Svalbard’s polar bears are doing just fine—for now

These days in Svalbard, local polar bears are being forced onto land for much of the year as sea ice becomes more and more scarce. Those that are more inclined to roam must swim long distances between the ice edge and their island destinations. Surprisingly, both groups are still in good shape, able to produce cubs and survive. But the ongoing loss of sea ice is bound to make their lives more difficult. The question for JON AARS is: How much change can they cope with?

The Barents Sea hosts some 3,000 of the estimated 26,000 polar bears in the Arctic. Since the 1960s, scientists from the Norwegian Polar Institute have been studying the population that calls the archipelago of Svalbard home. Almost all our scientific knowledge about polar bears comes from long-term research programmes like this one in Svalbard, which I have been part of for the past two decades.

Along with my colleague, Magnus Andersen, I have been doing polar bear fieldwork in this area since 2003. During this period, we have seen profound changes as the sea and the air temperatures have crept higher and higher. Over the last 30 years, the length of the season during which the areas around the islands are covered in sea ice has narrowed to about four months (with some variation between local areas).

This precipitous decline in the number of days with sea ice is more than twice the rate experienced by any of the other 18 recognized polar bear populations. This certainly makes studying the bears in this area interesting. But how well are they managing with this pace of change?

Homebodies and roamers

Before I start to explain what we know about how the Svalbard polar bears have responded to the effects of climate change, it’s important to understand that we do not find just one type of space use among these bears. Rather, we find two very different ones. Some bears (likely fewer than 300) are what we call “local”: that is, they never leave Svalbard. When there is sea ice around the islands, they do use it for hunting, but they are rarely more than a couple of hundred kilometres offshore.

The rest of the bears are what we call “pelagic”: they visit Svalbard from time to time, but are more often on the move. When the sea ice retreats from Svalbard, usually in summer, these bears follow the ice and continue to hunt at the ice edge. They have found a way to hunt seals from the ice year-round.

As sea ice disappears from Svalbard for longer and longer periods, you might think that local bears would respond by moving to the areas that have the most enduring sea ice. But actually, the local Svalbard bears are very local: they remain in the same areas not only year after year, but across generations. Daughters favour the same areas that their mothers and grandmothers did. They also prefer to have their maternity dens close to where they were born.

This means some local bears now have much less sea ice where they hunt compared to what their great-grandmothers had.

– Jon Aars, senior scientist, Norwegian Polar Institute

This means some local bears now have much less sea ice where they hunt compared to what their great-grandmothers had. So how does that affect them? Surprisingly, we have observed that although they spend a lot more time on land (because they have no sea ice for much of the year), they are not in worse condition. If they survive the first few difficult years of their lives, they still grow up, have cubs and grow old. They have a shorter season for hunting ringed seals on the ice, but they make up for this by consuming more eggs and birds. In some areas, harbour seals are now more common and serve as prey. We also see more bears taking reindeer than we once did.

The search for sea ice

And what about the pelagic bears? From decades of research, we know that they spend most of their time on the ice edge. Because that is now typically located 200 to 300 kilometres further north than a few decades ago, the bears are now located further north as well—and often further away from Svalbard—for much of the year.

If this means they can hunt seals year-round, you might wonder what the problem is. One issue is that in the years in which they reproduce, adult females need to reach land in autumn to build their maternity dens. But the sea ice in Svalbard is no longer stable enough in that season. In most recent years, it has not formed on time in historically important denning areas in east Svalbard. As a result, the bears are now more likely to den in new areas of Svalbard, if they reach Svalbard at all. Or they go to the western Russian Arctic (Franz Josef Land) instead.

In addition, if they have to swim as many as several hundred kilometres from the ice edge to the islands, they expend considerable energy—yet they need their fat reserves to last the winter so they can raise their cubs. Although this is worrisome, so far, the pelagic bears—like their local counterparts—seem to be in good condition.

The question is how much more sea ice loss both local and pelagic bears can tolerate before the energy balance between what they can get from food and what they need for reproduction and survival dips to the negative side.

For now, the good news is that by adapting their diets and following the ice further north, polar bears in Svalbard are doing just fine. The bad news is that research on climate and sea ice is showing us they are almost certain to lose more and more of their habitat in the coming decades. What is yet to be seen is how that may affect their survival.