Paw prints allow soft identification of polar bears | Polarjournal
Regular monitoring of polar bears is highly important to protect them efficiently. Unfortunately, taking samples under anesthesia killed some of the bears. Therefore, researchers were looking for a non-invasive method. (Photo: Julia Hager)

As polar bears walk over snow and ice, they leave tiny skin particles in their paw prints, which a University of Idaho research team used to identify individual bears through genetic analysis – a unique way to monitor polar bears without invasive measures.

Established methods for monitoring polar bears, mostly with helicopters, are extremely complex, costly, sometimes dangerous for the bears and increasingly difficult to implement due to climate change. However, monitoring is essential to protect the bears efficiently.

A research team with scientists from the University of Idaho, the North Slope Borough Department of Wildlife Management and the Alaska Department of Fish and Game therefore relies on collecting DNA samples from fresh paw prints left by polar bears on snow and ice. This method is risk-free for the bears and can be implemented with little effort on the sea ice or on land.

In the current issue of the journal Frontiers in Conservation Science, the scientists describe how they can identify polar bears in northern Alaska using DNA traces in their paw prints.

Collecting so-called “environmental DNA” or e-DNA – DNA released by organisms into the environment – for monitoring populations is not new and is already used for a number of animals, including marine mammals. However, according to the study, e-DNA has so far only been used to determine the species present, but not to identify individuals and their sex.

With every step, the polar bears lose tiny skin particles that provide information about their genotype and sex. All the research team has to do is collect the snow in the paw prints and analyse the samples in the lab. (Photo: Jennifer Adams)

With the help of Iñupiat hunters, who have intimate knowledge of polar bears, their migrations and habitat use, the researchers took samples from a total of 13 different polar bear tracks on the sea ice in the Chukchi and Beaufort Seas along the North Slope Borough in northern Alaska. They scraped a thin layer of snow off the paw prints and later extracted cells from the melted snow in the lab, which provided the DNA fingerprint of each bear.

The research team first checked the samples for mitochondrial DNA (mt-DNA) to determine if genetic material from polar bears was present in each snow sample, and identified polar bear DNA in 11 of the 13 samples. In further analysis, the team used nuclear DNA (n-DNA) to identify individual bears and their sex.

The samples are from the coastal fast ice of the Chukchi and Beaufort Seas along the North Slope Borough. (Map: From Duyke et al. 2023)

Of the 13 bear tracks sampled, the researchers were able to identify six individuals – five males and one female. According to the team of authors, this is the first time that polar bears have been individually distinguished from snow samples.

The method is still at the experimental stage, but so far it has proven to be a cost-effective and, above all, non-invasive way to learn more about polar bears in the wild. The researchers see it as a valuable addition to live capture methods by helicopter, which certainly cannot be completely replaced. It is also a good way to involve indigenous communities in the research, who are strongly affected by polar bear management decisions.

Julia Hager, PolarJournal

Featured image: Michael Wenger

Link to the study: Von Duyke Andrew L., Crawford Justin A., Quakenbush Lori, Adams Jennifer R., Waits Lisette P. Determination of polar bear (Ursus maritimus) individual genotype and sex based on DNA extracted from paw-prints in snow. Frontiers in Conservation Science 4, 2023. DOI: 10.3389/fcosc.2023.1166279

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