Shark! Yes, sharks are returning north, and eating seals

Dr. Steve Ferguson speaks at the Arctic Change conference in Ottawa in December 2014. (PHOTO BY DAVID MURPHY)

It’s a shark-eat-seal world out there people — at least, it could be more common in the future, warns one scientist.

Thousands of years ago, seals and sharks decided to get out of each other’s way, pretty much throughout the world.

“The sharks were eating seals, so the seals weren’t doing too well in areas where there’s a lot of sharks,” Fisheries and Oceans Canada scientist Steve Ferguson told Nunatsiaq News.

Seals, fed up of being preyed upon by sharks, migrated north to live on, and beneath, the Arctic ice.

But now that human beings have changed Earth’s climate and polar ice caps are melting, animals’ habitats worldwide are changing too and seals must be wary of foreign predators, like their age-old nemesis: the shark.

“We’re not sure that Greenland sharks are increasing. But they were fished in large numbers by Greenland in the past. So they may be coming back from that overfishing,” Ferguson said.

These Greenland sharks are “pretty good in cold water. And there’s evidence that sharks eat seals.”

And with sea ice rapidly melting, seals are losing ground, as it were.

“Looking at that global pattern, it suggests it could be tough on the seals. So we’ll have to keep an eye on that,” Ferguson said.

Ferguson described these changes in the food chain at the Arctic Change conference in Ottawa this past December based on a study he’d done called, “The ghosts of competition past: body size, trophic ecology, diversity and distribution of global shark and pinniped species.”

But sharks will need watch their backs as well — they’re also under threat from an unlikely species.

“We haven’t confirmed it yet, but it does look likely that we have some shark-eating killer whales,” Ferguson said.

He has observed samples of washed-up killer whale carcasses found in Newfoundland and Repulse Bay, and has studied tissues and contaminants in the whale’s system.

If the results are valid, it could be the first time scientists have confirmed that killer whales eat sharks in the North Atlantic.

“So maybe the seals have some friends,” Ferguson said with a chuckle.

Those killer whales might have more on their dinner plates, too.

Ferguson said most whale populations are starting to bounce back in the North Atlantic to what they were like 500 years ago — probably because Europeans and North Americans have stopped overharvesting.

“The North Atlantic was pretty messed up with all the commercial whaling and overharvesting that went on,” Ferguson said.

“So we may be seeing things starting to return. Not back to the way they were, but we’re having a lot more big whales. Humpbacks and bowheads are certainly increasing.”

And Ferguson said people have told him they’ve seen sperm whales and dolphin species off the coast of Baffin Island.

But while this burgeoning biodiversity may sound like a good thing, it spells trouble for ice-dependent mammals such as whales and seals.

“In fact there is some indication that they are having trouble already,” Ferguson said.

Inuit hunters have told Ferguson that ringed seals don’t seem to be doing well on Baffin Island.

“In the case of beluga and narwhal, and maybe bowhead as well, I think there’s more killer whale predation going on,” Ferguson said.

“And the killer whales avoid the ice. So the less ice they have, the bigger playground they have to do their killing and eating.

“So we don’t see a problem yet, but it’s something we have to watch.”

For now, ringed seal and bearded seal populations in Nunavut are fine, Ferguson said.

The U.S. National Ocean and Atmospheric Administration has put both species on its endangered species list, but the Canadian Arctic archipelago helps seals survive.

Those Arctic islands, “trap the ice in the area. So our seal populations are probably doing pretty good.”

So what happens when sea ice melts faster, or forms slower?

“We’re going to really notice problems with the seals that need ice and the whales that use ice, and the polar bear,” Ferguson said.

“They’re predicting a significant loss of sea ice in the next 20 and 30 years. So it’s coming pretty fast.”

To help stop the pace of climate change, people must change their habits, Ferguson said. And a big part of that means curbing our addiction to consumption.

“If we have big salaries we’re going to spend it. And when we spend it we’re going to destroy the environment incrementally.”