Stejneger's beaked whale
As with other species of beaked whale, the majority of information that is known about the species biology and life history is a result of strandings, primarily off the west coast of Japan and the Aleutian Islands. Strandings appear to peak in both the winter and spring months and this is thought to be indicative of a north-south migration of the species, although there is also evidence of a resident population in both the Sea of Japan and the Okhotsk Sea. It is thought to be the only species of Mesoplodon common in Alaskan waters.
This is a small, spindle shaped whale with a relatively small head. It has a sloping forehead and an arched mouthline, with two large spatulate teeth erupting from the middle of the lower jaw of males. In some individuals, these teeth grow extremely large and begin to converge, cutting into the upper jaw restricting the opening of the mouth. The females lack these teeth and their mouths are less strongly arched. The Stejneger's beaked whale has a small, triangular dorsal fin which is set far back on the body. Colouration is mostly black, dark grey, or brown dorsally, fading to the paler sides and belly. It is covered in white linear scars and blotches, and some individuals have a whitish starburst pattern on the underside of the triangular flukes. The neck is pale, but this characteristic varies between individuals. The Stejneger's beaked whale may be confused with the Blainville's, ginkgo-toothed, and Hubb's beaked whales however they all have different colouration and close observation is needed for proper identification.
Stejneger's beaked whales are found in small groups of between 3 and 4 individuals, but may be seen in groups of as many as 15 animals. They are known to swim in unison in tight groups, and are shy and difficult to approach. As a result they are rarely seen in the wild. They are thought to feed on deep-sea squid, and prefer deep oceanic and continental slope waters.
The Stejneger's beaked whale is found in cool temperate waters of the North Pacific and southwest Bering Sea. In recent years, this species was hunted along with Cuvier's beaked whales in Japanese fisheries. It is also at risk from incidental entanglement in fishing gear, and like other beaked whales may well be susceptible to loud anthropogenic noises. Other threats are the impacts of climate change and the ingestion of marine debris which can block the digestive tract and cause death. No global abundance estimate exists for Stejneger's beaked whale and the IUCN lists this species as ‘Data Deficient'.