Blainville's beaked whale (Mesoplodon densirostris), or the dense-beaked whale, is believed to be the widest ranging mesoplodont whale. The French zoologist Henri de Blainville first described the species in 1817 from a small piece of jaw—the heaviest bone he had ever come across—which resulted in the name densirostris (Latin for "dense beak"). Off the northeastern Bahamas, the animals are particularly well documented, and a photo identification project started sometime after 2002.
Taxonomy
thumb|left|Skull of Blainville's beaked whale
In 1817, Blainville named the species Delphinus densirostris, based on the description of a nine-inch piece of rostrum of unknown origin housed in the Paris Museum. It became one of the first beaked whales to be identified. Sometimes called dense-beaked whale as the current Latin name (Mesoplodon densirostris) derives from densus for 'dense' and rostrum for 'beak' . The melon of the whale is flat and comparatively small. Coloration is dark bluish grey on top and lighter gray on the bottom, and the head can be brownish shading to light grey around the lip and the jaw. They might have white oval scars possibly caused by cookie-cutter sharks. Adult males can also have long white 'scratch' scars. Males reach at least 4.4 m (14 ft 5 in) and 800 kg (1,800 lb), whereas females reach at least 4.6 m (15') and 1 tonne (2200 pounds). Juveniles are 1.9 m (6 ft 3 in) long when born and weigh 60 kg (130 lb). No data on lifespan is available. There is no evidence of seasonal migration.
Behavior
Foraging
This species feeds primarily on squid and small fish Recorded prey taxa include silver scabbardfish, hake, mantis shrimp, Octopoteuthis sicula, Histioteuthis meleagroteuthis and H. reversa, Taonius pavo, cod, lanternfish (Lampanyctus sp.), Cepola sp. and Scopelogadus sp.
Blainville's beaked whales do not capture prey by biting. They use suction feeding to capture prey. They create low pressure in the mouth by retracting tongue, and using throat grooves to expand throat volume. This creates a lower pressure in the mouth than the surrounding waters, allowing the whale to suck in water and whole prey.
Blainville's beaked whale shows similar foraging behaviour during the day and night; however, the time spent on surface is greater during the night.
Social behaviour
thumb|left|A cow–calf pair surfacing
Blainville's beaked whales can live in small cohesive groups of 3 to 7 individuals.
Two signals were identified with possible communicative function: fast series of ultrasonic frequencies modulated by clicks and harmonical rich short whistles with mean fundamental frequency of 12 kHz. Because Blainville's beaked whales almost exclusively vocalize while on their dives, most believe that they are using sound to help their foraging. However, while on their dives they will produce whistles which are most commonly known for communication among odontocetes rather than echolocation for foraging.
Blainville's beaked whales remain silent for up to 80% of the time, especially in depth shallower than 170m and during silent ascent from vocal dives. This behaviour might be a protection mechanism against shallow-diving predators such as killer whales.
In a study published in 2008, diving statistics of beaked whales were analyzed and no significant difference was found in diving behavior between day and night. For example, mean and max duration, number of deep dives, max depth, and ascent and descent rates were all calculated as equal during the day and night. However, the number of mid-depth dives was recorded to be six times higher during the day than at night. These results suggest that Blainville's beaked whales forage the same amount during the day and night, but switch to deeper-water prey at night.
Reproduction
Lifespan estimate is unknown.
Population status
NOAA Fisheries presents estimates of population size of U.S. stocks (Hawaiian, northern Gulf of Mexico, western North Atlantic) in stock assessment reports .
Threats
Protection status
thumb|200px|right|A male with an attached D-TAG for studying behavior swims in the U.S. Navy Atlantic Undersea Test and Evaluation Center testing range near [[Andros Island.]]
Blainville's Beaked Whale is protected throughout its range by CITES Appendix II and MMPA Protected. and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).
Whaling
The beaked whale has occasionally been hunted, but has never been a specific target.
Noise pollution
Beaked whales are susceptible to detrimental effects of anthropogenic noise pollution because they use sound for hunting, communication and navigation. The broadband ship noise can cause a change in beaked whale behaviour up to 5.2 km from the boat. Whales have been reported to move away from the noise source and decrease their activity level.
Entanglement
Blainville's beaked whales are occasionally reported as a bycatch throughout its range.
Marine debris
Marine debris has been identified in the stomach of stranded Blainville's Beaked Whale. Marine debris ingestion was reported as a cause of death of beaked whales.