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.
Description
The body of Blainville's beaked whale is robust, but also somewhat compressed laterally compared with other mesoplodonts. The males have a highly distinctive appearance, the jaws overarch the rostrum, like a handful of other species, but does it towards the beginning of the mandible and then sloped down into a moderately long beak. In adult males the crown of a tooth erupts from each side of the lower jaw as they reach maturity. Barnacles are often attached to the exposed tooth. One of the more remarkable features of the whale is the extremely dense bones in the rostrum, which have a higher density and mechanical stiffness than any other bone yet measured. At present, the function of these bones is unknown, as the surrounding fat and the brittleness of the bone make it unlikely to be used for fighting. It has been suggested that it may play a role in echolocation or as ballast, but without sufficient behavioral observation, this cannot be confirmed. 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. Skin discoloration might be caused by diatoms. 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.
Geographic range and distribution
This species of beaked whale is found in tropical and warm waters in all oceans, and is considered to be the most extensively distributed member of Mesoplodon genus. Sightings occur in higher latitudes probably in relation to warm water currents such as Gulf Stream and the Agulhas Current. Groups are regularly seen in at least three locations: Waianae coast, Hawaii; Society Islands of the South Pacific; northeastern Bahamas.
The mean group size is 4.1 individuals. There is no evidence of seasonal migration. It inhabits deep, offshore water (656 to 3281 feet deep) and is associated with steep underwater geological structures. Sub-adult males are found further offshore and in deeper water than adult males due to dominance hierarchy. Blainville’s beaked whales have a long-term site fidelity meaning they return to the same area repeatedly or stay in the area for extended periods of time. Resight rate is higher for females than males as they are more likely to base their distribution based on prey abundance when males follow females to increase mating opportunity
Behavior
Foraging
This species feeds primarily on squid and small fish and cephalopods.
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
Blainville's beaked whales can live in small cohesive groups of 3 to 7 individuals. Groups consist of both sexes and combination of ages or might be segregated. Harems of several females and a single mature male have been observed in productive continental shelf areas (eg. Bahamas). Males compete for females which probably causes scarring on individuals. The function of the group formation is protection (for females with small calves) and mating opportunity (for adult males).