USFWS
Marine Mammals Management
Alaska Region

 

Polar Bear

Aerial Surveys

Polar Bears in the Chukchi/Bering Seas, 2000

The Marine Mammal Protection Act requires FWS to identify and manage polar bear populations at optimum sustainable levels. To accomplish this, population parameters, such as size, status, and trend, must be known. Population size estimates are available for the southern Beaufort Sea population of polar bears in northern Alaska, but insufficient funding and logistical constraints have limited the success of obtaining this type of information in the Chukchi/Bering seas.

Results from studies conducted in 1987 and 1994 showed that aerial surveys could be a useful Geoff York/USGS-BRDmethod to assess density estimates for polar bear populations in the Bering, Chukchi, and western Beaufort Seas if surveys were conducted at the ice edge in late summer-early fall, when bears are most concentrated. Based on this information, the FWS partnered with the U.S. Coast Guard in August 2000 to conduct a pilot polar bear survey, using the Coast Guard’s ice-breaking vessel, the Polar Star, and its two ship-based Delphine 65 helicopters.

The objectives of the pilot study were to:

  1. assess the reliability and logistical constraints of using helicopter support from an icebreaking vessel;
  2. determine the feasibility of conducting future surveys from this platform; and
  3. develop a population density estimate.

The study area was defined as an area between the International Date Line (west) and 147° longitude (east), and the pack ice edge (south) and 75° latitude (north). Aerial surveys were conducted between August 2-28, 2000. Twenty-nine polar bears were sighted on 94 transects covering an area of 8,257 km. Density analyses indicate that the density of polar bears in the study area ranged from 71-313 km2/bear.

Results from this pilot study indicate that using an icebreaker with ship-based helicopters is a promising tool for future surveys in the Chukchi Sea. The Coast Guard provided excellent logistical support; however, several hurdles must be overcome to derive more reliable density estimates, e.g. more bears need to be encountered in order for the statistical tests to be reliable; better correction factors need to be developed for bears missed by observers; and icebreakers for future surveys must be obtained. The FWS continues to seek opportunities to conduct a ship-based aerial survey that extends into the western Chukchi Sea to derive a population estimate for the Chukchi/Bering seas population of polar bears.

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Polar Bears Along the Beaufort Sea Coastline, Alaska, 2000-2002

survey area 2001

The FWS, in cooperation with BP Exploration and LGL Research Associates, conducted aerial surveys for polar bears along the Beaufort Sea coastline of Alaska in 2000-2002.

The purpose of conducting aerial coastal surveys is to determine the frequency, timing, and location of polar bear use of coastal habitats and barrier islands during the open water period. The information provides the basis for developing specific mitigation measures that help conserve polar bears and their habitat, and also provides for safety and protection of North Slope workers by minimizing bear-human interactions. Information can also be used in oil spill response plans.

Results for surveys flown in 2000-2001 are described below.

Age and Sex Composition: In 2000, of the 232 polar bears observed, approximately 23% were identified as adult females, 3% as adult males, 5% as sub-adult bears, 9% as yearlings, and 21% as cubs-of-the-year. Family groups (adult females with dependent young) comprised approximately 53% of the total number of animals observed. Approximately 39% of the animals sighted were of unknown sex; of these, approximately 11% were identified as adults.

In 2001, Of the 97 bears observed, approximately 20% were identified as adult females, 3% as adult males, 14% as yearlings, and 16% as cubs-of-the-year. No sub-adults were identified. Family groups comprised approximately 50% of the total number of animals observed. Approximately 47% of the animals sighted were of unknown sex; of these, approximately 8% were identified as adults. The sex/age composition of observed bears appeared to be relatively consistent between years with a slight decrease in numbers of observed family groups.

Density (Frequency Rate of Encountering Polar Bears): The frequency rate of polar bears encountered along the survey route were compared among the following four segments: 1) Atigaru Point to Prudhoe Bay; 2) Prudhoe Bay to Brownlow Point; 3) Brownlow Point (the western tip of) to Barter Island; and 4) Barter Island to Jago Spit. Comparison of 2000 and 2001 results indicate that polar bears were less abundant throughout the study area in 2001 than in 2000. In both years, the segment with the highest encounter rate was between Barter Island and Jago Spit; the lowest was between Atigaru Point and Prudhoe Bay.

Habitat Use: As expected, the amount of open water decreased and the amount of shore-fast ice increased over the survey period during both years. In both years polar bears were most frequently seen on barrier islands (72% in 2000 and 69% in 2001). In 2001, the relative amount of mainland use decreased and the relative amount of shore-fast ice use increased.

Survey results confirm that large numbers of polar bears aggregate around Barter and Cross Islands, probably due to the presence of hunter-harvested bowhead whale remains which provide an alternate food source for polar bears. The age and sex composition of large aggregations of bears is difficult to assess by air, especially when animals are laying down. The FWS conducted additional surveys in 2002 and 2003; results will be presented as soon as they are available.

 

Last updated: September 10, 2008