Polar Bears: Facing a Changing Arctic
© A.E. Derocher, University of Alberta, Canada
Playing the long game
Understanding what fuels polar bear energy

Polar bears evolved from a brown, terrestrial omnivore to become a white, marine carnivore that has long thrived in the Arctic’s icy environment. But as Andrew Derocher explains, given the pace of change in the Arctic, evolution doesn’t favour this highly specialized bear of the ice.

Polar bear research has long been subject to unplanned interruptions: the nature of these fascinating animals and the environments they live in mean unpredictability is par for the course.

I once waited more than three weeks in a remote field camp for the fog to lift before I could start my work. A colleague once spent a month with a helicopter on standby waiting for good weather, and finally had to give up without even seeing a bear. Conservation takes a three-generation-length perspective—and for polar bears, that means 33 to 45 years. Arctic ecosystems are also incredibly dynamic, and snapshots in time can be misleading. As a result of all these factors, studying polar bears requires patience—and drawing conclusions about them requires long term data.

My research team recently investigated the population energy dynamics of polar bears in western Hudson Bay. Energy dynamics examines the total amount of energy stored in each bear in a population and its variation over time. Studying these changes allows us to understand the links the bears have to their prey and how changing ice conditions are affecting the population.

Our project built on the results of long-term research by Environment and Climate Change Canada and the University of Alberta. Monitoring the number of bears in a population is common, but we applied a new spin: we estimated the energy in each bear of a given sex, age and reproductive group in a population. Then we merged these data to estimate the energy in the overall population.

© Steve Morello / WWF

Taking an ecosystem approach

At this point, you might be wondering: Why study polar bear energy?

Gathering information about population abundance is useful for understanding harvest rates and population status, but it provides limited insights into the mechanics of a change over time. Increasingly, conservation biologists are interested in a broader ecosystem approach. The energy at one level of an ecosystem is affected by the level below. For example, the number of wolves that an area can support may be determined by the number of deer, moose and elk—and in turn, the number of herbivores in the area will be affected by the available vegetation.

The snow shows traces of a successful ringed seal kill made by a polar bear along a refrozen lead (crack in the ice). Such leads are prime polar bear hunting habitat because ringed seals maintain breathing holes in the young, thin ice.

The snow shows traces of a successful ringed seal kill made by a polar bear along a refrozen lead (crack in the ice). Such leads are prime polar bear hunting habitat because ringed seals maintain breathing holes in the young, thin ice.

©A.E. Derocher, University of Alberta, Canada

In our study, we found that the energy held by the western Hudson polar bear population declined by more than 50 per cent between 1985 and 2018.

That’s a major change—and obviously, if there is less energy in the bears, it means they’re either taking less energy from the seal populations (their main food source) or they’re using more energy. That’s the next question that needs answering.

Arriving at such insights requires us to take a long-term perspective, archive data, standardize methods and follow an incremental approach. Each research step takes us closer to understanding the natural and unnatural history of the bears.

From a conservation perspective, we’re most concerned about the complex effects of the climate crisis, which are increasingly complicated because of the possibility of new diseases and parasites travelling to the Arctic as southern species move north. We also know the bears are exposed to high levels of pollution, which weakens their immune system. Given that levels of pollutants circulating in polar bears’ blood increases as their condition declines—and that sea-ice loss also leads to skinnier bears—it’s easy to see the potential for new concerns.

© A.E. Derocher, University of Alberta, Canada
Merging local knowledge and long-term research and combating misinformation

Research provides a constant flow of insights, but we need to temper them against what has been seen in the past. Traditional ecological knowledge from northern people offers valuable context, and historic understandings can give us clues about modern observations.

But increasingly, observations made in the Arctic are communicated to the world without appropriate context. For example, we know that polar bears can eat more than 80 different species—from mushrooms to puffins to porcupines. However, does such a varied diet bode well for the future of polar bears in a warming Arctic?

It would be nice to think so, but we need a long-term perspective to be certain. Polar bears evolved from a grizzly bear (brown bear) ancestor. While it’s hard to be certain about exactly when the two species diverged—because of hybridization events in the distant past—it’s clear that polar bears retained the ability to eat almost anything in their environment that provides energy. Reports of polar bears eating a variety of foods are interesting, but they don’t provide meaningful insights into the bears’ likely future. Polar bears evolved to exploit an abundant food resource that was once spread widely across the Arctic sea ice: ringed seals and bearded seals. The seals’ blubber layer allows them to survive in the cold waters of the Arctic—and that same energy-rich blubber makes it possible for polar bears to survive.

Polar bears may eat a variety of species as the sea ice disappears, but they can only survive as long as they have an abundance of energy from seals as their primary prey. And we do know one thing for certain: polar bears used to live as far south as Sweden, but they disappeared from there as the ice melted. There are clear links between fossil fuel use and sea-ice loss, which means reducing greenhouse gas emissions is a critical part of polar bear conservation. We have an opportunity to act—and the sooner we do, the better the odds for polar bears.

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ANDREW DEROCHER is a biological sciences professor at the University of Alberta in Edmonton, Canada. He has been studying polar bears for 38 years.