A healthy polar bear on a Chukchi Sea beach.

In the biologically rich Chukchi Sea habitat, polar bears are thriving--at least for now--a new study shows. But without serious action on climate change, continued sea-ice loss and lengthening ice-free periods pose risks to the population over time.

© Dr. Eric V. Regehr/University of Washington

12/5/2018 3:49:34 PM

Chukchi Sea Polar Bears

By Dr. Eric V. Regehr

After a decade of research, my colleagues and I recently published the first-ever estimate of the size and status of the Chukchi Sea polar bear population, which is shared by the U.S. and Russia. And the news is good—at least for now. The bears are relatively abundant, with strong reproduction and high cub survival.

Although studies by the U.S. Geological Survey indicate that the Chukchi Sea population is showing behavioral effects of climate change (for example, some animals are spending a longer time on land each summer), the sea-ice loss the region has experienced to date apparently hasn’t yet led to negative nutritional or population-level effects. 

When it comes to communicating these findings, it can be challenging to explain that the following two statements are consistent: (1) sea-ice loss due to climate change is the primary threat to polar bears throughout the Arctic; and (2) new scientific data indicate that the Chukchi Sea population is doing well, despite sea-ice loss.

How is this possible? Although there are multiple potential explanations, I’d like to focus on two communication challenges related to the Chukchi Sea bears.   

First, the Arctic is a big and diverse place. The Chukchi Sea is a biologically rich habitat, with a large continental shelf that gives the bears a vast area for finding seals. Most other parts of the Arctic don’t have these features or have them to a lesser degree. 

Productivity and the amount of shelf habitat make a difference because they influence the degree to which changes in the amount of sea ice translates into lost hunting opportunities for polar bears, which in turn reduces their ability to accumulate the fat reserves needed for survival.

Here’s a rough analogy to help illustrate. If a person gets big, balanced meals seven days a week, they’re going to be happy and healthy. What if resources were reduced and they only got big, balanced meals six days a week? They’d probably still be in pretty good shape. But now imagine that the meals were small or less frequent to start with—just barely enough to get by. In that case, going hungry for an additional day could cause significant hunger and stress. Furthermore, imagine if more and more meals were taken away, year after year. No matter what the starting point was, the progressive loss of food could only be expected to have negative effects in the long run. This is basically what’s happening with polar bears. Different combinations of biological productivity, habitat area, and sea-ice loss are currently having different regional effects. And unless the underlying causes of climate change are addressed through the reduction of greenhouse gases, the continued loss of sea ice and associated opportunities to hunt will likely have negative impacts throughout the Arctic.  

Bearded seals hauled out on the sea ice in the Chukchi Sea

A large continental shelf that extends over shallow, highly productive waters provides ample hunting opportunities for polar bears in the Chukchi Sea, allowing them to build up fat reserves to sustain them during ice-free periods. Here, blubber-rich bearded seals haul out on the sea ice. Photo by the U.S Fish and Wildlife Service.

A second explanation for why communicating about polar bears can be challenging is that science is not perfect. Polar bears live in vast and remote regions, so we can only estimate population size and status; it’s never possible to count exactly how many bears are out there. In our recent paper, we estimated the most likely size of the Chukchi Sea population was 2,937 bears. But the same analysis indicated that the true number could fall anywhere between 1,500 and 6,000. That’s a wide range! In practice, uncertainty in science means that it can take years or even decades for biologists to detect changes in population size. 

Furthermore, climate change doesn’t just affect polar bear numbers, it affects where the animals go and what they do and the ecosystems they live in. For example, it can seem like a population is increasing because bears are temporarily moving into an area; or decreasing because bears are temporarily moving out. There are a lot of moving parts and our understanding of how they fit together continues to evolve.

What this all boils down to is that, currently, the best-available scientific information indicates that the status of the world’s 19 polar bear populations is variable. This variability is consistent with the fact that all polar bears depend fundamentally on sea ice, and with the expectation that continued, and more extensive, sea-ice loss will eventually be bad for most bears across the Arctic. In my opinion, communicating this message is a key challenge for polar bear conservation.

The new Chukchi Sea paper represents a step forward scientifically, giving us baseline information on the population for the first time. Although communicating the nuances is a challenge, our findings provide some (much needed) good news for polar bears in the near term. 

Dr. Eric V. Regehr is a principal research scientist at the University of Washington and the lead author of the paper cited: Regehr, E. V., N. J. Hostetter, R. R. Wilson, K. D. Rode, M. S. Martin, and S. J. Converse. 2018. Integrated Population Modeling Provides the First Empirical Estimates of Vital Rates and Abundance for Polar Bears in the Chukchi Sea. Scientific Reports 8:16780. 

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