volume=27|issue=3|pages=514–553|doi=10.1111/j.1748-7692.2010.00419.x}}</ref><ref>{{cite web| author = US Fish and Wildlife Service| title = Stock Assessment Report: Pacific Walrus – Alaska Stock| year = 2014| url = https://www.fws.gov/r7/fisheries/mmm/stock/Revised_April_2014_Pacific_Walrus_SAR.pdf| access-date = 16 June 2019| archive-date = 18 February 2020| archive-url = https://web.archive.org/web/20200218015145/https://www.fws.gov/r7/fisheries/mmm/stock/Revised_April_2014_Pacific_Walrus_SAR.pdf| url-status = dead}}</ref> There were roughly 200,000 Pacific walruses in 1990.<ref>{{cite journal| vauthors = Gilbert JR |year = 1992|title = Aerial census of Pacific walrus, 1990|journal = USFWS R7/MMM Technical Report 92-1}}</ref><ref>{{cite web|author= US Fish and Wildlife Service|title= Stock Assessment Report: Pacific Walrus – Alaska Stock|year= 2002|url= http://alaska.fws.gov/fisheries/mmm/walrus/pdf/Final_%20Pacific_Walrus_SAR.pdf|access-date= 3 October 2007|url-status= dead|archive-url= https://web.archive.org/web/20110515171808/http://alaska.fws.gov/fisheries/mmm/walrus/pdf/Final_%20Pacific_Walrus_SAR.pdf|archive-date= 15 May 2011}}</ref>

The much smaller population of Atlantic walruses ranges from the Canadian Arctic, across [[Greenland]], [[Svalbard]], and the western part of Arctic Russia. There are eight hypothetical subpopulations of Atlantic walruses, based largely on their geographical distribution and movements: five west of Greenland and three east of Greenland.<ref>{{cite journal| vauthors = Born E, Andersen L, Gjertz I, Wiig Ø |year = 2001|title = A review of the genetic relationships of Atlantic walrus (''Odobenus rosmarus rosmarus'') east and west of Greenland|journal = Polar Biology|volume = 24|pages = 713–718|doi = 10.1007/s003000100277|issue = 10| bibcode=2001PoBio..24..713E |s2cid = 191312}}</ref> The Atlantic walrus once ranged south to [[Sable Island]], off of [[Nova Scotia]]; as late as the 18th century, they could be found in large numbers in the Greater [[Gulf of St. Lawrence]] region, sometimes in colonies of 7-8,000 individuals.<ref>{{cite book | last = Bolster | first = W. Jeffrey | name-list-style = vanc | title = The Mortal Sea: Fishing the Atlantic in the Age of Sail | location = Cambridge | publisher = Harvard University Press | date =  2012 }}</ref> This population was nearly eradicated by commercial harvest; their current numbers, though difficult to estimate, probably remain below 20,000.<ref>{{cite book | author = [NAMMCO] North Atlantic Marine Mammal Commission. | date = 1995 | title = Report of the third meeting of the Scientific Committee. | series = NAMMCO Annual Report 1995 | publisher = NAMMCO | location = Tromsø | pages = 71–127 }}</ref><ref>{{cite web| author = North Atlantic Marine Mammal Commission| title = Status of Marine Mammals of the North Atlantic: The Atlantic Walrus| url = http://www.nammco.no/webcronize/images/Nammco/654.pdf| archive-url = https://wayback.archive-it.org/0/20071025220623/http://www.nammco.no/webcronize/images/Nammco/654.pdf| url-status = dead| archive-date = 25 October 2007| access-date = 3 October 2007| df = dmy-all}}</ref> In April 2006, the Canadian [[Species at Risk Act]] listed the populations of northwestern Atlantic walrus in [[Québec]], New Brunswick, [[Nova Scotia]], Newfoundland and Labrador as having been eradicated in Canada.<ref>{{cite web | author = Fisheries and Oceans Canada | title = Atlantic Walrus: Northwest Atlantic Population|access-date = 9 October 2007| url = http://www.dfo-mpo.gc.ca/species-especes/species/species_atlanticwalrus_e.asp | archive-url = https://web.archive.org/web/20070818123101/http://www.dfo-mpo.gc.ca/species-especes/species/species_atlanticwalrus_e.asp| archive-date = 18 August 2007}}</ref> A genetically distinct population existed in Iceland that was wiped out after Norse settlement around 1213–1330 AD.<ref>{{cite journal | vauthors = Keighley X, Pálsson S, Einarsson BF, Petersen A, Fernández-Coll M, Jordan P, Olsen MT, Malmquist HJ | display-authors = 6 | title = Disappearance of Icelandic Walruses Coincided with Norse Settlement | journal = Molecular Biology and Evolution | volume = 36 | issue = 12 | pages = 2656–2667 | date = December 2019 | pmid = 31513267 | pmc = 6878957 | doi = 10.1093/molbev/msz196 | url = }}</ref>

An isolated population is restricted, year-round, to the central and western regions of the [[Laptev Sea]], from the eastern [[Kara Sea]] to the westernmost regions of the [[East Siberian Sea]]. The current population of these Laptev walruses has been estimated at between 5-10,000.<ref name=MNRRF>{{cite web | title = Морж / Odobenus rosmarus | work = Ministry of Natural Resources of the Russian Federation protected species list | url = http://zapoved.ru/species/262/%D0%9C%D0%BE%D1%80%D0%B6 | archive-url = https://web.archive.org/web/20160304104207/http://zapoved.ru/species/262/%D0%9C%D0%BE%D1%80%D0%B6 | archive-date = 4 March 2016 | access-date = 4 October 2007 | url-status = live }}</ref>

Even though walruses can dive to depths beyond 500 meters, they spend most of their time in shallow waters (and the nearby ice floes) hunting for [[bivalves]].<ref>{{cite web|url=https://arcticwwf.org/species/walrus/|title=Walrus Facts |website= World Wildlife Fund (WWF) }}</ref><ref name="Gar18">{{cite journal | vauthors = Garde E, Jung-Madsen S, Ditlevsen S, Hansen RG, Zinglersen KB, Heide-Jørgensen MP | title = Diving behavior of the Atlantic walrus in high Arctic Greenland and Canada. | journal = Journal of Experimental Marine Biology and Ecology | date = March 2018 | volume = 500 | pages = 89–99 | doi = 10.1016/j.jembe.2017.12.009 | bibcode = 2018JEMBE.500...89G }}</ref>

In March 2021, a single walrus, nicknamed [[Wally the Walrus]], was sighted at [[Valentia Island]], [[Ireland]], far south of its typical range, potentially due to having fallen asleep on an iceberg that then drifted south towards Ireland.<ref name="First ever sighting of a walrus in Ireland after it is thought to have drifted across Atlantic after falling asleep on iceberg">{{cite web|title=First ever sighting of a walrus in Ireland after it is thought to have drifted across Atlantic after falling asleep on iceberg|url=https://www.independent.ie/news/first-ever-sighting-of-a-walrus-in-ireland-after-it-is-thought-to-have-drifted-across-atlantic-after-falling-asleep-on-iceberg-40195874.html|website=independent.ie| vauthors = Kelleher L, Palenque BK |date=14 March 2021|access-date=15 March 2021}}</ref> Days later, a walrus, thought to be the same animal, was spotted on the [[Pembrokeshire]] coast, [[Wales]].<ref>{{cite web|title=Walrus spotted in Wales, days after one seen off Ireland|url=https://www.bbc.co.uk/news/uk-wales-56470235|website=bbc.co.uk|publisher=BBC News|date=20 March 2021|access-date=4 April 2021}}</ref>
In June 2022, a single walrus was sighted on the shores of the [[Baltic Sea]] - at [[Rügen]] Island, [[Germany]], [[Mielno]], [[Poland]] and [[Skälder Bay]], [[Sweden]].<ref>{{cite news | url=https://www.thelocal.de/20220617/walrus-makes-rare-stop-on-german-beach-to-delight-of-locals/ | title=Walrus makes rare stop on German beach to delight of locals | newspaper=The Local Germany | date=17 June 2022 }}</ref><ref>{{cite web | url=https://notesfrompoland.com/2022/06/24/walrus-spotted-on-baltic-beach-in-first-ever-sighting-in-poland/ | title=Walrus spotted on Baltic beach in first ever sighting in Poland | date=24 June 2022 }}</ref><ref>{{cite web | url=https://cde.news/photo-story-rare-visit-by-walrus-in-skane-sweden/ | title=Photo Story: Rare visit by Walrus in Skane, Sweden | date=12 June 2022 }}</ref> In July 2022, there was a report of a lost, starving walrus (nicknamed as [[Stena (walrus)|Stena]]) in the coastal waters of the towns of [[Hamina]] and [[Kotka]] in [[Kymenlaakso]], [[Finland]],<ref>{{cite web|url=https://yle.fi/news/3-12538568|title=Visiting walrus causes stir in southern Finland town|work=[[Yle News]]|date=July 15, 2022|access-date=July 20, 2022}}</ref><ref>{{cite web|url=https://nord.news/2022/07/18/the-walrus-destroyed-equipment-worth-more-than-10000-euros-says-a-kotka-fisherman/|title=The walrus destroyed equipment worth more than 10,000 euros, says a Kotka fisherman|work=Nord News|date=July 18, 2022|access-date=July 20, 2022}}</ref> that, despite rescue attempts, died of starvation when the rescuers tried to transport it to the [[Korkeasaari Zoo]] for treatment.<ref>{{cite news|url=https://euroweeklynews.com/2022/07/20/rare-walrus-hamina-finland/|title=UPDATE: Walrus found on the shore in Hamina, Finland has died, causing some outrage|first=Matthew|last=Roscoe|work=[[EuroWeekly News]]|date=July 20, 2022|access-date=July 20, 2022}}</ref><ref>{{Cite web |date=2022-07-22 |title=Walrus' fate sparks online outrage |url=https://yle.fi/news/3-12546773 |access-date=2022-07-30 |website=[[Yle]] |language=en}}</ref>

===Diet===
[[File:Walrus - Kamogawa Seaworld - 1.jpg|thumb|right|[[Vibrissae]] of a captive walrus (Japan)|alt=Photo of walrus head in profile showing one eye, nose, tusks, and "mustache"]]
[[File:Walross paar.jpg|thumb|right|Walruses leaving the water|alt=Photo of two walruses in shallow water facing shore]]

Walruses prefer shallow [[Continental shelf|shelf]] regions and forage primarily on the sea floor, often from sea ice platforms.<ref name="Fay85"/> They are not particularly deep divers compared to other pinnipeds; the deepest dives in a study of Atlantic walrus near [[Svalbard]] were only {{convert|31|±|17|m|abbr=on}}.<ref>{{cite journal| vauthors = Schreer JF, Kovacs KM, O'Hara Hines RJ |year = 2001|title = Comparative diving patterns of pinnipeds and seabirds|journal = Ecological Monographs|volume = 71|pages = 137–162|doi = 10.1890/0012-9615(2001)071[0137:CDPOPA]2.0.CO;2}}</ref> However, a more recent study recorded dives exceeding {{Convert|500|m|ft}} in [[Smith Sound]], between NW Greenland and Arctic Canada – in general, peak dive depth can be expected to depend on prey distribution and seabed depth.<ref name="Gar18"/>

The walrus has a diverse and opportunistic diet, feeding on more than 60 genera of marine organisms, including [[shrimp]], crabs, [[Priapulida|priapulids]], [[Echiura|spoon worms]], [[Tube worm (body plan)|tube worms]], soft [[coral]]s, [[tunicate]]s, [[Holothuroidea|sea cucumber]]s, various [[Mollusca|mollusks]] (such as [[Sea snail|snail]]s, [[octopus]]es, and [[squid]]), some types of slow-moving [[fish]], and even parts of other pinnipeds.<ref>{{cite journal| vauthors = Sheffield G, Fay FH, Feder H, Kelly BP |year = 2001|title = Laboratory digestion of prey and interpretation of walrus stomach contents|journal = Marine Mammal Science|volume = 17| pages = 310–330|doi = 10.1111/j.1748-7692.2001.tb01273.x|issue = 2| bibcode=2001MMamS..17..310S }}</ref><ref>[https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/research_pdfs/pacific_walrus_saint_lawrence_island_harvest_sample_analyses_2012_2014_2016.pdf Pacific Walrus (Odobenus rosmarus divergens) Saint Lawrence Island Harvest Sample Analyses, 2012–2014 and 2016]</ref> However, it prefers benthic [[Bivalvia|bivalve mollusks]], especially [[clam]]s, for which it forages by grazing along the sea bottom, searching and identifying prey with its sensitive [[vibrissae]] and clearing the murky bottoms with jets of water and active flipper movements.<ref>{{cite journal | vauthors = Levermann N, Galatius A, Ehlme G, Rysgaard S, Born EW | title = Feeding behaviour of free-ranging walruses with notes on apparent dextrality of flipper use | journal = BMC Ecology | volume = 3 | issue = 9 | pages = 9 | date = October 2003 | pmid = 14572316 | pmc = 270045 | doi = 10.1186/1472-6785-3-9 | doi-access = free }}</ref> The walrus sucks the meat out by sealing its powerful lips to the organism and withdrawing its piston-like tongue rapidly into its mouth, creating a vacuum. The walrus palate is uniquely vaulted, enabling effective suction; researchers measured pressures in the oral cavity as low as -87.9 kPa in air, and -118.8 kPa underwater.<ref>{{cite journal|title=Oral suction of a Pacific walrus (''Odobenus rosmarus divergens'') in air and under water|vauthors = Kastelein RA, Muller M, Terlouw A |year=1994|pages=105-115|volume=59|journal=Zeitschrift für Säugetierkunde}}</ref> Walruses at the [[Tierpark Hagenbeck]] were easily able to suck the five-pound metal plug out of the bottom of their pool, at a water depth of 1.1 metres.<ref>{{cite journal|title=Notes on walruses (''Odobenus rosmarus'') in captivity|vauthors = Hagenbeck, CH |year=1962|pages=24-25|volume=4|journal=International Zoo Yearbook}}</ref> The diet of the Pacific walrus consist almost exclusively of benthic invertebrates (97 percent).<ref>{{cite book | chapter-url = {{google books |plainurl=y |id=6CE3AQAAMAAJ|page=SA4-PA277}} | chapter = Chapter 4.9.8.5: Other Pinnipeds | title = Alaska Groundfish Fisheries Final Programic Supplemental Environmental Impact Statement | work = Fishery Management Plans for the Groundfish Fishery of the Gulf of Alaska and the Groundfish of the Bering Sea and Aleutian Islands Area: Environmental Impact Statement |date=21 December 2018|via=Google Books}}</ref>

Aside from the large numbers of organisms actually consumed by the walrus, its foraging has a large peripheral impact on benthic communities. It disturbs ([[bioturbation|bioturbates]]) the sea floor, releasing nutrients into the water column, encouraging mixing and movement of many organisms and increasing the patchiness of the [[benthos]].<ref name="Ray06"/>

Seal tissue has been observed in a fairly significant proportion of walrus stomachs in the Pacific, but the importance of seals in the walrus diet is under debate.<ref>{{cite book| vauthors = Lowry LF, Frost KJ |year = 1981|chapter = Feeding and Trophic Relationships of Phocid Seals and walruses in the Eastern Bering Sea|title = The Eastern Bering Sea Shelf: Oceanography & Resources vol. 2.|chapter-url={{google books |plainurl=y |id=DJwTAAAAYAAJ|page=813}}|editor1=National Ocean and Atmospheric Administration (NOAA) |publisher = University of Washington Press|pages = 813–824}}</ref> There have been isolated observations of walruses preying on seals up to the size of a {{convert|200|kg|lb|abbr=on}} [[bearded seal]].<ref>{{cite journal|url=http://www.science.smith.edu/msi/pdf/i0076-3519-238-01-0001.pdf| vauthors = Fay FH | title=''Odobenus rosmarus''|journal=Mammalian Species|year=1985|pages=1–7|doi=10.2307/3503810|issue=238|jstor=3503810|url-status=dead|archive-url= https://web.archive.org/web/20130513012035/http://www.science.smith.edu/msi/pdf/i0076-3519-238-01-0001.pdf |archive-date=13 May 2013}}</ref><ref name="Spitsbergen_Online">{{cite web|title= Photos from Trips to Pyramiden |url=http://www.spitsbergentravel.com/Start/About-Svalbard/Geography/Svalbard-Videos-Pyramiden/Photos-from-Pyramiden/ | archive-url = https://web.archive.org/web/20131203001719/http://www.spitsbergentravel.com/Start/About-Svalbard/Geography/Svalbard-Videos-Pyramiden/Photos-from-Pyramiden/ | archive-date = 3 December 2013 |publisher=Spitsbergen Online}}</ref> Rarely, incidents of walruses preying on seabirds, particularly the [[Brünnich's guillemot]] (''Uria lomvia''), have been documented.<ref>{{cite journal| vauthors = Mallory ML, Woo K, Gaston A, Davies WE, Mineau P |year = 2004|title = Walrus (Odobenus rosmarus) predation on adult thick-billed murres (Uria lomvia) at Coats Island, Nunavut, Canada|journal = Polar Research|volume = 23|issue = 1|pages = 111–114|doi = 10.1111/j.1751-8369.2004.tb00133.x| doi-broken-date=2 November 2024 |bibcode = 2004PolRe..23..111M}}</ref> Walruses may occasionally prey on ice-entrapped [[narwhal]]s and scavenge on whale carcasses but there is little evidence to prove this.<ref name="Narwhals, Narwhal Pictures, Narwhal Facts">{{cite magazine|title=Narwhals, Narwhal Pictures, Narwhal Facts|url=http://animals.nationalgeographic.com/animals/mammals/narwhal/|archive-url=https://web.archive.org/web/20100112221908/http://animals.nationalgeographic.com/animals/mammals/narwhal/|url-status=dead|archive-date=12 January 2010|magazine=National Geographic|date=11 November 2010}}</ref><ref name="Walrus facts">{{cite web|title=Walrus facts|url=http://www.canadiangeographic.ca/article/animal-facts-walrus|publisher=Canadian Geographic|access-date=20 August 2016|date=2016-04-04}}</ref>

===Predators===
Due to its great size and tusks, the walrus has only two natural predators: the [[orca]] and the [[polar bear]].<ref>{{cite web| author  = Mr. Appliance |title=Walrus Predators|url=http://www.walrus-world.com/walrus-predators.html|access-date=10 November 2012|archive-url=https://web.archive.org/web/20130126224852/http://www.walrus-world.com/walrus-predators.html|archive-date=26 January 2013|url-status=dead}}</ref> The walrus does not, however, comprise a significant component of either of these predators' diets. Both the orca and the polar bear are also most likely to prey on walrus calves. The polar bear often hunts the walrus by rushing at beached aggregations and consuming the individuals crushed or wounded in the sudden exodus, typically younger or infirm animals.<ref>{{cite journal| vauthors = Ovsyanikov N |year = 1992|title = Ursus ubiquitous|journal = BBC Wildlife|volume = 10|issue = 12|pages = 18–26}}</ref> The bears also isolate walruses when they [[Overwintering|overwinter]] and are unable to escape a charging bear due to inaccessible diving holes in the ice.<ref>{{cite journal|jstor=3872939|title=Interactions between Polar Bears and Overwintering Walruses in the Central Canadian High Arctic| vauthors = Calvert W, Stirling I |year=1990|pages=351–356|volume=8|journal=Bears: Their Biology and Management |doi=10.2307/3872939 |s2cid=134001816}}</ref> However, even an injured walrus is a formidable opponent for a polar bear, and direct attacks are rare. Armed with its ivory tusks, walruses have been known to fatally injure polar bears in battles if the latter follows the other into the water, where the bear is at a disadvantage.<ref name="North American Bear Center - Polar Bear Facts">{{cite web|title=North American Bear Center – Polar Bear Facts|url=http://www.bear.org/website/bear-pages/polar-bear/22-/70-polar-bear-facts.html|publisher=North American Bear Center|access-date=2 August 2013|archive-url=https://web.archive.org/web/20130524061813/http://www.bear.org/website/bear-pages/polar-bear/22-/70-polar-bear-facts.html|archive-date=24 May 2013|url-status=dead|df=dmy-all}}</ref> Polar bear–walrus battles are often extremely protracted and exhausting, and bears have been known to break away from the attack after injuring a walrus. Orcas regularly attack walruses, although walruses are believed to have successfully defended themselves via counterattack against the larger cetacean.<ref>{{cite journal | vauthors = Jefferson TA, Stacey PJ, Baird RW |title=A review of Killer Whale interactions with other marine mammals: Predation to co-existence |year=1991 |journal=Mammal Review|volume=21|issue=4|page=151 |doi=10.1111/j.1365-2907.1991.tb00291.x |url=http://www.cascadiaresearch.org/robin/kwinteractionsrev.pdf }}</ref> However, orcas have been observed successfully attacking walruses with few or no injuries.<ref>{{cite journal | vauthors = Kryukova NV, Kruchenkova EP, Ivanov DI |title=Killer whales (''Orcinus orca'') hunting for walruses (''Odobenus rosmarus divergens'') near Retkyn Spit, Chukotka|year=2012 |journal=Biology Bulletin|volume=39|issue=9|pages=768–778 |doi=10.1134/S106235901209004X |bibcode=2012BioBu..39..768K |s2cid=16477223}}</ref>