Polar Bear Research in a Changing Arctic

In January of 1992, a lone female cub was born in a den located on the lee side of a pressure ridge on the pack ice of the Beaufort Sea. In late March, the mother bear popped her nose through the den’s ceiling to let in the first rays of daylight for her cub, and over the next week slowly acclimated the cub to life outside the den. Eventually, the mom felt confident in her cub’s ability to tolerate the challenging environment and left the den for good to find her first meal in roughly five months. That April, researchers from the U.S. Geological Survey’s Polar Bear Research Program captured the family on the sea ice north of Prudhoe Bay, Alaska—giving the mom and her cub small ear tags with unique identification numbers and adding them to the database.

Twenty years later, I was part of a research team flying in a helicopter over the snow-covered sea ice of the southern Beaufort Sea in search of polar bears to sample for the program’s long-term population dynamics study, research that helps us understand how the bears are faring. We had been slowly flying over a network of intertwined leads (narrow slivers of open water between ice floes) when someone shouted, “There’s a bear!” It took me a moment to isolate the small flash of pale yellow within the flat light of the vast and snowy-white background. It was my first time seeing a polar bear in the wild and it was majestic. Once we were on the ice with the bear, we noted the ear tag indicating a previous capture. The grizzled 20-year-old, 200-kilogram female was the same individual captured as a 13-kilogram cub in 1992.

I have since seen hundreds of polar bears and the excitement has never waned. My colleagues and I are privileged to study the bears and feel the weight on our shoulders to continue to produce rigorous and timely science that can be used to ensure their long-term persistence. But over the past two decades, a looming question has emerged: How do you study an ice-dependent species when your study area is melting away?

A changing Arctic and the loss of “bear-able” days

The loss of sea ice habitat from human-caused climate warming is the primary threat to polar bears—and to the ability of researchers to study them. In 1992, sea ice was present in the southern Beaufort Sea throughout the year. In 2012, it was functionally ice-free in August and September. More recently, it has been ice-free, on average, for upwards of three months each year. The ice-free period is expected to continue to increase in duration unless greenhouse gas emissions are meaningfully reduced.

Changes to summer and fall sea ice conditions have been dramatic and garnered a lot of media attention. But winter and spring conditions have also deteriorated, which has increased the challenges and risks to field crews working on the sea ice. The thinner first-year ice that now dominates the southern Beaufort Sea is more mobile in winter and spring. It has become harder to judge ice stability and thickness—critical factors when deciding whether it’s safe to capture a bear.

Moreover, the frequency of wind-storm events in winter and spring has increased. Strong winds can crack and shear the sea ice, further fragmenting habitat and creating expanses of open water. Water vapor from the warmer exposed ocean mixes with the much colder air and condenses into fog. The fog can arrive with little warning, grounding air crews or leading to “boomerang flights” where conditions are suitable for take-off but deteriorate offshore, necessitating a hasty retreat to avoid getting stuck on the ice. Since 2001, our program has experienced a substantial decline in “bear-able” days (i.e., days we are able to fly and search for bears) due to poor weather conditions like extensive fog or high winds that create dangerous flight conditions. From 2001-05, we were grounded due to weather an average of 23% of the field season. From 2017-21, we were grounded an average of 56% of the field season.

Coping with uncertainty

If you are familiar with the television series Breaking Bad, then you probably recognize the name Heisenberg. Werner Heisenberg was a theoretical physicist best known for his uncertainty principle, which states (paraphrasing) there will always be a fundamental limit to the accuracy we can achieve for an estimated or predicted value. That said, a primary goal for scientists is to strive to reduce the uncertainty of results.

Consider wildlife abundance estimates. Accurate and precise population abundance estimates are “the coin of the realm” in wildlife biology. When accuracy and precision are high, uncertainty is low, and managers feel confident using those abundance estimates to inform essential management actions.

One of the ways to reduce uncertainty is to increase sample size—i.e., the number of observations analyzed. You can probably see the conundrum here for polar bear research: How do you increase sample size when the number of bear-able days is declining?

Our solution has been to invest in diversifying the methods for collecting data. Capture and handling bears (collecting measurements, taking samples for health assessments, and attaching tracking devices) yields the most diverse and highest quality data. Yet, deteriorating ice conditions are already impacting our work and will make capture less feasible in the years to come. Looking ahead, it will be important to adapt data collection methods to the sea ice conditions encountered during a given field season. In years when capture is infeasible, field crews will need to seamlessly switch to remote sampling methods like biopsy darting, passive genetic sampling (e.g., hair and scat collection), and observational surveys, even though they yield less data. We are also investing in developing statistical methods that can integrate multiple data sources, including Indigenous Knowledge.

A final thought

I often think about that first bear I saw in 2012. I wonder if she’s still alive (if so, she’d be 30 years old) and how she coped with the dramatic changes to sea ice habitat that occurred over her lifetime. Polar bear researchers also face challenges—not existential like the bears, but in continuing to provide rigorous science to guide conservation efforts. The U.S. Geological Survey’s Polar Bear Research Program is working to meet those challenges head-on. But time is running short to reduce greenhouse gas emissions, conserve Arctic sea ice, and ensure the long-term persistence of polar bears.

Dr. Todd Atwood is a research biologist and project leader with the U.S. Geological Survey’s Polar Bear Research Program. He has studied polar bears since 2012.