Exploring Orca Colonization in the North Pacific
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.
Genetic and Vocal Analysis Reveal Orca Lineage
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.
Orca Migration and Climate Change
So far, two ice age refugiums have been discovered, providing us with insight into how orcas may handle current and future climate changes: they will likely move northward as the ice melts, and this colonization may happen in small, individual families or pods rather than in large waves.
The discovery of the two ice age refugiums not only contributes to knowledge about how orcas survived during the ice age, but it also paints a picture of orcas as very different animals that may not fit neatly into one species.
“Many believe that orcas should be divided into several species. I agree – at least into subspecies because they are so different that it doesn’t make sense to talk about one species when discussing their place in the food chain or when allocating quotas to fishermen,” says Olga Filatova.
Dietary Preferences and Their Impact on Ecosystems
Some orcas eat fish, some only herring, some only mackerel, some only a specific type of salmon. Others only eat marine mammals such as seals, porpoises, and dolphins. Some take a little of everything, and still others live so far out in the open sea that we fundamentally know very little about them.
Whether a pod eats fish – and which fish – has a significant impact on the fishing that takes place in their habitat. When a country calculates fishing quotas, it must take into account how many fish are naturally hunted by predators, and since an orca can consume 50-100 kg (110-220 lb) of fish in a day, it greatly affects the quota calculation.
If pods eat marine mammals and do not touch fish, this matters if they are to be captured and sold to marine parks, where it is difficult to feed them marine mammals. While marine parks’ popularity is declining worldwide, there is still a large market for orcas in Chinese marine parks.
Since there is only one scientifically recognized species of orcas, researchers have resorted to a different form of classification to distinguish between different types of orcas and categorize them into so-called ecotypes. In the northern Pacific, three ecotypes have been defined so far, and in the southern hemisphere, four or five have been described.
There are probably more – perhaps up to 20 different ecotypes, according to Olga Filatova.
“We need to know the different ecotypes. Orcas are at the top of the food chain, and it affects the entire ecosystem around them what they eat, and where they do it,” says Olga Filatova.
In the Danish waters, Skagerrak and Kattegat, close to SDUs Marine Biological Research Center, orcas are occasionally seen. Yet, no one knows if they eat fish or marine mammals – and therefore, also, how they affect the food chain and fishing.
“I look forward to learning more about them. Maybe they turn out to belong to a new ecotype,” says Olga Filatova.
Pods, families, and clans:
Orcas live in families, led by matriarchs. Families gather in close-knit groups, called pods. Clans consist of pods with similar vocal dialects.
Ecotypes of orcas:
Ecotypes have different dialects, and different habitats, and do not mate with each other. Researchers believe that there may be up to 20 different ecotypes.
Known ecotypes in the Northern Pacific:
Residents: Close-knit families and pods that stay in the same areas along the coasts. Feed on fish.
Transients: Smaller, less cohesive pods that feed on marine mammals. Habitat from Russia to California.
Offshore: Live far out in the open sea in groups of 20-200 individuals. Poorly studied.
Known ecotypes in the southern Antarctic:
Type A: Travel in open waters and seems to feed mostly on minke whales.
Type B: Smaller than Type A. Seems to feed mostly on seals.
Type C: The smallest. Live in larger groups than the others. Seems to feed mostly on fish.
Type D: Range between the 40th and 60th southern latitudes. These are poorly studied.
Possible new ecotypes:
Groups that feed on fish in the North Atlantic.
Groups that feed on marine mammals in the North Atlantic.
Groups that feed on penguins and sea lions on the coast of South America.
Groups around Gibraltar, feeding on tuna.
Groups in the tropics around Hawaii and Gulf of Mexico.
Groups around New Zealand, primarily feeding on rays and sharks.
Reference: “Genetic and cultural evidence suggests a refugium for killer whales off Japan during the Last Glacial Maximum” by Olga A. Filatova, Ivan D. Fedutin, Ekaterina A. Borisova, Ilya G. Meschersky and Erich Hoyt, 6 July 2023, Marine Mammal Science.
DOI: 10.1111/mms.13046
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