Orcas: Marine mammals are spreading further into the Arctic Ocean as sea ice melts

Orcas – also known as killer whales – used to be unusual visitors to the Arctic Ocean off Alaska, but they are becoming more common there, which might be bad news for local ecosystems

By Chen Ly

Orcas are venturing much further into the Arctic Ocean and more frequently, perhaps due to decreasing sea ice in the region caused by climate change. Their growing presence could threaten marine ecosystems in the area.

Orcas (Orcinus orca) – also known as killer whales – are intelligent and versatile predators. While they can be found in the majority of our planet’s oceans, they don’t typically journey to ice-covered Arctic waters near Alaska because sea ice makes the region difficult to access and also leaves the mammals at risk of becoming trapped below the surface.

But Brynn Kimber at the University of Washington and her colleagues have found more and more orcas there in recent years. To track orca populations, the researchers used underwater acoustic recordings of north-western Arctic waters. They collected data between 2012 and 2019 from four recorders that were attached to anchors dotted around the area, ranging from the northerly edge of the Chukchi Sea to the more southerly Bering Strait, just off the Alaskan coast.

To estimate the size of orca populations, the researchers analysed these recordings for the prevalence of orca vocalisations, then compared the numbers with changes to ice cover in the region.

They found that in the southern regions near the Bering Strait, orcas now make a regular appearance each summer. What’s more, they were arriving in these areas up to a month earlier in the summer of 2019 than they did in the summer of 2012, possibly due to earlier ice disappearance. In the northern Chukchi borderlands, they also found that orcas were present more frequently and consistently by 2019, again perhaps due to reducing ice cover.

“We are seeing them more often in areas that I wouldn’t have seen them at all in the early years [of the study],” says Kimber.

These findings could have serious consequences for the marine ecosystems in the region. For example, previous studies have shown that bowhead whales, which primarily frequent Arctic waters, have had more and more aggressive interactions with orcas in recent years.

This is a cause for concern because some bowhead whale populations are endangered, and the species is important to Inuit communities, says Kimber. In addition, orcas are known to hunt other marine mammals, such as beluga whales and seals.

“With this ice going away, there’s going to be more and more changes in the area. I think this [case] is just one of many,” says Kimber. “The different ecosystem shifts we might see and all the various impacts it could have is important to think about.”

Journal reference: The Journal of the Acoustical Society of America, DOI: 10.1121/10.0008306

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