Orca Refugiums: Uncovering the Mysterious Ice Age Colonization of the North Pacific

Friday - August 25 2023, 11:26 UTC - 1 year ago

Whale expert Olga Filatova from the University of Southern Denmark has dedicated her research to unraveling the mysteries of orca colonization in the northern Pacific. She has now found two refugiums from the ice age – near the Aleutian Islands and in northern Japan – where orcas have stayed since the last ice age, some 20,000 years ago. This is based on genetic analysis and the vocal repertoire of the whales being studied. These orcas are highly diverse in genetics and sound, and don't interact with one another.

The northern Pacific near Japan and Russia is home to several different groups of orcas yet they never interact, hunt different prey, communicate in distinct dialects, and avoid mating with one another. How can this be when they live so close to each other and belong to the same species? .

Whale expert Olga Filatova from the University of Southern Denmark has dedicated her research to unraveling the mysteries of orca colonization in the northern Pacific. During her tenure at a Moscow University, she led multiple expeditions to study these enigmatic creatures. Currently, she is affiliated with the Marine Biological Research Center at the University of Southern Denmark.

Now, some of her latest results have been published. In a recent paper, she and colleagues explore the complex interaction between orca culture and the post-glacial history of their colonization of the North Pacific, showing that the orca pods currently living near Nemuro Strait in northern Japan are descendants of orcas that settled there during the last ice age, around 20,000 years ago. The location was chosen as a refugium by distant ancestors, and their descendants have lived there ever since.

"Orcas are conservative and tradition-bound creatures who do not move or change their traditions unless there is a very good reason for it. We see that in this population," says Olga Filatova.

This is the second time she finds an orca refugium from the ice age. The first one is near the Aleutian Islands, some 2500 km away. The pods there are just as conservative and tradition-bound as their Japanese conspecifics and are also descendants of ice age ancestors who found refuge in ice-free waters.

"When the ice began to retreat again, and orcas and other whales could swim to new ice-free areas, some of them did not follow. They stayed in their refugiums, and they are still living there," says Olga Filatova.

The studies are based on genetic analyses (the researchers took skin biopsies of the animals) and analyses of sounds made by the animals (recorded with underwater microphones).

"Orcas in the Nemuro Strait had unusually high genetic diversity, which is typical for glacial refugiums, and their vocal repertoire is very different from the dialects of orcas living to the north off the coast of Kamchatka. Kamchatkan orcas are most likely the descendants of the few pods that migrated west from the central Aleutian refugium, that’s why they are so different", says Olga Filatova.

Orcas’ vocalizations are highly diverse, and no two pods make the same sounds. Therefore, these sounds can be used to identify individuals’ affiliations with families and pods. Orcas are not genetically programmed to produce sound like, for example, a cat is. A cat that grows up among other animals and has never heard another cat will still meow when opening its mouth. In contrast, orcas learn to communicate from their mother or other older family members. Each pod has its own dialect, not spoken by others.

"When we combine this with genetic analyses, we get a strong idea of how different orca communities relate to each other," says Olga Filatova.

So far, two ice age refugiums have been identified for orcas in the North Pacific. But is there a third? .