DENSE BEAKED WHALE Mesoplodon densirostris

Description Medium; length averages 4.5--4.8 m (15-16 ft). Weight averages about 1,000 kg (about 1 ton).
The general body form and shape are similar to those of other beaked whales, but the head is strikingly different. The entire middle third of the mandible is dominated by a huge tooth that rises up above the top of the beak and is enveloped and supported by a massive bony protruberance. This alters the whole shape of the jaw, giving the mouth a high arching contour which sweeps up over the rostrum and only dips down again in front of the eye, making it virtually impossible for the whale to see forwards at all.
The flippers are short and the throat grooves inconspicuous. The dorsal fin is relatively large and noticeably curved backwards to a point. There is no notch in the tail flukes, which sometimes even bulge outwards and backwards in the centre.
The colour is a bluish dark grey, with a slightly lighter grey throat and chest. The anal area is often splashed almost white. All Dense Beaked Whales seem to be marked with paler blotches, most of which are the result of parasites. There is some evidence also of scarring produced by the teeth of rival males.

Field Identification If any adult males are present, there should be no difficulty in identifying a group of Dense Beaked Whales moving along together at the surface. They invariably seem to lift the beaks up until the rostrum is clear of the water before blowing. In this position, the high contour of the lower jaw is distinctly visible in the single large male in each group, rising vertically like leather blinder flaps on a horse's bridle. Even the smaller animals, presumably females and young, show a curve at the back of the mouth.

The blow is indistinct, but on a calm day can be seen to shoot forwards at a sharp angle. The whales spend several minutes at or near the surface, breathing at 15- or 20-second intervals, before diving together for longer periods which may end in their disappearance. The fin is prominent and clearly shown at the end of a long curve of back with every breath.
The tail flukes seldom raise above the surface.
The chances are that any beaked whale seen in warm tropical waters will be M. densirostris, so it is worth looking specifically for the distinctive bulging jaw line.
length of the jawbone and, in a live animal, more than two¬thirds of the length of the gape. Each tooth is almost 20 cm (8 inches) high, but all the root and most of the body are enclosed in a heavy bulge of bone that rises from the jaw and usually only a small part of the tooth tip protrudes, facing slightly forwards. The teeth of female whales are small and totally buried in the gum, but the lower jaw still has a marked bulge. There are 47 vertebrae. The first 7 of 11 pairs of ribs are double headed and, in addition to the normal chest ribs, there is often an extra pair of slimmer ribs attached to the last neck vertebra.
Analysis of the stomach contents of one stranded animal show that, at the time, it was feeding entirely on squid. Our sightings, and others by Captain Morzer Bruyns, suggest that the Dense Beaked Whale is normally social, living in small family units of 3-6 animals.
Nothing is known of its reproductive behaviour.