Back on the Sea Ice

Few places are as remote and wild as the habitat that polar bears call home, but it’s also one of the most challenging places to study them. While many people have seen polar bears up close and personal near Churchill, Manitoba during the autumn migration, the density falls dramatically when the bears disperse onto the sea ice to hunt seals. There, they work hard to regain the fat they need to undergo the summer ice-free period when food is scarce or, for most bears, non-existent. The sea ice is where polar bears make their living and if one wants to understand them, it’s best to study them where they work and less so where they holiday.

Spring 2022 gave my research program the chance to return to gain new insights into the natural and unnatural history of the bears out on the sea ice. Two years of research were lost to the pandemic, and this interrupted my on-ice research in Hudson Bay. The focus of this study is to understand the relationship between polar bears, seals (ringed and bearded), and sea ice in a warming Arctic.

I’ve worked with many polar bear populations across the Arctic and the sea ice of Hudson Bay is by far the most challenging. We find polar bears by following their tracks. For the study I’m conducting, I seek subadults and adult males so we can attach ear tag satellite transmitters.

One of the key monitoring parameters for polar bears in a warming Arctic is the number of days they must fast each year when they are unable to hunt. Thanks to collars, which can only be safely worn by adult females, we’ve gained good insights on the movements of those bears from years of tracking; we know when they come off the ice and when they return. But we still have a lot to learn about subadults and adult males.

Climate change is altering the sea ice conditions and it’s not making research easier. Polar bear researchers are truly fair-weather biologists. We need sunny days, not too cold, a good bit of snow on the ice, enough stable ice, and not too much wind. In reality, that’s a very big ask. Why such wondrous conditions? Snow is needed so the bears leave tracks, sun is needed so we can see those tracks from a helicopter and follow the bears, low wind is mandatory as blowing snow will erase tracks, and if there’s no ice, there’s no polar bears. The cold part? If temperatures are really low, we risk not being able to start the helicopter if the battery gets chilled. I love working on the sea ice but overnighting there is something to be avoided.

Now, the stable ice part. Ponder a jigsaw puzzle on a table and then take a marker and draw a curvy line across it to represent the path of a polar bear. Next, scramble the puzzle and find the bear that’s supposed to be at the end of the path. This gives one an inkling about how sea ice is affecting both polar bears and polar bear researchers. Warmer conditions produce thinner ice, and that ice is more prone to break off and drift on winds and currents. Also, because the ice often now forms later in the autumn, it misses the accumulation of snow that helps us find the bears. Trying to piece together a polar bear’s fragmented tracks from a zigzagging helicopter is not for the faint of stomach.

The right amount of snow is also critical for ringed seals as they rely on the snow piling up along pressure ridges (bumps where ice sheets collide) to make birthing lairs where they can rear their pups in a somewhat safer microenvironment. Of course, polar bears spend much of their spring seeking these lairs. More snow helps protect seal pups from polar bears: thicker snow cover means polar bears must work harder (and take longer) to gain access to the pups, which can escape into the water.

On the other end of the spectrum, too little snow can mean female ringed seals give birth to their pups on the sea ice surface. I saw evidence of this when I worked in Svalbard, Norway. I recall flying out one day and seeing the ice dotted with fluffy ringed seal pups. We flew over the next day and the ice was spotted with dots of red. Arctic fox had cleaned up the pups. It’s a Goldilocks issue for polar bears when it comes to ringed seal pups: not too much snow, not too little (or it’s a bonanza for fox), it must be just right.

In many ways, the same pattern applies to sea ice. Not too thick, not too thin. If ice is too thick, such as what we see in the High Arctic with multiyear ice, the ecosystem isn’t very productive as sunlight is blocked and the phytoplankton at the bottom of the food chain languish. If the ice is too thin or doesn’t last long enough, those species that rely on it for habitat can’t thrive there.

Looking back on the spring 2022 field season, it was an amazingly rejuvenating and inspiring trip. We met our objectives, set the path for coming years, and I got the best photo of a ringed seal I’ve ever managed. How did I get the photo? Well, tracking polar bears from a helicopter can create havoc with folks prone to airsickness, which is pretty much everyone on their first flights. One of the crew was feeling a tad poorly and we flew by a ringed seal that had been caught out by shifting ice and couldn’t get back in the water. It was a perfect opportunity to land and take some photos while waiting for the crew member to settle their stomach. I don’t think the seal was as happy as I was about the photo op but he did find his way back into the water when the crack widened a bit. Being locked out of the water is a Darwinian dead end for ringed seals with polar bears about. It doesn’t happen often or if it does, those seals likely don’t last long and are on the menu for any passing bear.

Dr. Andrew Derocher is a professor of biological sciences at the University of Alberta. He is also a long-time scientific advisor to Polar Bears International. PBI has helped fund his sea ice ecology study for several years.

Hero Image: Path of a polar bear breaking through thin ice that froze over a lead, April 26, 2022.