Arch Beaked Whale

Head Shape Melon is moderately bulbous and merges smoothly with rostrum, such that there is little demarcation between the forehead and long, narrow beak. The posterior half of the jaw is prominently arched in males; in females this arch is less pronounced, but still has a noticeable sinusoidal curve. Coloration In adult males, the rostrum and anterior portion of the mandible back to the posterior edge of the tooth are white. There is also a distinctive white patch of variable extent centered on the dorsal prominence of the melon. The rest of the body is relatively uniform dark grey to black, with no discernable differentiation between dorsal and ventral surfaces. Males often have extensive linear and ovate scars, especially on the flanks. The ventral surface of the body is lighter in females and juveniles, grading from medium gray dorsally to white on the midventral portions. The flipper pocket in females is darker than adjacent areas of thorax. Females and juveniles also have less contrast in the head coloration, but the rostrum and mandible are lighter than the rest of the head. Females appear to show greater variation in the pigmentation patterns around the rostrum. Both sexes exhibit fluke coloration that is lighter on the ventral surface than the dorsal surface. Flukes are also marked on ventral surface with concentric striations radiating anteriorly from the position of the caudal vertebra. Size Adult body length ranges between 4.8 to 5.3 m. Recorded maximum body length for both adult males and females is 5.3 m. Body length at birth is 2.5 m. Most Likely Confused With: Mesoplodon densirostris Mesoplodon ginkgodens Mesoplodon stejnegeri

Diagnostic features of the skull and mandible On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal. Separates from Berardius and Ziphius. A sulcus (groove) running along the middle of the combined surfaces of the nasal bones so depresses their middle that it is the lateral portion of each nasal bone that reaches farthest forward on the vertex. Separates from Tasmacetus and Indopacetus. When the skull is upright and the long axis of the anterior half of the beak is horizontal, a horizontal plane transecting the summit of either maxillary prominence transects the mesethmoid bone. Separates from Hyperoodon. Tooth alveoli of mandible overlap the mandibular symphysis. Separates from Berardius, Ziphius, Tasmacetus, Indopacetus, Hyperoodon, M. grayi, M. europaeus, M. hectori, M. mirus, M. perrini, M. densirostris, M. ginkgodens, M. peruvianus, and M. stejnegeri. Basirostral groove absent or present as a shallow groove that does not extend past the prominental notch. Separates from M. layardii. The maxillary prominences rise 15 mm higher than the height of the premaxillaries where the latter passes between the former. Separates from M. bidens. In dorsal view, the right premaxilla extends slightly posterior beyond the right nasal. Separates from M. traversii. Antorbital tubercle formed by the maxilla and is underlain by the jugal bone. Separates from M. bowdoini.

Stranding Distribution M. carlhubbsi occurs in the temperate waters of the North Pacific, with a majority of stranding records occurring along the Pacific coast of North America. The northernmost record in eastern North Pacific occurs at Prince Rupert, British Colombia ~ 54o N; southernmost record is in San Diego, California, although the southern limit of the species may not be adequately known as there are limited records along the Pacific coast of Central America. In the western North Pacific the northernmost stranding record occurs at 38o N off the eastern coast of Japan near the confluence of the cold southerly flowing Oyashio current and the warm northerly flowing Kuroshio current.

Tooth position A single pair of teeth is positioned midway along the mouthline at the top of the jaw arch. Teeth are square at the root base and the teeth sit relatively upright in the jaw. Tooth exposure Erupted teeth in adult males are covered by gum tissue, with only the tip of tooth exposed. Teeth do not erupt in females or juveniles. Tooth shape The denticle is situated posterior to the anterior edge of the tooth forming a “shoulder” in the lateral profile of the tooth.