As climate change reshapes Arctic food webs, ringed seals will swim into risky polar bear territory if the menu is varied enough.
That's the central finding of a new study published in Ecology Letters . UBC researchers tracked 26 ringed seals and 39 polar bears in eastern Hudson Bay, using GPS and dive information to analyze how the animals found, and avoided becoming, food.
"Climate change is reshaping the Arctic, an area often seen as a foreshadowing of climate changes around the world," said lead author Dr. Katie Florko, who conducted the research as a doctoral student at UBC's Institute for the Oceans and Fisheries (IOF). "It's not just melting sea ice: climate change is affecting everything: the predators, the prey and their habitats, effectively reshuffling a complex, intertwined system. If we map critical habitat while ignoring how bears and seals interact, we risk potentially protecting areas that animals are actually avoiding in a climate-changed future."
"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," said senior author Dr. Marie Auger-Méthé, UBC professor in the department of statistics and IOF.
A mix of food outweighs fear
Dr. Florko's team combined GPS data with daily sea-ice maps and yearly models of the mix of fish species available in Hudson Bay, following where seals and bears went, how seals moved and dived, and what the fish buffet looked like beneath them. Feeding these data into ecological models, they identified how the seals reacted to the bears' presence, or their 'landscape of fear'.
They found something surprising: while seals avoided spots where bears were very active—moving through them quickly—they rolled the dice and dived for longer when the fish mix was especially varied. This was true even in bear hotspots. In safer places, however, greater fish variety meant shorter dives, likely because food was easy to get.
The researchers theorize this could be due to the 'portfolio effect'. Just as investors have many different investments to reduce overall risk, animals select varied food sources to increase their chances of finding something to eat in ever-changing ocean conditions. "The seals aren't putting all their fish in one basket," said Dr. Florko.
Dr. Florko located the bears from the air by helicopter, waiting for a ranger to shoot a tranquilizing dart, before landing to clip the GPS collars on. "They smelled like a big wet dog."
Listening for paws on the ice
The research also suggests that ringed seals may have tactics for identifying high-traffic polar bear areas. Dr. Florko looked into whether seals might listen for bears walking on the ice while the animals are underwater, delaying their return to the surface if they detect danger. "We didn't end up finding a relationship, but that may be because it's a fine-scale event occurring in a matter of seconds that we weren't able to capture—yet."
These tactics could also inform how seals respond to other predators gaining better access as sea ice melts, including killer whales. If seals are attuned to polar bears' footsteps on the ice, the same tactics might not work as well with killer whales. "I think potentially, killer whales could be a harder predator to avoid because one of the ways seals escape polar bears is they're generally better swimmers. But killer whales are excellent swimmers."
The team also notes that as the sea ice shrinks, relative bear density on the remaining ice could spike, raising short term risk for seals even before long term bear numbers continue to decline. For planners, the message is simple: build habitat models that include both sides of the equation—food and fear—so protections match how animals actually live. "This is about giving managers the most accurate picture possible," said Dr. Florko. "When we factor in predators and prey together, we make smarter decisions for wildlife and for the people who depend on them."
This study was conducted by researchers from UBC, York University, the Department of Oceans and Fisheries, and the Ontario Ministry of Natural Resources and Forestry.
