Whales snatching pole position from bears
ARCTIC: Killer whales and Greenland sharks could be replacing polar bears as the Arctic’s top predator - and even targeting them as prey - as the receding icecap allows them to penetrate deep into polar waters.
Seals, narwhal and beluga and bowhead whales face relentless attacks as the dense ice that covered Arctic waters for much of the year, and which they relied on to keep killer whales away, recedes.
The killer whales ‘‘are there to eat’’, said Steve Ferguson, a researcher at Manitoba University in Hudson Bay on Canada’s northeast coast, one of the areas hit by receding ice.
‘‘They appear to be eating other whales and seals and, I would imagine, if we lose our sea ice they will replace polar bears as that top predator,’’ he was reported as saying at the ArcticNet scientific conference this month.
Polar bears have always been the top predators in ice-bound coasts and seas - but they rely on being able to wander across packed floes or swim between them to hunt seals.
Shrinking ice leaves them stranded on shore or making long voyages between floes - when they could be at risk of becoming prey.
Killer whales, by contrast, steer clear of ice because it can damage their long dorsal fins. As more of the Arctic icecap melts each summer and less reforms each winter, killer whales are able to range further north than ever.
The National Snow and Ice Data Centre in America has reported record melting rates in recent summers. This year it also reported that the ice is failing to regrow.
The ice cover last month of 9 million square kilometres 3.5m square miles was 1.9 million sqkm below normal.
In Hudson Bay, home to 57,000 beluga whales, Ferguson and colleagues have seen them hunted by packs of killer whales in areas where they were previously safe.
Killer whales are not the only predator exploiting the great melt. Greenland sharks, which can reach lengths of up to six metres, are also making their way into some parts of Hudson Bay and, on the other side of the Arctic, have been found approaching the shores of Svalbard, to hunt seals.
Another possibility is that polar bears are not just being driven out by marine predators but also falling prey to them.
Kit Kovacs, professor of marine biology at the Norwegian Polar Institute, has reported finding a polar bear’s jaw in a shark’s stomach.
Such changes are likely to increase as global warming continues, with scientists predicting that the Arctic will be almost free of summer ice within 15-20 years.
This would be a disaster for other smaller species.
Polar cod spend their early lives living in holes in the ice to protect them from predators.
‘‘Polar cod make up 80 per cent of the diet of ringed seals, which are polar bears’ main prey,’’ Kovacs said.
‘‘So if the ice goes, so do the fish. It means the seals starve and so do the bears.’’ - Sunday Times