Polar bears of western Hudson Bay and climate change: Are warming spring air temperatures the ‘‘ultimate’’survival control factor?

John GarciaLuisa Ricaurte

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Based on Dyck et al. (2007) Polar bears of western Hudson Bay and climate change: Are warming spring air temperatures the ‘‘ultimate’’ survival control factor? ecological complexity 4:73 – 8 4

Overview:- Introduction- Polar Bears: Food availability,

competition and interactions with human populations.

- Air temperature and climate variability around Hudson Bay

- Extrapolating findings to global population of Polar Bears

- Conclusions- Questions

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Polar Bears (Ursus maritimus)

“a multipurpose natural resource”

Charismatic megafauna that symbolize the Artic Traditional role for the Canadian Inuit: spiritual, mystical, cultural Economic role Sport hunting: local communities

“is endangered due to climate change and environmental stress” (Stirling, WWF, Derocher)

or simply “due to unsustainable harvests by human hunters” (Taylor et al., 2005)

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9h March 2009 4Polar bears of western Hudson Bay and climate change

Discussion points

An earlier break-up of Hundson Bay iceand Increase of the air temperature in spring

„a long-term warming trend of spring atmospheric temperatures“(Sterling et al.,….)

NOT SHOWN DIRECTLY TO BE THE „ULTIMATE FACTOR“Polar bears and shrinking ice habitat:

used to argue severity of climate change and global warming to the

general public

Most cited bears: Southern Hudson Bay polar bear–1 of 14 populations

found in Canada-reaches farther south

Population stresses have been observed: decreases of reproduction, subadult survival, body mass of some of those bears

Cause:

Nonclimatic causes

Nonclimatic causes

Human-polar bear interactions in Western Hudson Bay

1. Scientific research

2. Tourism

3. Polar Bear Alert System

•Since 1966. Marked 80% of bears. Capturing and handling wildlife repeatedly: effects on females with cubs•Works in spring: high stress-lactation, emerge from dens, end of fasting period

•Since 1980, during the fall, Oct.-Nov., early freezy-up, north migration•Polar bear viewing, short season, intensive, 6000 tourists, 15 tundra vehicles per day•Baiting, harassment and chasing of bears have been documented to occur

•Initiated in 1969, to protect local residents and vice versa•Bears will be deterred, captured, handled or destroyed•up to 2000: 1547 bears have been handled, average of 48 per year

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Data are not clearly reported and

conflicting information exists

Handled bears

2772 captured bears, 145/ year1100 recaptured bears (52-90%)

WH polar bear population between around 1100 bears

WH most stable population

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Decline of WH Polar bear has accelerated over the

time (Stirling et al.)

Decline has been constant! (Dyck et al.)

Up to 1997 did not change significantly, aprox. 1200

bears

Estimate of WH Bay polar bear. Regehr et al., 2007.

Dyck et al., 2008.

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Food availability and competition

1. Derocher and Stirling (1995): 1977-1992 - increasing trend (F = 4.16, p = 0.06, r2 = 0.23) not significant

2. Lunn et al. (1997a), 1984 -1995 - indicate a stable population (F = 0.71, p = 0.42, r2 = 0.07)

3. When both data sets are combined there is a significant increase in the population size (F = 6.40, p = 0.02, r2 = 0.27)

“Incoherence between the long-term data on population estimates and the predictions made by the authors”

- Stirling et al, the data responses reflect density-dependent population control mechanisms- Dyck et al., argue that these responses are typically detected in increasing populations

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South Hudson polar bear

Population distribution of Ursus maritimus in the southern HB

„independent populations; Increasing competition; food supply insufficient“Bears have learned to hunt seals during the ice-free period along the shores in

tidal flats

Western Hudson polar bear

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Air temperature and climate variability around Hudson Bay

Source of Data: NASA and U.S. National Climatic Data Center

9h March 2009 10Polar bears of western Hudson Bay and climate change

Air temperature and climate variability around Hudson Bay

Source of Data: NASA and U.S. National Climatic Data Center

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Temperature and Artic Circulation Oscillation Index

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- Strong cooling trend (about 0.4 ºC per decade since 50s)

- Temperature and AO (Artic Circulation Oscillation Index) are strongly correlated

- AO appers to be responsible for the changes in the tickness of sea-ice in the region.

- Because of the sea-ice becomed less thin, the air Tº increased.

Conclusions from Dyck et al., on Stirling et al. 1999

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Warming temperatures are the ultimate factor that explain Polar Bear population

conditions status in WH and in the Artic in general – unsupportable! Not scientific

sound.

Models do not support the disappearance of Polar Bear as a species

Uni-dimensional or reductionist thinking – not useful on complex systems!

Polar bear WH is exposed to several environmental perturbations :unknown seal

populations size, competition with other polar bear populations and human

interactions.

Dyck et al, argue:

„global warming may indeed have an effect on the ecology of polar bears, but it must be assessed with all the likely stress factors and their cumulative impacts“

“it needs the combined assessment of both natural and social systems”

“rather the consideration of isolated components”

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QUESTIONS???

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9th March 2009 16Polar bears of western Hudson Bay and climate change