First aerial observation of Sato's beaked whales (Berardius minimus) above the Abashiri Submarine Canyon, Hokkaido, Japan

Abstract

The Sato's beaked whale (Berardius minimus) is the most recently described species classified within the genus Berardius (Yamada et al., 2019). The type specimen of Sato's beaked whale stranded at Tokoro, Hokkaido, Japan, and five additional specimens were subsequently collected along the coasts of the Okhotsk Sea and the Nemuro Strait off Eastern Hokkaido (Yamada et al., 2019). Although information on the distribution of Sato's beaked whales is limited, this species has also stranded on Sakhalin and Kunashir Islands (Fedutin et al., 2020) and farther east at the Bering Sea, ranging from the eastern Aleutian Islands (Unalaska Island) to the Alaska Peninsula (e.g., Morin et al., 2017). Sato's beaked whales are genetically and morphologically distinct from other Berardius species (B. bairdii and B. arnuxii). The external morphological characteristics of two of them, B. bairdii and B. minimus, found in the Sea of Okhotsk and the North Pacific Ocean (Morin et al., 2017; Yamada et al., 2019), can be used to aid in species identification: Sato's beaked whales have (1) a significantly smaller body length in mature males: an average of 661 cm (n = 4; Yamada et al., 2019) vs. 998.9 cm (n = 34; Kishiro, 2007); (2) darker, closer to black, body coloration (in contrast to Baird's beaked whale, which has a light or slate gray coloration); (3) fewer scratch marks on their body (Baird's beaked whales have scars caused by teeth during intraspecific interactions); (4) visible bite marks from cookie-cutter sharks (Isistius brasiliensis) on their body and in higher density than on Baird's beaked whales; and (5) a relatively short rostrum compared to body length (Yamada et al., 2019). Experienced whalers and whale-watchers can thus potentially identify Berardius species (B. bairdii and B. minimus) based on these characteristics if they are able to observe them at relatively close range (Kasuya, 2017).Baird's beaked whales are known to be highly sensitive to ship approaches (Kasuya, 2017), and Sato's beaked whales are even more skittish and thus rarely taken by small-type whalers from Abashiri (Brownell & Kasuya, 2021), making it more challenging to identify and observe their behavior from a boat.In 2022, a group of beaked whales near Kunashir Island in the Nemuro Strait was biopsied, and genetic analysis confirmed they were Sato's beaked whales, marking the first confirmed live observation of this