Halibut spared as beluga move on to new prey in warming Arctic waters

Climate change seems to be driving a tiny fish species northward as Arctic waters grow warmer thanks to climate change — and they're getting gobbled up by whales that would normally find larger fish more tantalizing.

University of Manitoba research fellow David Yurkowski says beluga whales in parts of the North appear to be shifting away from eating Greenland halibut and are instead targeting capelin — a small, shiny fish that is becoming more common in the Arctic due to climate change.

"Both those species are really capitalizing on this forage fish [capelin] resource base, reconfiguring part of the food web," said Yurkowski.

The research was published in the journal Biology Letters on Wednesday.

Belugas used to eat more Greenland halibut from the 1980s through the early 2000s. But Yurkowski says now, in his research area of Cumberland Sound — an inlet that stretches inland in the southeast of Baffin Island — the whale species is preying on the comparatively smaller capelin.

Arctic cod have traditionally been a keystone prey item in the area, but they're becoming less common there. Yurkowski said the cod populations could be dwindling thanks to increased competition for food with capelin or other southerly species that are starting to colonize the Arctic oceans.

What's more likely, he says, is that the cod are heading further north into new habitats of their own, leaving a void behind that capelin are filling.

All the better for the Greenland halibut. Data from the Department of Fisheries and Oceans indicates the halibut population has been stable or increasing, and Yurkowski says that could be good news for northern Inuit-led commercial fishing industries.

The current beluga preoccupation with capelin has relieved some of the whale predation pressure usually faced by halibut, which are enjoying a boom of their own in the area as they, too, chow down on capelin.

Scientists don't really know how abundant capelin are around Baffin Island's southeast tip, but Inuit fishers and people in remote local communities say they're seeing "capelin numbers exploding," Yurkowski said.

"Capelin are one that has high colonizing potential," he said. "They're very plastic in terms of spawning habitat and spawning temperature, and as climate warming continues it can really benefit capelin."

Other marine predators are also taking notice. Researchers have been seeing capelin turn up in the diets of sea birds in Hudson Bay in recent years, Yurkowski said.

'We can strongly say' food web change driven by warming: researcher

Changes to the bird, beluga and halibut diets points to bigger changes occurring in the Arctic.

"With sea birds and marine mammals, [we can] kind of use them as sentinel species for ecosystem changes," Yurkowski said. "These species are generally opportunistic, so if there's been a large change in their diets there's likely been a change in the prey base."

Yurkowski says warmer water is leading to a reduction in sea ice and longer periods of time in the summer when the Arctic Ocean is exposed to the surrounding environment.

Yurkowski said chances are if more fish and marine predators make their way north due to climate change, it could have big implications on life beneath the ocean surface.

"The food web and how these species are interacting [is] changing, and I think we can strongly say that it is driven by climate [warming]," he said.

"It can effect the endemic Arctic species, which has ramifications for the entire Arctic food web."