HomeScienceClimate change is shifting polar bears’ Arctic menu, research shows

Climate change is shifting polar bears’ Arctic menu, research shows

Polar bear (<em>Ursus maritimus</em>) standing upright on fjord ice at Sabinebukta Bay at Irminger Point on a summer morning.
Enlarge / Polar bear (Ursus maritimus) standing upright on fjord ice at Sabinebukta Bay at Irminger Point on a summer morning.

The Arctic is warming three times faster than the rest of the world. Because of that warming, some organisms are adapting by shifting their natural stomping grounds, and the region is seeing some species move in as they follow the warmth north and stick around there for longer.

As such, the menu for polar bears is changing, according to a recently published paper. The research also suggests that studying fat tissue from polar bears—a practice that can shed light on what prey they’ve been consuming—can be a useful tool in monitoring how species distribution in the Arctic is changing as temperatures increase and ice melts.

“The Arctic is changing. It is changing at a very rapid pace, especially in comparison to really any other region of the world. Temperatures are warming faster,” Melissa Galicia, a PhD candidate in York University’s department of biology and one of the authors of the paper, told Ars. “The ice is declining. Sea ice is becoming more fragmented. The water temperatures are warming. You’re getting an ecosystem that is changing rapidly, and all of the species within that ecosystem also need to adapt.”

What’s cookin’?

In Nunavut, one of Canada’s northern territories, Inuit people are allowed to hunt polar bears. Over the years, the Inuit hunters have been sending muscle and fat samples to York University. It is these fat samples, dating back to around 2010, that Galicia and her team looked at for their findings.

According to Galicia, you can find around 70 different types of fatty acids—like Omega 3s and 6s—in marine ecosystems. Because of this diversity, each bear’s fat sample will have a kind of unique signature based on its diet. The researchers ran the samples through a dietary model to suss out the proportions of each bear’s diet; for instance, the fat could indicate that one bear ate 50 percent ring seal, 25 percent beluga whale, and 25 percent bearded seal.

“It’s mainly looking at their fatty acid signatures and comparing it to what they would potentially eat,” she said.

By matching diet sources with the sites that samples came from, the study also identified hot spots of different prey species in the region as a kind of baseline for where the prey would normally be. From this data, the team believes that it can get a sense of polar bear prey distribution. While Galicia’s research took place in Nunavut, its results could potentially hold true elsewhere, she said.

Research bears fruit

The primary diet of polar bears in the region is made up of ring seals, though bearded seals—which are a bit larger—can also be taken down by adult male polar bears. They will eat other things as well, such as harp seals or whales that get trapped in the ice. It varies based on geography.

The study found that polar bears’ diets increasingly contain bowhead whale carcasses. This could be because killer whales are moving farther north and staying there for longer and—true to their name—are killing more bowheads. The bodies sometimes end up within reach of the bears.

Polar bear diets are particularly useful in this way because the animals are top predators in the Arctic—they hunt and eat a lot of things. But their prey (whales and seals) move around a great deal, so tracking their populations is no easy task. As such, studying the diets of polar bears could be used to get an early glimpse into distribution changes in Arctic life.

Ecological Indicators, 2021. DOI: doi.org/10.1016/j.ecolind.2021.108245 (About DOIs)

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