Our Liviiifi Resources — Alaska 



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The polar bear (Ursiis maiitimus) is the top 

 predator of the Arctic marine ecosystem. 

 Polar bears prey primarily on ringed seals 

 (Plioca hispida) and bearded seals (Erignathus 

 barhatus). which live exclusively on the sea ice 

 (Smith and Stirling 1975: Stirling and 

 Archibald 1977: Smith 1980), but they also can 

 kill larger prey such as walruses (Odobemts ros- 

 nuiriis) and white whales {Delphmapteriis leii- 

 cas: Kiliaan and Stirling 1978: Fay 1982: 

 Calvert and Stirling 1990: Stirling and Derocher 

 1990). 



Polar bears move several thousand kilome- 

 ters annually and over years occupy areas that 

 can exceed 500,000 km- (nearly 200,000 mi": 

 Gainer et al. 1990: Amstrup and Dumer, unpub- 

 lished data: Fig. 1 ). Polar bears are circumpolar 

 in the northern hemisphere, but they live in sev- 

 eral largely discrete subgroups, rather than one 

 homogeneous pan-Arctic population 



(Harington 1968). We used radio telemetry to 

 show that two partially discrete subpopulations 

 live adjacent to Alaska (Fig. 2). One subpopula- 

 tion occurs largely in the Beaufort Sea of 

 Alaska and neighboring Canada. Animals from 

 this Beaufort Sea stock appear to spend about 

 25% of their time along the Chukchi Sea coast 

 of northwestern Alaska (Amstrup and Durner, 

 unpublished data). The Chukchi Sea subpopula- 

 tion winters in the northern Bering Sea and 

 southern Chukchi Sea adjacent to Russia and 

 western Arctic Alaska, and its members seldom 

 enter the Beaufort Sea (Fig. 2). 



Low reproductive rates make polar bears 

 vulnerable to excessive hunting. Yankee 

 whalers, local resident Native people, and aeri- 

 al hunters reduced numbers and local distribu- 

 tions of polar bears in many areas (Leffingwell 

 1919: Hanna 1920: Lono 1970: Mowat l984: 

 Amstrup et al. 1986). Polar bears are also poten- 

 tially vulnerable to industrial developments and 

 other human activities that have increased in the 

 Arctic recently (Lentfer 1983: Amstrup et al. 

 1986). Polar bears and the seals on which they 

 prey may also be among the first species to 

 show effects of climate warming and other 

 global changes (Stirling and Derocher 1993). 



In 1973 the five nations within whose 

 boundaries polar bears occur negotiated the 

 International Agreement on Conservation of 

 Polar Bears. The agreement, ratified in 1976, 

 prohibited the taking of polar bears by hunters 

 in aircraft or large motor vessels, creating a de 

 facto sanctuary in active offshore ice habitats. 

 The agreement required each nation to conduct 

 a research program and coordinate management 

 and research, with other jurisdictions, for popu- 

 lations that overlap international boundaries. 



In the United States, the agreement was 

 implemented by enactment of the Marine 



Mammal Protection Act of 1972. Under the act, 

 only Native people living along the Alaska coast 

 were allowed to take polar bears. The act, how- 

 ever, removed restrictions on the take of cubs 

 and females with cubs and the mandatory 

 reporting requirement of the state's manage- 

 ment program. Despite elimination of many 

 management tools, the act required the 

 Department of the Interior to manage polar 

 bears within the bounds of optimum sustainable 

 population levels. 



Counting Polar Bears 



We captured polar bears and marked them 

 with ear tags and tattoos. Selected adult female 

 polar bears also were fitted with radio collars. 

 Captured bears were weighed and measured, 

 and a vestigial premolar tooth was removed for 

 age detennination (Stirling et al. 1975: Hensel 

 and Sorensen 1980). Each year, we tallied new 

 captures and recaptures, and updated capture 

 and reproductive histories of previously marked 

 animals. We constiucted life tables from the 

 capture data (Seber 1973: Caughley 1977), and 

 estimated survival rates from radio-collared 

 bears and their young (Kaplan-Meier method: 

 Pollock et al. 1989). We examined patterns of 

 population size with matrix models (Leslie 

 1945, 1948). 



Polar Bears in 

 Alaska 



by 



Steven C. Amstrup 



Gerald W. Garner 



George M. Durner 

 National Biological Sen'ice 



Population Estimates 



Recaptures were too few in the Chukchi Sea 

 to evaluate population status for that subpopula- 

 tion. Many data were available from the 



Fig. 1. Outlines of the annual 

 activity areas for one radio-col- 

 lared polar bear (Ursus maritimus) 

 monitored during 4 consecutive 

 years. The boundaries of the mul- 

 tiyear activity area enclosed 

 .SI 7.000 km- (about 200,000 mi-). 



