© Ian Stirling
1/9/2017 3:48:58 AM
Tough Times for Hudson Bay Polar Bears
Being a polar bear scientist requires an intense interest in sea ice. I confess to being addicted to ice-monitoring products. If we’ve learned anything about polar bears over the last 50 years, it’s that their population dynamics and populations trends are related directly to sea ice. Polar bears thrive in a “sweet spot” of sea ice conditions: not too thick, not too much, not too thin, and not too little.
Going forward in time, we’re unlikely to ever see negative effects from too thick or too much sea ice: Those days are long gone across the Arctic. The biggest challenge we face is ice that is too little or too thin. A lot of the research my group conducts at the University of Alberta revolves around the theme of “How little is too little for polar bears to persist?”. That trivializes what is really a very complex question, but it’s helpful to have a simpler perspective as we wade through statistical analyses and mountains of data on polar bears and sea ice.
Having spent a week on the shores of Hudson Bay with Polar Bears International in early November, I was stunned by how warm it was. I harkened back to the conditions I experienced in 1984 when I started research there. It was a different place. I was a lot younger but absolutely jazzed by the opportunity to study polar bears. It was an amazing time back then: Polar bears were roly-poly, triplets cubs were everywhere, lone yearlings thrived even without their mothers, and there were lots of bears.
Back then, there were about 1,200 bears living in the core monitoring area between the Churchill River and Nelson River. Most of this area is now part of Wapusk National Park, which includes most of the denning area for the Western Hudson Bay population. In those days, the bears were on the sea ice by mid-November and, some years, even earlier. Now with only 800 bears in the denning area and fewer in the coming years, things have changed.
This year, as I was rumbling back into Churchill from the Tundra Buggy Lodge, I reflected on the contrast with 1984: Now we see fewer cubs (and rarely triplets), few roly-poly bears, a lot of skinny bears, and far fewer bears overall. In fact, the last bear I saw was a skinny adult male burying the remains of a recently killed polar bear cub: behind him not a bit of sea ice, even though it was November.
It was sobering but such observations seem more common now. Perhaps cannibalism is on the rise or perhaps it’s just more people on the land are seeing it happen. We don’t have good data on this aspect of polar bear ecology, but desperate bears do desperate things and 2016 was a challenging autumn for the population.
After I left Churchill in early November, I watched the sea ice situation. It’s been a very slow freeze-up and the bears are late returning to the ice. The ice failed to form until December and only in the last few days has there been enough ice for some bears to move offshore. While the autumn freeze-up doesn’t present the best hunting conditions, it does allow some bears to kill seals. Those bears that do kill seals can shift from burning 1 kg/day (2.2 lbs/day) of their own stored reserves to using the fat of ringed seals—fat that makes being a polar bear possible. The simplest way to think of a polar bear is as a “fat vacuum”—fat is where it’s at for polar bears, and they need sea ice to access their prey.
We won’t really know what the late freeze-up in 2016 will mean for the Western Hudson Bay population until 2017. It’s likely not good but a late break-up in 2017 would help. Unfortunately, further south in Ontario, those bears are all still on land waiting for ice. It’s tough being a polar bear in Hudson Bay these days.