Polar bear diet, hunting habits can be indicators of climate change: study
TORONTO -- Polar bears can be used as an indicator of environmental shifts, a new study suggests, as the animals change where they eat and what they hunt due to climate change.
The study, led by York University in Ontario, says that climate change and global warming will likely force widespread changes in where species live and roam, particularly in polar environments, but that tracking those shifts is a difficult task. It will be published in the December issue of the journal Ecological Indicators.
By instead following the dietary habits of predators such as polar bears, described as “flexible eaters” that will eat what is available, researchers may get an early warning system of what they call “distributional change in prey populations.”
“Polar bears need the sea ice to hunt. When there is a reduction in the sea ice, they’re hunting less or they’re potentially hunting different prey species,” said researcher Melissa Galicia in a press release. “Prey species, like whales and seals, also need certain habitat conditions and because of environmental changes in the Arctic, some marine mammals, such as prey species of bears, are redistributing. You’re getting an increase in more sub-Arctic species, like killer whales for instance.”
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The study analyzed samples provided by subsistence hunters (who hunt strictly to provide food for themselves and their families), from polar bears across Nunavut from 2010 to 2018.
Researchers then extrapolated “hot spots” of where prey species were gathering from studying the fatty acids and other indicators from fat tissue in the polar bear samples. The study suggests polar bears’ diet may provide evidence of early changes in where mammals and other prey species live due to climate change.
“Each bear will have a specific fatty acid signature, a kind of fingerprint for individual bears and because of that you can see what that particular individual is eating and what percentage of their diet that represents,” Galicia said.
One example of a shift in prey distribution noted in the study was that bowhead whale carcasses were becoming more common in the polar bears’ diet, potentially linked to killer whales venturing further north and staying for longer periods of time to hunt.
The study noted that ringed seals were the primary prey of polar bears around Nunavut, followed by bearded seals. A consistent hot spot of ringed seals was found in the Gulf of Boothia, indicating they were present in the area year-round and clusters of bearded seals and Atlantic walrus throughout Foxe Basin suggest an overlapping seasonal presence.
Beluga whale hot spots were detected year-round along eastern Baffin Island and southern Viscount Melville Sound, however there was only one hot spot found for narwhal during spring-summer in Barrow Strait.
With the Arctic ecosystem experiencing climate warming up to three times faster than any other region, the changes brought on will likely “force widespread species redistribution,” the study says, particularly in polar environments. Polar bears in Nunavut aren’t experiencing climate change to the same degree as some polar bear populations in western Hudson’s Bay or Beaufort sea areas – but researchers say that will likely change.
“As temperatures across the Arctic warm and sea ice loss increases, there will be profound cascading ecological consequences. What’s not known is how that will affect species, such as seals and whales, but by monitoring the seasonal prey consumption of polar bears, scientists can better keep track of where marine mammal prey species are showing up and their seasonal distribution,” said professor Gregory Thiemann of the Faculty of Environmental and Urban Change at York University in the release.
Currently, information is scarce on the numbers and distribution of marine mammals across the Artic, so researchers posit that this study offers a way to provide data on a much-needed subject. Researchers said they hope future studies of polar bear diets will include prey species not normally found in the region and help predict the severity of climate-induced change in the environment.