Stejneger's Beaked Whale (Mesoplodon stejnegeri)

Did You Know?

· 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.

Status
MMPA - Stejneger's beaked whales, like all marine mammals, are protected under the MMPA.

Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Ziphiidae
Genus: Mesoplodon
Species: stejnegeri

Species Description
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.

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).

Stejneger's Beaked Whale Range Map
(click for larger view PDF)

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.

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.

Threats
Stejneger's beaked whales have been incidentally taken as bycatch in the driftnet and gillnet fisheries in the Sea of Japan and off the west coast of North America. They have also been hunted in a Japanese fishery targeting beaked whales. Marine debris is another threat to this species, which has been known to ingest dangerous items such as plastic bags and string (Jefferson et al. 2008). They are not considered threatened or endangered. Underwater sounds and anthropogenic noise may be harmful to this species of beaked whales.

Conservation Efforts
The International Union for Conservation of Nature and Natural Resources (IUCN's) Red List of Threatened Species considers this species "Data Deficient" due to insufficient information on population status and trends.

Regulatory Overview
This species is protected under the Marine Mammal Protection Act of 1972 as amended.

Key Documents
(All documents are in PDF format.)

Title	Federal Register	Date
Stock Assessment Reports	n/a	various

More Information

References:

Reeves, R. R., P. A. Folkens, et al. (2002). Guide to Marine Mammals of the World. New York, Alfred A. Knopf. p. 296-298.
Jefferson, T. A, M. A. Webber, and R. L. Pitman. (2008). Marine Mammals of the World, A Comprehensive Guide to their Identification. Amsterdam, Elsevier. p. 144-147.
Shirihai, H. and B. Jarrett (2006). Whales, Dolphins and Other Marine Mammals of the World. Princeton, Princeton University Press. p.171-174.

Updated: August 9, 2012