Concentration of seals in fjords or areas with
then it is possible that some bears near the edge or
freshwater influx that may continue to freeze over for
southern limit of the pack may lose contact with the
longer periods could create a concentrated food re-
main body of ice and subsequently drift into inappro-
source for polar bears. However, there is an increased
priate habitats from which return may be difficult.
likelihood of competition for prey with subordinate an-
Southwest Greenland and the island of Newfoundland
imals likely suffering more than dominant bears that
168
A. E. DEROCHER ET AL.
can confiscate or monopolize prey. Because polar
ficult to project trends with confidence as our knowl-
bears are not territorial, loss of habitat may not result
edge of how ringed and bearded seals use and depend
in an immediate loss hunting opportunity through loss
on sea ice is limited as is our ability to forecast their
of individual home ranges as it would for terrestrial
responses to changes in climate and ice conditions.
ursids. Regardless, it seems logical overall to predict
There are several species of seals whose current dis-
that a major loss of sea ice habitat will result in a
tributions lie at the southern edge of polar bear range
decline in polar bear abundance over time.
and could expand northward if ice conditions are al-
Polar bears preferentially feed on the blubber of
tered. In the north Atlantic, harp seals and hooded
their prey and adult bears in particular often leave
seals ( Crystophora cristata), both ice-breeding species, much of the protein behind (Stirling and McEwan,
already migrate to the ice edge in summer and cur-
1975) and do not typically remain with prey (Stirling,
rently form a part of the polar bear’s diet. It is possible
1974; Stirling and Archibald, 1977). Immature bears
that these species could expand northward and come
are not as efficient at catching seals (Stirling and La-
into greater contact with polar bears particularly if
tour, 1978) and the remains of kills made by other
whelping areas are relocated to higher latitudes. In the
bears may be important for this age class. It is possible
Barents Sea, a portion of the harp seal population in
that if polar bears experience decreased kill rates,
the White Sea migrates to the sea ice edge in summer
greater use of kills may occur and result in relatively
(Haug et al. , 1994). However, if the ice edge migrates less food for younger bears to scavenge. Scavenging
too far north, harp seals may not reach the sea ice
dynamics and competition for prey suggest age-related
where they are vulnerable to predation by polar bears
Downloaded from
differences in response to climate warming.
and the seals may shift to a more pelagic distribution
How the primary prey species of polar bears (ringed
already shown by part of the population (Haug et al. , and bearded seals) will be affected by climatic warm-1994). However, this assumes that both harp and hood-
ing is also uncertain but it appears possible that habitat
ed seals are able to find suitable pupping habitat. Loss
for ringed seals in particular may be reduced. Both
of southern pupping areas due to inadequate or highly
these seal species are territorial during the breeding
variable ice conditions may reduce these species as
icb.oxfordjournals.org
season (Smith and Hammill, 1981; Van Parijs et al. ,
polar bear prey.
2001) and as suitable sea ice habitats are reduced, seal
Harbour seals, spotted seals ( P. largha), ribbon seals productivity will probably be reduced. Changes to the
( Histriophoca fasciata), and gray seals ( Halichoerus distribution and timing of sea ice formation can have
grypus) populations already exist at the edges of the a significant impact on ringed seal productively. For
range of polar bears and are not currently common
example, years of very heavy ice in the 1970s and
prey. Woolett et al. (2000) showed from archaeologi-
by guest on March 20, 2011
1980s in the eastern Beaufort Sea resulted in markedly
cal data that during periods of warmer weather and
lower productivity of ringed seals and resulted in re-
presumably less ice, harbour seal bones had a higher
duced polar bear productivity (Stirling, 2002). In 1998,
frequency of occurrence relative to ringed seals along
ringed seal pup development in Prince Albert Sound,
the coast of northern Labrador and south-eastern Baf-
Northwest Territories, was significantly retarded by ei-
fin Island and that the opposite was true when the
ther reduced area of suitable breeding habitat or an
weather was colder and there was more ice. This sug-
unusually early break-up (Smith and Harwood, 2001).
gests that as the climate warms and there is more open
What effect, if any, this may have had on polar bear