Orcas off the coast of Hokkaido, Japan, can be split into two distinct ecotypes – resident and transient – according to a new study published in Marine Mammal Science.
Also known as killer whales, orcas are currently categorised as one species (Orcinus orca). However, the distinct forms, or ecotypes, are so different that some researchers believe they might be different species.
There are three known ecotypes in the North Pacific – resident, transient and offshore – each with its own genetics, appearance, language and diet.
Residents eat fish, transients hunt mammals – including seals, humpback whales, blue whales and sperm whales – and offshore orcas eat fish but are also known to hunt sharks. They have been recorded killing great whites and enormous whale sharks by turning them belly up – to subdue them – then tearing out their liver and feasting on its nutrients.
Killer whales in the eastern North Pacific, off the coastline of Canada and Alaska, are incredibly well-studied but less is known about the orcas in the western North Pacific. This new research aimed to change that by analysing the genomes of 25 individuals from around Hokkaido – the most northerly of Japan’s islands.
An earlier study of these North Pacific orcas had suggested that some ate fish while others ate mammals and this new research takes that further by confirming the population can be split into resident and transient ecotypes.
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Their in-depth DNA analysis also showed that resident killer whales shared the same haplotype (group of inherited genes) while the transients had eight different haplotypes making them more genetically diverse. This finding suggests that transient killer whales used Hokkaido as a refuge during the last Ice Age, the researchers say.
“Clarifying the ecological characteristics of killer whales is crucial for achieving coexistence with them,” says first author Momoka Suzuki, Kyoto University, in a statement.
Understanding the diet and behaviour of orcas in Japanese waters gives conservationists important information that can help protect the animals from threats. “They are deeply entwined with human activities such as tourism and fisheries in Hokkaido,” adds Suzuki.
Shiretoko, a UNESCO World Heritage site in the northeast of Hokkaido, is known as one of the best killer whale watching hotspots in Japan. The scientists hope their research can help fill in the gaps about the little-studied population found here. “We will continue to collect ecological data using a wide range of methods, including behavioural observation and genetic analysis,” says Suzuki.
Top image: Orcas off the coast of Hokkaido. Credit: Getty
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