This is a ‘mini web-site’ I had to create for my U316 Open university Course in 2008. I really enjoyed putting it together and I’m planning to review the issue for a future blog, so I thought I would share my original article first… enjoy
Image via Wikipedia
Polar Bears – Walking on thin Ice
The population of polar bears, Ursus maritimus, in West Hudson Bay, Canada is in decline. Is sea-ice reduction to blame or are other factors affecting the survival of polar bears?
Rationale for this website
There has been some argument as to whether or not polar bears should be classified as an endangered species. A lot of this may be due to a lack of data on population sizes, denial around the impact of climate change and disagreement as to what factors may be affecting population sizes. West Hudson bay is one of the most studied regions where the polar bear population has shown to be decreasing and while many factors may have a role in this reduced sea ice seems to be a significant factor, changes in sea ice coverage have been documented, which I hope to explain in this website.
I am speaking from a personal view based on my own research of the topic, but hope to be as unbiased as possible in my approach so people can make up their own minds based on the evidence presented.
My target audience is the general public, anyone interested in the current status and future of the polar bear.
The population of Polar bears in West Hudson bay is in decline.
The reasons for this are not entirely clear and further research is needed to establish the true extent of the problem and its causes.
At the current time with the evidence available it seems there are two main factors that may be behind the declining population, these are:
• Sea-Ice reduction as a result of climate change
• Over Hunting/Harvesting due to excessive quota
An overview and Introduction to the Issue
Polar Bear Swimming
There has been some argument as to whether or not polar bears should be classified as an endangered species. A lot of this may be due to a lack of data on population sizes, denial around the impact of climate change and disagreement as to what factors may be affecting population sizes.
The world population of polar bears is in the region of 20,000 to 25,000 bears with around 15,500 of those in Canada alone (3). In West Hudson Bay, Canada, the estimated population size in 2004 (the most recent date for which figures are available) was 935 bears (4). This population of polar bears is expected to decline by more than 30% within the next 3 generations (around 45 years) (5).
Whilst the West Hudson Bay population is one of the most studied polar bear populations, data is still scarce and what data is out there is subject to interpretation.
Dennis Compayre a local, born and raised in the Churchill area of West Hudson Bay, feels that there are as many polar bears in Churchill now as there were when he was a child and he also believes that all the scaremongering about the declining population is only good for one thing, the tourism industry, as he says “what better way to keep people coming than to tell them they’d better hurry to see the disappearing bears” (6).
On the United States Endangered Species Act polar bears are listed as ‘threatened’, on the Canada Species at Risk Act (SARA) they are listed as ‘Special Concern’ and on the International Union for the Conservation of Nature and Natural Resources (IUCN) red list polar bears are listed as ‘Vulnerable’ (7), this equates to a 10% or greater probability that species may be extinct in 100 years, ‘Vulnerable’ is the lowest division in the IUCN ‘threatened’ category which also includes ‘endangered’ and ‘critically endangered’ species (8).
For and against sea ice as a factor in the declining polar bear population in West Hudson Bay
West Hudson bay is one of the most studied regions where the polar bear population has shown to be decreasing and while many factors may have a role in this reduced sea ice seems to be a significant factor, changes in sea ice coverage have been well documented and there is more information available on the perceived effects of sea-ice reduction on polar bear populations than any other potential threat to polar bear populations. The population in West Hudson Bay has declined by around 22% between 1987 and 2004(4) as shown in Table 1 below.
Estimated population based on aerial survey
||Risk of Future Decline
|Estimated population based on aerial survey
Table 1: West Hudson Bay estimated population data (3, 4, 9)
Sea Ice Reduction
The ice cover in Hudson Bay normally melts completely every summer, however now the break up of sea ice is around three weeks earlier than it was 30 years ago; this means the bears have to stop hunting earlier (10). The maximum sea ice cover is down by around 1.5% per decade and permanent polar pack ice has declined by around 10% per decade (11). Polar bears are dependent on sea ice for breeding and feeding. Earlier melting and later freezing increase the amount of time polar bears a restricted to land thus limiting access to food (12).
Polar Bears fast on shore for at least four months until sea ice refreezes in autumn and hunting resumes. The Polar bears survive the summer by using stored fat reserves, scavenging, feeding on vegetation and hunting other marine mammals however these food sources are not adequate to maintain a healthy body weight, the bears need to obtain the majority of their annual energy intake form the hunting of seals on the sea ice (11).
Pregnant females can fast for up to eight months. Once they have given birth they nurse cubs until they reach 10/12 Kg before returning to the sea ice to hunt (11). The average mass of female polar bears has decreased from around 290Kg in 1980 to around 230Kg in 2004(11). There are indications that females below 189Kg do not reproduce (11). Adult health is in decline and cubs in their first year are in poorer condition, as well as there being a decline in the numbers of cubs surviving (12). The decreased cub survival rates correlate to the earlier break up of the sea ice (11).
Earlier Sea ice break up is a result of climate change; spring air temperatures are increasing the rates of warming between 1971 and 2001 show a rise of between 0.5oC to 0.8oC (9). Increasing temperatures also decrease ice thickness and increase drift (5). Earlier sea-ice break up has been shown to be directly affecting the survival rates of 0-1year, 2-4 year and 20+ year old polar bears, with only the 5-19 year age group not being adversely affected (9).
Between 1991 and 2005 the annual home range size, annual ice cover and minimum ice cover have declined, leading to increases in the total distance travelled and seasonal ,movements of the polar bears (9). Increased open water means there are greater distances between land and sea ice which leads in increased travel and swimming times which may lead to increased drowning of polar bears (11). Other threats induced by sea ice reduction include starvation as a result of reduced access to and abundance of seals (3).BBC TV Wildlife Presenter Nigel Marven is concerned about the deliberate ‘seeking out’ of skinny polar bears to be used as ‘evidence’ that bears are starving due to climate change (6).
As one of the southern most populations the West Hudson Bay region is and will continue to be amongst the first affected by climate change and sea ice reduction and may indicate what could happen in more northerly regions (9).
Image:The normal extent of sea ice cover in Winter (left) and summer (right) (14)
A new book from one of the top global warming skeptics, Bjorn Lomburg, tries to downplay or even dismiss global warming as a threat to polar bears, stating they are at greater risk from hunting (13). Andrew Derocher, Scientist for the World Conservation Union, feels that the only reason for denying the danger of climate change to polar bears is by those who have a “Clear interest in hunting them” (Telegraph).
The main reasons for the hunting/harvesting of polar bears are traditional Inuit harvesting for food and materials and hunting for sport (5). Polar bears are an important part of Inuit culture (14).
The current harvest in West Hudson Bay of up to 64 bears per year is too high, the IUCN state that this figure is unsustainable due to declining numbers as a result of climate change and may be a contributing factor to the decline in numbers. There would need to be a population of at least 1400 to sustain a harvest at current levels, more than 500 bears more than the estimated 2004 population of 935 bears (9). The life history of polar bears shows how the populations can be easily depleted by harvesting. Natural population increases are slow to recover due to late maturation, long intervals between births, small litter sizes and high adult survival rates (16). Low reproduction rates increase the vulnerability of polar bears to all threats and reduce their adaptability to change (5).
Reports of increased sightings of polar bears near human settlements have been interpreted as evidence of increasing population size by Inuit hunters; this has led to increases in the harvest quotas. A more likely explanation of the increase in sightings is that of bears searching for food during the prolonged open-water season (17).
Table 2 below shows how the quoted harvest levels compare with population data (that were also shown in Table 1 above), it can be seen that at a rate of removal of 46.8 bears per year for the 2002-2007 period alone amounts to 234 bears, only 25 bears below the total decline for the 1987-2004 period (3,4,9). This shows how the same data that has been used as evidence of population decline as a result of sea ice reduction due to climate change can also be interpreted as evidence of population decline due to over-harvesting.
||Permitted Kill quota per year (p/y)
||2002-2007 mean kill p/y
||2002-2007 Total kill
|Number of Polar Bears
Table 2: West Hudson Bay Hunt/harvest Quota compared to population decline
Other than Climate change and Hunting/Over-harvesting the WWF (World Wildlife Fund) (18) and ICUN (5, 9) list the following as the main additional threats to the polar bear population:
• Food pollution/contamination – toxic chemicals (pollutants such as dioxins) and heavy metals (such as mercury)(18)*
• Oil Pollution of water – due to shipping and industry (18) commercial and industrial (9)*
• Habitat loss/disturbance/degradation – due to industrial development and oil and gas explorations (18). Mining and transport (5)
And to a lesser extent:
• Cannibalism (18) (which may increase with a decreasing availability of prey (11)
• Tourism (18)
• Scientific research (18)
• Human conflicts (18)
*(The threat of pollution is that the pollutants accumulate, building up as they move up the food chain before being ingested by polar bears, who are at the top of the food chain, where it can affect reproduction rates and the immune system, making polar bears more vulnerable to disease (14).)
Towards a sustainable future?
What is/can be done to protect the future of the West Hudson Bay Polar Bear populations?
The IUCN (5,9) recommendations to protect polar bear populations are that harvest quotas should only be increased where local knowledge is supported by scientific evidence and that management plans should be introduced, but it does not specify what these plans should include. Other recommendations include increasing research and protected areas (5,9).
The WWF (18) make the following suggestions to tackle and prevent further decline of polar bear populations:
• Cut greenhouse gas emissions
• Conservation management plans – that manage all threats
• No industrial developments – in areas important to the survival of polar bears
• Reduce hunting/harvesting quotas to sustainable levels.
Image: Polar Bear scavenging for food (21)
Some claim that polar bears may be able to adapt to terrestrial life by “eating birds, caribou and other terrestrial species” (19) however the reality is that the low food resources, for sustaining a large body mass, in arctic regions mean that adaptation to terrestrial life is unlikely for polar bears (11) and as the bears get hungrier they are more likely to wander in to human settlements in search of food, leading to increased sighting including such things as polar bears being seen eating plastic bags and petroleum products(3).
Overall there are very few formal marine conservation areas and no formal protection for polar bears across most of Canada. There is some protection for denning and onshore habitats for polar bears of the Wapusk National Park and Polar Bear Provincial Park in the Hudson Bay region, with management plans being developed for maternity denning in the Cape Tatnum and Cape Churchill Wildlife management areas (3).
There is a proposal to reduce the harvest/hunt quota for the 2008-09 period to just 8 animals in the West Hudson Bay region (3).
Answers to some frequently asked questions about Polar Bears:
1. What does Ursus maritimus mean? It is the Latin scientific name for the polar bear that means ‘sea-bear’ (14, 20)
2. Where do Polar bears live? In the Arctic Circle across Canada, USA (Alaska), Russia, Greenland and Norway (14)
3. Do Polar bears live in Antarctica too? No, despite the regular use of images of polar bears and penguins together the two live at opposite ends of the Earth.
4. How many polar bears are there? Worldwide there are between 20,000 and 25,000 polar bears, of which 15,500 are in Canada. In West Hudson Bay there are around 935 polar bears. (3, 4, 14, 20)
5. What do polar bears eat? The main prey for polar bears is Ringed Seals, although they will eat some other marine and terrestrial animals and other food sources if they need to (20).
6. How long do polar bears live? The natural life span for polar bears is between 15-25 years, with females usually living longer than males and bears in captivity living longer than those in the natural environment (14,20).
7. Is the polar bear an endangered species? Most national and International endangered species lists classify the polar bear as ‘threatened’ ‘vulnerable’ or of ‘special concern’, in short this means the polar bear is an endangered species (7, 14, 20)
8. How many cubs do polar bears have? The usual litter size is 1-2 cubs, occasionally larger litters, not usually more than 3 cubs, do occur but this is not common (20)
9. Is polar bears fur actually white? No, it is actually transparent and reflects light giving the appearance of being white (14).
10. How big are polar bears? A male polar bear can weigh 400-600 kg or more and measure 2.5 to 3 metres, while females are about half the size of males and usually weigh much between 150-300kg, measuring 1.5 to 2.5 metres (14,20)
Blog and local information, direct from Churchill, West Hudson Bay Polar Bear Alley
Science based non-governmental blog and discussion forum Climate progress
Greenpeace’s project Thin Ice website, with videos and blogs from polar explorers.
International Polar Year 2007-2008 , A scientific programme to study the arctic and antarctic regions in 2007-2008
The Natural Resources Defence Council (NRDC), Polar Bear SOS , information pages from the NRDC environmental action group.
Comprehensive Polar Bear information from Polar Bears International , a non-profit organisation
(1) WWF (2008) Polar Bear Image [online] Available from: http://www.worldwildlife.org/climate/images/polar-bear0901.jpg
(2) Robby Bubble Website (2008) Polar bear swimming image
(3) COSEWIC (2008) Assessment and Update Status Report on the Polar Bear Ursus maritimus in Canada
SPECIAL CONCERN [online] SARA Available from: http://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_polar_bear_0808_e.pdf
(4) Carlton, J., (2005) Is Global warming killing the polar bears? The Wall Street Journal 14 December 2005, pB1.
(5) Schliebe, S. Wiig, Ø., Derocher, A. & Lunn, N. 2006. Ursus maritimus. [online] IUCN 2007. 2007 IUCN Red List of Threatened Species. Available from: www.iucnredlist.org [accessed 10 September 2008].
(6) Jones, D., (2007) ‘Polar bears on the brink? Don’t you believe it’ [online] Daily Mail. Available from: http://www.dailymail.co.uk/news/article-500424/Polars-bears-brink-Dont-believe-it.html
(7) WWF-Canada (2008) WWF-Canada position statement on polar bears. [online] WWF Available from: http://wwf.ca/NewsAndFacts/NewsRoom/RESOURCES/PDF/WWF-Canada_Statement_PolarBears.pdf
(8) U316 Book 2, section 1.3.3
(9) Aars, J., Lunn, N.J., and Derocher, A.E.,(eds) (2006). Polar Bears: Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group, 20?24 June 2005, Seattle, Washington, USA. IUCN, Gland, Switzerland and Cambridge, UK.
(10) Stirling, I., and Derocher, A.E., (2007) Melting Under Pressure: The real scoop on climate warming and polar bears. The Wildlife Professional. Fall 2007 pp24-27
(11) Derocher, A.E., (2008) Polar bears and Climate change [online] Action Bioscience. Available from: http://actionbioscience.org/environment/derocher.html
(12) Anisimov, O.A., D.G. Vaughan, T.V. Callaghan, C. Furgal, H. Marchant, T.D. Prowse, H. Vilhjálmsson and J.E. Walsh, 2007: Polar regions (Arctic and Antarctic). Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, 653-685.
(13) Jowit, J., (2007) Row erupts over risk to polar bears [online] The Guardian. Available from: http://www.guardian.co.uk/environment/2007/oct/14/climatechange.conservation
(14) Armstrop, S.L., (2008) Polar Bears in depth [online] Available from: http://www.polarbearsinternational.org/polar-bears-in-depth/
(15) Langan, F., and Leonard, T., (2007) Polar bears ‘thriving as the Arctic warms up’ [online] The Telegraph. Available from: http://www.telegraph.co.uk/news/worldnews/1545036/Polar-bears-%27thriving-as-the-Arctic-warms-up%27.html
(16) Stirling, I., and Derocher, A.E., (1995) Estimation of polar bear population size and survival in Western Hudson Bay. Journal of Wildlife Management. 59(2):2 15-22 1
(17) Stirling, I., and Parkinson. C.L., (2006) Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic. ARCTIC Vol. 59, 3 P. 261?275.
(18) WWF (2008) Polar Bears in Canada: The current facts (January 2008) [online] WWF Available from: http://www.wwf.ca/NewsAndFacts/NewsRoom/factsheet_polarbears.asp
(19) Kizzia, T., (2008) Lacking studies, state still disputes polar bear ‘doom’. [online] Anchorage daily news. Available from: http://www.adn.com/polarbears/story/295420.html
(20)IUCN/PBSG (2001) Frequently asked questions about polar bears [online] IUCN/PBSG Available from: http://pbsg.npolar.no/
(21) Scavenging polar bear image [online] Available from: http://www.danitadelimont.com/Pix/US/02/US02_HRO0598_T.JPG