Chapter 4: Whales in Boso

Boso Peninsula is blessed with whale species visiting the rich marine environment around it. You will learn about which whales can be seen off the coast of the peninsula in Chapter 4.

The Boso Peninsula is sandwiched between the shallow Tokyo Bay and the open Pacific Ocean, which reaches depths of thousands of meters or more in places. The warm and cold Kuroshio and Oyashio currents collide off the coast on the Pacific side of the peninsula. This creates an extremely biodiverse marine ecosystem, which accounts for the fact that, among Japanese prefectures, Chiba Prefecture has the highest number of species sightings, and, indeed, 35 of the approximately 90 whale species of the world can be seen off the prefecture. The records include Narrow-ridged finless porpoises and Grey whales, species which prefer relatively shallow waters, and Cuvier’s beaked whales and Sperm whales, species which dive into very deep waters. Species that inhabit the cold waters of the higher latitudes of the northern hemisphere, such as Harbour porpoises and Dall’s porpoises, and those that prefer warmer waters, such as Omura’s whales and Melon-headed whales, have also been spotted. The sea off Boso is either the southern or northern limit of their distributions.

Cetaceans are occasionally found washed ashore dead or alive around the world and the causes of this are still yet to be discovered. There are about 20 beaching reports annually in Chiba Prefecture and the species that have been stranded in the prefecture range widely from small whales, such as Narrow-ridged finless porpoises, to large whales over 15 meters long, and even rare ones. There have been incidents where dozens of individuals have beached on a shore at the same time. In 2006, for example, a mass beaching of about 100 Melon-headed whales was found on the beach at Ichinomiya, and in 2013 about 60 of the same species were washed up on the beaches of Kujukuri in one month. The rarest species that has been found stranded was a Ginkgo-toothed beaked whale, which beached for the first time in 27 years in Shirako-Town in 2021.

back to Menu