As Sea Ice Melts, Western Hudson Bay Polar Bears Head to Land for the Summer

With summer underway, the sea ice in Canada’s Hudson Bay is melting rapidly, transforming it from a solid hunting platform for polar bears to open water. This annual pattern forces polar bears to land and marks the beginning of their fasting period, as their main prey, seals, become inaccessible to them until the bay freezes over again in winter.

Updated: July 14

Sea ice has now almost completely disappeared from Hudson Bay. It’s not record-setting this year, but it’s still on the early side. We generally calculate the time bears spend on land from the date when 30% of sea ice in the bay is left. By that metric, Western and Southern Hudson Bay saw their 4th and 9th earliest sea ice break-up in 47 years of satellite data.

However, we're seeing several polar bears hanging on to very small patches of sea ice east of Wapusk National Park until as late as July 9. 

While this behavior isn’t new, until now researchers haven’t fully understood why bears choose to stay on such marginal ice, and how many do so. A new multi-partner project led by the Mushkegowuk Council in Ontario and including support from PBI will help us understand for the first time what’s happening as the ice melts. For example, do they need a minimum thickness or concentration of ice to support their weight and allow them to hunt successfully? Understanding how polar bears use these shrinking patches of ice will help us understand how they might adapt to changing sea ice conditions.

Updated: June 18

This year, sea ice in Hudson Bay started to melt relatively early. Western Hudson Bay’s sea ice cover just dropped to below 50%, while Southern Hudson Bay just dropped below 80%. By late July, Hudson Bay will have melted out completely for the year. Readers might recall last year’s extremely unusual ice melt season, which saw persistent winds push and pile up sea ice in Western Hudson Bay, preserving the ice there and providing hunting opportunities for polar bears deep into July. However, this meant that at the same time there was very little sea ice left in Southern Hudson Bay, which saw its earliest sea ice disappearance date on record, with potentially negative impacts for polar bears there.

However, it’s not just the extent of sea ice that matters to polar bears, but also the “quality” of the ice. This year, the sea ice is already broken-up into many small ice floes, as can be seen on satellite images, possibly due to the generally declining sea ice thickness and recent windy conditions in the region. While this type of ice still provides some opportunities to hunt for seals, it is overall difficult for bears to navigate efficiently. Indeed, looking at the recent distribution of GPS-tracked bears in Western Hudson Bay, we see that most have made their way to the western edge of the sea ice and are getting ready to come ashore to their typical summer grounds around the town of Churchill, Manitoba; some bears already have. 

Dr. Andrew Derocher, a Professor of Biological Sciences from the University of Alberta, reports from field work this spring that bears weren’t in great shape and seemed to struggle to kill the typical number of seals. He expects the bears to come ashore soon, unless a strong easterly wind event pushes sea ice back into Western Hudson Bay and delays the disappearance of sea ice. However, the weather forecast for the next week is for the opposite – continued winds from the West, as is typical in that region this time of year. Together with the current sub-optimal sea ice conditions, this does not bode well for polar bears in Western Hudson Bay. As the bears come ashore this summer, researchers will be able to get a better look at them to determine their health. 

Polar bears consider a variety of factors when deciding between coming ashore or staying on the ice a little longer. If they are desperate for food, they might stay, but the melting and drifting sea ice might then require them to put in a longer swim later to get back to shore. As often in nature, it is a tradeoff between energy expenditure and food. Historically, bears have chosen to come ashore early rather than stay out longer on such thin and patchy ice. It’s an open research question whether bears will adapt their behavior if ice conditions change. While polar bears are adapted to handle some such uncertainty, the warming climate and ever-lengthening ice-free period in Hudson Bay make it increasingly difficult for bears to stay well-fed and healthy.