Sowerby's Beaked Whale

About the Species

Sowerby's beaked whales, sometimes known as the "North Atlantic beaked whale," are little known members of the beaked whale family, Ziphiidae. The first beaked whale to be discovered, this species prefers the deep, cold, temperate and subarctic waters throughout the North Atlantic Ocean, but has also been reported near the ice pack. Their scientific name, bidens, is derived from the Latin words bi for "two" and dens for "teeth" and refers to the pair of visible teeth that erupt from the lower jaw of mature males.  

The beaked whale family is cryptic and skittish. Due to the rarity of sightings at sea, there is little information on the abundance of Sowerby’s beaked whales worldwide. 

Like all marine mammals, Sowerby’s beaked whales are protected under the Marine Mammal Protection Act. They face threats from entanglement in fishing gear and human-caused noise. Sowerby’s beaked whales are considered “data deficient” by the IUCN list of threatened species, meaning that there is not enough information to assess their population status. 

Status

NOAA Fisheries estimates population size for Sowerby’s beaked whales in its stock assessment reports. A stock is a group of animals that occupy the same area and interbreed. There is little information on the abundance of this species worldwide. Thus, data are insufficient to estimate population trends. 

Protected Status

Appearance

As adults, Sowerby's beaked whales can reach estimated lengths of 14.5 to 21 feet and weigh 2,200 to 2,900 pounds. Males, which are generally larger, can be distinguished from females and juveniles by a pair of visible teeth that erupt from their slightly arched lower jaw. Females and juveniles also have teeth, but they remain hidden beneath the gum tissue, and their jawline is straight. 

Sowerby's beaked whales have a small- to medium-sized body with a very long, slender beak relative to other beaked whales, 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 hooked dorsal fin located about two-thirds down their back. Most of their body is charcoal gray with a pale underside, and calves are generally darker than adults. The lower jaw is usually light gray or white. This species has less visible scarring than most other beaked whale species. 

Behavior and Diet

Sowerby's beaked whales are usually found individually or in small, closely associated groups averaging between three and 10 individuals. Regular dives range from 10 to 15 minutes, but dives of at least 28 minutes and reaching depths up to 4,920 feet have been recorded. While diving, they use suction to feed on small, deep-sea fish and cephalopods (e.g., squid) in deep waters. When surfacing, this species often lifts its head up out of the water at a 45-degree angle.

Many species of beaked whales (especially those in the genus Mesoplodon) are very difficult to distinguish from one another (even when dead) because they lack easily discernible or apparent physical characteristics. At sea, they are challenging to observe and identify to the species level because of their cryptic, skittish behavior; low profile; and a small, inconspicuous blow at the water’s surface. Therefore, much of the available characterization for beaked whales is to the genus level only, and there is relatively little information about most individual species. 

Where They Live

Sowerby's beaked whales prefer the deep, cold temperate and subarctic waters off the continental shelf edge of the North Atlantic Ocean but have also been reported near the ice pack. They are distributed throughout the North Atlantic Ocean (30° to 71° North), ranging from the Norwegian Sea, Labrador Sea, Iceland, and Baltic Sea to the north, and waters off the northeast United States, Madeira, and the Canaries to the south.  

Sowerby’s beaked whales may be  more common in the eastern than the western North Atlantic Ocean. However, they rarely occur in the Mediterranean Sea. Strandings have occurred in Florida and Italy, but these areas are considered outside their normal range. Their distribution may vary depending on the movements of oceanographic currents. It is unknown whether they undertake seasonal movements or migrations. 

Lifespan & Reproduction

Sowerby's beaked whales may reach sexual maturity at about age 7, and 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 to 9 feet long and weighs about 375 pounds. The estimated lifespan of this species is unknown. 

Threats

Entanglement in Fishing Gear 

Sowerby’s beaked whales have become entangled or captured in commercial fishing gear, such as driftnets and gillnets, off the U.S. Atlantic and Canadian coasts.

Ocean Noise  

Deep-diving cetaceans like Sowerby's beaked whales rely on sound to feed, communicate, and navigate in the ocean. Sound pollution threatens them by interrupting their normal behavior and driving them away from areas important to their survival.

Scientific Classification

Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Cetacea
Family	Ziphiidae
Genus	Mesoplodon
Species	bidens