Japanese researchers now believe it is possible that the northernmost breeding region for humpback whales has shifted far northward to around Tokyo’s Hachijo Island.
Waters off the island of Kagoshima Prefecture’s Amami Oshima, some 500 kilometers south of Hachijo Island, have been known as the northernmost breeding region for humpback whales, which are popular among whale-watchers for their dynamic jumps and spouting.
But since November 2015, when a Hachijo Island resident found a pod of humpback whales near the island for the first time, an increasing number of the baleen whale species have been spotted in the waters, according to Gen Nakamura, assistant professor at Tokyo University of Marine Science.
In a joint research project with the Hachijo town government, Nakamura and his colleagues found that the number of humpback whales spotted off the island increased to 151 in the season between winter 2017 and spring 2018, up from 60 a year earlier. So far this season, the team has already confirmed over 100 whales.
Humpback whales give birth to cubs in warm waters near Japan, including those around Okinawa and Amami Oshima, from winter to spring. The whales then spend the summer in waters near the Kamchatka Peninsula in Russia, where there is plenty of food.
Of the whales spotted in the 2017-2018 season, six were identified from markings on their flukes as the same creatures that were in the area the previous season.
The researchers also confirmed several cases of pre-mating behavior, including courtship vocalizations by males for females and males chasing after females.
With waters around Okinawa getting crowded in terms of whales, some may have started looking for new breeding grounds off Hachijo Island, Nakamura said.
In the seas near the main island of Okinawa, the number of the whales is estimated to have been increasing by some 10 percent every year since 1990, he noted.
However, Nakamura said further research is necessary to determine if Hachijo Island is the new northernmost breeding region, because neither mating nor calves swimming with their parents have been seen yet.