Sowerby's Beaked Whale (Mesoplodon bidens)

Did You Know?

· Sowerby's beaked whale was the first living species of beaked whale to be discovered.

· Sowerby's beaked whale's scientific species name (bidens) is derived from the Latin word bi for "two" and dens for "teeth."

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

Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ziphiidae
Genus: Mesoplodon
Species: bidens

Species Description
Sowerby's beaked whales, sometimes known as the "North Atlantic beaked whale," are little known members of the beaked whale family (Ziphiidae). As adults, Sowerby's beaked whales can reach estimated lengths of 14.5-21 ft (4.4-5.5 m) and weigh 2,200-2,900 lbs (1,000-1,318 kg). Males, which are generally larger, can be distinguished from females and juveniles by a pair of visible teeth that erupt from the slightly arched lower jaw. Females and juveniles have teeth as well, but the teeth remain hidden beneath the gum tissue of the mouth, and their jawline is straight. 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.

Sowerby's beaked whales have a small to medium-sized body with a very long, slender beak relative to other mesoplodonts, as well as a bulge on the forehead area. The beak often emerges at a steep angle when surfacing. They have a small, wide-based, slightly "falcate" "dorsal" fin located far down (about two-thirds) the animal's back. Most of the body has a charcoal gray coloration with a pale underside. The lower jaw is usually light gray or white. Calves are generally darker than adults. This species has less visible scarring than most other beaked whale species.

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.

Sowerby's whales are usually found individually or in small, closely associated groups averaging between 3-10 individuals. Regular dives range from 10-15 minutes, but dives of at least 28 minutes reaching depths up to 4,920 ft (1,500 m) have been recorded. While diving, they use suction to feed on small fish (e.g., Atlantic cod) and cephalopods (e.g., squid) in deep waters.

Sowerby's beaked whales may reach sexual maturity at about 7 years of age. Their breeding season may be from late winter to spring. A sexually mature female will give birth to a single newborn calf that is about 8-9 ft (2.4-2.7 m) long and weighs about 375 lbs (170 kg). The estimated lifespan of this species is unknown.

Habitat
Sowerby's beaked whales prefer the deep, cold temperate and subarctic waters of the North Atlantic Ocean, but have been reported near the ice pack as well.

Distribution
Sowerby's beaked whales are distributed throughout the North Atlantic Ocean (30-71° North), which includes the Norwegian Sea, Labrador Sea, Iceland, Baltic Sea, and south to Massachusetts, Madeira, and the Canaries. Reports of this species in Canadian waters are considered rare. They are not known to occur in the Mediterranean Sea. Strandings have occurred in Florida and Italy, but these are considered outside their normal range. Their distribution may vary depending on the movements of oceanographic currents. There are no known seasonal movements or migrations for this species.

Population Trends
For management purposes, Sowerby's beaked whales inhabiting U.S. waters have been placed in the Western North Atlantic stock. No current population estimates are available for this species of beaked whale. The status of the stock is unknown, but is classified as "strategic." This species may be relatively abundant in the North Sea. There are insufficient data to determine the population trends for this species, but they are probably not rare.

Threats
Sowerby's beaked whales have been incidentally taken as bycatch in fishing gear, such as driftnets and gillnets off the U.S. Atlantic coast. This species has been occasionally taken in hunts targeting cetaceans in Newfoundland and by Norwegian whalers off of Iceland and in the Barents Sea. This species of beaked whale may be sensitive to underwater sounds and anthropogenic noise. Anthropogenic noise levels in the world's oceans are an increasing habitat concern, particularly for deep-diving cetaceans like Sowerby's beaked whales that use sound to feed, communicate, and navigate in the ocean.

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. 280-281.