When a polar bear approaches, the sensible thing to do is get out of the way. So, scientists in the Arctic were surprised to find that ringed seals sometimes put themselves at risk by swimming into polar bear territory if the area had a large variety of fish.
The seals quickly passed through habitats where polar bears were active – understandably, not wanting to become a tasty snack themselves. However, they spent longer diving in areas with a high diversity of fish for them to eat even if these were in high-risk areas where polar bear might be prowling.
“The seals aren’t putting all their fish in one basket,” says lead author Katie Florko in a press release. Florko conducted the research as a doctoral student at the University of British Columbia's (UBC) Institute for the Oceans and Fisheries (IOF).
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The scientists think the seal’s strategy could be down to something called the 'portfolio effect'. In the same way that financial investors manage risk by spreading money over a wide variety of different investments, animals with more varied prey have a better chance of finding something to eat.
This is particularly important as climate change impacts different prey species within the food web. “Climate change is affecting everything: the predators, the prey and their habitats, effectively reshuffling a complex, intertwined system,” says Florko.
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Tracking Arctic animals
The scientists put satellite tags on 26 ringed seals and GPS collars on 39 female polar bears in eastern Hudson Bay to track the animals’ movements. The data gave them more information about how seals balanced the trade-off between finding food and avoiding becoming prey themselves.
Although the polar bears “smelled like a big wet dog,” according to Florko, it was much more challenging to attach collars to these huge white predators compared with our canine companions.
First, they had to find the bears: flying over the landscape in a helicopter to scout them out. When they spotted one, the ranger shot it with a tranquillising dart to knock it out so they could land safely and attach the collar.
Alongside this tracking data, they looked at sea ice maps and models of which fish species were present in Hudson Bay. Their findings are published in Ecology Letters.
Why is the study important?
Understanding the complex interactions between polar bears and their prey, such as ringed seals, is key if conservation measures are to be effective.
Protecting the animals that live in this fragile ecosystem, with rapidly melting sea ice, is also an important way of supporting the people living here. “Communities across the North rely on healthy seal and fish populations, so more accurate maps of these populations also help support food security and wildlife management,” says senior author Marie Auger-Méthé, a professor at UBC / IOF.
“When we factor in predators and prey together, we make smarter decisions for wildlife and for the people who depend on them,” says Florko.
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