The elusive nature of Gray's beaked whale, together with its far offshore habitat and apparent rarity, mean that little is known about the biology and behaviour of this marine species (5) (6). Like other member of the genus, it is likely to feed mainly on cephalopods such as squid (1) (5) (10), with most prey being caught in deep water, below depths of 200 metres, and believed to be swallowed whole (3) (5). Some fish may also be taken (5) (10), and prey is thought to be sucked into the mouth with the aid of a muscular tongue and throat pleats, which allow the mouth floor to be distended (5). The teeth of Gray's beaked whale are no longer needed for feeding, and in the adult male these have evolved into fighting weapons, with males often bearing long, white tooth scars, which are thought to be evidence of dominance battles (3) (5) (10). Most Gray's beaked whales are seen alone or in pairs or small groups, though a mass stranding of 28 animals has suggested that this species may be more social than other beaked whales (3) (6) (9). Very little information is available on the breeding behaviour of Gray's beaked whale (10), but, as in all cetaceans, females give birth to a single calf (5).
One of the more easily distinguished members of its genus, Gray's beaked whale has a particularly long, slender snout, or 'beak', which is white in adults, with a straight mouthline, and which is often raised up out of the water when the whale surfaces (3) (5) (6). The spindle-shaped body is dark bluish-grey to black on the upper surface, with a paler underside, white patches in the genital region and sometimes on the forehead, and often bears white oval scars from the bites of cookie-cutter sharks (2) (3) (6). The dorsal fin is small and set quite far back on the body, the tail is unnotched, and the small flippers fit into depressions in the body, reducing water resistance when the whale is swimming (3) (5) (7). Juveniles have dark patches around the eyes and on top of the head, lighter bellies, and a shorter and darker beak than the adult (3) (8). Mature male Gray's beaked whales possess a single pair of functional teeth, which are triangular in shape and located midway along the lower jaw (2) (3) (9). These teeth project up, outside of the mouth, and can be seen when the mouth is closed (5) (10). In the female, these teeth are much smaller and do not usually erupt above the gums (3) (6) (10). Both sexes also have a row of small, non-functional teeth in the upper jaw (3) (9).
Gray's beaked whale is found throughout cool, temperate waters of the Southern Hemisphere, with records from Antarctic and sub-Antarctic waters, as well as around New Zealand, southern Australia, South Africa, Argentina, Chile and Peru (1) (3) (11). However, as with all members of this group, Gray's beaked whale is rarely sighted and often difficult to identify out at sea, and information on its distribution is largely based on strandings (5) (7). There is a single record of a stranding in the Netherlands, but it is thought that this was an unusual occurrence, outside of the species' normal range (1) (3) (7). Many sightings occur around New Zealand and the Chatham Islands (1) (3), though this may merely be due to more intensive recording efforts here (9).