Shrinking sea ice may mean new opportunities for killer whales in the Arctic

Transient killer whales typically only call after they have made a kill. Their prey—other marine mammals—listen closely for these efficient and capable predators, hoping to avoid encounters. In the Alaska Arctic, sea ice has historically kept killer whales at bay. But as BRYNN KIMBER writes, the triumphant calls of transient killer whales are sounding more and more frequently in Alaska as the Arctic warms and sea ice melts.

For resident Arctic species, such as the bowhead whale, there is safety in sea ice: it protects them from killer whales. Killer whales are one of the only animals (aside from humans) who hunt bowheads, but they lack the bowheads’ ability to break through sea ice to create vital breathing holes.

Frozen areas offer refuge and protection for bowheads and other Arctic species. But as climate change warms the Arctic, sea ice is melting—and some icy areas that were once safe are now characterized by open water and danger. Based on their growing acoustic presence in areas where they were once rarely seen or heard, transient killer whales may be taking advantage of these changes.

Eavesdropping on whales

Passive acoustic monitoring is an invaluable tool that scientists can use to detect the presence of marine mammals, especially in remote areas that are difficult to access, such as the ice-covered Arctic. Many marine mammals make distinct calls that enable us to identify them. When we pick up these calls on moored recorders, we can assess marine mammals’ locations throughout the year.

Since 2008, the Marine Mammal Laboratory at the National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center has been building a dataset from more than 20 recorders used year-round in Alaska waters. This dataset provides a look at how the acoustic presence of animals varies from year to year. The data can be used for a variety of purposes, including tracking migration patterns and observing changes in animal movements over time. In an area such as the Arctic, which is undergoing rapid change due to rising temperatures and decreasing sea ice, this can provide a vital look into how species distributions might change with ecosystem shifts.

When I analyzed these recordings, one such shift jumped out: transient killer whales were calling in areas where they had seldom been recorded before, particularly in areas that had been completely ice-covered in the past.

When I looked more closely, three distinct patterns emerged. First, killer whales were arriving at the Bering Strait—the southern entrance to the Alaska Arctic Ocean—earlier and earlier in the spring, just after the ice disappeared each year. Second, they were lingering in the area longer and more consistently than they had before. And third, they were being detected in areas where they had seldom been detected before, including far up in the Chukchi Sea, much further north than historically recorded.

Impacts on ecosystems and communities

Killer whales are efficient predators that are capable of significantly impacting the populations of their prey. If the increased acoustic presence of killer whales means more overlap with Arctic species, such as bowhead whales, beluga whales and various seal species, this may indicate increased predation, which could affect population numbers for these prey species. In addition to direct predation pressure, there is also concern that the mere presence of killer whales might cause significant stress to these prey species, potentially altering their foraging and reproductive behaviours.

Not only could increased pressure from predation negatively affect endemic Arctic species—it may also affect Indigenous Peoples in Alaska who rely on subsistence hunting to maintain their way of life. The species that would be most vulnerable to disruptions caused by transient killer whales—bowhead whales, belugas and seals—are the same ones that Alaska Native hunters rely on to feed their communities.

Unfortunately, the increased presence of killer whales is just one result of climate change that could affect both the people and animals living in the Arctic. As the ocean warms and sea ice melts, it’s important for scientists, citizens and organizations to monitor how the ecosystem is changing and figure out how best to manage it.