Lindsay Towns, M.Sc. Candidate

Patterns of polar bear distribution in western Hudson Bay during the ice-free period

There are 20 relatively discrete polar bear (Ursus maritimus) populations distributed throughout the circumpolar Arctic1.

Aerial view of inland area dominated by lichen tundra habitat, riparian and lakeshore habitats Each population differs in distribution and movements as a result of the seasonal distribution of sea ice and prey. Some populations remain on the sea year round while other populations are forced on land when the ice melts completely. The western Hudson Bay polar bear population is an example of the latter. Hudson Bay undergoes a yearly pattern of sea ice freeze-up and break-up and for a 4 month period (July to November) the bears are forced ashore and must survive off their fat reserves which they acquired on the sea ice while preying on seals2. Once on land, the bears segregate by age, sex and reproductive class2. Pregnant females and females with young tend to travel inland (10-100 km). Adult males remain close to the coast while subadult bears, both male and female, can be found throughout the inland and coastal areas2. All bears show site fidelity and return to the same denning area or coastal area year after year2,3.

Taking the axillary girth of an adult female
to obtain an estimate of weight
In recent years, studies have shown that climate change effects (e.g., increasing temperatures) are most evident in the Arctic4. The Arctic sea ice, critical to polar bear survival, has shown an overall decrease in extent and thickness5,6 and a shortening of the sea ice season7. The effects of climatic warming will likely be first detected near the southern limits of the polar bears range, the western Hudson Bay population8 and effects have already been documented in this area. Ice break-up is now occurring 3 weeks earlier compared to the early 1970s9 and there is a significant relationship between the timing of break-up and body condition when bears arrive on shore (i.e., earlier break-up results in poorer condition)10. This means the bears have less time on the sea ice to accumulate fat reserves and a longer period on land using their limited reserves. There is also a strong correlation between the dates of break-up and where and when the bears come ashore8.

Formation of sea ice along the northern coast of Hudson
Bay in late October

The North Atlantic Oscillation and Arctic Oscillation are large scale patterns of circulation and pressure describing the world’s weather patterns. They have become a focus of study in the climate change debate since it has been shown that these indices are associated with strong inter-seasonal and inter-annual variability in both marine and terrestrial ecosystems11. The Arctic Oscillation index influences variations in the age of Arctic sea ice and summer sea ice extent12. The North Atlantic Oscillation may be associated with atmospheric circulation causing variations in the timing of sea ice retreat and formation13,14.

A polar bear sitting around, waiting for the sea
ice to form

Another important aspect of climate change is how it will affect human-bear interactions. Churchill is situated along the northern coast and when the sea ice begins to form in November the bears travel north. Therefore, bears can be found in town or in the surrounding area and can result in conflicts with the towns people. It is predicted that climate change will increase human-bear interactions due to the extended length of time the bears spend on land8. More bears will become nutritionally stressed and could show up in town or at the town dump searching for food.

Ear tagging an adult female with cubs of
year with a unique number that allows for
identification in future captures

The western Hudson Bay polar bear population has been a focus of research for over 30 years (1966-ongoing) providing an excellent opportunity to examine long term dynamics in distribution relative to large scale phenomena (i.e., climate change). The objectives of my project are to 1) describe the dynamics of polar bear distribution relative to age-sex-reproductive class over time, specifically examining segregation and fidelity, 2) examine correlates with polar bear distribution over time (e.g., North Atlantic Oscillation, Arctic Oscillation, sea ice break-up and formation), and 3) describe the spatial and temporal components of problem bears near Churchill.

Following a creek searching for polar bears in
Wapusk National Park, MB

The study is Geographic Information System (GIS) based and uses data collected by the Canadian Wildlife Service. The results of this study will provide insight into how the western Hudson Bay polar bear population has responded over time to both local (sea ice break-up and formation) and global environmental variables. This will lead to better predictions being made and a better understanding concerning the response of the western Hudson Bay polar bears to climate change. The results will also provide wildlife managers with information that can be used to make more informed management decisions with respect to the problem bears, tourism, and conservation.
Literature Cited

1. IUCN/SSC Polar Bear Specialists Group 2002. Polar Bears. In Proceedings of the 13th Working Meeting of IUCN/SSC Polar Bear Specialist Group. Edited by N. Lunn, S. Schliebe, and E. Born. IUCN Species Survival Commission. Occasional Paper No. 26 , IUCN, Gland, Switzerland and Cambridge, UK.
2. Derocher, A.E. and Stirling, I. 1990. Distribution of Polar Bears (Ursus maritimus) During the Ice-Free Period in Western Hudson-Bay. Canadian Journal of Zoology 68: 1395-1403.
3. Ramsay, M.A. and Stirling, I. 1990. Fidelity of Female Polar Bears to Winter-Den Sites. Journal of Mammalogy 71: 233-236.
4. Manabe, S., Stouffer, R.J., Spellman, M.J., and Bryan, K. 1991. Transient Response of a Coupled Ocean-Atmosphere Model to Gradual Changes of Atmospheric CO2, I. Annual Mean Response. Journal of Climate 4: 785-818.
5. Maslanik, J.A., Serreze, M.C., and Barry, R.G. 1996. Recent Decreases in Arctic Summer Ice Cover and Linkages to Atmospheric Circulation Anomalies. Geophysical Research Letters 23: 1677-1680.
6. Parkinson, C.L., Cavalieri, D.J., Gloersen, P., Zwally, H.J., and Comiso, J.C. 1999. Arctic Sea Ice Extents, Areas, and Trends, 1978-1996. J. Geophys Res. 104: 20 837-20 856.
7. Parkinson, C.L. 2000. Variability of Arctic Sea Ice: the View From Space, an 18-Year Record. Arctic 53: 341-358.
8. Stirling, I. and Derocher, A.E. 1993. Possible Impacts of Climatic Warming on Polar Bears. Arctic 46: 240-245.
9. Stirling, I., Lunn, N.J., Iacozza, J., Elliott, C., and Obbard, M. 2004. Polar Bear Distribution and Abundance on the Southwestern Hudson Bay Coast During Open Water Season, in Relation to Population Trends and Annual Ice Patterns. Arctic 57: 15-26.
10. Stirling, I., Lunn, N.J., and Iacozza, J. 1999. Long-Term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change. Arctic 52: 294-306.Hurrell, J.W. 1995. Decadal Trends in the North Atlantic Oscillation Regional Temperatures and Precipitation. Science 169: 676-679.
11. Hurrell, J.W., Kushnir, Y., Ottersen, G., and Visbeck, M. 2003. The North Atlantic Oscillation: Climate Significance and Environmental Impact. Geophysical Monographs 134: 1-279.
12. Rigor, I.G. and Wallace, J.M. 2004. Variations in the Age of Arctic Sea-Ice and Summer Sea-Ice Extent. Geophysical Research Letters 31.
13. Hurrell, J.W. 1995. Decadal Trends in the North Atlantic Oscillation Regional Temperatures and Precipitation. Science 169: 676-679.
14. Hurrell, J.W. and van Loon, H. 1997. Decadal Variations in Climate Associated with the North Atlantic Oscillation. Climate Change 36: 301-326.

For more information contact:

Lindsay Towns
CW405 Biological Sciences Centre
University of Alberta
Edmonton, Alberta
Canada, T6G 2E9
Phone: (780) 492-7599
Fax: (780) 492-9234
Email: ltowns@ualberta.ca

Andrew E. Derocher
CW405 Biological Sciences Centre
University of Alberta
Edmonton, Alberta
Canada, T6G 2E9
Phone: (780) 492-5570
Fax: (780) 492-9234
Email: derocher@ualberta.ca

Churchill dump

Unpredictable weather (e.g. fog) forcing a stop to the capture efforts for the day