Why Some Orcas Stay Close to Home While Others Roam — And Rarely Interact

From the cliffs of the Shiretoko Peninsula, killer whales are a familiar sight. Pods surface offshore, drawing tourists to one of Japan’s most celebrated wildlife destinations and anchoring the region’s identity as a marine hotspot. Yet for all their visibility, scientists have struggled to answer a basic question: which types of killer whales live here?

New genetic research published in Marine Mammal Science helps answer that question. Orcas cruising the waters around Hokkaido belong to at least two deeply distinct lineages — fish-eating residents and mammal-hunting transients — whose differences in diet, behavior, and evolutionary history may trace back to the last Ice Age.

Read More: Some Orcas Are Flipping Juvenile White Sharks and Devouring Their Livers

Different Diets, Different Cultures in Orcas

Although killer whales are classified as a single species, they are divided into populations known as ecotypes. Each ecotype represents a specialized way of life — from what the whales eat to how they hunt and socialize. In the North Pacific, scientists recognize three main ecotypes: residents, which primarily eat fish; transients, which hunt marine mammals; and offshore orcas, another fish-eating group that tends to roam farther from shore.

Resident and transient orcas can live in the same waters, yet barely interact. They use different vocalizations, hunt different prey, and even raise their young differently. In some regions, these differences are so pronounced that scientists have debated whether the groups should be considered separate species.

Around Hokkaido, earlier studies hinted that both fish-eating and mammal-eating orcas were present — but the genetic data used to support that idea were limited.

A Closer Genetic Look at Hokkaido’s Whales

To get clearer answers, researchers from Kyoto University and collaborating institutions analyzed the entire mitochondrial genomes of 25 killer whales sampled around Hokkaido — a level of detail missing from earlier studies. Because mitochondrial DNA is passed down through maternal lines, it offers a window into population history and long-term separation.

The analysis confirmed that Hokkaido’s orcas fall into two ecotypes: residents and transients, with no evidence of offshore whales in the region.

The two groups showed different genetic patterns. All resident whales shared the same mitochondrial haplotype — the most common one in the western North Pacific. Transient whales, by contrast, showed extraordinary diversity: eight distinct haplotypes among just 19 individuals, including seven never documented before.

That level of variation is higher than previously documented in transient killer whales anywhere else in the North Pacific.

From Ice Age Refuges to Modern Conservation

The team believes this genetic richness may be a legacy of the Last Glacial Maximum, when advancing ice sheets reshaped marine ecosystems. During that period, the waters around Hokkaido may have acted as a refugium — a place where transient orcas survived while other populations declined or shifted range, preserving genetic lineages over thousands of years.

Beyond evolutionary history, the findings have real-world implications. In regions with well-studied orca populations, conservation strategies are often tailored to specific ecotypes, reflecting their different prey, behaviors, and vulnerabilities. Around Hokkaido, such targeted management has been difficult without clear ecological and genetic data.

"Clarifying the ecological characteristics of killer whales is crucial for achieving coexistence with them, as they are deeply entwined with human activities such as tourism and fisheries in Hokkaido," says first and corresponding author Momoka Suzuki, in a press release.

As researchers continue to combine genetic data with behavioral observations, the picture of Hokkaido’s orcas is coming into sharper focus — revealing not just iconic predators but a living record of how climate, evolution, and ecology shape life in the sea.

Read More: In a First, Watch as Orcas Team Up With Dolphins to Boost Their Salmon-Hunting Success

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• This article references information from a study published in Marine Mammal Science: Whole Mitochondrial Genome Analysis of Killer Whales Reveals the Presence of Resident and Transient Ecotypes Around Hokkaido