Emily Parks, M.Sc. Candidate
Polar bears and sea ice in a changing climate: How do variations in sea ice affect
polar bear habitat selection on Hudson Bay?

Polar bears (Ursus maritimus) inhabit the ice-covered waters of the circumpolar
Arctic, particularly near active annual ice where productivity is higher and
their primary prey, ringed (Phoca hispida) and bearded seals (Erignathus barbatus),
are more densely distributed.1,2 Polar bears are a long-lived species with delayed
maturation and low rates of reproduction, which make them particularly sensitive
to disturbances in their habitat or prey.3

Large adult male captured during population inventory studies

Climate change is one of the key disturbances
for species dependent on ice,4 and there is increasing evidence that
ice extent, concentration, thickness, and ice season duration have all declined
significantly since the 1960s.5 Polar bears living at more southern
latitudes, such as those in the Hudson Bay region, may be affected sooner and
more severely by these changes.
The bears of western
Hudson Bay live and hunt on the sea ice from November to July, and are forced
ashore each summer as the ice melts. They tend to show strong site fidelity
when returning to land and while off the ice they survive almost entirely on
their fat reserves.6 The ice season in Hudson Bay has become shorter over the
last three decades, meaning there is less time for polar bears to hunt and accumulate
fat, and this has resulted in bears coming off the ice in poorer condition.7
As ice continues to change in Hudson Bay, it is important to understand how
polar bears may be affected.

Flying over a stretch of sea ice showing cracks and ridges

There are two factors that
make Hudson Bay unique as a habitat for polar bears: 1. It is an inland sea,
almost entirely enclosed by land unlike most of the Arctic, and 2. it becomes
ice-free each summer, so that bears are forced back to land, and this means
that near break-up, bears may be balancing foraging needs with the need to move
toward shore. The goal of my research is to quantify the relationship between
variations in sea ice and polar bear distribution in western Hudson Bay.
I have three main research
questions. 1. Are the seasonal home range sizes, movement rates, and mean directions
of movement of polar bears on the ice of Hudson Bay related to sea ice characteristics?
How do these space-use strategies of Hudson Bay polar bears compare to those
of bears in other Arctic populations? 2. How do variations in several habitat
characteristics such as ice concentration and stage of development, floe size,
and bathymetry influence polar bear habitat selection on Hudson Bay? How does
polar bear habitat selection in Hudson Bay compare to habitat selection in other
Arctic regions? 3. Have movement patterns or habitat selection changed over
the past decade?
I will address these questions
using data from bears fitted with satellite collars between 1991 and 1998 combined
with new data from bears collared in September 2004. I will analyse the location
data along with data on ice conditions from the years of interest in a Geographic
Information System (GIS). Advances in both GPS-satellite collar technology and
GIS technology make it possible to look in detail at what bears are doing out
on the ice.

Adult female
bear from the western Hudson Bay population newly fitted with a GPS-satellite
collar that will provide 6 locations per day

The results of this study
will help us better understand how polar bears in Hudson Bay are affected by
variations in ice condition, and how these bears may differ from high Arctic
bears in their habitat selection strategies. This can provide insight into what
drives polar bear movement patterns and distribution. In addition, models of
habitat selection will allow researchers to predict polar bear distribution
on the Bay given specific ice conditions, which will help researchers predict
how the local ecosystem may be altered as the global climate changes.
Literature cited:

1. Lunn NJ, Schliebe S,
Born EW. (comps. and eds.) 2002. Polar Bears: Proceedings of the 13th Working
Meeting of the IUCN/SSC Polar Bear Specialist Group, Nuuk, Greenland. IUCN,
Gland, Switzerland and Cambridge, UK.
2. Smith TG. 1980. Polar bear predation of ringed and bearded seals in the land-fast
sea ice habitat. Can. J. Zool. 58:2201-2209.
3. Ramsay MA, Stirling I. 1988. Reproductive biology and ecology of female polar
bears (Ursus maritimus). J. Zool. 214:601-634.
4. Stirling I, Derocher AE. 1993. Possible impacts of climatic warming on polar
bears. Arctic 46: 240-245.
5. Parkinson CL, Cavalieri DJ, Gloersen P, Zwally HJ, Comiso J. 1999. Arctic
sea ice extents, areas, and trends, 1978-1996. J. Geophys. Res. 104:20837-20856.
6. Stirling I, Jonkel C, Smith P, Robertson R, Cross D. 1977. The ecology of
the polar bear (Ursus maritimus) along the western coast of Hudson Bay. Can.
Wildl. Serv. Occas. Paper No. 33.
7. Stirling I, Lunn NJ, Iacozza J. 1999. Long-term trends in the population
ecology of polar bears in western Hudson Bay. Arctic 52:294-306.