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 method
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:
- assess the reliability and logistical constraints of using helicopter
support from an icebreaking vessel;
- determine the feasibility of conducting future surveys from this
- 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
Polar Bears Along the Beaufort Sea Coastline, Alaska, 2000-2002
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
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