Due to climate change and warming, orcas (Orcinus orca) are moving into previously inaccessible parts of the Arctic or moving in sooner and staying longer due to ice melt — and that is having an impact on narwhals (Monodon monoceros) and most likely their closest living relatives, belugas (Delphinapterus leucas), as well as other whales and seals. The narwhals are completely stressed by the presence of the orcas, say the researchers who used tracking tags to follow a pod of killer whales and several narwhals over an 18-day period in Admiralty Inlet on the northern end of Baffin Island. The time period — during the Arctic summer — is when several thousand narwhals gather to feed and raise their young in relative safety. Narwhals live year-round in the Arctic waters around Greenland, Canada, and Russia.

Extensive year-round sea ice once limited the number of killer whales in the region. As the ice melts due to global warming, say the scientists, the killer whales arrive earlier, stay later, and are found in greater numbers. The orcas hunt like a pack of wolves, and their presence can be unnerving to their prey, including narwhals, according to the research.

The results of the research, “Sustained Disruption of Narwhal Habitat Use and Behavior in the Presence of Arctic Killer Whales,” were published in the Proceedings of the National Academy of Sciences. The “narwhals, one of many marine mammal species preyed on by killer whales, change their behavior substantially when they’re so much as sharing a fjord with killer whales,” note the study authors. “This kind of large, long-lasting behavioral change suggests that the mere presence of new predators changes ecosystems at a level previously unsuspected.”

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“I think the narwhal are scared to death,” Steve Ferguson, of Canada’s Department of Fisheries and Oceans, told the Canadian Press. Ferguson is a co-author of the paper. “Watching your brother or sister or mother get killed and eaten by a killer whale would cause a little post-traumatic stress in most of us.”

While most other research focuses on what the predators are eating and in what number, this research looked at the behavior of the narwhals when the orcas were nearby. When killer whales weren’t around, the narwhals hunted prey fish between two and six miles from shore. But when the orcas were anywhere in the inlet, the narwhals huddled within 1,000 feet of shore.

Ferguson says the research may upend previous theories on environmental change.

“Most traditional science views changes to occur from the bottom up – the food supply changes and it ripples its way up the food web,” said Ferguson. “A few of us believe the changes can happen from the top down and be just as significant.”

“Given current reductions in sea ice and increases in Arctic killer whale sightings, killer whales have the potential to reshape Arctic marine mammal distributions and behavior,” the study authors concluded. “Second and of more general importance, predators have the potential to strongly affect movement behavior of tracked marine animals. Understanding predator effects may be as or more important than relating movement behavior to resource distribution or bottom-up drivers traditionally included in analyses of marine animal tracking data."

It’s not clear what this actually means for the narwhals' health, and researchers say more research is needed on this topic.