Killer whales feast on endangered bowhead whales as ice recedes

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Sea ice cover over the Arctic is receding to levels not seen in 500,000 years, leading to more widespread energy availability for killer whales to feast on endangered bowhead whales and other types of wildlife.

Researchers working on a collaborative study documenting the effects of climate change on Arctic life have found that the killer whale population has experienced “robust increases in abundance, prey abundance, and complexity.”

Over the last few years, researchers have documented more than 300 cases of people observing whales diving in the presence of bowhead whales, which are endangered in the North Atlantic and Western Arctic. The presence of the bowhead whales indicated that the killer whales, a class of large creatures that includes a variety of species and grows to as many as 90 metres, are reproducing and finding a plentiful source of prey.

“Basically what we found is that in general, the predator ecosystem is evolving into something that looks like a type of a herd,” said Christine Hannah, a graduate student at Louisiana State University who is working on the research.

The study was published in October in the journal Marine Conservation Biology.

‘A lot more complex’

Bowhead whales, which they don’t eat, have slim pink patches on their tails, which are caused by the shell breaking off of their teeth in the presence of dead killer whales, called killer whales because they hunt both humans and other sea creatures. While it is rare to see bowhead whales dive in the presence of killer whales, more frequently they’re encountered in the open waters surrounding the Arctic sea ice.

“You can see the color of their tails, you can see if they’re about to do something. You can see if they’re about to strike, or if they’re just lurking around waiting for the prey, or if they’re trying to feign or camouflage,” Hannah said.

“Usually what they are doing is just waiting for the right prey. Once they find it, then they’ll go take it,” Hannah said.

A year ago, researchers also noticed that bowhead whales would sit for hours at a time and then dive before going back out to find food. It’s possible that they’re gathering the same prey, but it’s also possible that the bowhead whales are starting to defend themselves better against possible attacks by killer whales, Hannah said.

“It’s really intriguing to see that that’s happening. And the thing that’s driving it is we’re seeing so much snow melt out in the open ocean. If they’re going out for a long period of time, they’re still going to come back. What we don’t know is whether that longer feeding time they have actually is protecting them or damaging them. And this may be the peak of this,” Hannah said.

Despite an increase in genetic diversity across the killer whale population, the researchers report a decrease in hunting by grey seals in the wild. Gray seals are a large variety of huge seals that hunt both on land and in the open sea.

“What’s interesting about grey seals is that there’s not been such a huge genetic change over time. And what we see is that the population is starting to go from gray and white (blue gray and white) to males that are black to get away from the grey seals,” Hannah said.

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