The weather in Hudson Bay last year had positive and negative impacts for its polar bear populations this year.
According to Polar Bears International (PBI), due to an unusual ice breakup in June, the southern Hudson Bay polar bears were stranded ashore for 198 days––a record amount of time. In fact, they were only able to head out on the ice for the first time just before Christmas 2024.
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If that sounds like an awfully long time, it is. That amount of time ashore exceeds the critical fasting threshold of 180 days for polar bears, according to PBI. Any number of days above that margin can lead to the starvation of up to 21 per cent of adult males and 63 per cent of subadults.
In 2024, unusual winds pushed Hudson Bay’s sea ice to its west coast, giving polar bears in western sections of the bay along Manitoba and Nunavut nearly an extra month on the sea ice, says Flavio Lehner, chief climate scientist at PBI and assistant professor at Cornell University.
The western Hudson Bay bears had a relatively late breakup of July 15, according to PBI, similar to patterns of the 1980s.
Hudson Bay sea ice extent/Polar Bears International (PBI)/Submitted to The Weather Network
Hudson Bay sea ice extent. (Polar Bears International (PBI)/Submitted to The Weather Network)
However, the result left southern and eastern Hudson Bay ice-free, so the bears that came off the sea ice along the coasts of Ontario and Quebec were forced to stay on land for a longer period of time, he added.
“Unless the bears were really stuck on the Quebec coast, they should have had some time on some sea ice by now. [But] not sure about the quality of the ice, though. The full consequences of this historically bad ice year for [southern Hudson Bay] bears might take a little longer to be revealed,” said Lehner, in a recent email interview with The Weather Network. “It also depends on whether this spring will be better than last year’s, as successive bad years are a bigger issue.”
The most ‘lopsided’ ice breakup
The different wind direction that Hudson Bay experienced in May 2024 was attributed to the ice breakup. Lehner noted it was the “unusual winds coming from the east rather than the west” during the month that led to what was the “most lopsided breakup in recorded history.”
“In fact, more often than not, western Hudson Bay sea ice breaks up a bit before southern Hudson Bay. [In 2024], the south broke up over 40 days before the west, so very unusual,” said Lehner.
Southern Hudson Bay polar bears/Coexistence Films/Mitch Bowmile (Submitted to The Weather Network)
Southern Hudson Bay polar bears. (Coexistence Films/Mitch Bowmile (Submitted to The Weather Network)
There is also a possibility that as sea ice thins more quickly in spring due to global warming, it can be pushed around more easily by winds, he added, but it’s still unclear how big of an effect, if any, it had on this year’s breakup.
Too early to know how the southern bears responded
Geoff York, PBI’s senior director of research and policy, said researchers don’t know, yet, how the southern population reacted to the atypical year. They are still waiting for results from long-term monitoring data and tracking collected in both the southern and western Hudson Bay regions from the fall.
Some of the bears likely remained on the sea ice drifting west in the spring, potentially profiting from it, but ending up far from traditional use areas, he added. Others, however, might have chosen to get off the ice early to stay close to traditional areas, but consequently missed out on food.
“When we were up in Churchill, Man., this fall, there seemed to be more untagged bears, and bears that were perhaps experiencing tourism for the first time. That lined up with what our research colleagues were seeing during their fall survey efforts,” said York, in a recent email interview with The Weather Network. “Ongoing analysis of satellite tracking data, hair snare samples, and genetic biopsy dart data will help clarify how bears responded.”
Southern Hudson Bay polar bears camera trap/Alexandra Langwieder
Camera trap photo from community-led research in the Eeyou Marine Region of eastern James Bay. (Alexandra Langwieder/Submitted to The Weather Network)
York pointed out that “true adaptation” for organisms at the genetic and physiologic levels happen over fairly long time periods, but said the rate of change in the Arctic is exceeding the pace at which a long-lived mammal can fully adapt.
What scientists are now seeing across the polar bear spectrum would be better referred to as “behavioural adaptation.”
“While polar bears are one of the most narrowly adapted of all bear species, having fully adapted over time to hunting, consuming and uniquely processing a fat-focused diet, they still have some plasticity,” said York.
Some bears on land with higher energy needs, he said, including juveniles and the growing, pregnant, caring for dependent-young, or just adult bears who came ashore a little thin, do forage and have been documented to raid shorebird and goose nests, catch and eat anadromous fish if available, and scavenge any carcass.
Southern Hudson BayCoexistence Films/Mitch Bowmile 2
Southern Hudson Bay polar bears. (Coexistence Films/Mitch Bowmile (Submitted to The Weather Network)
“We also have documentation from Svalbard of polar bears stalking and killing small reindeer, and in southeastern Greenland, some polar bears are substituting freshwater, glacial-front ice for sea ice in accessing seal prey,” said York.
Sea ice is like a ‘giant dinner plate’ for polar bears
For polar bears, if hunting on sea ice continues to decrease because of warmer days, land-based foods “are simply no replacement for marine mammal prey at the population level,” York said.
“Options are less abundant range-wide and they simply lack that high fat that polar bears need to thrive,” said York. “While the southeastern Greenland situation is heartening, and those bears appear to be thriving today, as the world continues to warm, those glacial front habitats are also threatened.”
Southern Hudson Bay polar bear/Alexandra Langwieder
Southern Hudson Bay polar bear. (Alexandra Langwieder/Submitted to The Weather Network)
York said the sea ice “acts like a giant dinner plate” for polar bears since they need the coverage to hunt their blubbery seal prey. When they’re on land, they are largely fasting and lacking their high-fat marine mammal prey, losing about two kilograms of weight per day.
Polar bears spending more time on land over time
Spanning the last 30 years, polar bears in western Hudson Bay have begun spending nearly a month longer on land than their predecessors did, resulting in the bears stretching their limits of how long they can fast, York added.
“Furthermore, if polar bear moms didn’t have a long enough hunting period on the ice, then they may not be healthy enough to give birth and successfully raise their cubs,” said York. “
“We basically need three good years in a row for a mom to successfully have cubs and then raise them to subadults, with higher chances of surviving each of those critical years. One bad year in the middle, and we can see the survival of dependent young decline rapidly.”
Freeze-up and ice-free days in Hudson Bay/Polar Bears International (PBI)/Submitted to The Weather Network
Average freeze-up, breakup and ice-free days in southern Hudson Bay. (Polar Bears International (PBI)/Submitted to The Weather Network)
In western Hudson Bay, the 10-year average number of the ice-free period was about 125 days per year in the 1980s and about 150 days in more recent times, Lehner noted. In southern Hudson Bay, those numbers were about 140 days in the 1980s and 155 days today.
The long-term trends show a lengthening of the ice-free period of more than seven and five days per decade for the two regions, respectively.
However, there is a lot of year-to-year variation because of random weather variations like what occurred in 2024, Lehner was quick to point out.
“Those weather variations are natural and not strongly affected by climate change, but they now happen on top of a gradual trend towards a warmer and more ice-free world. This means more time on land for polar bears,” said Lehner.
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What will 2025 and beyond hold for Hudson Bay polar bears?
With a new year, temperatures in the region have returned to below freezing and wind directions have switched back to normal. Sea ice in southern Hudson Bay has started to advance again, Lehner said.
However, the southern locale enters the new year with record-low sea ice coverage. It was 38 per cent on Jan. 1 whereas the normal would be 100 per cent. The next lowest was approximately 70 per cent. It is expected to freeze up relatively quickly now, perhaps with a few hiccups depending on local weather, Lehner said.
Southern Hudson Bay sea ice extent/Polar Bears International/Submitted to The Weather Network
Southern Hudson Bay sea ice extent. (Polar Bears International/Submitted to The Weather Network)
“This will cap an incredible sea ice year for southern Hudson Bay. A glimpse into the future, should we fail to halt climate change. We might expect a year like this to be common rather than unusual once we warm by 2 C globally, according to Stroeve et al 2024,” said Lehner.
“We currently stand at [approximately] 1.3 C already. This again is estimated to happen in the 2050s or 2060s, based on current climate mitigation policies.”
York said it’s hard to say that what happened in 2023 will cause a measurable shift in population abundance or distribution, but it will be more likely if the pattern repeats itself.
“Prime-age adult polar bears are incredibly resilient, but older bears, reproductive females, and cubs will likely struggle if in areas with delayed ice formation,” said York.
While a bad year can have “immediate, negative consequences” for more vulnerable bears, and potentially hurt reproduction in a given year, the focus is on the multi-year patterns for significant shifts to occur at the population level, York stated.
“Detecting the effects from a single bad year will take a few years to understand,” said York.
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Thumbnail courtesy of Coexistence Films/Mitch Bowmile.
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