This article published by Sumi et al in 2022 lists the little known tooth whales species witnessed in Sagami Bay and Tokyo Bay from 1927 to 2021 have been collected and analyzed. Cetaceans encountered are sighted but often stranded, lost in the bay, drifting or bycatch. Ten species has been recorded, 6 of them are IUCN Least concerned but others are labeled as vulnerable, critical endangered or little known (data insufficient). In majority, the observation reports stranded animals often resulting in death but not only.
Sperm Whale
Sperm whale (Physter macrocephalous, IUCN Vulnerable), has been observed a total of 36 times with 2 times between 2017 and 2021. The records found the cetaceans in Sagami Bay shores (near Odawara and Izu) whom washed from exhaustion. Sperm whales death from being stranded has occurred in multiple occasions. In 2023, a sperm whale of 15m has been spotted, affectionately got called Yodo-chan and monitored for several days in the Bay of Osaka. Unfortunately, the animal passed away and got displaced by maritime convoy. More recently, 3 sperm whales (males, 12-14m) got washed away on Chiba Prefecture shore on August 2025.
Fortunately, this unfortunate ending is not the norm: in 2024, a sperm whale has been observed in Tokyo bay and the young mammal ended up leaving the bay in good shape. We note also 9 records mentioned in the publication of mammal observed alive in the area.
Pygmy Sperm Whale
Pygmy Sperm Whale (Koga Breviceps, IUCN Least Concern), has been observed a total of 21 times with 1 time between 2017 and 2021. A male of 3.11m has been found in the Sagami bay, near the Shonan area. Older record mention females pygmy sperm whales breeding in the Shonan area (1975), Chiba area (1986) and Izu area (1991). Majority of the records are female ranging from 1.67m to 2.87m.
Pygmy sperm whales have a small, compact body with a small and rounded dorsal fin. Each individual whale’s dorsal fin is a slightly different shape. Their head is sometimes described as shark-like because of their pointed snout and narrow, underslung lower jaw. Pygmy sperm whales have wrinkled skin and a brown to blue-gray back. Their underside is paler with white or pink tones. They do not have teeth in their upper jaw but have 10 to 16 pairs of teeth in the lower jaw. They are rare mammal. (NOAA)
Dwarf Sperm Whale
Dwarf sperm whale (Koga sima, IUCN Least Concern), has been found stranded a total of 6 times on the shore of Sagami bay and occurrences happen mostly in March. The most recent record, 2021, mentions a female of 1.5m found stranded in the Zushi shore. Although described as least concerned by the IUCN, this species is described as rare by NOAA.
Due to their appearance being similar to the pygmy sperm whale and the difficulty to spot them at sea, limited information is available on these mammal. Dwarf sperm whales have a small, compact body with a small dorsal fin located near the middle of their back. Each individual whale’s dorsal fin is a slightly different shape. While on the water’s surface, dwarf sperm whales have a low profile because their head and back are somewhat flat. (NOAA)
Baird’s Beaked Whale
Baird’s beaked whale (Berardius bairdii, IUCN Least Concern), has been observed a total of 8 times in the Sagami bay and occurrences happen mostly in July. The last records are from 2006 and 2008 of males between 7 and 10m have been fond on the shore of Chiba prefecture and Izu peninsula. It inhabits the warm to cold temperate regions of the North Pacific, mainly in the deep parts of the continental shelf slope, and appears along the Pacific coast of Japan in the summer from May to August. (Yamada, 2015a).
In Japanese waters, this species has been observed in the northern Pacific Ocean (Nishimura, 1970; Nishiwaki & Oguro, 1971; Balcomb, 1989; Kasuya & Miyashita, 1997). Differences in population density and seasonal migration suggest the existence of three distinct populations around Japan: the Pacific Ocean, the Sea of Japan, and the Okhotsk Sea (Kasuya, 1986). Population sizes range from 1–30 individuals, with most consisting of 2–9 individuals (Kasuya, 2002). Furthermore, because males have a longer lifespan than females, there are more males in adult populations (Yamada, 2015a).
Hubb’s Beaked Whale
Ginkgo Toothed Beaked Whale (?)
Ginkgotoothed beaked whale (Mesoplodon ginkgodens, IUCN Data Deficient), has been found a total of 10 times exclusively in Sagami bay. Occurrences happen at different time with peaks in March, August and September. The most recent record is of 2019: a male found stranded on the shore.
The species is distributed in tropical and temperate waters of the Pacific and Indian Oceans. It is occasionally stranded on the Pacific coast of the Japanese archipelago from Okinawa to Ibaraki, and approximately 50% of records have been recorded off the coasts of Shizuoka, Kanagawa, and Chiba prefectures, with the exception of one record from Muroran, Hokkaido. Little is known about this species.
The picture used above might be the only footage of an alive Ginkgotoothed beaked whales but the cliche is still recorded as “unidentified species” to now. Hence, the species has only be encountered and identified stranded.
Curvier’s Beaked Whale
Curvier’s Beak Whale (Ziphius Cavirostris, IUCN Least Concern), has been found a total of 31 times exclusively in Sagami bay. Occurrences happen at different time with peaks in January and March. The most recent record is of 2021 and mentions a female of 5.49m, lost in the port whom ended up strengthless. It is one of the most widely distributed species within the beaked whale family having been recorded in all regions except in polar areas.
Strandings off the coast of Japan have been reported mainly on the Pacific coast (Omura et al., 1955; Nishiwaki & Oguro, 1972). This species regularly dives for 48–68 minutes to depths exceeding 800 m (maximum 1,450 m) (Yamada, 2015g). It is found in small groups of 2–7 individuals, although solitary sightings are not uncommon (Jefferson et al., 1993).
Yangtze Finless Porpoise
Yangtze Finless Porpoise (Neophocaena Asiaeorientalis, IUCN Critically Endangered), has been found a total of 61 times exclusively in both Sagami bay and Tokyo bay. Occurrences happen at different time with a peak in May. The most recent records are of 1 individual in 2019, 3 in 2020 and 1 in 2021. The sighting of 2020 mentions the mammal alive near the shore of Chiba prefecture.
The Yangtze finless porpoise is a small toothed whale, reaching a maximum body length of approximately 2 m. It is found in temperate coastal waters of the Western Pacific, including the Taiwan Strait, northern China, Korea, and Japan, as well as the middle and lower reaches of the Yangtze River (Jefferson & Wang, 2011). The Japanese coastal waters are at the eastern edge of its range. This species is found in five coastal waters: Ariake Sea – Tachibana Bay, Omura Bay, Seto Inland Sea – Hibikinada, Ise Bay – Mikawa Bay, and Sendai Bay – Tokyo Bay (Shirakihara & Yoshioka, 2015). It is often found alone, in pairs, or in groups of up to 12 individuals, although groups of up to 50 individuals have also been reported.
The species is protected under the Fisheries Resources Protection Act, along with the blue whale (Balaenoptera musculus), bowhead whale (Balaena mysticetus), and gray whale (Eschrichtius robustus), and all capture and retention has been prohibited since 1993 (Suzuki et al., 2015).
This is the most frequently recorded cetacean of any species recorded off the coasts of Sagami Bay and Tokyo Bay.
Hubb’s Beaked Whale
Dall’s Porpose (dalli type)
Dall’s Porpoise (Phocoena dally, IUCN Least Concern), has been found a total of 3 times on the period 2 times in Tokyo bay, once in Sagami bay, the most recent being 2005. Occurrences happened in April, May and October.
It is endemic to the northern North Pacific and adjacent seas (Bering Sea, Sea of Okhotsk, and Sea of Japan) (Yoshioka, 2015b). In Japan, it inhabits the Pacific coast north of Chiba Prefecture and the Sea of Japan coast north of Shimane Prefecture (Miyashita & Kasuya, 1988).
There are two color morphs: the dalli-type (Ishi’s dolphin), which has a small white patch on the side of the body extending from the anus to the dorsal fin, and the truei-type (Rikuzen’s dolphin), which has a large white patch on the side of the body extending to the front of the pectoral fin (Yoshioka, 2015b).
The Ishi’s dolphin type is distributed from the coast of Japan to the coast of the North American continent, moving south in March and being spotted off the coast of Boso on the Pacific side in March (Miyashita, 2003). The distribution of the Rikuzen’s dolphin type is limited to the area from off the coast of Sanriku to the Sea of Okhotsk, with the southern limit estimated to be around the coast of Boso (Miyashita & Kasuya, 1988).