Despite a troubling forecast for the Southern Hudson Bay polar bear population if we fail to meet the goals set at the Paris Climate Agreement, a recent study led by Dr. Joseph Northrup of the Ontario Ministry of Natural Resources and Forestry shows a spot of good news for these bears. A population survey taken in 2021 estimated just over 1,000 Southern Hudson Bay bears, up from 780 bears in 2016, but within the margin of error for both studies.
The study, which was funded primarily by the Government of Nunavut, comes on the heels of a reported drop in the Western Hudson population during the same time frame, from 949 bears to 618.
“The polar bear story is very nuanced at short time scales, and this is a clear illustration of recent, regional variation among polar bear populations, including responses to recent good ice years versus bad ice years among other factors,” said Dr. John Whiteman, Polar Bears International's chief research scientist and assistant professor of biology at Old Dominion University.
Over the time period measured, Southern Hudson Bay experienced a string of better ice years due to natural variation, with the sea ice in early summer lingering longer there than in Western Hudson Bay, although the exact opposite took place this year (see “An Unusual Summer in Hudson Bay”). Scientists have long documented seasonal exchange between the two populations going back to the late 1980s through present, from both capture studies and coastal surveys.
Looking at just the sea ice habitat, on average, the Southern Hudson Bay bears had roughly 10 extra days per year on the sea ice during the study period. This means they had 10 more days to hunt seals before the summer melt forced them ashore, where they are largely food deprived. Longer hunting seasons have been linked to improved reproduction and cub survival rates.
Southern Hudson Bay is also likely recovering from an unusually high harvest event in 2010, both in total harvest and the percentage that was female. That singular episode could partially explain both the past decline, as abundance was reduced along with depressed reproductive output, and play a role in this potential increase, as females previously too young to reproduce are finally reaching maturity and seeing success.
A tale of two populations
“The Southern Hudson Bay bears benefited from natural variability in the weather,” said Dr. Flavio Lehner, our chief climate scientist and assistant professor of earth and atmospheric sciences at Cornell University. “During the ‘better’ ice years, slightly stronger westerly winds caused ice to pile up in the east and south of Hudson Bay, making it thicker and causing it to take a bit longer to melt in summer.
“While this is good news today for the Southern Hudson Bay population (and perhaps the Western Hudson Bay population if they drift on the ice to the south), a new study shows that it’s likely to be a very short gain as global warming will continue to gradually lengthen the ice-free season in both populations, with local extinction of the Southern Bay bears predicted if temperatures exceed two degrees Celsius of warming.”
Western Hudson Bay, on the other hand, has largely seen a continuation of the trend towards a longer ice-free season, with negative effects on the reproductive success of bears. These bears are now off the ice three to four weeks longer than their grandparents were.
“The results of the new analysis for both Western and Southern Hudson Bay are not surprising,” said Geoff York, our senior director of science and policy. “For the past five years or so, a number of us who have had long term experience viewing polar bears in Churchill have noticed what appeared to be far fewer bears in the Wildlife Management Area compared to historically high numbers, along with fewer family groups. At the same time, reports from colleagues suggested that some bears may be jumping off melting ice further east within Manitoba or in Ontario, suggesting some potential changes in onshore distribution within Hudson Bay.”
Need for further research
“Since the survey, we have continued to collect data, and it now looks like much (possibly most) of the increase in Southern Hudson Bay bears was due to the temporary redistribution of bears from Western Hudson Bay, likely in response to annual variation in the sea ice,” said Northrup. “We are seeing more bears than in the past near the boundary between the two populations and a lot of interannual variation in distribution in that area. This is probably natural variation in distribution that just so happens to be right at the boundary.”
Taken together, the two reports highlight the need for increased scientific monitoring, collaboration between regions, and, most importantly, climate action. In addition, the findings underscore the importance of increased vigilance and support of community coexistence efforts across the Hudson Bay Region.
“Shifts in abundance, and possibly distribution, have direct links to potential issues around polar bear-human conflict,” York said. “Unlike the drivers of climate warming, conflict-reduction and coexistence efforts are fully in the hands of those who live, work, and recreate in polar bear country. We have the knowledge and the tools to reduce threats to people while eliminating a source of mortality for bears already facing a challenging future in this region.”
While the uptick in Southern Hudson Bay bears is good news for now, it is critical to remember that any population gain in Southern Hudson Bay, or in other polar bear populations, can only be viewed as temporary as long as the greenhouse gas emissions which drive sea ice loss remain unabated. Without greenhouse gas mitigation, warming temperatures will mean ever-longer ice-free periods across Hudson Bay and beyond, and ultimately, declining polar bear abundance.
