Interactions between Polar Bears and Overwintering Walruses in the Central Canadian High Author(s): Wendy Calvert and Ian Stirling Source: Bears: Their Biology and Management, Vol. 8, A Selection of Papers from the Eighth International Conference on Bear Research and Management, Victoria, British Columbia, Canada, February 1989 (1990), pp. 351-356 Published by: International Association of Bear Research and Management Stable URL: http://www.jstor.org/stable/3872939 Accessed: 03/01/2009 20:40

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http://www.jstor.org INTERACTIONSBETWEEN POLAR BEARS AND OVERWINTERINGWALRUSES IN THE CENTRALCANADIAN HIGH ARCTIC

WENDY CALVERT, Canadian Wildlife Service, 5320 122 Street, Edmonton, AB T6H 3S5 IAN STIRLING, Canadian Wildlife Service, 5320 122 Street, Edmonton, AB T6H 3S5 and Department of Zoology, , Edmonton, AB T6G 2E9

Abstract:There are few recordsof predationby polarbears (Ursus maritimus) on walruses(Odobenus rosmarus), although their distributions overlap extensively. During the late winter and early springfrom 1981 through 1989, we recordedinteractions between polar bears and walrusesin the centralCanadian High Arctic, where walrus movementsare severely restrictedin the winterby limited areasof open waterfor breathingand haulout holes. Predatorybehaviour of bearsand anti-predatorbehaviour of walruseswere observed. We found evidence thatpolar bears made woundingbut non-fatalattacks on 3 walruses,killed 3 walruses,and probably killed 4 others. One walrus was frozen out of its breathing hole and vulnerable to predation. Although the vulnerability of walruses to predation would vary with habitats and seasons, it is clear that polar bears are importantpredators of walruses in the centralCanadian High Arctic in late winter-earlyspring.

Int. Conf. Bear Res. and Manage: 8:351-356

Walrusand polar bear distributionsoverlap in a vari- ety of habitats and seasons including the floe edge or drifting pack ice throughout the year in some areas, terrestrialhaulouts where all the ice has melted in the summer,and polynyas of variablesizes duringthe winter. The vulnerabilityof walrusesto predationby polarbears may vary significantly among these sharedhabitats, but thereare few confirmedreports of predation(Perry 1966, Kiliaanand Stirling 1978) andlittle quantitativeinforma- tion about the nature and magnitude of the predation. Most of the observationsof interactionsbetween polar bears and walruses have been made at terrestrialor ice- edge hauloutsor in pack ice. Polar bears are powerful predators,capable of taking large prey such as bearded seals (Erignathusbarbatus) (Stirlingand Archibald 1977) and belugas (Delphinapterus leucas) (Lowry et al. 1987), but walruses are the largest of the polarbear's possible prey, and they are able to use their tusks for defence. Loughrey (1959) felt there was little doubtpolar bearsprey on calves and subadults,but found factual accounts scarce. Fay (1982) statedthat he knew of no confirmed records of predationby bears on walruses. He concludedthat contact between polarbears and walruses occurredmainly in summerand that only younger walruses are really vulnerable to predation. AlthoughFay (1985) listed predationby polarbears as 1 of 3 primarycauses of mortality among walrus calves (along withpredation by killer whales [Orcinusorca] and crushing),he noted that Mansfield (1958) has calculated Fig. 1. Kills or attacks by polar bears on walruses in the Penny Strait and Queens that total of walrus calves is low to Channel area from 1981 through 1988: 1)10 Apr 1981, confirmed kill of young mortality compared adult, found partially eaten, tusks <30 cm; 2) 3 Apr 1982, confirmed kill, 1 large otherpinnipeds.It is hardto assess if this predationwould bear pulling adult walrus (length 247 cm) from hole, 2 walruses hauled out be to the nearby; 3) 26 Apr 1983, evidence of attack but not kill; 4)12 Apr 1984, young adult significant population. female frozen out >2 days, not killed, tusks -20 cm; 5) 19 Mar 1985, possible In the centralCanadian High Arctic, small groups of attack, blood around hole; 6) and 7) 30 Mar 1985, old kill of 1 adult and 1 yearling walruseswinter in a of 50- 100 walrus, carcasses dismembered, adult female polar bear and 2-year cub feeding polynyas, including group on them; 8) 30 Mar 1985, confirmed fresh kill of young female walrus, tusks 10 walruses at the Dundas Polynya at Cape Collins (Fig. 1) cm, 2 adult bears feeding; 9) 11 Apr 1985, possible attack, blood near hole, bear on the northeastern of Dundas Island et al. tracks windblown; 10) 21 Apr 1986, kill of young walrus, length 185 cm, tusks tip (Stirling 3.8 cm; 11) 23 Apr 1987, adult male carcass (length >275 cm, tusks 33 cm) at tide 1981). Open waterwhere walrusescan breatheand feed crack, probably killed by a polar bear, scavenged by many bears. 352 BEARS-THEIR BIOLOGY AND MANAGEMENT

duringthe winteris maintainedthere and at severalother overlookingthe polynya. On an opportunisticbasis, we locations in easternPenny Straitby strongtidal currents recordedthe huntingbehaviour of polarbears, occasional (Tophamet al. 1983). In addition,multiyear floes that interactionsbetween polar bears and walruses, and the become groundedin shallow water in the late summer behaviourof walruseswhile hauledout andvulnerable to throughoutthis regionwill remainfrozen in placethrough predation. the winter. These floes are rockedby tidal currentsand We used a helicopter to survey Penny Strait and winds, creating a border of weaker broken ice where Queens Channelalso. On each survey, we followed the walruses are also able to breathe and haul out. The same generalroute north from the DundasPolynya along walrusesmay remainat these floes for weeks or months the western coast of Devon Island and returnedvia the at a time (Stirlinget al. 1981: Fig. 3). middle of Penny Straitand Queens Channelpast Hyde On 2 occasions,Kiliaan and Stirling (1978) foundlone ParkerIsland, the CheyneIslands, and the northernend of walruses,one an adult,the otheralmost 2-years-old,that Baillie-HamiltonIsland (Fig. 1). The exact routevaried had been attackedand killed by a polarbear at a haulout withinand among years, depending on the distributionof hole. They also reporteda kill by Inuit of a walrus at a walruses,changes in ice conditions,and prevailing weather frozen-overhole, and an observationof an adult walrus conditions. Surveyswere conducted2-6 times each year thathad been attackedby a polarbear but survived. From at approximately2-week intervalsbetween mid-March these observations,they suggested that walruses over- andearly May andcovered a distanceof 150-400 km. We winteringin areas with restrictedbreathing and haulout flew betweenabout 1000 and2000 hrsEST, at an altitude sites might be more vulnerable to predation,and that of about70 m and an airspeedof about 100 km/hr. The predationby polar bears might be more frequent than surveyswere primarilyto map walrusand polynya distri- previouslyseemed apparent.This paperpresents obser- bution and recordthe underwatervocalizations of wal- vations of predationby polar bears on both young and ruses and seals for anotherstudy, but we also noted all adultwalruses in a polynyaarea during the late winterand polar bears,polar bear tracks(and an estimationof their early spring. freshness), and any indicationsof interactionsbetween We gratefully acknowledge the supportof the Polar polar bears and walruses. When a walrus carcass was ContinentalShelf Project,the CanadianWildlife Service, found, ice conditionsand presenceof bears were noted. World Wildlife Fund (Canada),and the Departmentof When possible, measurementsand photographswere Fisheriesand Oceans. We thankJ.J. Burs, Fairbanks;T. taken, and a tooth was collected for age determination. Eley andK. Frost,Alaska Department of Fish andGame, Fairbanks;D. Grant,Yellowknife; and M.Taylor, North- RESULTS AND DISCUSSION west TerritoriesDepartment of Renewable Resources, to use their observations. In for permission unpublished Sightings of Polar Bears the field, we had the help and good company of D. Polarbears den, huntand feed on seals, andmate in the H. I. D. N. B. Andriashek, Cleator, Cote, Keith, Lunn, study area(Stirling et al. 1984), andbears of all age- and J.J. A. Sjare, and C. Spencer. S.C. Amstrup, Burs, sex-classes were seen on the ice adjacentto the polynya Derocher,and T.G. Smith providedmany helpful com- where the walruseshaul out to rest. Polar bears hunted earlier draftof this S. MacEachran ments on an paper. along pressureridges and small refrozen cracks in the drew the figure. area for the subniveanbreathing holes and birthlairs of ringedand beardedseals. Bears also searchedalong the METHODS edges of the main polynya and smaller areas of open We conductedstudies of the biological importanceof water and investigatedthe breathingholes used by wal- the Dundas Polynya to overwinteringmarine mammals ruses, their haulout sites, and the hauled-out walruses in the late winter and early spring from 1981 through themselves. 1989. Our observationsconcentrated on walruses and In most years, bearswere observedevery 2-4 days at weresome when polarbears and to a lesser extent on ringed seals (Phoca CapeCollins (Table 1),but there periods undoubt- hispida) and beardedseals. none were seen for severalweeks. Therewere We were able to observe polarbears and walrusesup edly some bears presentin the area that were not seen. to 6 km away almost continuallyduring daylight hours. There was no obvious trend in numbersor correlations recorded. Visibility was occasionally obscured by poor weather, amongmonths or yearsand the numberof bears but it was rarely <2 km. The animals appearedundis- The variationin numbersof bearsseen amongyears was or turbedby our presence in a hut at the top of a 90-m cliff also independentof the numberof walrusespresent the POLARBEAR AND WALRUS INTERACTIONS * Calvert and Stirling 353

Table 1. Number of days of observation at the Dundas Polynya at Cape Collins ice at the edge of the breathing holes is smooth and and number of polar bears seen. slipperyfrom the movementsof water and animals,and is often thin enough to bend and slope into the water Year Month Daysof Bears Minimum beneaththe of 1 walrus. In these circumstances, observation seen bears/day weight a slight movementby a walrusallows it to slide into the 1981 Apr 25 9 0.36 water. 1982 Apr 19 5 0.26 Females and calves usually hauledout in groupsof 4 or more, were more vigilant than all-male groups, and 1983 Apr 19 4 0.21 were easily disturbed.We sometimessaw themrush into 1984 Apr 23 1 0.04 the water even when we could see no cause for the 1985 Mar 20 6 0.30 disturbance.In groupsof females and young, the calves Apr 13 2 0.15 were as near, or nearer,the water than the adults. Al- 1986 Apr 26 14 0.54 thoughcalves often slept, the females remainedalert. In adultmale walruseswere muchless 1987 Feb 6 1 0.17 contrast, easily Mar 31 21 0.68 disturbedwhen hauledout andmore reluctant to enterthe Apr 30 10 0.33 water. People or bearscould often approachto within a May 20 5 0.25 few metres. When approachedclosely, large male wal- 1988 Feb 17 27 1.59 ruses often backed into the water slowly, ready to fight Mar 31 4 0.13 with their tusks if necessary. 30 12 0.40 Apr Bearsare able to use roughice for cover to close to May 9 0 0 get a walrus before charging, which could be particularly 1989 Feb 20 3 0.15 to subadultanimals that are less of Mar 31 0 0 dangerous capable off a bear. Smaller walruses hauled Apr 26 1 0.04 fending up alone often enteredthe waterhead-first shortly after a human, or in some observed instances, a bear, was detected. If several male walruses were hauled out together, the size of the polynya (unpubl.data). Althoughthere was a largestmales tendedto lie furthestfrom the hole, with the walrus carcass immediatelybelow the hut in 1987, and subadultsnearest. The subadultswere more restless and bears scavenged there regularly,we saw them no more possibly more observantof predators.The combination often that year than in 1988. It is likely that the number of being watchful and nearest the water probably in- of bearsseen at the DundasPolynya is affected more by creasedtheir chances of escaping safely from a charging seal densities in nearbyareas such as WellingtonChan- bear that must first face the tusks of the larger male nel, which has high ringedseal densities (Kingsley et al. walruses. 1985), than by ice conditions or walrus numbersin the Stirling (1984) observed 20 or more walrusesgive a PioneerChannel. coordinatedthreat display to a young adultfemale polar bearthat had been huntingalong the edge of the Dundas Sightings and Behaviour of Walruses Polynya and scaringhauled-out walruses into the water. The presenceof walrusesin and adjacentto the Dun- The walruses swam rapidly toward the bear and a few das Polynya was confirmed by continual underwater larger individualsat the front of the group slapped the vocalizations heard on our monitoring and recording waterwith their hind flippers and made sufficient noise to equipment.Walruses were also heardor seen throughout frightenthe bear from the area. eastern Penny Straitand Queens Channelon most heli- All these observationssuggest thatpredation by polar copter surveys. Even in mid-February,some walruses bears on walruses, or at least the threat of it, occurs hauledout on most days when winds were light, andafter frequentlyenough that walruses have evolved behav- early April, over 60 animals, scattered in many small iouralresponses to reducethe risk. However,unlike the groups,were countedseveral times fromthe observation other northernice-inhabiting seals, which defecate pre- hut on sunny calm days. dominantlyin the water, possibly to reduce their scent All walruseswe approachedon the sea ice or observed arounda breathinghole (Stirling 1977), walrusesoften from the hutor the helicopterwere withina metreof their defecate on the ice surface. Possibly this indicatespolar haulout holes, often with their hind limbs (more fre- bearsare not as seriousa threatto walrusesas they are to quently than theirforelimbs) partially in the water. The the smallerphocids. 354 BEARS-THEIR BIOLOGYAND MANAGEMENT

Evidence of Predation Barrow, Alaska, K. Frost (pers. commun.) observed a Between 1981 and 1989, we found evidence of 10 large male polar bear dragging a medium-sized adult walrusesthat we believe were woundedor killed by polar male walrus,with approximately25-cm tusks,out of the bears(Fig. 1). The dateof deathis knownonly for the kill water at the edge of a floe. The walrus was bleeding at site 2 wherethe bearwas observedkilling a largeadult profusely, indicating it had just been killed. It had male walrusand pulling it fromits haulouthole (D. Grant, apparentlybeen alone at the edge of a floe in an areaof pers. commun.). All the othercarcasses were frozen and brokenice, and was farthereast than walrusesnormally partially eaten when found. Wind-blown snow often occur in that region. obscuredthe beartracks in the area,making it difficultto reconstructthe attack, but the presence of bear claw Vulnerabilityto Predation marks, blood smears, and scratching marks made by Certainaspects of the sea ice habitat in the central walrusflippers indicated an interactionhad occurred. In CanadianHigh Arctic may make walrusesmore vulner- 2 cases, the haulouthole nearthe carcasswas still unfro- able thanthey are in the packice. In particular,breathing zen, suggestingthe walruseswere killed on the ice before andhaulout holes areoften small, proneto freezingover, they could escape, andthat freezing-out was not a factor. andprobably more difficult for severalanimals to escape There was blood soaked into the snow beneaththe head throughquickly. Also, the high relief of multiyearfloes of the adult male found dead in February 1987 at the or of active pressureice nearpolynyas gives good cover shorelinetidal cracksbelow our camp (site 11), suggest- for stalkingbears. ing thata bearkilled him, thoughpossibly only afterthe Between freeze-upand break-up,movements of wal- ice shifted and he was frozen out. At 6 of 7 sites of kills ruses in our study area are restricted because of the or probablekills, polarbears were feeding on the carcass paucityof breathingholes andthe small size of polynyas. when it was sighted, but we did not know if they were The dependence on groundedsmall multiyearfloes to predatorsor scavengers. breathe by and haul out on (e.g., Stirling et al. 1981: Although walruses hit each other on the neck and Fig. 3) could markedly reduce movements during the shoulder with their tusks when fighting, they are pro- winter, especially in years when there are few floes tected by a thick skin. Most wounds are superficialand present. This reducedability to move elsewhere could bleeding is limited. At site 3, there was no carcass, but makewalruses vulnerable to a high degreeof harassment from the tracks we determineda bear had stalked the by polarbears. Forexample, on 24 April 1980, I. Stirling walrus from a distance, using a ridge of rough ice to and T.G. Smith (pers. commun.) found a subadultmale conceal itself until it was close enough to charge the walrus, with 20-cm tusks, hauled out beside an open walrusas it lay by its haulouthole at the edge of a frozen- breathinghole at the edge of a small (5-m diameter) in multiyearfloe. There was blood sprayedon the snow iceberg frozen into the annual ice. The walrus was at 3 separatebreathing holes aroundthe edge of the floe covered with frost and ice, suggestingit had been hauled in a patternthat probablyresulted from the blood being outfor severaldays. The walruscould have been stranded mixed with expiredair from the nostrils. We suspectthe there;no otherwalruses, breathing holes, or open cracks bearhad time to hit the walruson the head with a paw, or were found in the area. bite it on the face or nose, before the walrusescaped into Walrusesthat haul out to rest and sleep adjacentto the water. The bear's trackswent to all 3 holes, suggest- small breathingholes also increasetheir vulnerability to of the hole ing that it tried unsuccessfullyto capturethe walrusfor predationbecause of the possibility being some time afterthe initial attempt,possibly because the closed by ice movement,or freezingover in cold weather. had wounded animal kept resurfacingat different holes to Onedead walrus found by Kiliaanand Stirling (1978) breathe. We also found unusualamounts of blood that blood on the surfaceof her haulouthole, suggesting she a bear after her hole had appearedto be from woundingattacks at breathingholes may have been killed by polar at sites 5 and 9, but it was difficult to interpretwhat had frozen over. In April 1981, M. Taylor (pers. commun.) walrus with about 10-cmtusks, happenedbecause most of the tracks were covered by founda subadult carcass, driftedsnow. about20 km southof Maxwell Bay on the southcoast of was no water and it In spring 1976, T. Eley (Alas. Dep. Fish and Game, Devon Island. There open nearby a bearafter Fairbanks,unpubl. data) tracked polar bears as partof a appearedthe animalhad been killed by polar The adultfemale first observed at site study on polar bear predation. He recorded 1 kill of a it becamestranded. on 12 1984 was in an areaof thin but un- young yearlingwalrus by a polarbear at Cape Lisbure, 4 (Fig. 1) April Alaska. On 13 June 1987, about60 km northeastof Point brokenice near shore. We back-trackedher in a nearly POLARBEAR AND WALRUSINTERACTIONS * Calvert and Stirling 355 straightline formore than 6 km offshorewithout reaching parison,but we suspectthis is a higherencounter rate than the beginningof hertrail. In thatdistance, we counted 10 occurs in the pack ice. Partof the reasonthe relationship spots where she hadrested long enoughto melt a depres- is not betterdocumented is that most areas where the 2 sion into the ice, suggesting she had travelledacross the species overlapare generally inaccessible, so encounters ice for at least 1 andpossibly more days. She did notmove are simply not recorded. Polar bears are often sighted fartherand was at the same site near shorethe following near aggregations of walruses in the ice front of the day, still apparentlyhealthy and making defending lunges ChukchiSea duringmid-summer and early autumnsur- at us with hertusks. Whenthat area was next searched25 veys (J.J.Burs, pers.commun.) but there are few dataon April, the only open water within 10 km was a 500-m kills. Althoughencounter and predation rates likely vary diameterpolynya within 1 km of whereshe was last seen. among differenthabitats, we suggest thatpolar bears are This polynya recursat the same locationeach year and it importantpredators of walruses in our study area. The is possible she knew the areaor detectedthe thinnerice. dataalso suggest thatsubadult walruses are most vulner- We foundno sign of bloodor otherevidence she hadbeen able, but thatlarge male bearsare capableof also killing attackedwhile frozen out. adult male walruses. Polar bears may also kill more Most authorssuggest polarbears prey on young wal- walruses in pack ice situations than has been reported ruses only (Loughrey 1959, Fay 1985). This results, at previously. least in part,from the perceptionthat polar bears cannot kill or do so with large walruses, only great difficulty. LITERATURECITED This impressionis reinforcedby anecdotalsuggestions EARLE, M. 1987. A flexible body mass in social carnivores. that a large walrus may occasionally kill an attacking Am.Nat. 129:755-760. polar bear (Freuchen 1935, Kiliaan and Stirling 1978). FAY, F.H. 1982. Ecologyand biology of the Pacificwalrus, However, the relationshipbetween the weight of a soli- Odobenusrosmarus divergens Illiger. North Am. Fauna 74:1-279. tary predatorand the maximum size of prey regularly .1985. Odobenus killed a adultmale bear should be rosmarus.Mamm. Species 238:1-7. predicts 400-kg polar FREUCHEN,P. 1935. Mammals, Part II. Field notes and able to kill in excess of 600 That prey kg (Earle 1987). biologicalobservations. Rep. Fifth Thule Expedition would includeadult walruses. The 2 adultmale walruses 1921-1924.2:68-278. observedbeing draggedfrom the water(Fig. 1, site 2; K. KILIAAN,H.P.L., ANDI. STIRLING.1978. Observations on Frost, pers. commun.) were both killed by single large, overwintering walruses in the eastern Canadian High Arctic.J. Mammal.59:197-200. probablymale, polar bears. Presumedadult male polar KINGSLEY,M.C.S., I. STIRLING,AND W. CALVERT.1985. The bears have also been recorded and from killing hauling distributionand abundance of sealsin theCanadian High the wateradult belugas weighing over 600 kg (Lowry et Arctic,1980-82. Can. J. Fish.Aquat. Sci. 42:1189-1210. al. 1987) and adult female narwhals (Monodonmono- LOUGHREY,A.G. 1959. Preliminary investigation of the ceros) (Smith and Sjare 1990). We suggest female polar Atlanticwalrus Odobenus rosmarus rosmarus (Linnaeus). bears with cubs and subadult bears seen on Can.Wildl. Serv. Wildl.Manage. Bull. Ser. 1. 14:1-123. feeding LOWRY,L.F., J.J. BURNS,AND R.R. NELSON.1987. Polar walruscarcasses were Polarbears are bear, only scavenging. Ursus maritimus,predation on belugas, Delphinapterus opportunistichunters, however, and we have observed leucas, in the Bering and Chukchiseas. Can. Field-Nat. bearsof all age- andsex-classes stalkwalruses; a subadult 101:141-146. or young adult bear would attemptto kill a walrusif the MANSFIELD,A.W. 1958. The biology of the Atlantic walrus conditions were Odobenus rosmarus rosmarrus(Linnaeus) in the eastern right. CanadianArctic. Fish. Res. Board walruses not be Can., ManuscriptRep. Although may killed frequently,the Ser. (Biol.) 653:1-146. returnto a bear from energetic killing one mightjustify PERRY,R. 1966. The worldof the polarbear. Univ. Washing- the amount of time spent unsuccessfully investigating ton Press, Seattle. 195pp. and stalkinghauled-out animals. A carcasscould be fed SMITH,T.G., ANDB. SJARE.1990. Predationof odontocete whales bears in nearshoreareas of the upon for a protractedperiod by a large bear even when by polar Canadian High Arctic. Arctic 43:In Press. scavenged other bears. For the carcass by example, STIRLING,1. 1984. A groupthreat display given by walrusesto below our observation hut was already partially eaten a polar bear. J. Mammal.65:352-353. when we occupied the camp on 23 February1987, but .1977. Adaptationsof Weddell and ringed seals to bearscontinued to feed on it until late April. exploit polarfast ice habitatin the presenceor absence of land 741-748 in G.A. Fromour observations at the Dundas Polynya (Table 1), predators.Pages Llano,ed. Adap- tationswithin antarctic ecosystems. Proc. Third it seems possible a walruscould see a bear few Sympo- polar every sium on AntarcticBiology. Gulf Publ.Co., Houston, days throughoutthe winter. We have no data for com- Texas. 1252pp. 356 BEARS-THEIR BIOLOGY AND MANAGEMENT

_ , ANDR. ARCHIBALD.1977. Aspects of predation of seals tions in the CanadianHigh Arctic. Pages 201-222 in R. by polar bears. J. Fish. Res. BoardCan. 34:1126-1129. Olsen, R. Hastings,and F. Geddes,eds. Northernecology _ , H. CLEATOR,AND T.G. SMITH. 1981. Marine mammals. and resourcemanagement. Univ. AlbertaPress, Edmon- Pages 45-58 in I. Stirling,and H. Cleator,eds. Polynyasin ton. 438pp. the CanadianArctic. Can. Wildl. Serv. Occas. Pap. 45. TOPHAM, D.R., R.G. PERKIN, S.D. SMITH, R.J. ANDERSON, AND 70pp. G. DENHARTOG. 1983. An investigation of a polynya in , W. CALVERT, AND D. ANDRIASHEK. 1984. Polar bear the CanadianArchipelago: 1. Introductionand oceanog- (Ursus maritimus)ecology andenvironmental considera- raphy. J. Geophys. Res. 88:2888-2899.