Blainville's Beaked Whale (Mesoplodon densirostris)

Blainville's Beaked Whale, photographed during BRS-07

Blainville's Beaked Whale
(Mesoplodon densirostris)
Photo: Ari Friedlaender,
Duke University

Did You Know?

· The scientific name Mesoplodon densirostris is derived from the Latin words densus for "thick" or "dense" and rostrum for "beak."

· The erupted tusk-like teeth of adult males are sometimes covered with barnacles.

Status
MMPA - Blainville'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: densirostris

Species Description
Blainville's beaked whales, sometimes known as the "dense-beaked whale," are little known members of the beaked whale family (Ziphiidae). As adults, Blainville's beaked whales can reach estimated lengths of approximately 15-20 ft (4.5-6 m) and weigh 1,800-2,300 lbs (820-1,030 kg). Males can be easily distinguished from females and juveniles by a pair of large visible tusk-like teeth that erupt and point forward from the heavily 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 less-curved.

Blainville'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 bluish. The face and underside of the animal is pale gray or white, giving it a counter-shading appearance. The skin may appear wrinkled on the dorsal area and is covered with linear and oval-shaped scars and other markings. Individuals, especially mature males, accumulate scars and scratches with age. Also, "diatom" infestation may discolor areas of the skin.

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.

Blainville's beaked whales are usually found individually or in small social groups averaging between 3-7 individuals, but have been occasionally seen in larger groups of up to 12 animals. Groups may consist of various combinations and/or be segregated depending on age or sex. Adult populations in productive waters over the continental shelf (like the Bahamas) may be grouped in harems and consist of several adult females with a single adult mature male (Jefferson et al. 2008). Males commonly battle over access to females, which is probably the cause of the long linear scars seen on individuals.

Like other beaked whales, these whales are deep divers. Regular dives range from 20-45 minutes, and commonly reach depths of at least 1,600-3,300 ft (500-1000 m), but dives of over 54 minutes and up to 4,600 ft (1,400 m) have been recorded (Jefferson et. al., 2008). While diving, they use suction to feed on small fish and cephalopods (e.g., squid) in deep water.

Blainville's beaked whales may reach sexual maturity at about 9 years of age. A sexually mature female will give birth to a single newborn calf that is about 6-8.5 ft (1.9-2.6 m) long and weighs about 130 lbs (60 kg). The estimated lifespan of this species is unknown.

Habitat
Blainville's beaked whales occur in tropical to temperate waters worldwide. They are generally found in deep, offshore waters of the continental shelf. This species is often associated with steep underwater geologic structures such as banks, submarine canyons, seamounts, and continental slopes.

Distribution
Blainville's beaked whales' distribution is considered the most extensive of the Mesoplodon genus. They have a cosmopolitan distribution throughout the world's oceans and range from the Mediterranean, England, Iceland, Nova Scotia (Canada), Brazil and South Africa in the Atlantic; to California, Chile, Japan, New Zealand and Australia in the Pacific. This species is commonly sighted in the northeastern Bahamas, Caribbean Sea, Gulf of Mexico, Hawaiian Islands, Sea of Japan, and the Society Islands of the South Pacific. During studies, individuals have been identified and resighted in certain geographic areas that may have resident populations. In productive waters, adult animals are more commonly found in waters over the continental shelf and submarine canyons, and sub-adult animals are found both inshore and offshore. Their distribution may vary depending on the movements of warm-water currents; however, there are no known seasonal movements or migrations.

Population Trends
For management purposes, Blainville's beaked whales inhabiting U.S. waters have been divided into three stocks: the Hawaiian stock, the Northern Gulf of Mexico stock, and Western North Atlantic stock. The estimated number of animals in the Hawaiian Stock is 1,200-2,200, the Northern Gulf of Mexico is about 100 animals (for Mesoplodon spp.), and there is no current estimate for the Western North Atlantic Stock (350-600 total unidentified beaked whales). The Northern Gulf of Mexico and Western North Atlantic stocks are considered "strategic" because of uncertainty regarding stock size and evidence of fishery-related mortality and serious injury. There are insufficient data to determine the population trends for this species, but they are probably not rare because estimates do not include a correction factor for submerged animals (with long dive times) which may be substantial and underestimate actual abundance.

Threats
Unidentified beaked whales (which may include Blainville's beaked whales) have been incidentally taken in the pelagic drift gillnet fishery off the U.S. Atlantic coast. Beaked whales are often undifferentiated in the field and at sea due to a lack of distinct characteristics and the difficulty of positively identifying animals to the species level. In the Indian Ocean (off of the Seychelles and western Australia), Blainville's beaked whales have been incidentally taken by Japanese fishing boats (Jefferson et al. 2008). This species has been occasionally taken in hunts targeting small cetaceans. Blainville's beaked whales may be sensitive to underwater sounds and anthropogenic noise. Recently, strandings of this species in the Bahamas due to acoustic trauma, have been associated with active sonar during naval military activities and exercises. Anthropogenic noise levels in the world's oceans are an increasing habitat concern, particularly for deep-diving cetaceans like Blainville'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.

In 1997, NMFS implemented the Pacific Offshore Cetacean Take Reduction Plan, which requires the use of pingers and 6-fathom net extenders in the CA/OR drift gillnet fishery to reduce bycatch of cetaceans, including Mesoplodont beaked whales. The Pacific Offshore Cetacean Take Team continues to meet and recommend measures to further reduce bycatch and achieve MMPA goals.

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
Pacific Offshore Cetacean Take Reduction Plan (POCTRP) Interim Final Rule to Amend Pinger Specifications	64 FR 3431	01/22/1999
POCTRP Final Rule to Require New Training, Equipment, and Gear Modifications for CA/OR Drift Gillnet Fishery	62 FR 51805	10/03/1997
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. 294-295.
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. 112-115.