Two Concerns for Managers of Polar Bear Populations in the Near Future Presentation to the Polar Bear Range States Meeting 24-26 October, 2011 Ian Stirling, PhD, FRSC on behalf of the IUCN Polar Bear Specialist Group ( Ian Stirling)
We have been losing sea ice in the summer at a rate of 10-11% per decade in response to climate warming. This is confirmed directly from real time satellite data. The first year the whole of the Arctic Basin could be monitored by satellite was 1979. This graph presents real data not results from a model.
Timing of Break-up in Relation to Year, Western Hudson Bay, 1971-2007 (after Stirling et al. 1999, Arctic 52:294-306; Lunn & Stirling unpublished data) 31 Jul Note: The decline is not linear. There is much large-scale inter-annual variation. Date of Sea Ice Break-up 21 Jul 11 Jul 1 Jul 21 Jun 11 Jun 1 Jun Comment: The average date of sea ice breakup in Western Hudson Bay is now a three weeks earlier than it was only 30 years ago. This rate of change is huge. r = -0.536 p = 0.0006 3 weeks 1975 1980 1985 1990 1995 2000 2005 Year
Comment: The average estimated weight of adult female in the fall has declined from about 280-290 kg to 230-240 kg in only 25 years. This loss of condition of adult females (and bears of all other age and sex classes) has resulted in smaller litters, lower cub survival and population decline. in Western Hudson Bay. 189 kg in fall (Stirling and Parkinson 2006)
On land without food: Mortality rates of adult males on land in Western Hudson Bay in relation to the number of days of open water between breakup in spring and freeze-up in autumn. The current open period is already in the 150-160 day range. 3% 6% 10% 20% 28 48% 130 or less 140 150 160 170 or more number of days Molnár et al. 2010)
Comment: As of December 31, 2010, there was still no ice forming in Davis Strait and eastern Hudson Bay. Recall how much interannual variation there was in breakup dates in Western Hudson Bay. That degree of variation, combined with demonstration of the lengthy delay of freeze-up in eastern Hudson Bay indicates such a delay is likely in Western Hudson Bay is possible, and likely sometime in the foreseeable future. If this happens, there will be significant mortality of polar bears and many hungry bears entering settlements in search of food. Sea ice concentration Value Percent Water 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 Ice 90-100 (Data source: http://nsidc.org/data/nsidc-0081.html)
What happened to the bears fasting on land in northern Labrador and Davis Strait during that extended period of open water in 2011? We don t know. But, we do know there was a significant die-off of harp seals along the coast of Labrador that bears may have fed on. We also know that in 2011, dead ringed seals (the main normal food of polar bears) that have died of an unidentified virus have been found in several areas of the Alaskan and Canadian Arctic. This is potentially worrisome for polar bears. ( Department of Fisheries and Oceans, Canada)
This diagram illustrates a critical part of the life history of the ringed seal, which makes up 80-90% of the food of polar bears. Adult female seals use the Claws on their front flippers To keep breathing holes in the ice open through the Winter. Snow drifts form over the breathing holes and females dig out small birth lairs under the snow drifts in which to hide their newborn pups from predation by polar bears. (from Smith and Stirling 1975)
( Ian Stirling) Ringed seal pups are about 3-4 kg at birth in early April, and 20-25 kg when they are weaned at 6 weeks of age. At that point, they are 50% fat and relatively naïve about predators (i.e., polar bears). They are the most critical part of the diet of the polar bear. In years when there is a reproductive failure of ringed seals, birth rates and survival of polar bear cubs are low.
Seals that breathe at newly formed breathing holes in young ice are vulnerable to polar bears when they surface to breathe. Adult female ringed seals have birth lairs beneath snow drifts like this to protect their pups from predation by polar bears. ( Ian Stirling) ( Ian Stirling)
The thickness of the snow cover over this ringed seal birth lair illustrates how much protection it provides from polar bear predation ( Ian Stirling)
This polar bear pounding down on the roof of a ringed seal birth lair illustrates how important a thick lair of snow cover is for the survival of ringed seal pups. ( Mireille de la Lez)
The protective lair of snow over this ringed seal birth lair was washed away by rain in an unseasonal warm spell when the temperature would normally be -20-30 C. All the seal pups in the area died of predation by foxes and polar bears. Widespread warm weather and early rain will accompany climate warming resulting in high mortality of ringed seals, and loss of food for polar bears. ( Ian Stirling)
Dead cub Dead cub Warm weather and possibly unseasonal rain in winter, that will accompany climate warming, can result in the collapse of polar bear maternity dens, resulting in she death of the mother and her cubs. ( P. Clarkson) ( Peter Clarkson)
The greatest long-term threat to the survival of polar bears is the melting of their sea ice habitat by climate warming. The timing and rate of climatedriven change for polar bears and their habitats will differ in different populations. However, there is a significant risk of a crisis situation due to an unusually long ice-free periods in Western Hudson Bay, or other populations of polar bears in a Seasonal Ice Zone, in the foreseeable future. Similarly, unseasonably early warm weather and rain in ringed seal birth lair habitat is likely to result in high mortality, with significant subsequent effects on polar bears. Managers in the Range States need to develop both long-term strategies and response plans for these events. ( Ian Stirling)
Thank you for listening