They all hang out together, but family is most important for Norwegian orcas
In the North Pacific, orcas eating different foods live in separate groups. This is not the case off Norway’s coasts.
Research on orcas in the North Pacific over 40 years has revealed a clear pattern.
“There’s a very strict distinction between those that eat marine mammals and those that eat fish,” says whale researcher Eve Jourdain at the University of Oslo.
How is it in Norway?
Here too, researchers see that orcas consume different foods. Most eat fish, while some eat both fish and marine mammals.
Jourdain and colleagues wondered if there is a clear distinction between them, as seen in the North Pacific.
Live separately
In the North Pacific, orcas can be divided into fish-eaters and those who eat seals, porpoises, dolphins, and whales.
“Even though they are the same species and share the same areas. Over many years of research, we’ve almost never seen the different types interact,” says Jourdain.
This is also evident in the whales’ genes, which show genetic differences.
“They haven’t interbred for years,” she says.
Not the case in Norway
It’s easy to think that the same applies to killer whales in Norway.
But that’s not the case, Jourdain and colleagues conclude in a new study.
“Everyone hangs out with everyone. Genetics support this. There is no division. This is one population,” Jourdain says.
This contrasts with what we see in the North Pacific, Jourdain notes. It is therefore not a global feature that orcas divide into groups based on what they eat.
Observations over 13 years
Researchers have monitored orcas in Norway for 13 years.
Orcas can be identified by their dorsal fin.
The study includes 457 killer whales, each observed between 3 and 22 times over the years.
The researchers mapped those that only ate fish and those that also consumed mammals like seals and porpoises. They also recorded family associations.
Skin samples and genetic analyses were taken from around a hundred orcas.
Meet where there is an abundance of food
“Over the years, we’ve discovered that each family group differs in what they eat. This is quite important for species conservation because those eating marine mammals have more chemicals stored in their body tissue due to feeding higher up the food chain,” she says.
Jourdain and colleagues have now discovered that those eating mammals are not a unique subgroup.
They can associate with fish-eating orcas and interbreed.
Orcas with different diets gather together when there is an abundance of food in one place.
“It's like visiting a popular restaurant where you run into other people,” she says.
During certain seasons, large numbers of herring gather in a particular area, attracting orcas.
“They’ll spend a day or two together, socializing and learning from one another before splitting up and going their separate ways again,” she says.
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Stay with their mother
Orcas otherwise live in close family groups.
“The small, solid groups stick together almost forever. They consist of mothers, children, and maybe grandchildren. Males also stay with their mother, even into their 20s or 40s,” Jourdain says.
Female orcas can live up to 90 years, while males can live between 50 and 60.
Family groups do not have to eat the same food all their lives. They can change tactics depending on what kind of food is available, the researchers found.
Perhaps this happens through learning from other groups of whales.
“This will be the focus of our next study. Now that we know more about how these networks are built, we can study how knowledge transfers through them,” she says.
Not always healthy to eat seals
Eve Jourdain is the founder of the Norwegian Orca Survey research organisation. They study orcas in Norway.
Researchers previously thought that the Norwegian killer whale population mainly ate herring and other fish, according to this past article on sciencenorway.no.
It later became clear that some also eat mammals like seals, which may not be so good for them.
A previous study found that orcas that consumed seals had many environmental toxins.
“We found that all the seal-eaters we investigated had such high levels of pollutants in the body that it exceeded a threshold value for a risk of health effects,” said Clare Andvik at the University of Oslo’s Department of Biosciences.
“This means that they are in danger for a suppressed immune system, hormone disruption, and reduced ability to reproduce.”
Reference:
Jourdain et al. Social and genetic connectivity despite ecological variation in a killer whale network, Proceedings of the Royal Society B: Biological Sciences, 2024. DOI: 10.1098/rspb.2024.0524
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Translated by Alette Bjordal Gjellesvik
Read the Norwegian version of this article on forskning.no
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