Current Status of the Southern Hudson
Bay Polar Bear Population
Martyn Obbard
Wildlife Research and Development Section
Ontario Ministry of Natural Resources
Will this…
…change to this?
If so, where, and how quickly?
Canadian Populations
Hudson Bay System
Annual Cycle
Hudson Bay System
Annual Cycle
Hudson Bay Sea-Ice
• Stirling et al. 1999. Arctic 52:294-306.
– Non-significant decrease in break-up date, 1979-1998; P = 0.07
• Stirling et al. 2004. Arctic 57: 15-26
– Trend in break-up dates now statistically significant (to 2002)
• Gough et al. 2004. Arctic 57:299-305.
– Incr. in ice-free season SW Hudson Bay 1971-2003; breakup
advance 3 d/decade
• Gagnon & Gough. 2005. Arctic 58:370-382.
– Earlier break-up James Bay, southern and western Hudson Bay;
~10 d/decade James Bay, W. H. Bay
– Later freeze-up in northern and northeastern Hudson Bay; ~3-5
d/decade
• Changes in break-up started earlier in western Hudson
Bay
Implications of Future Ice trends
• Sep 7 2007 – USGS releases 9 reports to inform
•
•
the USFWS polar bear listing decision
Overall conclusion: Projected changes in future
sea ice conditions, if realized, will result in loss
of approximately 2/3 of the world’s current polar
bear population by the mid 21st century.
Because the observed trajectory of Arctic sea ice
decline appears to be underestimated by
currently available models, this assessment of
future polar bear status may be conservative.
• USGS divided range into 4 ‘ecoregions’:
• Seasonal Ice Ecoregion which includes Hudson
Bay, and occurs mainly at the southern extreme
of the polar bear range (SH, WH, FB, DS, BB)
• Polar Basin Divergent Ecoregion where ice is
formed and then drawn away from near-shore
areas, especially during the summer minimum
ice season (SB, CS, LVS, KS, BS)
• Polar Basin Convergent Ecoregion where sea ice
formed elsewhere tends to collect against the
shore (NB, QE, EG)
• Archipelagic Ecoregion of the Canadian Arctic
(KB, NW, LS, GB, MC, VM)
USGS Conclusions
• Seasonal Ice Ecoregion – extirpation by 45 y
from present
• Polar Basin Divergent Ecoregion – extirpation by
45 y from present
• Polar Basin Convergent Ecoregion – extirpation
by 75 y from present
• Archipelagic Ecoregion - polar bears could occur
through the end of the century, but in smaller
numbers than now.
Ringed seal
Bearded seal
Ringed seal pup
Reduced time on sea ice
will…
• Decrease feeding period
→ Reduce stored fat
• Increase fasting period
→ Increase need for stored fat
• Reduce number of successful pregnant
females able to rear young
→ Population decline
Western Hudson Bay
• Stirling et al. 1999
– Declines between 1981 and 1998 in body condition,
cub survival, proportion of lone yearlings
– No detectable decline in population size
• Regehr et al. 2007
– Decline from 1194 (95% CI = 1,020—1,368) in 1987
to 935 (95%
CI = 794—1,076) in 2004
(
– Survival of adults stable
– Survival of juvenile, subadult and senescent bears
correlated with break-up date (~3 weeks earlier than
in 1987)
– Causal relation between earlier breakup and survival
Annual Ice-Free Period E. Hudson Bay, 1971-2007
Number of Ice-free Days E. Hudson Bay, 1971-2007
Southern Hudson Bay
• Obbard et al. 2006
– Significant declines in body condition for all
age and sex classes between 1984-86 and
2000-05
– Magnitude of decline greatest for pregnant
females and subadults
Mean Body Condition Index values (Cattet et al. 2002) for Southern Hudson
Bay polar bears, 1984-1986 and 2000-2005. (SF = solitary adult females,
AF = adult females with young, M = adult males, SA = subadults, ALL = all
classes combined).
• Obbard et al. 2007 Polar Bear Population Status
in Southern Hudson Bay, Canada
– No change in population size 1984-86 vs. 2003-05
– Some evidence for declines in survival in some age
classes
– Coupled with evidence of major declines in body
condition suggests population is at a tipping point and
declines are likely in the future
– Changes lagged in comparison to Western Hudson
Bay population
Survival
1984-86
Female Male
Cub
Yrlg
Subad
Adult
Senescent
0.739
0.738
0.921
0.923
0.533
0.601
0.596
0.858
0.858
0.397
Cub
Yrlg
Subad
Adult
Senescent
0.678
0.672
0.903
0.902
0.486
0.524
0.517
0.828
0.828
0.328
2003-05
Model averaged estimates of age and sex structured survival for the Southern
Hudson Bay polar bear population, 1984–86 and 2003–05. Bars are 95% confidence
intervals and include both model selection and estimation uncertainty.
Model averaged estimates of the size of Southern Hudson Bay polar bear
population, derived during years with intensive capture effort. Bars are
95% confidence intervals, and include both model selection and estimation
uncertainty.
Permafrost?
• Gough & Leung. 2002. Reg. Environ.
Change 2:177-184
• 50% reduction in distribution of
permafrost in Hudson Bay region by 2100
Maternity dens
Maternity dens
Food chain impacts –
Mismatch, alternative food?
Bearded seals
Born May
Weaning - 45 kg fat
Ringed seals
Born April-May
Weaning - 11 kg fat
Harbor seals
Born June-July
Weaning - 10 kg fat
Adaptation?
Adaptation?
Adaptation?
Adaptation?
Adaptation?
Adaptation?
Adaptation?
Adaptation to Climate Change?
• Can probably den successfully in other than
•
•
permafrost features
Cannot switch diet in any substantial way that
meets the annual energy budget—on average a
polar bear needs 43 ringed seal “equivalents” to
meet annual energy budget (Stirling & Øritsland
1995)
Suggestions that polar bears will adapt by
becoming “more terrestrial” are unrealistic
The Future?
• If the ice goes, so will the polar bears
• Even if Hudson Bay freezes over it may
not provide a functional hunting platform
for the bears sufficient to meet energy
requirements
• Bears in James Bay will be affected
soonest
Implications for northern communities
• Management agencies and user groups have
•
•
•
•
limited ability to provide direct response
Co-management agreements to reduce harvest
to slow population declines
Implications for “country food”, income
Pressure on federal and provincial/territorial
governments to make meaningful attempts to
reduce GHG emissions
Polar bear as in icon for societal change