Counting polar bears. A new method to monitor their population

Polar bears, one of the most iconic species of the Arctic, have a nomadic nature, often swimming through the polar wastelands. This makes monitoring these endangered animals challenging, yet essential. Precise data on the size of individual polar bear populations, as well as the connections between these populations, are still lacking.

An innovative tool that could facilitate the identification and count of polar bears involves analyzing DNA from skin cells left in their tracks in the snow. This method is non-invasive and poses no threat to either the animals or the people involved.

Dr. Melanie Lancaster from the Global Arctic Program of the World Wide Fund for Nature, who led the research published in "Frontiers in Conservation Science," explained: "Finding and counting polar bears in the Arctic, not to mention understanding their response to climate change, is especially challenging, costly, and time-consuming."

The scientists incorporated forensic techniques suitable for small, degraded DNA samples. Using environmental DNA eliminates the need to physically capture bears. This reduces stress and danger for both bears and people, potentially disturbing local indigenous communities less.

Elisabeth Kruger, a World Wildlife Fund representative and a co-author of the study, stated: "Many Inuits have concerns about invasive research methods. They worry about the well-being of the individual polar bear and the health and safety of those who might encounter the bear later. This is why we are excited about these new types of methods - the sampler doesn't need to see or be seen by the polar bear."

In the past, environmental DNA was collected from animal feces. However, the quality of DNA obtained this way often wasn't high enough for a detailed analysis. Moreover, for territorial animals like lynxes and snow leopards, fecal sample collection could disrupt their behavior. As such, researchers started using skin cells from tracks left in the snow.

Lead author of the study, Dr. Micaela Hellström from MIX Research Sweden AB, noted, "Tracks usually contain fresh cells, and DNA is well-preserved due to the low temperature. On the other hand, DNA that has passed through the intestines is often more degraded, making it harder to work with."

The team collected snow from single tracks left by polar bears in Alaska and both wild and captive Swedish lynxes. They also collected snow from tracks left by captive snow leopards. Samples of additional materials, such as hair, saliva, and mucus, were taken, and their analysis showed that the tracks provided accurate genotypes.

After melting and filtering the snow from 24 tracks of wild polar bears and 44 tracks of wild lynxes to collect DNA, they analyzed DNA microsatellite markers. Although the concentrations of DNA recovered from wild tracks were quite low, they successfully recovered nuclear DNA from 87.5 percent of wild polar bear tracks and 59.1 percent of wild lynx tracks. This analysis revealed the identities of 12 unique polar bears from 13 samples.

The authors of the study believe that their new technique holds enormous potential for the protection of these animals. It can provide better insight into their populations and behaviors, and could manage human-animal conflicts through exact animal identification. Despite the lower success rate of non-invasive sampling, its simplicity allows for the collection of many more samples.

Dr. Lancaster concluded: "We hope this method will be adopted by the broader community involved in polar bear research. Employing hunters, volunteers, and indigenous communities can create a new way to gather information about polar bears. We'd also like to see the method extended to other animals in snowy environments. We've already proved that it works for lynxes and snow leopards."