By studying polar bears at the southern edge of their range, where sea ice loss is greatest, scientists can predict what will happen with other populations as the Arctic continues to warm.

© Dan Guravich/Polar Bears International

4/3/2018 1:25:43 PM

Sea Ice Ecology Study

Scientists are getting ready to head out for spring field work on Hudson Bay as part of the Sea Ice Ecology project. Why do they study sea ice and the polar bear’s relationship to it? Alysa McCall, our director of conservation outreach and staff scientist, explains.

Polar bears rely on sea ice to reach their seal prey—which is why scientists pay close attention to Arctic sea ice, tracking it as it grows in winter and shrinks in summer. Every year, sea ice reaches its maximum at the end of winter (usually in March) and the minimum at summer’s end (usually in September).

Satellites have been tracking Arctic sea ice for decades. Their data shows that, this year, the ice reached its maximum on March 17th—and it was shockingly low. In fact, it was the second lowest maximum in the satellite record, just behind 2017.

To put this into context, this year’s area of missing ice was more than 1.5 times larger than the state of Texas—or 1.16 million km2 (448,000 mi2) below the 1998-2010 average (15.64 million km2/6.04 million mi2). What’s more, the four lowest maximums in the satellite record have all occurred in the last four years.

What Hudson Bay ice can tell us

The Western Hudson Bay polar bear population is one of 19 worldwide populations; these bears live near the southern limit of the polar bear’s range. Scientists have studied them since 1980, allowing us to identify population trends related to the amount of sea ice coverage. Hotter temperatures have resulted in earlier sea ice breakup dates and later freeze-ups on Hudson Bay, leading these polar bears to spend longer periods on land, away from their seal prey.

Research shows that the date of sea ice breakup has a significant impact on the survival of cubs, sub-adult bears, and bears older than 20 years of age (i.e., the youngest and oldest). Furthermore, studies have linked long ice-free periods with declines in body condition, reproduction, and abundance. As a result, the Western Hudson Bay population has dropped from 1,200 polar bears in 1987 to 806 in 2011.

The neighboring Southern Hudson Bay polar bear population has also been impacted by changing sea ice. This population was stable for decades, but over the past few decades, sea ice loss has led to declines in body condition. By 2012, these bears were spending 30 days longer on land on average compared to 1980—a shift linked to weight loss across sex and age classes. Between 2011 and 2016, their numbers declined from about 943 bears to 780 bears, a drop of 17% in five years. During the same period, the proportion of yearlings (1-2 years old) declined, while the proportion of cubs (0-1 years old) remained fairly steady, suggesting a decline in cub survival rates.

Long-term data sets like these are critical to helping scientists understand the link between sea ice and polar bear health—and that’s why Polar Bears International helps support such research. Polar bears in more southerly areas can help us predict what will happen in other populations as sea ice loss continues to impact the Arctic.

Ear tags and more

Current studies in Hudson Bay are asking a host of important questions about both populations. PBI is supporting multiple aspects of this research, which is being conducted by different agencies, including Environment and Climate Change Canada, the University of Alberta, and the Ontario Ministry of Natural Resources.

In particular, scientists are deploying GPS ear tags in the spring and fall on sub-adult and male bears, giving us a glimpse into how these poorly understood groups use the sea ice. Additionally, PBI has helped extend fall population surveys toward the south to help us understand areas where Western Hudson Bay bears may overlap with Southern Hudson Bay bears. This information will help refine population estimates and boundaries, provide insights into how sea ice changes may impact population distribution, and support the management of sustainable harvest levels. 

Researchers are currently packing up to head back to Churchill in mid-April as part of the Sea Ice Ecology project. Once there, they’ll stay for about three weeks, heading out over the ice as weather allows while searching for Western Hudson Bay bears of all age and sex classes. Scientists will measure bears and assess their health; they’ll also fit some bears with GPS ear tags that should operate up to six months. This will be one more important piece to add to the polar bear conservation puzzle.

In a warming Arctic, the duration of sea ice is predicted to continue to decline and Hudson Bay will be affected earlier than some other regions. By continuing to work with various partners to collect data on some of the first populations impacted by climate change, we can help provide science-based advice for the ongoing management and conservation of polar bears.

You can also help by acting on climate change and supporting the reduction of carbon emissions in your community–here’s how to get involved.

Thank you to Banrock Station Wines and SeaWorld Busch Gardens Conservation Fund for continuing to support the Sea Ice Ecology project.

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