Bering Sea Beaked Whale

• Stejneger's beaked whales receive their common and scientific name from Leonhard Stejneger, who was a naturalist and curator at the Smithsonian Institution, after he described the species from a single skull discovered on Bering Island in 1885 (Reeves et al. 2002). • Male Stejneger's beaked whale's have an unusually shaped lower jaw and huge tusk-like teeth.

Distribution Stejneger's beaked whales have a distribution throughout the North Pacific that includes California, the Aleutian Islands, southwest Bering Sea, Kamchatka, Okhotsk Sea, and the Sea of Japan. Strandings of this species have commonly occurred in the Aleutian Islands of Alaska and on the west coasts of Japan. Scientists speculate that this species may migrate north in the summer (Jefferson et al. 2008). Information on the distribution of these whales mostly comes from stranding records.

Head Shape The melon is flattened compared to other Mesoplodon species. The melon slopes smoothly onto the medium length beak. The mouthline curves upward posteriorly, forming a prominent arch. Coloration Males are gray to black over a majority of their bodies. The head has a prominent black cap on dorsal surface encompassing the blowhole and converging laterally to encompass the eye. The flipper pocket is also darker than surrounding skin. Females and juveniles are dark brownish-grey dorsally with lateral areas grading to a much lighter ventral coloration. The head has a prominent black cap on dorsal surface encompassing the blowhole and converging laterally to encompass the eye. The flipper pocket is also darker than surrounding skin. The ventral surface of the flukes may exhibit concentric, striations that radiate out laterally from insertion of caudal peduncle. These striations can vary from light gray to white. Diffuse mottling or spotted pigmentation may occur on the ventral body surface from the throat region to the caudal peduncle. These markings are consistent with scars caused by Penella sp. and / or the cookie cutter shark, Isistius brasiliensis. Penella sp. causes small 1-2 cm diameter punctate scars, while Isistius bites lightly pigmented circular to oval shaped scars 4-8 cm in diameter. Isistius scars are generally concentrated on the posterior half of body. Size Adult body length ranges between 5 to 6 m. Recorded maximum body length for adult males and females is 6.0 m and 5.4 m, respectively. Body length at birth is 2.2 m. Most Likely Confused With: Mesoplodon carlhubbsi Mesoplodon densirostris Mesoplodon ginkgodens

Habitat Stejneger's beaked whales prefer the cold temperate and subarctic waters of the North Pacific Ocean. They are generally found in deep, offshore waters from 2,500-5,000 ft (750-1,500 m), on or beyond the continental slope (Reeves et al. 2002).

Population Trends For management purposes, Stejneger's beaked whales inhabiting U.S. waters have been placed in the Alaska Stock and California/Oregon/Washington Stock. The estimated population for Mesoplodon spp. (Blainville's, Perrin's, Pygmy, Gingko-toothed, Hubb's, and Stejneger's beaked whales) in the California/Oregon/Washington stock is 575-1,000 animals. No current population estimates are available for this species of beaked whale and the status of the stocks is unknown. Scientists suggest that resident populations of this species may inhabit the southern Okhotsk Sea and the Sea of Japan. There are insufficient data to determine population trends for this species.

Diagnostic features of the skull and mandible On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal bones. Separates from Berardius and Ziphius. A sulcus (groove) running along the middle of the combined surfaces of the nasal bones so depresses their combined middle that it is the lateral portion of each nasal bone that reaches farthest forward on the vertex. Separates from Tasmacetus and Indopacetus. When the skull is upright and the long axis of the anterior half of the beak is horizontal, a horizontal plane transecting the summit of either maxillary prominence transects the mesethmoid bone. Separates from Hyperoodon. Tooth alveoli of mandible are posterior to the mandibular symphysis. Separates from Berardius, Ziphius, Tasmacetus, Indopacetus, Hyperoodon, M. bowdoini, M. bidens, M. carlhubbsi, M. grayi, M. europaeus, M. hectori, M. layardii, M. mirus, M. perrini, and M. traversii. Right premaxilla extends posteriorly beyond the right nasal a distance exceeding 70% of dorsal length of right nasal. Separates from M. ginkgodens. Antorbital notches form obtuse angles. Separates from M. peruvianus. A transverse plane perpendicular to the long axis of the rostrum and transecting the apex of the left antorbital notch, very nearly also transects the anterior most point reached by the pterygoid sinus. Separates from M. densirostris.

Stejneger's beaked whales, sometimes known as the "Bering Sea beaked whale" or the "Saber-toothed whale," are little known members of the beaked whale family (Ziphiidae). As adults, Stejneger's beaked whales can reach lengths of about 18.5 ft (5.7 m) and weigh up to 3,520 lbs (1,600 kg). Females may be slightly larger than males. Males can be easily distinguished from females and juveniles by a pair of large, visible, forward-pointing tusk-like teeth that erupt from the arched lower jaw. Females and juveniles have teeth as well, but they remain hidden beneath the gum tissue of the mouth, and their jawline is generally less-curved. This species of beaked whale is difficult to observe and identify at sea due to a low profile at the surface and a small inconspicuous blow. Stejneger's beaked whales have a relatively medium-sized, round body with a small wide-based, slightly "falcate" dorsal fin located far down (about two-thirds) the animal's back. The whale's head has a low sloping forehead and indistinct melon. Their coloration varies from dark gray to brownish and black. There is a dark cap that extends across the top of the head from eye to eye and the lower jaw is usually white or pale gray. The skin may be covered with linear and oval-shaped scars and other markings. Individuals, especially mature males, accumulate more scars and scratches with age. Mature males often will battle one another for access to females. Stejneger's beaked whales are usually found singly or in small, tight social groups averaging between 3-15 individuals. These groups may contain animals of mixed sexes, ages and life stages, or can be segregated. Like most beaked whales, this species is difficult to approach and generally avoids vessels. Stejneger's beaked whales usually make 5-6 shallow dives followed by a longer dive that lasts 10-15 minutes and may reach depths of 4,920 ft (1,500 m) (Shirihai and Jarrett 2006). While diving, they use suction to feed on small deep-water fish, tunicates, and cephalopods (e.g., squid) of the families Gonatidae and Cranchiidae in deep "mesopelagic" and "bathypelagic" waters. Stejneger's beaked whales may become sexual mature when they reach about 14.8 ft (4.5 m) in length. A sexually mature female will give birth to a single calf that is about 7.5-8 ft (2.3-2.5 m) long and weighs about 175 lbs (80 kg). The calving season is generally between spring and autumn. The estimated lifespan of this species is at least 36 years. Many species of beaked whales (especially those in the genus Mesoplodon) are very difficult to distinguish from one another (even when dead). At sea, they are challenging to observe and identify to the species level due to their cryptic, skittish behavior, a low profile, and a small, inconspicuous blow at the waters surface; therefore, much of the available characterization for beaked whales is to genus level only. Uncertainty regarding species identification of beaked whales often exists because of a lack of easily discernable or distinct physical characteristics.

Distributed throughout the cold temperate and subarctic waters of the North Pacific. On the eastern side of the North Pacific its distribution ranges from Saint Paul Island to southern California, with a majority of stranding records reported from the Alaskan coastlines. In the west it ranges from the Commander Islands to Japan. The center of its distribution seems to be the Aleutian Islands, where it has been known to strand in small groups. It is more likely that that this species frequents the Aleutian Basin and the Aleutian Trench rather than the shallow waters of the northern or eastern Bering Sea. Presence of Isistius scars suggests its movements are not restricted to cold temperate waters, but include temperate waters of North Pacific latitudes 38oN and lower where the Isistius populations are at greatest abundance.

Incidental take/ bycatch in the driftnet and gillnet fisheries in the Sea of Japan and off the west coast of North America Hunted in a Japanese fishery targeting beaked whales Marine debris, they are known to have ingested dangerous items such as plastic bags and string (Jefferson et al. 2008) Underwater sounds and anthropogenic noise may be harmful

Tooth position A single pair of teeth is positioned immediately ahead of the apex of the arch on the mouthline and are inclined anteriorly. Tooth exposure In adult males, nearly all the tooth that erupts from the lower jaw is exposed above the gumline. Teeth do not erupt above the gumline in females or juveniles. Tooth shape The anterior edge of the tooth is longer than the posterior.