Scientists Uncover Rare Beaked Whale Species in Frigid Japanese Waters

A full-body photograph from the left side of the ginkgo-toothed beaked whale detailed in this study is shown. It was taken by Wojtek Bachara, Kuroda Mika and others, and was published in the Aquatic Mammals on July 9, 2023.

Cetaceans are recognized as wholly aquatic animals and they include whales, dolphins, and porpoises. This classification comprises over 90 living species, divided into baleen whales (Mysticeti) and toothed whales (Odontoceti). In particular, toothed whales are differentiated by their use of teeth and they comprise various species, among which is the lesser-known Mesoplodon genus. These animals are usually found in offshore oceanic areas and rarely surface, rendering their distribution and ecology fairly obscure.

A stranded ginkgo-toothed beaked whale was recently discovered on the shore of Yakumo, Southern Hokkaido by a research team which included Assistant Professor Kuroda Mika from the Field Science Center for Northern Biosphere at Hokkaido University and Professor Matsuishi Takashi Fritz from the Faculty of Fisheries Sciences. Their discovery was documented in the Aquatic Mammals journal.

Kuroda explains that the Mesoplodon genus is comprised of more than 15 recognized species and is the largest genus in the Ziphiidae family. The variety of species in this group can be identified by the head shape and the distinct teeth of the males. Specifically, the males of the ginkgo-toothed beaked whale, known as Mesoplodon ginkgodens, bear 10-cm-wide teeth that are shaped like the leaves of the Ginkgo biloba, a ginkgo tree.

A part of the phylogenetic tree illustrating that the whale examined in this study (SNH22005) is positioned in the Mesoplodon ginkgodens clade. This image was taken by Wojtek Bachara, Kuroda Mika and others, and was published in the Aquatic Mammals on July 9, 2023.

Our existing knowledge of the ginkgo-toothed beaked whales comes almost entirely from 95 individual examples found at 88 separate whale stranding occurrences. Of these, 30 stranding incidents took place across Japan.

A whale stranding in the town of Yakumo, Hokkaido was reported on February 4, 2022. The deceased whale body was taken to the Hakodate Research Centre for Fisheries and Oceans for both measurement and autopsy. The whale was male, with a body length of 477 cm and in the early stages of decomposition, leading to indications that the animal had been dead for quite a while. The morphology was in line with that of M. ginkgodens, and genetic analysis of mitochondrial DNA positioned this specimen within the M. ginkgodens clade, with one matching sequence.

Previous strandings have been reported in various locations, inclusive of Japan, the western coast of the United States, Australia, Galapagos Islands, Thailand, New Zealand, Micronesia, Marshall Islands, China, South Korea, and Mexico. These are all areas with moderate, subtropical, and tropical waters. This research represents the first instance of Mesoplodon ginkgodens being reported in the colder waters of the North Pacific.

"On November 29, 2021, another stranding was reported that might have been a ginkgo-toothed beaked whale, but the sample was lost due to bad weather," reports Kuroda. "Our studies suggest that these whales may have migrated near Hokkaido during winter."

Acknowledgment: "Northernmost Record of the Ginkgo-Toothed Beaked Whale (Mesoplodon ginkgodens)" was authored by Wojtek Bachara, Kuroda Mika among others, and was published in the Aquatic Mammals journal on July 9, 2023.