North Pacific orca culture sheds light on killer whale colonies

Genetic analyses and vocal interpretations have revealed more about killer whales that live in the North Pacific.

Marine biologist Olga Filatova from the University of Southern Denmark and her colleagues explored the complex interaction between orca culture and the post-glacial history of their time living in the North Pacific. The results of their study are reported in Marine Mammal Science.

In it, they show the orca pods currently living near Nemuro Strait in northern Japan descend from animals that settled there during the last glacial maximum (LGM), around 20,000 years ago, when heavy ice covered extensive areas in the western North Pacific.

The authors say revealing migration patterns of orcas since the LGM helps understand contemporary genetic diversity and population structure and could help future conservation initiatives.

Although orcas are commonly referred to as killer whales, they are actually the largest member of the dolphin family.

“The southern resident killer whale community inhabiting the waters of southern British Columbia and Washington State is socially and genetically isolated from the northern resident community,” says the report. “Southern residents are critically endangered, numbering only about 70 whales and declining, while northern residents comprise more than 300 individuals and their numbers are growing.

“The lack of contact between these communities likely results from the historical geographical isolation due to range shifts during the LGM; after the retreat of the glaciers, their ranges expanded but social isolation persisted likely due to the differences in cultural traits (for example vocal dialects) accumulated over the period of geographical isolation.”

Filatova told Phys.org in an interview about the paper that orcas are conservative and tradition-bound creatures “who do not move or change their traditions unless there is a very good reason for it”.

According to Filatova, highly mobile species were able to shift their ranges to warmer regions that remained ice-free during glacial periods. These ‘glacial refugia’ often preserved higher levels of genetic diversity than areas that were colonised after the retreat of glaciers. 

“When the ice began to retreat again [after the LGM], and orcas and other whales could swim to new ice-free areas, some of them did not follow. They stayed in their [refugia], and they are still living there,” says Filatova.

The research team data was collected from free-ranging orcas in Nemuro Strait in May-June 2021 and 2022, using camera equipment to record their movements from an inflatable boat, the researchers performed remote biopsies of the animals using crossbows and floating arrows and identified individual whales by their unique markings.

By identifying individuals, the researchers were able to study the patterns of orca movement within the region.

“As top predators, killer whales are sensitive to the disturbances in their prey resources, which may be impacted by rapid climate change,” they write.

“When predators return to their former range they can cause knock-on effects in an ecosystem if the predators are effective enough to reduce the abundance or alter the behaviour of their prey,  changing the pressure on the next lower trophic level.”

In a recent report in Cosmos marine biologist Melissa Marquez explored the social behaviour of orcas describing their high level of intelligence and vocal activities.