Narwhals beware: Killer whales are on the rise in the Arctic

Narwhals are Arctic-dwelling whales with a unique feature: the males have spirally, sword-like tusks that can extend up to 3 meters (10 feet). But these magical-looking creatures are facing a new threat. As climate change shrinks the ice in the Arctic, killer whales are moving in, and narwhals are an appealing food source for them.

Killer whales (Orcinus orca) aren’t necessarily newcomers to the Arctic. One study shows that killer whales were spotted at Davis Strait and Baffin Bay in the Canadian Arctic as early as the 1800s, as reported in old whaling logbooks. However, these sightings were quite rare.

“These killer whales didn’t use the Arctic because the Arctic sea ice … would break their dorsal fins, and [they’d] die if they dove under the edge,” Colin Garroway, assistant professor at the University of Manitoba and co-author of a new study on killer whale abundance in the Arctic, told Mongabay.

But as climate change accelerates ice loss, killer whales have gained open access to the Arctic during the warmer summer season, which lasts approximately 90 days. According to the new study authored by Garroway and two colleagues, which was published in Global Change Biology, there were about 136 to 190 killer whales in Canada’s northern Baffin Island region each year between 2009 and 2018. This population estimate is based on photographic capture and mark information.

The killer whales’ presence in the Arctic is proving consequential to other species, including the narwhal (Monodon monoceros), which has become a primary food source for killer whales during the open-water season in the Arctic. By analyzing the killer whale population’s calorie requirements as well as narwhals’ calorie content, Garroway and his colleagues estimated that killer whales were preying on about 1,076 and 1,504 narwhals each season.

“It’s possible that narwhal are unable to escape killer whales because they represent a new threat,” Brandon Laforest, a narwhal expert and senior specialist of Arctic species and ecosystems at WWF, told Mongabay in an email. “Killer whales are large, intelligent, fast predators capable of hunting a wide variety of prey across their global range.”

At present, killer whales do not seem to pose a substantial threat to the overall narwhal population in the Canadian Arctic, which has a global population of about 200,000, said Garroway. The bigger threats, according to him, are climate change and habitat degradation. However, if the trend continues, it could endanger the narwhal population and prompt an ecosystem transformation through a top-down trophic cascade.

“If the sea ice continues to melt, killer whales would continue to move into the region,” Garroway said. “That could potentially change the behavior of all sorts of prey species including narwhal.”

Narwhal is also a traditional food source for people living in the Canadian and Greenland Arctic, so any decline in the narwhal population could affect food security, said Laforest, who was not involved in the new study.

“This is a system in flux so it will be critical to monitor the presence of killer whales in partnership with northerners who live and hunt on Arctic waters,” Laforest said. “As the people best situated to study killer whale-narwhal dynamics as well as the most impacted by any associated changes, Inuit in Canada’s Arctic will be integral to future monitoring efforts.”

An increase of killer whales into the Arctic is also a sign of expansive changes in the environment, according to Laforest.

“We should be concerned about the presence of killer whales in the Arctic as an indicator of broader changes happening in the ecosystem,” he said. “It is relatively easy to see changes that present themselves in the manner of a giant carnivore spending time in a new habitat. Still, a warming climate has implications at all levels of the food web, starting at the ice algae that live under the sea ice and form the basis of the Arctic marine food web.”

Citations:

Ferguson, S. H., Higdon, J. W., & Westdal, K. H. (2012). Prey items and predation behavior of killer whales (Orcinus orca) in Nunavut, Canada based on Inuit hunter interviews. Aquatic Biosystems, 8(1), 3. doi:10.1186/2046-9063-8-3

Lefort, K. J., Garroway, C. J., & Ferguson, S. H. (2020). Killer whale abundance and predicted narwhal consumption in the Canadian Arctic. Global Change Biology, 26(8), 4276-4283. doi:10.1111/gcb.15152

Banner image caption: A group of narwhals. Image by Our Breathing Planet / Flickr.

Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.

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