Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for the Polar Bear (Ursus maritimus) Throughout Its Range, 28212-28303 [E8-11105]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 73, Number 95 (Thursday, May 15, 2008)]
[Rules and Regulations]
[Pages 28212-28303]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-11105]



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Part II





Department of the Interior





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Fish and Wildlife Service



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50 CFR Part 17



Endangered and Threatened Wildlife and Plants; Determination of 
Threatened Status for the Polar Bear (Ursus maritimus) Throughout Its 
Range; Final Rule

Federal Register / Vol. 73 , No. 95 / Thursday, May 15, 2008 / Rules 
and Regulations

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[FWS-R7-ES-2008-0038; 1111 FY07 MO-B2]
RIN 1018-AV19


Endangered and Threatened Wildlife and Plants; Determination of 
Threatened Status for the Polar Bear (Ursus maritimus) Throughout Its 
Range

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine 
threatened status for the polar bear (Ursus maritimus) under the 
Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et 
seq.). Polar bears evolved to utilize the Arctic sea ice niche and are 
distributed throughout most ice-covered seas of the Northern 
Hemisphere. We find, based upon the best available scientific and 
commercial information, that polar bear habitat--principally sea ice--
is declining throughout the species' range, that this decline is 
expected to continue for the foreseeable future, and that this loss 
threatens the species throughout all of its range. Therefore, we find 
that the polar bear is likely to become an endangered species within 
the foreseeable future throughout all of its range. This final rule 
activates the consultation provisions of section 7 of the Act for the 
polar bear. The special rule for the polar bear, also published in 
today's edition of the Federal Register, sets out the prohibitions and 
exceptions that apply to this threatened species.

DATES: This rule is effective May 15, 2008. The U.S. District Court 
order in Center for Biological Diversity v. Kempthorne, No. C 08-1339 
CW (N.D. Cal., April 28, 2008) ordered that the 30-day notice period 
otherwise required by the Administrative Procedure Act be waived, 
pursuant to 5 U.S.C. 553(d)(3).

ADDRESSES: Comments and materials received, as well as supporting 
scientific documentation used in the preparation of this rule, will be 
available for public inspection, by appointment, during normal business 
hours at: U.S. Fish and Wildlife Service, Marine Mammals Management 
Office, 1011 East Tudor Road, Anchorage, AK 99503. Copies of this final 
rule are also available on the Service's Marine Mammal website: https://
alaska.fws.gov/fisheries/mmm/polarbear/issues.htm.

FOR FURTHER INFORMATION CONTACT: Scott Schliebe, Marine Mammals 
Management Office (see ADDRESSES section) (telephone 907-786-3800). 
Persons who use a telecommunications device for the deaf (TDD) may call 
the Federal Information Relay Service (FIRS) at 1-800-877-8339, 24 
hours a day, 7 days a week.

SUPPLEMENTARY INFORMATION: 

Background

    Information in this section is summarized from the following 
sources: (1) The Polar Bear Status Review (Schliebe et al. 2006a); (2) 
information received from public comments in response to our proposal 
to list the polar bear as a threatened species published in the Federal 
Register on January 9, 2007 (72 FR 1064); (3) new information published 
since the proposed rule (72 FR 1064), including additional sea ice and 
climatological studies contained in the Intergovernmental Panel on 
Climate Change (IPCC) Fourth Assessment Report (AR4) and other 
published papers; and (4) scientific analyses conducted by the U.S. 
Geological Survey (USGS) and co-investigators at the request of the 
Secretary of the Department of the Interior specifically for this 
determination. For more detailed information on the biology of the 
polar bear, please consult the Status Review and additional references 
cited throughout this document.

Species Biology

Taxonomy and Evolution

    Throughout the Arctic, polar bears are known by a variety of common 
names, including nanook, nanuq, ice bear, sea bear, isbj[oslash]rn, 
white bears, and eisb[auml]r. Phipps (1774, p. 174) first proposed and 
described the polar bear as a species distinct from other bears and 
provided the scientific name Ursus maritimus. A number of alternative 
names followed, but Harington (1966, pp. 3-7), Manning (1971, p. 9), 
and Wilson (1976, p. 453) (all three references cited in Amstrup 2003, 
p. 587) subsequently promoted the name Ursus maritimus that has been 
used since.
    The polar bear is usually considered a marine mammal since its 
primary habitat is the sea ice (Amstrup 2003, p. 587), and it is 
evolutionarily adapted to life on sea ice (see further discussion under 
General Description section). The polar bear is included on the list of 
species covered under the U.S. Marine Mammal Protection Act of 1972, as 
amended (16 U.S.C. 1361 et seq.) (MMPA).
    Polar bears diverged from grizzly bears (Ursus arctos) somewhere 
between 200,000 and 400,000 years ago (Talbot and Shields 1996a, p. 
490; Talbot and Shields 1996b, p. 574). However, fossil evidence of 
polar bears does not appear until after the Last Interglacial Period 
(115,000 to 140,000 years ago) (Kurten 1964, p. 25; Ingolfsson and Wiig 
2007). Only in portions of northern Canada, Chukotka, Russia, and 
northern Alaska do the ranges of polar bears and grizzly bears overlap. 
Cross-breeding of grizzly bears and polar bears in captivity has 
produced reproductively viable offspring (Gray 1972, p. 56; Stirling 
1988, p. 23). The first documented case of cross-breeding in the wild 
was reported in the spring of 2006, and Wildlife Genetics International 
confirmed the cross-breeding of a female polar bear and male grizzly 
bear (Paetkau, pers. comm. May 2006).

General Description

    Polar bears are the largest of the living bear species (DeMaster 
and Stirling 1981, p. 1; Stirling and Derocher 1990, p. 190). They are 
characterized by large body size, a stocky form, and fur color that 
varies from white to yellow. They are sexually dimorphic; females weigh 
181 to 317 kilograms (kg) (400 to 700 pounds (lbs)), and males up to 
654 kg (1,440 lbs). Polar bears have a longer neck and a proportionally 
smaller head than other members of the bear family (Ursidae) and are 
missing the distinct shoulder hump common to grizzly bears. The nose, 
lips, and skin of polar bears are black (Demaster and Stirling 1981, p. 
1; Amstrup 2003, p. 588).
    Polar bears evolved in sea ice habitats and as a result are 
evolutionarily adapted to this habitat. Adaptations unique to polar 
bears in comparison to other Ursidae include: (1) White pelage with 
water-repellent guard hairs and dense underfur; (2) a short, furred 
snout; (3) small ears with reduced surface area; (4) teeth specialized 
for a carnivorous rather than an omnivorous diet; and (5) feet with 
tiny papillae on the underside, which increase traction on ice 
(Stirling 1988, p. 24). Additional adaptations include large, paddle-
like feet (Stirling 1988, p. 24), and claws that are shorter and more 
strongly curved than those of grizzly bears, and larger and heavier 
than those of black bears (Ursus americanus) (Amstrup 2003, p. 589).

Distribution and Movements

    Polar bears evolved to utilize the Arctic sea ice niche and are 
distributed throughout most ice-covered seas of the Northern 
Hemisphere. They occur throughout the East Siberian, Laptev, Kara, and 
Barents Seas of Russia; Fram Strait (the narrow strait between northern 
Greenland and Svalbard),

[[Page 28213]]

Greenland Sea and Barents Sea of northern Europe (Norway and Greenland 
(Denmark)); Baffin Bay, which separates Canada and Greenland, through 
most of the Canadian Arctic archipelago and the Canadian Beaufort Sea; 
and in the Chukchi and Beaufort Seas located west and north of Alaska.
    Over most of their range, polar bears remain on the sea ice year-
round or spend only short periods on land. However, some polar bear 
populations occur in seasonally ice-free environs and use land habitats 
for varying portions of the year. In the Chukchi Sea and Beaufort Sea 
areas of Alaska and northwestern Canada, for example, less than 10 
percent of the polar bear locations obtained via radio telemetry were 
on land (Amstrup 2000, p. 137; Amstrup, USGS, unpublished data); the 
majority of land locations were bears occupying maternal dens during 
the winter. A similar pattern was found in East Greenland (Wiig et al. 
2003, p. 511). In the absence of ice during the summer season, some 
populations of polar bears in eastern Canada and Hudson Bay remain on 
land for extended periods of time until ice again forms and provides a 
platform for them to move to sea. Similarly, in the Barents Sea, a 
portion of the population is spending greater amounts of time on land.
    Although polar bears are generally limited to areas where the sea 
is ice-covered for much of the year, they are not evenly distributed 
throughout their range on sea ice. They show a preference for certain 
sea ice characteristics, concentrations, and specific sea ice features 
(Stirling et al. 1993, pp. 18-22; Arthur et al. 1996, p. 223; Ferguson 
et al. 2000a, p. 1,125; Ferguson et al. 2000b, pp. 770-771; Mauritzen 
et al. 2001, p. 1,711; Durner et al. 2004, pp. 18-19; Durner et al. 
2006, p. pp. 34-35; Durner et al. 2007, pp. 17 and 19). Sea-ice habitat 
quality varies temporally as well as geographically (Ferguson et al. 
1997, p. 1,592; Ferguson et al. 1998, pp. 1,088-1,089; Ferguson et 
al.2000a, p. 1,124; Ferguson et al.2000b, pp. 770-771; Amstrup et al. 
2000b, p. 962). Polar bears show a preference for sea ice located over 
and near the continental shelf (Derocher et al. 2004, p. 164; Durner et 
al. 2004, p. 18-19; Durner et al. 2007, p. 19), likely due to higher 
biological productivity in these areas (Dunton et al. 2005, pp. 3,467-
3,468) and greater accessibility to prey in near-shore shear zones and 
polynyas (areas of open sea surrounded by ice) compared to deep-water 
regions in the central polar basin (Stirling 1997, pp. 12-14). Bears 
are most abundant near the shore in shallow-water areas, and also in 
other areas where currents and ocean upwelling increase marine 
productivity and serve to keep the ice cover from becoming too 
consolidated in winter (Stirling and Smith 1975, p. 132; Stirling et 
al. 1981, p. 49; Amstrup and DeMaster 1988, p. 44; Stirling 1990, pp. 
226-227; Stirling and [Oslash]ritsland 1995, p. 2,607; Amstrup et al. 
2000b, p. 960).
    Polar bear distribution in most areas varies seasonally with the 
seasonal extent of sea ice cover and availability of prey. The seasonal 
movement patterns of polar bears emphasize the role of sea ice in their 
life cycle. In Alaska in the winter, sea ice may extend 400 kilometers 
(km) (248 miles (mi)) south of the Bering Strait, and polar bears will 
extend their range to the southernmost proximity of the ice (Ray 1971, 
p. 13). Sea ice disappears from the Bering Sea and is greatly reduced 
in the Chukchi Sea in the summer, and polar bears occupying these areas 
move as much as 1,000 km (621 mi) to stay with the pack ice (Garner et 
al. 1990, p. 222; Garner et al. 1994, pp. 407-408). Throughout the 
polar basin during the summer, polar bears generally concentrate along 
the edge of or into the adjacent persistent pack ice. Significant 
northerly and southerly movements of polar bears appear to depend on 
seasonal melting and refreezing of ice (Amstrup 2000, p. 142). In other 
areas, for example, when the sea ice melts in Hudson Bay, James Bay, 
Davis Strait, Baffin Bay, and some portions of the Barents Sea, polar 
bears remain on land for up to 4 or 5 months while they wait for winter 
and new ice to form (Jonkel et al. 1976, pp. 13-22; Schweinsburg 1979, 
pp. 165, 167; Prevett and Kolenosky 1982, pp. 934-935; Schweinsburg and 
Lee 1982, p. 510; Ferguson et al. 1997, p. 1,592; Lunn et al. 1997, p. 
235; Mauritzen et al. 2001, p. 1,710).
    In areas where sea ice cover and character are seasonally dynamic, 
a large multi-year home range, of which only a portion may be used in 
any one season or year, is an important part of the polar bear life 
history strategy. In other regions, where ice is less dynamic, home 
ranges are smaller and less variable (Ferguson et al. 2001, pp.51-52). 
Data from telemetry studies of adult female polar bears show that they 
do not wander aimlessly on the ice, nor are they carried passively with 
the ocean currents as previously thought (Pedersen 1945 cited in 
Amstrup 2003, p. 587). Results show strong fidelity to activity areas 
that are used over multiple years (Ferguson et al. 1997, p. 1,589). All 
areas within an activity area are not used each year.
    The distribution patterns of some polar bear populations during the 
open water and early fall seasons have changed in recent years. In the 
Beaufort Sea, for example, greater numbers of polar bears are being 
found on shore than recorded at any previous time (Schliebe et al. 
2006b, p. 559). In Baffin Bay, Davis Strait, western Hudson Bay and 
other areas of Canada, Inuit hunters are reporting an increase in the 
numbers of bears present on land during summer and fall (Dowsley and 
Taylor 2005, p. 2; Dowsley 2005, p. 2). The exact reasons for these 
changes may involve a number of factors, including changes in sea ice 
(Stirling and Parkinson 2006, p. 272).

Food Habits

    Polar bears are carnivorous, and a top predator of the Arctic 
marine ecosystem. Polar bears prey heavily throughout their range on 
ice-dependent seals (frequently referred to as ``ice seals''), 
principally ringed seals (Phoca hispida), and, to a lesser extent, 
bearded seals (Erignathus barbatus). In some locales, other seal 
species are taken. On average, an adult polar bear needs approximately 
2 kg (4.4 lbs) of seal fat per day to survive (Best 1985, p. 1035). 
Sufficient nutrition is critical and may be obtained and stored as fat 
when prey is abundant.
    Although seals are their primary prey, polar bears occasionally 
take much larger animals such as walruses (Odobenus rosmarus), narwhal 
(Monodon monoceros), and belugas (Delphinapterus leucas) (Kiliaan and 
Stirling 1978, p. 199; Smith 1980, p. 2,206; Smith 1985, pp. 72-73; 
Lowry et al. 1987, p. 141; Calvert and Stirling 1990, p. 352; Smith and 
Sjare 1990, p. 99). In some areas and under some conditions, prey other 
than seals or carrion may be quite important to polar bear sustenance 
as short-term supplemental forms of nutrition. Stirling and 
[Oslash]ritsland (1995, p. 2,609) suggested that in areas where ringed 
seal populations were reduced, other prey species were being 
substituted. Like other ursids, polar bears will eat human garbage 
(Lunn and Stirling 1985, p. 2,295), and when confined to land for long 
periods, they will consume coastal marine and terrestrial plants and 
other terrestrial foods (Russell 1975, p. 122; Derocher et al. 1993, p. 
252); however the significance of such other terrestrial foods to the 
long-term welfare of polar bears may be limited (Lunn and Stirling 
1985, p. 2,296; Ramsay and Hobson 1991, p. 600; Derocher et al. 2004, 
p. 169) as further expanded under the section entitled ``Adaptation'' 
below.

[[Page 28214]]

Reproduction

    Polar bears are characterized by late sexual maturity, small litter 
sizes, and extended parental investment in raising young, all factors 
that contribute to a low reproductive rate (Amstrup 2003, pp. 599-600). 
Reproduction in the female polar bear is similar to that in other 
ursids. Females generally mature and breed for the first time at 4 or 5 
years and give birth at 5 or 6 years of age. Litters of two cubs are 
most common, but litters of three cubs are seen sporadically across the 
Arctic (Amstrup 2003, p. 599). When foraging conditions are difficult, 
polar bears may ``defer'' reproduction in favor of survival (Derocher 
et al. 1992, p. 564).
    Polar bears enter a prolonged estrus between March and June, when 
breeding occurs. Ovulation is induced by mating (Wimsatt 1963, p. 72), 
and implantation is delayed until autumn. The total gestation period is 
195 to 265 days (Uspenski 1977, cited in Amstrup 2003, p. 599), 
although active development of the fetus is suspended during most of 
this period. The timing of implantation, and therefore the timing of 
birth, is likely dependent on body condition of the female, which 
depends on a variety of environmental factors. Pregnant females that 
spend the late summer on land prior to denning may not feed for 8 
months (Watts and Hansen 1987, p. 627). This may be the longest period 
of food deprivation of any mammal, and it occurs at a time when the 
female gives birth to and then nourishes new cubs.
    Newborn polar bears are helpless and have hair, but are blind and 
weigh only 0.6 kg (1.3 lb) (Blix and Lentfer 1979, p. 68). Cubs grow 
rapidly, and may weigh 10 to 12 kg (22 to 26 lbs) by the time they 
emerge from the den in the spring. Young bears will stay with their 
mothers until weaning, which occurs most commonly in early spring when 
the cubs are 2.3 years of age. Female polar bears are available to 
breed again after their cubs are weaned; thus the reproductive interval 
for polar bears is 3 years.
    Polar bears are long-lived mammals not generally susceptible to 
disease, parasites, or injury. The oldest known female in the wild was 
32 years of age and the oldest known male was 28, though few polar 
bears in the wild live to be older than 20 years (Stirling 1988, p. 
139; Stirling 1990, p. 225). Due to extremely low reproductive rates, 
polar bears require a high survival rate to maintain population levels 
(Eberhardt 1985, p. 1,010; Amstrup and Durner 1995, pp. 1,313, 1,319). 
Survival rates increase up to a certain age, with cubs-of-the-year 
having the lowest rates and prime age adults (between 5 and 20 years of 
age) having survival rates that can exceed 90 percent. Amstrup and 
Durner (1995, p. 1,319) report that high survival rates (exceeding 90 
percent for adult females) are essential to sustain populations.

Polar Bear--Sea Ice Habitat Relationships

    Polar bears are distributed throughout the ice-covered waters of 
the circumpolar Arctic (Stirling 1988, p. 61), and rely on sea ice as 
their primary habitat (Amstrup 2003, p. 587). Polar bears depend on sea 
ice for a number of purposes, including as a platform from which to 
hunt and feed upon seals; as habitat on which to seek mates and breed; 
as a platform to move to terrestrial maternity denning areas, and 
sometimes for maternity denning; and as a substrate on which to make 
long-distance movements (Stirling and Derocher 1993, p. 241). Mauritzen 
et al. (2003b, p. 123) indicated that habitat use by polar bears during 
certain seasons may involve a trade-off between selecting habitats with 
abundant prey availability versus the use of safer retreat habitats 
(i.e., habitats where polar bears have lower probability of becoming 
separated from the main body of the pack ice) of higher ice 
concentrations with less prey. Their findings indicate that polar bear 
distribution may not be solely a reflection of prey availability, but 
other factors such as energetic costs or risk may be involved.
    Stirling et al. (1993, p. 15) defined seven types of sea ice 
habitat and classified polar bear use of these ice types based on the 
presence of bears or bear tracks in order to determine habitat 
preferences. The seven types of sea ice are: (1) stable fast ice with 
drifts; (2) stable fast ice without drifts; (3) floe edge ice; (4) 
moving ice; (5) continuous stable pressure ridges; (6) coastal low 
level pressure ridges; and (7) fiords and bays. Polar bears were not 
evenly distributed over these sea ice habitats, but concentrated on the 
floe ice edge, on stable fast ice with drifts, and on areas of moving 
ice (Stirling 1990 p. 226; Stirling et al. 1993, p. 18). In another 
assessment, categories of ice types included pack ice, shore-fast ice, 
transition zone ice, polynyas, and leads (linear openings or cracks in 
the ice) (USFWS 1995, p. 9). Pack ice, which consists of annual and 
multi-year older ice in constant motion due to winds and currents, is 
the primary summer habitat for polar bears in Alaska. Shore-fast ice 
(also known as ``fast ice'', it is defined by the Arctic Climate Impact 
Assessment (2005, p. 190) as ice that grows seaward from a coast and 
remains in place throughout the winter; typically it is stabilized by 
grounded pressure ridges at its outer edge) is used for feeding on seal 
pups, for movement, and occasionally for maternity denning. Open water 
at leads and polynyas attracts seals and other marine mammals and 
provides preferred hunting habitats during winter and spring. Durner et 
al. (2004, pp. 18-19; Durner et al. 2007, pp. 17-18) found that polar 
bears in the Arctic basin prefer sea ice concentrations greater than 50 
percent located over the continental shelf with water depths less than 
300 m (984 feet (ft)).
    Polar bears must move throughout the year to adjust to the changing 
distribution of sea ice and seals (Stirling 1988, p. 63; USFWS 1995, p. 
4). In some areas, such as Hudson Bay and James Bay, polar bears remain 
on land when the sea ice retreats in the spring and they fast for 
several months (up to 8 months for pregnant females) before fall 
freeze-up (Stirling 1988, p. 63; Derocher et al. 2004, p. 163; Amstrup 
et al. 2007, p. 4). Some populations unconstrained by land masses, such 
as those in the Barents, Chukchi, and Beaufort Seas, spend each summer 
on the multi-year ice of the polar basin (Derocher et al. 2004, p. 163; 
Amstrup et al. 2007, p. 4). In intermediate areas such as the Canadian 
Arctic, Svalbard, and Franz Josef Land archipelagos, bears stay on the 
sea ice most of the time, but in some years they may spend up to a few 
months on land (Mauritizen et al. 2001, p. 1,710). Most populations use 
terrestrial habitat partially or exclusively for maternity denning; 
therefore, females must adjust their movements in order to access land 
at the appropriate time (Stirling 1988, p. 64; Derocher et al. 2004, p. 
166).
    Sea ice changes between years in response to environmental factors 
may have consequences for the distribution and productivity of polar 
bears as well as their prey. In the southern Beaufort Sea, anomalous 
heavy sea ice conditions in the mid-1970s and mid-1980s (thought to be 
roughly in phase with a similar variation in runoff from the Mackenzie 
River) caused significant declines in productivity of ringed seals 
(Stirling 2002, p. 68). Each event lasted approximately 3 years and 
caused similar declines in the birth rate of polar bears and survival 
of subadults, after which reproductive success and survival of both 
species increased again.

Maternal Denning Habitat

    Throughout the species' range, most pregnant female polar bears 
excavate

[[Page 28215]]

dens in snow located on land in the fall-early winter period (Harington 
1968, p. 6; Lentfer and Hensel 1980, p. 102; Ramsay and Stirling 1990, 
p. 233; Amstrup and Gardner 1994, p. 5). The only known exceptions are 
in western and southern Hudson Bay, where polar bears first excavate 
earthen dens and later reposition into adjacent snow drifts (Jonkel et 
al. 1972, p. 146; Ramsay and Stirling 1990, p. 233), and in the 
southern Beaufort Sea, where a portion of the population dens in snow 
caves located on pack and shore-fast ice. Successful denning by polar 
bears requires accumulation of sufficient snow for den construction and 
maintenance. Adequate and timely snowfall combined with winds that 
cause snow accumulation leeward of topographic features create denning 
habitat (Harington 1968, p. 12).
    A great amount of polar bear denning occurs in core areas 
(Harington 1968, pp. 7-8), which show high use over time (see Figure 
8). In some portions of the species' range, polar bears den in a more 
diffuse pattern, with dens scattered over larger areas at lower density 
(Lentfer and Hensel 1980, p. 102; Stirling and Andriashek 1992, p. 363; 
Amstrup 1993, p. 247; Amstrup and Gardner 1994, p. 5; Messier et al. 
1994, p. 425; Born 1995, p. 81; Ferguson et al. 2000a, p. 1125; Durner 
et al. 2001, p. 117; Durner et al. 2003, p. 57).
    Habitat characteristics of denning areas vary substantially from 
the rugged mountains and fjordlands of the Svalbard archipelago and the 
large islands north of the Russian coast (L[oslash]n[oslash] 1970, p. 
77; Uspenski and Kistchinski 1972, p. 182; Larsen 1985, pp. 321-322), 
to the relatively flat topography of areas such as the west coast of 
Hudson Bay (Ramsay and Andriashek 1986, p. 9; Ramsay and Stirling 1990, 
p. 233) and north slope of Alaska (Amstrup 1993, p. 247; Amstrup and 
Gardner 1994, p. 7; Durner et al. 2001, p. 119; Durner et al. 2003, p. 
61), to offshore pack ice-pressure ridge habitat (Amstrup and Gardner 
1994, p. 4; Fischbach et al. 2007, p. 1,400). The key characteristic of 
all denning habitat is topographic features that catch snow in the 
autumn and early winter (Durner et al. 2003, p. 61). Across the range, 
most polar bear dens occur relatively near the coast. The main 
exception to coastal denning occurs in the western Hudson Bay area, 
where bears den farther inland in traditional denning areas (Kolenosky 
and Prevett 1983, pp. 243-244; Stirling and Ramsay 1986, p. 349).

Current Population Status and Trend

    The total number of polar bears worldwide is estimated to be 
20,000-25,000 (Aars et al. 2006, p. 33). Polar bears are not evenly 
distributed throughout the Arctic, nor do they comprise a single 
nomadic cosmopolitan population, but rather occur in 19 relatively 
discrete populations (Aars et al. 2006, p. 33). The use of the term 
``relatively discrete population'' in this context is not intended to 
equate to the Act's term ``distinct population segments'' (Figure 1). 
Boundaries of the 19 polar bear populations have evolved over time and 
are based on intensive study of movement patterns, tag returns from 
harvested animals, and, to a lesser degree, genetic analysis (Aars et 
al. 2006, pp. 33-47). The scientific studies regarding population 
bounds began in the early 1970s and continue today. Within this final 
rule we have adopted the use of the term ``population'' to describe 
polar bear management units consistent with their designation by the 
World Conservation Union-International Union for Conservation of Nature 
and Natural Resources (IUCN), Species Survival Commission (SSC) Polar 
Bear Specialist Group (PBSG) with information available as of October 
2006 (Aars et al. 2006, p. 33), and to describe a combination of two or 
more of these populations into ``ecoregions,'' as discussed in 
following sections. Although movements of individual polar bears 
overlap extensively, telemetry studies demonstrate spatial segregation 
among groups or stocks of polar bears in different regions of their 
circumpolar range (Schweinsburg and Lee 1982, p. 509; Amstrup et al. 
1986, p. 252; Amstrup et al., 2000b, pp. 957-958.; Garner et al. 1990, 
p. 224; Garner et al. 1994, pp.112-115; Amstrup and Gardner 1994, p. 7; 
Ferguson et al. 1999, pp. 313-314; Lunn et al. 2002, p. 41). These 
patterns, along with information obtained from survey and 
reconnaissance, marking and tagging studies, and traditional knowledge, 
have resulted in recognition of 19 relatively discrete polar bear 
populations (Aars et al. 2006, p. 33). Genetic analysis reinforces the 
boundaries between some designated populations (Paetkau et al. 1999, p. 
1,571; Amstrup 2003, p. 590) while confirming the existence of overlap 
and mixing among others (Paetkau et al. 1999, p. 1,571; Cronin et al. 
2006, p. 655). There is considerable overlap in areas occupied by 
members of these groups (Amstrup et al. 2004, p. 676; Amstrup et al. 
2005, p. 252), and boundaries separating the groups are adjusted as new 
data are collected. These boundaries, however, are thought to be 
ecologically meaningful, and the 19 units they describe are managed as 
populations, with the exception of the Arctic Basin population where 
few bears are believed to be year-round residents.

[[Page 28216]]

[GRAPHIC] [TIFF OMITTED] TR15MY08.002

    Population size estimates and qualitative categories of current 
trend and status for each of the 19 polar bear populations are 
discussed below. This discussion was derived from information presented 
at the IUCN/SSC PBSG meeting held in Seattle, Washington, in June 2005, 
and updated with results that became available in October 2006 (Aars et 
al. 2006, p. 33). The following narrative incorporates results from two 
recent publications (Stirling et al. 2007; Obbard et al. 2007). The 
remainder of the information on each population is based on the 
available status reports and revisions given by each nation, as 
reported in Aars et al. (2006).
    Status categories include an assessment of whether a population is 
believed to be not reduced, reduced, or severely reduced from historic 
levels of abundance, or if insufficient data are available to estimate 
status. Trend categories include an assessment of whether the 
population is currently increasing, stable, or declining, or if 
insufficient data are available to estimate trend. In general, an 
assessment of trend requires a monitoring program or data to allow 
population size to be estimated at more than one point in time. 
Information on the date of the current population estimate and 
information on previous population estimates and the basis for

[[Page 28217]]

those estimates is detailed in Aars et al. (2006, pp. 34-35). In some 
instances a subjective assessment of trend has been provided in the 
absence of either a monitoring program or estimates of population size 
developed for more than one point in time. This status and trend 
analysis only reflects information about the past and present polar 
bear populations. Later in this final rule a discussion will be 
presented about the scientific information on threats that will affect 
the species within the foreseeable future. The Act establishes a five-
factor analysis for using this information in making listing decisions.
    Populations are discussed in a counterclockwise order from Figure 
1, beginning with East Greenland. There is no population size estimate 
for the East Greenland polar bear population because no population 
surveys have been conducted there. Thus, the status and trend of this 
population have not been determined. The Barents Sea population was 
estimated to comprise 3,000 animals based on the only population survey 
conducted in 2004. Because only one abundance estimate is available, 
the status and trend of this population cannot yet be determined. There 
is no population size estimate for the Kara Sea population because 
population surveys have not been conducted; thus status and trend of 
this population cannot yet be determined. The Laptev Sea population was 
estimated to comprise 800 to 1,200 animals, on the basis of an 
extrapolation of historical aerial den survey data (1993). Status and 
trend cannot yet be determined for this population.
    The Chukchi Sea population is estimated to comprise 2,000 animals, 
based on extrapolation of aerial den surveys (2002). Status and trend 
cannot yet be determined for this population. The Southern Beaufort Sea 
population is comprised of 1,500 animals, based on a recent population 
inventory (2006). The predicted trend is declining (Aars et al. 2006, 
p.33), and the status is designated as reduced. The Northern Beaufort 
Sea population was estimated to number 1,200 animals (1986). The trend 
is designated as stable, and status is believed to be not reduced. 
Stirling et al. (2007, pp. 12-14) estimated long-term trends in 
population size for the Northern Beaufort Sea population. The model-
averaged estimate of population size from 2004 to 2006 was 980 bears, 
and did not differ in a statistically significantly way from estimates 
for the periods of 1972 to 1975 (745 bears) and 1985 to 1987 (867 
bears), and thus the trend is stable. Stirling et al. (2007, p. 13) 
indicated that, based on a number of indications and separate annual 
abundance estimates for the study period, the population estimate may 
be slightly biased low (i.e., might be an underestimate) due to 
sampling issues.
    The Viscount Melville Sound population was estimated to number 215 
animals (1992). The observed or predicted trend based on management 
action is listed as increasing (Aars et al. 2006, p. 33), although the 
status is designated as severely reduced from prior excessive harvest. 
The Norwegian Bay population estimate was 190 animals (1998); the 
trend, based on computer simulations, is noted as declining, while the 
status is listed as not reduced. The Lancaster Sound population 
estimate was 2,541 animals (1998); the trend is thought to be stable, 
and status is not reduced. The M'Clintock Channel population is 
estimated at 284 animals (2000); the observed or predicted trend based 
on management actions is listed as increasing although the status is 
severely reduced from excessive harvest. The Gulf of Boothia population 
estimate is 1,523 animals (2000); the trend is thought to be stable, 
and status is designated as not reduced. The Foxe Basin population was 
estimated to number 2,197 animals in 1994; the population trend is 
thought to be stable, and the status is not reduced. The Western Hudson 
Bay population estimate is 935 animals (2004); the trend is declining, 
and the status is reduced. The Southern Hudson Bay population was 
estimated to be 1,000 animals in 1988 (Aars et al. 2006, p. 35); the 
trend is thought to be stable, and status is not reduced. In a more 
recent analysis, Obbard et al. (2007) applied open population capture-
recapture models to data collected from 1984-86 and 1999-2005 to 
estimate population size, trend, and survival for the Southern Hudson 
Bay population. Their results indicate that the size of the Southern 
Hudson Bay population appears to be unchanged from the mid-1980s. From 
1984-1986, the population was estimated at 641 bears; from 2003-2005, 
the population was estimated at 681 bears. Thus, the trend for this 
population is stable. The Kane Basin population was estimated to be 
comprised of 164 animals (1998); its trend is declining, and status is 
reduced. The Baffin Bay population was estimated to be 2,074 animals 
(1998); the trend is declining, and status is reduced. The Davis Strait 
population was estimated to number 1,650 animals based on traditional 
ecological knowledge (TEK) (2004); data were unavailable to assess 
trends or status. Preliminary information from the second of a 3-year 
population assessment estimates the population number to be 2,375 bears 
(Peacock et al. 2007, p. 7). The Arctic Basin population estimate, 
trend, and status are unknown (Aars et al. 2006, p. 35).
    On the basis of information presented above, two polar bear 
populations are designated as increasing (Viscount Melville Sound and 
M'Clintock Channel-both were severely reduced in the past and are 
recovering under conservative harvest limits); six populations are 
stable (Northern Beaufort Sea, Southern Hudson Bay, Davis Strait, 
Lancaster Sound, Gulf of Bothia, Foxe Basin); five populations are 
declining (Southern Beaufort Sea, Norwegian Bay, Western Hudson Bay, 
Kane Basin, Baffin Bay); and six populations are designated as data 
deficient (Barents Sea, Kara Sea, Laptev Sea, Chukchi Sea, Arctic 
Basin, East Greenland) with no estimate of trend. The two populations 
with the most extensive time series of data, Western Hudson Bay and 
Southern Beaufort Sea, are both considered to be declining.
    As previously noted, scientific information assessing this species 
in the foreseeable future is provided later in this final rule.

Polar Bear Ecoregions

    Amstrup et al. (2007, pp. 6-8) grouped the 19 IUCN-recognized polar 
bear populations (Aars et al. 2006, p. 33) into four physiographically 
different functional groups or ``ecoregions'' (Figure 2) in order to 
forecast future polar bear population status on the basis of current 
knowledge of polar bear populations, their relationships to sea ice 
habitat, and predicted changes in sea ice and other environmental 
variables. Amstrup et al. (2007, p. 7) defined the ecoregions ``on the 
basis of observed temporal and spatial patterns of ice formation and 
ablation (melting or evaporation), observations of how polar bears 
respond to those patterns, and how general circulation models (GCMs) 
forecast future ice patterns.''
    The Seasonal Ice Ecoregion includes the Western and Southern Hudson 
Bay populations, as well as the Foxe Basin, Baffin Bay, and Davis 
Strait populations. These 5 IUCN-recognized populations are thought to 
include a total of about 7,200 polar bears (Aars et al. 2006, p. 34-
35). The 5 populations experience sea ice that melts entirely in 
summer, and bears spend extended periods of time on shore.

[[Page 28218]]

[GRAPHIC] [TIFF OMITTED] TR15MY08.003

    The Archipelago Ecoregion, islands and channels of the Canadian 
Arctic, has approximately 5,000 polar bears representing 6 populations 
recognized by the IUCN (Aars et al. 2006, p. 34-35). These populations 
are Kane Basin, Norwegian Bay, Viscount Melville Sound, Lancaster 
Sound, M'Clintock Channel, and the Gulf of Boothia. Much of this region 
is characterized by heavy annual and multi-year ice that fills the 
inter-island channels year round and polar bears remain on the sea ice 
throughout the year.
    The polar basin was split into a Convergent Ecoregion and a 
Divergent Ecoregion, based upon the different patterns of sea ice 
formation, loss (via melt and transport) (Rigor et al. 2002, p. 2,658; 
Rigor and Wallace 2004, p. 4; Maslanik et al. 2007, pp. 1-3; Meier et 
al. 2007, pp. 428-434; Ogi and Wallace 2007, pp. 2-3).
    The Divergent Ecoregion is characterized by extensive formation of 
annual sea ice that is transported toward the Canadian Arctic islands 
and Greenland, or out of the polar basin through Fram Strait. The 
Divergent ecoregion includes the Southern Beaufort, Chukchi, Laptev, 
Kara, and Barents Seas populations, and is thought to contain up to 
9,500 polar bears. In the Divergent Ecoregion, as in the Archipelago 
Ecoregion, polar bears mainly stay on the sea ice year-round.
    The Convergent Ecoregion, composed of the Northern Beaufort Sea, 
Queen Elizabeth Islands (see below), and East Greenland populations, is 
thought to contain approximately 2,200 polar bears. Amstrup et al. 
(2007, p. 7) modified the IUCN-recognized population boundaries (Aars 
et al. 2006, pp. 33,36) of this ecoregion by redefining a Queen 
Elizabeth Islands population and extending the original boundary of 
that population to include northwestern Greenland (see Figure 2). The 
area contained within this boundary is characterized by heavy multi-
year ice, except for a recurring lead system that runs along the Queen 
Elizabeth Islands from the northeastern Beaufort Sea to northern 
Greenland (Stirling 1980, pp. 307-308). The area may contain over 200 
polar bears and some bears from other regions have been recorded moving 
through the area (Durner and Amstrup 1995, p. 339; Lunn et al. 1995, 
pp. 12-13). The Northern Beaufort Sea and Queen Elizabeth Islands 
populations occur in a region of the polar basin that accumulates ice 
(hence, the Convergent Ecoregion) as it is moved from the polar basin 
Divergent Ecoregion, while the East Greenland population occurs in area 
where ice is transported out of the polar basin through the Fram Strait 
(Comiso 2002, pp. 17-18; Rigor and Wallace 2004, p. 3; Belchansky et 
al. 2005, pp. 1-2; Holland et al. 2006, pp. 1-5; Durner et al. 2007, p. 
3; Ogi and Wallace 2007, p. 2; Serreze et al. 2007, pp. 1,533-1536).
    Amstrup et al. (2007) do not incorporate the central Arctic Basin 
population into an ecoregion. This population was defined by the IUCN 
in 2001 (Lunn et al. 2002, p.29) to recognize polar bears that may 
reside outside the territorial jurisdictions of the polar nations. The 
Arctic Basin region is characterized by very deep water, which is known 
to be unproductive (Pomeroy 1997, pp. 6-7). Available data indicate 
that polar bears prefer sea ice over shallow water (less then 300 m 
(984 ft) deep) (Amstrup et

[[Page 28219]]

al. 2000b, p. 962; Amstrup et al. 2004, p. 675; Durner et al. 2007, pp. 
18-19), and it is thought that this preference reflects increased 
hunting opportunities over more productive waters. Also, tracking 
studies indicate that few if any bears are year-round residents of the 
central Arctic Basin, and therefore this relatively unpopulated portion 
of the Arctic was not designated as an ecoregion.

Sea Ice Environment

    As described in detail in the ``Species Biology'' section of this 
rule, above, polar bears are evolutionarily adapted to life on sea ice 
(Stirling 1988, p. 24; Amstrup 2003, p. 587). They need sea ice as a 
platform for hunting, for seasonal movements, for travel to terrestrial 
denning areas, for resting, and for mating (Stirling and Derocher 1993, 
p. 241). Moore and Huntington (in press) classify the polar bear as an 
``ice-obligate'' species because of its reliance on sea ice as a 
platform for resting, breeding, and hunting, while Laidre et al. (in 
press) similarly describe the polar bear as a species that principally 
relies on annual sea ice over the continental shelf and areas toward 
the southern edge of sea ice for foraging. Some polar bears use 
terrestrial habitats seasonally (e.g., for denning or for resting 
during open water periods). Open water is not considered to be an 
essential habitat type for polar bears, because life functions such as 
feeding, reproduction, or resting do not occur in open water. However, 
open water is a fundamental part of the marine system that supports 
seal species, the principal prey of polar bears, and seasonally 
refreezes to form the ice needed by the bears (see ``Open Water 
Habitat'' section for more information). Further, the open water 
interface with sea ice is an important habitat used to a great extent 
by polar bears. In addition, the extent of open water is important 
because vast areas of open water may limit a bear's ability to access 
sea ice or land (see ``Open Water Swimming'' section for more detail). 
Snow cover, both on land and on sea ice, is an important component of 
polar bear habitat in that it provides insulation and cover for young 
polar bears and ringed seals in snow dens or lairs (see ``Maternal 
Denning Habitat'' section for more detail).

Sea Ice Habitat

Overview of Arctic Sea Ice

    According to the Arctic Climate Impact Assessment (ACIA 2005), 
approximately two-thirds of the Arctic is ocean, including the Arctic 
Ocean and its shelf seas plus the Nordic, Labrador, and Bering Seas 
(ACIA 2005, p. 454). Sea ice is the defining characteristic of the 
marine Arctic (ACIA 2005, p. 30). The Arctic sea ice environment is 
highly dynamic and follows annual patterns of expansion and 
contraction. Sea ice is typically at its maximum extent (the term 
``extent'' is formally defined in the ``Observed Changes in Arctic Sea 
Ice'' section) in March and at its minimum extent in September 
(Parkinson et al. 1999, p. 20,840). The two primary forms of sea ice 
are seasonal (or first year) ice and perennial (or multi-year) ice 
(ACIA 2005, p. 30). Seasonal ice is in its first autumn/winter of 
growth or first spring/summer of melt (ACIA 2005, p. 30). It has been 
documented to vary in thickness from a few tenths of a meter near the 
southern margin of the sea ice to 2.5 m (8.2 ft) in the high Arctic at 
the end of winter (ACIA 2005, p. 30), with some ice also that is 
thinner and some limited amount of ice that can be much thicker, 
especially in areas with ridging (C. Parkinson, NASA, in litt. to the 
Service, November 2007). If first-year ice survives the summer melt, it 
becomes multi-year ice. This ice tends to develop a distinctive 
hummocky appearance through thermal weathering, becoming harder and 
almost salt-free over several years (ACIA 2005, p. 30). Sea ice near 
the shore thickens in shallow waters during the winter, and portions 
become grounded. Such ice is known as shore-fast ice, land-fast ice, or 
simply fast ice (ACIA 2005, p. 30). Fast ice is found along much of the 
Siberian coast, the White Sea (an inlet of the Barents Sea), north of 
Greenland, the Canadian Archipelago, Hudson Bay, and north of Alaska 
(ACIA 2005, p. 457).
    Pack ice consists of seasonal (or first-year) and multi-year ice 
that is in constant motion caused by winds and currents (USFWS 1995, 
pp. 7-9). Pack ice is used by polar bears for traveling, feeding, and 
denning, and it is the primary summer habitat for polar bears, 
including the Southern Beaufort Sea and Chukchi Sea populations, as 
first year ice retreats and melts with the onset of spring (see ``Polar 
Bear-Sea Ice Habitat Relationships'' section for more detail on ice 
types used by polar bears). Movements of sea ice are related to winds, 
currents, and seasonal temperature fluctuations that in turn promote 
its formation and degradation. Ice flow in the Arctic often includes a 
clockwise circulation of sea ice within the Canada Basin and a 
transpolar drift stream that carries sea ice from the Siberian shelves 
to the Barents Sea and Fram Strait.
    Sea ice is an important component of the Arctic climate system 
(ACIA 2005, p. 456). It is an effective insulator between the oceans 
and the atmosphere. It also strongly reduces the ocean-atmosphere heat 
exchange and reduces wind stirring of the ocean. In contrast to the 
dark ocean, pond-free sea ice (i.e., sea ice that has no meltwater 
ponds on the surface) reflects most of the solar radiation back into 
space. Together with snow cover, sea ice greatly restricts the 
penetration of light into the sea, and it also provides a surface for 
particle and snow deposition (ACIA 2005, p. 456). Its effects can 
extend far south of the Arctic, perhaps globally, e.g., through 
impacting deepwater formation that influences global ocean circulation 
(ACIA 2005, p. 32).
    Sea ice is also an important environmental factor in Arctic marine 
ecosystems. ``Several physical factors combine to make arctic marine 
systems unique including: a very high proportion of continental shelves 
and shallow water; a dramatic seasonality and overall low level of 
sunlight; extremely low water temperatures; presence of extensive areas 
of multi-year and seasonal sea-ice cover; and a strong influence from 
freshwater, coming from rivers and ice melt'' (ACIA 2005, p. 454). Ice 
cover is an important physical characteristic, affecting heat exchange 
between water and atmosphere, and light penetration to organisms in the 
water below. It also helps determine the depth of the mixed layer, and 
provides a biological habitat above, within, and beneath the ice. The 
marginal ice zone, at the edge of the pack ice, is important for 
plankton production and plankton-feeding fish (ACIA 2005, p. 456)

Observed Changes in Arctic Sea Ice

    Sea ice is the defining physical characteristic of the marine 
Arctic environment and has a strong seasonal cycle (ACIA 2005, p. 30). 
There is considerable inter-annual variability both in the maximum and 
minimum extent of sea ice, but it is typically at its maximum extent in 
March and minimum extent in September (Parkinson et al. 1999, p. 20, 
840). In addition, there are decadal and inter-decadal fluctuations to 
sea ice extent due to changes in atmospheric pressure patterns and 
their associated winds, river runoff, and influx of Atlantic and 
Pacific waters (Gloersen 1995, p. 505; Mysak and Manak 1989, p. 402; 
Kwok 2000, p. 776; Parkinson 2000b, p. 10; Polyakov et al. 2003, p. 
2,080; Rigor et al. 2002, p. 2,660; Zakharov 1994, p. 42). Sea ice 
``extent'' is normally defined as the area of the ocean with at least 
15 percent ice coverage, and sea ice ``area'' is normally defined as 
the integral sum of areas actually covered by sea ice

[[Page 28220]]

(Parkinson et al. 1999). ``Area'' is a more precise measure of the 
areal extent of the ice itself, since it takes into account the 
fraction of leads (linear openings or cracks in the ice) within the 
ice, but ``extent'' is more reliably observed (Zhang and Walsh 2006). 
The following sections discuss specific aspects of observed sea ice 
changes of relevance to polar bears.

Summer Sea Ice

    Summer sea ice area and sea ice extent are important factors for 
polar bear survival (see ``Polar Bear-Sea Ice Habitat Relationships'' 
section). Seasonal or first-year ice that remains at the end of the 
summer melt becomes multi-year (or perennial) ice. The amount and 
thickness of perennial ice is an important determinant of future sea 
ice conditions (i.e., gain or loss of ice) (Holland and Bitz 2003; Bitz 
and Roe 2004). Much of the following discussion focuses on summer sea 
ice extent (rather than area).
    Prior to the early 1970s, ice extent was measured with visible-band 
satellite imagery and aircraft and ship reports. With the advent of 
passive microwave (PM) satellite observations, beginning in December 
1972 with a single channel instrument and then more reliably in October 
1978 with a multi-channel instrument, we have a more accurate, 3-decade 
record of changes in summer sea ice extent and area. Over the period 
since October 1978, successive papers have documented an overall 
downward trend in Arctic sea ice extent and area. For example, 
Parkinson et al. (1999) calculated Arctic sea ice extents, areas, and 
trends for late 1978 through the end of 1996, and documented a decrease 
in summer sea ice extent of 4.5 percent per decade. Comiso (2002) 
documented a decline of September minimum sea ice extent of 6.7 percent 
plus or minus 2.4 percent per decade from 1981 through 2000. Stroeve et 
al. (2005) analyzed data from 1978 through 2004, and calculated a 
decline in minimum sea ice extent of 7.7 percent plus or minus 3 
percent per decade. Comiso (2006, p. 72) included observations for 
2005, and calculated a per-decade decline in minimum sea ice extent of 
up to 9.8 percent plus or minus 1.5 percent. Most recently, Stroeve et 
al. (2007, pp. 1-5) estimated a 9.1 percent per-decade decline in 
September sea ice extent for 1979-2006, while Serreze et al. (2007, pp. 
1,533-1,536) calculated a per-decade decline of 8.6 percent plus or 
minus 2.9 percent for the same parameter over the same time period. 
These estimates differ only because Serreze et al. (2007, pp. 1,533-
1,536) normalized the trend by the 1979-2000 mean, in order to be 
consistent with how the National Snow and Ice Data Center \1\ 
calculates its estimates (J. Stroeve, in litt. to the Service, November 
2007). This decline translates to a decrease of 60,421 sq km (23,328 sq 
mi) per year (NSIDC Press Release, October 3, 2006).
---------------------------------------------------------------------------

    \1\ The NSIDC is part of the University of Colorado Cooperative 
Institute for Research in Environmental Sciences (CIRES), is funded 
largely by the National Aeronautics and Space Administration (NASA), 
and is affiliated with the National Oceanic and Atmospheric 
Administration (NOAA) National Geophysical Data Center through a 
cooperative agreement. A large part of NSIDC is the Polar 
Distributed Active Archive Center, which is funded by NASA.
---------------------------------------------------------------------------

    The rate of decrease in September sea ice extent appears to have 
accelerated in recent years, although the acceleration to date has not 
been shown to be statistically significant (C. Bitz, in litt. to the 
Service, November 2007). The years 2002 through 2007 all exceeded 
previous record lows (Stroeve et al. 2005; Comiso 2006; Stroeve et al. 
2007, pp. 1-5; Serreze et al. 2007, pp. 1,533-1,536; NSIDC Press 
Release, October 1, 2007), and 2002, 2005, and 2007 had successively 
lower record-breaking minimum extent values (https://www.nsidc.org). The 
2005 absolute minimum sea ice extent of 5.32 million sq km (2.05 
million sq mi) for the entire Arctic Ocean was a 21 percent reduction 
compared to the mean for 1979 to 2000 (Serreze et al. 2007, pp. 1,533-
1,536). Nghiem et al. (2006) documented an almost 50 percent reduction 
in perennial (multi-year) sea ice extent in the East Arctic Ocean (0 to 
180 degrees east longitude) between 2004 and 2005, while the West 
Arctic Ocean (0 and 180 degrees west longitude) had a slight gain 
during the same period, followed by an almost 70 percent decline from 
October 2005 to April 2006. Nghiem et al. (2007) found that the extent 
of perennial sea ice was significantly reduced by 23 percent between 
March 2005 and March 2007 as observed by the QuikSCAT/SeaWinds 
satellite scatterometer. Nghiem et al. (2006) presaged the extensive 
decline in September sea ice extent in 2007 when they stated: ``With 
the East Arctic Ocean dominated by seasonal ice, a strong summer melt 
may open a vast ice-free region with a possible record minimum ice 
extent largely confined to the West Arctic Ocean.''
    Arctic sea ice declined rapidly to unprecedented low extents in 
summer 2007 (Stroeve et al. 2008). On August 16-17, 2007, Arctic sea 
ice surpassed the previous single-day (absolute minimum) record for the 
lowest extent ever measured by satellite (set in 2005), and the sea ice 
was still melting (NSIDC Arctic Sea Ice News, August 17, 2007). On 
September 16, 2007 (the end of the melt season), the 5-day running mean 
sea ice extent reported by NSIDC was 4.13 million sq km (1.59 million 
sq mi), an all-time record low. This was 23 percent lower than the 
previous record minimum reported in 2005 (see Figure 3) (Stroeve et al. 
2008) and 39 percent below the long-term average from 1979 to 2000 (see 
Figure 4) (NSIDC Press Release, October 1, 2007). Arctic sea ice 
receded so much in 2007 that the so-called ``Northwest Passage'' 
through the straits of the Canadian Arctic Archipelago completely 
opened for the first time in recorded history (NSIDC Press Release, 
October 1, 2007). Based on a time-series of data from the Hadley 
Centre, extending back before the advent of the PM satellite era, sea 
ice extent in mid-September 2007 may have fallen by as much as 50 
percent from the 1950s to 1970s (Stroeve et al. 2008). The minimum 
September Arctic sea ice extent since 1979 is now declining at a rate 
of approximately 10.7 percent per decade (Stroeve et al. 2008), or 
approximately 72,000 sq km (28,000 sq mi) per year (see Figure 3 below) 
(NSIDC Press Release, October 1, 2007).

[[Page 28221]]

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[GRAPHIC] [TIFF OMITTED] TR15MY08.005


[[Page 28222]]


    In August 2007, Arctic sea ice area (recall that ``area'' is a 
different metric than ``extent'' used in the preceding paragraphs) also 
broke the record for the minimum Arctic sea ice area in the period 
since the satellite PM record began in the 1970s (University of 
Illinois Polar Research Group 2007 web site; https://
arctic.atmos.uiuc.edu/cryosphere/). The new record was set a full month 
before the historic summer minimum typically occurs, and the record 
minimum continued to decrease over the next several weeks (University 
of Illinois Polar Research Group 2007 web site). The Arctic sea ice 
area reached an historic minimum of 2.92 million sq km (1.13 million sq 
mi) on September 16, 2007, which was 27 percent lower than the previous 
(2005) record Arctic ice minimum area (University of Illinois Polar 
Research Group 2007 web site). In previous record sea ice minimum 
years, ice area anomalies were confined to certain sectors (North 
Atlantic, Beaufort/Bering Sea, etc.), but the character of the 2007 
summer sea ice melt was unique in that it was both dramatic and covered 
the entire Arctic Basin. Atlantic, Pacific, and the central Arctic 
sectors all showed large negative sea ice area anomalies (University of 
Illinois Polar Research Group 2007 web site).
    Two key factors contributed to the September 2007 extreme sea ice 
minimum: thinning of the pack ice in recent decades and an unusual 
pattern of atmospheric circulation (Stroeve et al. 2008). Spring 2007 
started out with less ice and thinner ice than normal. Ice thickness 
estimates from the ICESat satellite laser altimeter instrument 
indicated ice thicknesses over the Arctic Basin in March 2007 of only 1 
to 2 m (3.3 to 6.6 ft) (J. Stroeve, in litt. to the Service, November 
2007). Thinner ice takes less energy to melt than thicker ice, so the 
stage was set for low levels of sea ice in summer 2007 (J. Stroeve, 
quoted in NSIDC Press Release, October 1, 2007). In general, older sea 
ice is thicker than younger ice. Maslanik et al. (2007) used an ice-
tracking computer algorithm to estimate changes in the distribution of 
multi-year sea ice of various ages. They estimated: that the area of 
sea ice at least 5 years old decreased by 56 percent between 1985 and 
2007; that ice at least 7 years old decreased from 21 percent of the 
ice cover in 1988 to 5 percent in 2007; and that sea ice at least 9 
years old essentially disappeared from the central Arctic Basin. 
Maslanik et al. (2007) attributed thinning in recent decades to both 
ocean-atmospheric circulation patterns and warmer temperatures. Loss of 
older ice in the late 1980s to mid-1990s was accentuated by the 
positive phase of the Arctic Oscillation during that period, leading to 
increased ice export through the Fram Strait (Stroeve et al. 2008). 
Another significant change since the late 1990s has been the role of 
the Beaufort Gyre, ``the dominant wind and ice drift regime in the 
central Arctic'' (Maslanik et al. 2007). ``Since the late 1990s * * * 
ice typically has not survived the transit through the southern portion 
of the Beaufort Gyre,'' thus not allowing the ice to circulate in its 
formerly typical clockwise pattern for years while it aged and 
thickened (Maslanik et al. 2007). Temperature changes in the Arctic are 
discussed in detail in the section entitled ``Air and Sea 
Temperatures.''
    Another factor that contributed to the sea ice loss in the summer 
of 2007 was an unusual atmospheric pattern, with persistent high 
atmospheric pressures over the central Arctic Ocean and lower pressures 
over Siberia (Stroeve et al. 2008). The skies were fairly clear under 
the high-pressure cell, promoting strong melt. At the same time, the 
pattern of winds pumped warm air into the region. While the warm winds 
fostered further melt, they also helped push ice away from the Siberian 
shore.

Winter Sea Ice

    The maximum extent of Arctic winter sea ice cover, as documented 
with PM satellite data, has been declining at a lower rate than summer 
sea ice (Parkinson et al. 1999, p. 20,840; Richter-Menge et al. 2006, 
p. 16), but that rate appears to have accelerated in recent years. 
Parkinson and Cavalieri (2002, p. 441) reported that winter sea ice 
cover declined at a rate of 1.8 percent plus or minus 0.6 percent per 
decade for the period 1979 through 1999. More recently, Richter-Menge 
et al. (2006, p. 16) reported that March sea ice extent was declining 
at a rate of 2 percent per decade based on data from 1979-2005, Comiso 
(2006) calculated a decline of 1.9 plus or minus 0.5 percent per decade 
for 1979-2006, and J. Stroeve (in litt. to the Service, November 2007) 
calculated a decline of 2.5 percent per decade, also for 1979-2005.
    In 2005 and 2006, winter maximum sea ice extent set record lows for 
the era of PM satellite monitoring (October 1978 to present). The 2005 
record low winter maximum preceded the then-record low summer minimum 
during the same year, while winter sea ice extent in 2006 was even 
lower than that of 2005 (Comiso 2006). The winter 2007 Arctic sea ice 
maximum was the second-lowest in the satellite record, narrowly missing 
the March 2006 record (NSIDC Press Release, April 4, 2007). J. Stroeve 
(in litt. to the Service, November 2007) calculated a rate of decline 
of 3.0 plus or minus 0.8 percent per decade for 1979-2007.

Cumulative Annual Sea Ice

    Parkinson et al. (1999) documented that Arctic sea ice extent for 
all seasons (i.e., annual sea ice extent) declined at a rate of 2.8 
percent per decade for the period November 1978 through December 1996, 
with considerable regional variation (the greatest absolute declines 
were documented for the Kara and Barents Sea, followed by the Seas of 
Okhotsk and Japan, the Arctic Ocean, Greenland Sea, Hudson Bay, and 
Canadian Archipelago; percentage declines were greatest in the Seas of 
Okhotsk and Japan, at 20.1 percent per decade, and the Kara and Barents 
Seas, at 10.5 percent per decade). More recently, Comiso and Nishio 
(2008) utilized satellite data gathered from late 1978 into 2006, and 
estimated an annual rate decline of 3.4 percent plus or minus 0.2 
percent per decade. They also found regions where higher negative 
trends were apparent, including the Greenland Sea (8.0 percent per 
decade), the Kara/Barents Seas (7.2 percent per decade), the Okhotsk 
Sea (8.7 percent per decade), and Baffin Bay/Labrador Sea (8.6 percent 
per decade). Comiso et al. (2008) included satellite data from 1979 
through early September 2007 in their analyses. They found that the 
trend of the entire sea ice cover (seasonal and perennial sea ice) has 
accelerated from a decline of about 3 percent per decade in 1979-1996 
to a decline of about 10 percent per decade in the last 10 years. 
Statistically significant negative trends in Arctic sea ice extent now 
occur n all calendar months (Serreze et al. 2007, pp. 1,533-1,536).

Sea Ice Thickness

    Sea ice thickness is an important element of the Arctic climate 
system. The sea ice thickness distribution influences the sea ice mass 
budget and ice/ocean/atmosphere exchange (Holland et al. 2006a). Sea 
ice thickness has primarily been measured with upward-looking sonar on 
submarines and on moored buoys; this sonar provides information on ice 
draft, the component of the total ice thickness (about 90 percent) that 
projects below the water surface (Serreze et al. 2007, pp. 1,533-
1,536). Rothrock et al. (1999, p. 3,469) compared sea-ice draft data 
acquired on submarine cruises between 1993 and 1997 with similar data 
acquired between 1958 and 1976, and concluded that the mean sea-ice 
draft at

[[Page 28223]]

the end of the melt season (i.e., perennial or multi-year ice) had 
decreased by about 1.3 m (4.3 ft) in most of the deep water portion of 
the Arctic Ocean. One limitation of submarine sonar data is sparse 
sampling, which complicates interpretation of the results (Serreze et 
al. 2007, pp. 1,533-1,536). Holloway and Sou (2002) noted concerns 
regarding the temporal and spatial sampling of ice thickness data used 
in Rothrock et al. (1999), and concluded from their modeling exercise 
that ``a robust characterization over the half-century time series 
consists of increasing volume to the mid-1960s, decadal variability 
without significant trend from the mid-1960s to the mid-1980s, then a 
loss of volume from the mid-1980s to the mid-1990s.'' Rothrock et al. 
(2003, p. 28) conducted further analysis of the submarine-acquired data 
in conjunction with model simulations and review of other modeling 
studies, and concluded that all models agree that sea ice thickness 
decreased between 0.6 and 0.9 m (2 and 3 ft) from 1987 to 1996. Their 
model showed a modest recovery in thickness from 1996 to 1999. Yu et 
al. (2004, p. 11) further analyzed submarine sonar data and concluded 
that total ice volume decreased by 32 percent from the 1960s and 1970s 
to the 1990s in the central Arctic Basin.
    Fowler et al. (2004) utilized a new technique for combining 
remotely-sensed sea ice motion and sea ice extent to ``track'' the 
evolution of sea ice in the Arctic region from October 1978 through 
March 2003. Their analysis revealed that the area of the oldest sea ice 
(i.e., sea ice older than 4 years) was decreasing in the Arctic Basin 
and being replaced by younger (first-year) ice. The extent of the older 
ice was retreating to a relatively small area north of the Canadian 
Archipelago, with narrow bands spreadin