The vast ice sheets that historically kept killer whales out of the Arctic Ocean are melting as the region rapidly warms.

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Killer whales (Orcinus orca) are finding a new place to roam in the rapidly changing Arctic Ocean. Though Indigenous people in the region have seen the whales, also known as orcas, pop up sporadically for centuries, the predators now have more access to the chilly waters than ever before.

Two distinct killer whale populations now claim habitats in the Arctic, according to a team led by researchers at the University of Manitoba in Winnipeg, Canada. But the whales’ presence raises conservation concerns that may be difficult to address, the team reported recently in Global Change Biology.

Killer whales haven’t often been able to access the Arctic. Thick ice sheets posed a natural barrier, breaking their dorsal fin if they pushed too hard into it. But as the northern polar regions warm up faster than anywhere else on Earth, the ice melts, letting in more of the voracious predators.

The researchers, led by evolutionary geneticist Colin Garroway of the University of Manitoba, were curious about the Arctic’s growing population of killer whales and their impacts. They decided to peek into the genomes of a few of the animals to find out where they came from.

Initially, they used samples of blubber and skin collected over time by field biologists. “We did an analysis that’s something like 23AndMe,” said Garroway. The results: Two distinct populations of killer whales were sharing the Arctic Ocean. “We were super surprised,” Garroway said.

The results prompted the researchers to extend the study. They traveled to the eastern Canadian Arctic Ocean once again, watching the waves for telltale fins and black-and-white patches. Even when orcas have satellite trackers, they can be hard to pin down. They travel quickly and are often shy around boats. “It really is just a matter of being in the right place at the right time,” said Cory Matthews, a marine biologist at the University of Manitoba who did field work for the study.

When the sleek animals show themselves, researchers set aside their excitement and try to get up close. Using crossbows, they shoot the whales with small biopsy darts, which collect tiny amounts of skin and blubber. The samples immediately go into a liquid nitrogen–cooled container.

DNA results confirmed that the two groups of whales are so distinct that they might not recognize one another as potential mates. The populations are small: About 200 individuals currently live near Baffin Island, Garroway said. In the long run, they might be unable to adapt to evolutionary pressures because of their lack of genetic diversity — a pressing concern as marine habitats evolve due to climate change.

However, killer whales also might tip scales in the balanced Arctic ecosystem. “Arctic whales are just chubby, slow and delicious,” Garroway said. Belugas, bowhead whales and narwhals are protected by the ice sheets that usually keep killer whales out. Now, the predators can get to them more easily than ever before.

Arctic whale populations still outnumber killer whales in the region. There are likely hundreds of thousands of narwhals compared to the few hundred killer whales that have moved in, Garroway said. “They’re not yet making a big difference, but they could eventually,” he noted.

But that assessment might be premature, said marine biologist Mads Peter Heide-Jørgensen of the Greenland Institute of Natural Resources, who was not involved in the research. “I find that the authors exaggerate the importance of killer whales when claiming that they cause ‘major ecosystem changes,’” he wrote in an email to Mongabay.

Local Indigenous groups will watch closely as this story unfolds: Arctic whales are an important food, cultural and economic resource, and are harvested sustainably. Killer whales could threaten those hunting traditions if their populations grow, the research team noted.

For now, these new Arctic residents serve as a case study for the profound shifts in population dynamics that ecologists are monitoring worldwide. “It’s a massive global experiment in climate change,” Garroway said, “and we get to watch a short part of it.”

Citation:

Garroway, C.J., de Greef, E., et al. (2024). Climate change introduces threatened killer whale populations and conservation challenges to the Arctic. Global Change Biology, 30(6), e17352. doi: 10.1111/gcb.17352

Source:

Caroline Hemphill at MongaBay

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