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Article Excerpt
ABSTRACT. Alaska has two polar bear populations: the Southern Beaufort Sea population, shared with Canada, and the Chukchi/Bering Seas population, shared with Russia. Currently a reliable population estimate for the Chukchi/Bering Seas population does not exist. Land-based aerial and mark-recapture population surveys may not be possible in the Chukchi Sea because variable ice conditions, the limited range of helicopters, extremely large polar bear home ranges, and severe weather conditions may limit access to remote areas. Thus line-transect aerial surveys from icebreakers may be the best available tool to monitor this polar bear stock. In August 2000, a line-transect survey was conducted in the eastern Chukchi Sea and western Beaufort Sea from helicopters based on a U.S. Coast Guard icebreaker under the "Ship of Opportunity" program. The objectives of this pilot study were to estimate polar bear density in the eastern Chukchi and western Beaufort Seas and to assess the logistical feasibility of using ship-based aerial surveys to develop polar bear population estimates. Twenty-nine polar bears in 25 groups were sighted on 94 transects (8257 km). The density of bears was estimated as 1 bear per 147 k[m.sup.2] (CV = 38%). Additional aerial surveys in late fall, using dedicated icebreakers, would be required to achieve the number of sightings, survey effort, coverage, and precision needed for more effective monitoring of population trends in the Chukchi Sea.
Key words: aerial survey, Ursus maritimus, polar bear, Beaufort Sea, Chukchi Sea, line transect, icebreaker
RESUME. L'Alaska a deux populations d'ours polaires: celle du sud de la mer de Beaufort, commune avec le Canada, et celle de la mer des Tchouktches / mer de Bering, commune avec la Russie. A l'heure actuelle, on ne possede pas d'estimation fiable de la population de la mer des Tchouktches / mer de Bering. En raison des conditions variables de la glace, de la portee limitee des helicopteres, de la tres grande etendue du domaine vital de l'ours polaire et des conditions meteorologiques particulierement mauvaises--facteurs qui limitent l'acces aux regions eloignees--, il n'est peut-[^.e]tre pas possible d'effectuer des releves aeriens a base terrestre de la population ou des releves par marquage-recapture. Le meilleur outil disponible pour une surveillance continue de cette population d'ours polaires semble donc [^.e]tre le releve de transects effectue depuis les airs par un appareil embarque sur un brise-glace. En ao[^.u]t 2000, un releve de transect a ete effectue dans l'est de la mer des Tchouktches et dans l'ouest de la mer de Beaufort depuis des helicopteres embarques sur un brise-glace de la grade c[^.o]tiere americaine sous les auspices du programme des navires de passage. Les objectifs de cette etude pilote etaient d'estimer la densite de l'ours polaire dans l'est de la mer des Tchouktches et l'ouest de la mer de Beaufort, et d'evaluer la faisabilite logistique de l'utilisation d'helicopteres embarques pour etablir des estimations de la population d'ours polaires. Vingt-neuf ours polaries repartis en 25 groupes ont ete apercus dans 94 transects (8257 km). La densite des ours etait evaluee a 1 animal par 147 k[m.sup.2] (CV = 38%). Il faudrait realiser d'autres releves aeriens a la fin de l'automne, en ayant recours a des brise-glace specialises, pour en arriver au nombre d'observations, aux activites de releves, a la couverture et a la precision necessaires a une surveillance plus efficace des tendances demographiques dans la mer des Tchouktches.
Mots cles: releve aerien, Ursus maritimus, ours polaire, mer de Beaufort, mer des Tchouktches, mer de Bering, transect, brise-glace
Traduit pour la revue Arctic par Nesida Loyer.
INTRODUCTION
The Chukchi/Bering Seas polar bear (Ursus maritimus) population is jointly managed by the United States and the Russian Federation (Lunn et al., 2002). In the United States, the Fish and Wildlife Service (USFWS) is responsible under provisions of the Marine Mammal Protection Act of 1972 (MMPA) to manage polar bear populations within the optimum sustainable population level. Under the MMPA, only Alaska Natives are allowed to hunt polar bears for subsistence needs and for making handicrafts; they currently harvest 60 to 100 bears annually from the Chukchi/Bering Seas polar bear population (Lunn et al., 2002). Russia prohibited polar bear hunting in 1956 in response to population declines caused by overharvest; however, in recent years, an increase in illegal harvest from the Chukchi/Bering Seas stock has been noted (Nikita Ovsyanikov, pers. comm. 2002, 2003). On 16 October 2000, the United States and the Russian Federation signed the Agreement on the Conservation and Management of the Alaska-Chukotka Polar Bear Population (Lunn et al., 2002). The Agreement supports polar bear hunting for subsistence purposes by both Alaskan and Russian Natives, and it provides a framework for the future management, enforcement, and allocation of harvest between the two countries. This agreement requires accurate population data to determine sustainable harvest levels. Although population estimates are available for the Southern Beaufort Sea population of northern Alaska (n = 2272, USFWS, 2002b), population data are limited for the Chukchi/Bering Seas population of western Alaska (McDonald et al., 1999; USFWS, 2002a). In August 2000, we conducted an aerial survey to estimate polar bear density in the eastern Chukchi and western Beaufort Seas and to assess the logistical feasibility of using ship-based aerial surveys for this purpose.
METHODS
Study Area
The aerial survey was conducted in the eastern Chukchi Sea and western Beaufort Sea between 70[degrees] and 75[degrees]30' N latitude and 168[degrees] and 146[degrees] W longitude (Fig. 1). Amstrup et al....
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