True's Beaked Whale (Mesoplodon mirus)

Did You Know?

· True's beaked whales receive their common name from Frederick W. True, who was a curator at the Smithsonian Institution, and described the species from an animal that stranded on a beach in North Carolina (Reeves et al. 2002).

· Animals living in the northern hemisphere have different coloration from those living in the southern hemisphere.

Status
MMPA - True'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: mirus

Species Description
True's beaked whales are little known members of the beaked whale family (Ziphiidae). As adults, True's beaked whales can reach lengths of 15.5-17.5 ft (4.8-5.4 m) and weigh at least 2,200-3,000 lbs (1,020-1,400 kg). Females may be slightly larger than males. Adult males can be distinguished from females and juveniles by a pair of teeth visible on the tip of the lower jaw. The mouthline is typically straight or slightly curved.

True's beaked whales have a relatively small to medium-sized body with a moderately short beak, as well as a rounded sloping melon. They have a small, wide-based, slightly "falcate" "dorsal" fin located far down (about two-thirds) the animal's back. Their coloration varies from gray to brown on the dorsal side with a paler ventral side. The coloration in the southern hemisphere is different from animals in the northern hemisphere. Individuals in the southern hemisphere have more white coloration on their back, tailstock and underside. Mature males may have more linear scarring covering the body than other animals. The linear scars are probably the result of males battling for access to females during mating. 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. Few have been seen alive at sea.

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.

When observed, True's beaked whales are usually alone or in small, closely associated groups averaging 2-6 animals. While diving, they use suction to feed on small fish and cephalopods (e.g., squid) in deep waters. This species has been known to breach and occasionally display surface active behaviors.

Very little is known about reproduction in True's beaked whales. Females generally give birth to a single newborn calf that is about 6.5-8 ft (2.0-2.5 m) long and weighs about 300 lbs (136 kg). The estimated lifespan of this species is unknown.

Habitat
True's beaked whales prefer deep warm temperate waters of the North Atlantic Ocean as well as at least two other areas in the Southern Hemisphere (e.g., Indian Ocean).

Distribution
True's beaked whales occur throughout the northern and southern hemispheres. Their range includes areas off of Nova Scotia (Canada), Ireland, Europe, the Canary Islands, Bermuda, Florida, and the Bahamas in the Atlantic, as well as off the coasts of Brazil, Madagascar, South Africa, and southern Australia. There are no known seasonal movements or migrations for this species.

Population Trends
For management purposes, True'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. There are insufficient data to determine the population trends for this species. The status of this stock is unknown, but is considered "strategic."

Threats
True's beaked whales may have been previously taken as incidental bycatch in fisheries using driftnets and gillnets off the U.S. Atlantic coast, but no recent reports exist. This species is not known to have been directly targeted by whalers. This species of beaked whales 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 True'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.276-277.