Transcript Polar Bears

Polar bears of western Hudson Bay and climate change: Are
warming spring air temperatures the ‘‘ultimate’’survival control
factor?
John Garcia
Luisa Ricaurte
9th March 2009
Polar bears of western Hudson Bay and climate change
1
 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
9h March 2009
Polar bears of western Hudson Bay and climate change
2
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)
9h March 2009
Polar bears of western Hudson Bay and climate change
3
Discussion points
Population stresses have been observed: decreases of reproduction,
subadult survival, body mass of some of those bears
Cause:
An earlier break-up of Hundson Bay ice
and 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“
Most cited bears: Southern Hudson
Bay polar bear–1 of 14 populations
found in Canada-reaches farther south
Polar bears and shrinking ice habitat:
used to argue severity of climate
change and global warming to the
general public
Nonclimatic causes
9h March 2009
Polar bears of western Hudson Bay and climate change
4
Nonclimatic
causes
Human-polar bear interactions in Western Hudson Bay
1. Scientific research
2. Tourism
3. Polar Bear Alert System
9th March 2009
•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
Polar bears of western Hudson Bay and climate change
5
Data are not clearly
reported and
conflicting information
exists
WH polar bear population between
around 1100 bears
WH most stable population
2772 captured bears, 145/ year
1100 recaptured bears (52-90%)
Handled bears
9th March 2009
Polar bears of western Hudson Bay and climate change
6
Dyck et al., 2008.
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.
9th March 2009
Polar bears of western Hudson Bay and climate change
7
Food availability and competition
“Incoherence between the long-term data on population estimates and the
predictions made by the authors”
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)
- 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
9th March 2009
Polar bears of western Hudson Bay and climate change
8
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
South Hudson
polar bear
9th March 2009
Polar bears of western Hudson Bay and climate change
9
Air temperature and climate variability around Hudson
Bay
Source of Data: NASA and U.S. National Climatic Data Center
9h March 2009
Polar bears of western Hudson Bay and climate change
10
Air temperature and climate variability around Hudson
Bay
Source of Data: NASA and U.S. National Climatic Data Center
9h March 2009
Polar bears of western Hudson Bay and climate change
11
Temperature and Artic Circulation Oscillation Index
- 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.
9h March 2009
Polar bears of western Hudson Bay and climate change
12
Conclusions from Dyck et al., on Stirling et al. 1999

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.
9h March 2009
Polar bears of western Hudson Bay and climate change
13
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”
9th March 2009
Polar bears of western Hudson Bay and climate change
14
QUESTIONS???
9th March 2009
Polar bears of western Hudson Bay and climate change
15
9th March 2009
Polar bears of western Hudson Bay and climate change
16