Stejneger's beaked whale
Stejneger's beaked whale (scientific name: Mesoplodon stejnegeri) is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), medium-sized whales with distinctive, long and narrow beaks and dorsal fins set far back on their bodies. They are marine mammals within the order of cetaceans.
Thirty-one of the 48 sightings of Stejnegers beaked whale have come from Alaskan waters. It is suspected this species favors deep waters, including the Aleutian Trench and the Aleutian Basin, which is some 3500 meters deep, rather than the shallow waters of the Bering Sea. The whales were seen traveling in groups of five to fifteen; some individuals were large and some were small. This species is also known as the Sabre-toothed beaked whale, hinting at the shape of the adult male's teeth.
Stejneger's beaked whale ranges in length from three to seven meters, although they are generally longer than 5.3 m. Females are normally longer than males, and the crania of females are larger than those of males.
Both sexes are uniformly gray to black, with light pale countershading ventrally, although males tend to be more uniformly dark.
Stejneger's beaked whale is distinguished from other Mesoplodons by tooth shape and position. Members of this species have two large, exposed, tusk-like teeth on the lower jaw (Nowak 1999). These teeth are also distinctively larger in males.
Scarring, which is present on most Stejneger's beaked whale, results from intraspecific fighting over mates, and is inflicted by the teeth while the mouth is closed (Nowak, 1999; Ridgway and Harrison, 1989).
Other Physical Features: Endothermic; Homoiothermic; Bilateral symmetry
Sexual Dimorphism: Female larger; Male more colorful; Ornamentation
These beaked whales are deep divers. They swim at three to four knots on average, with maximum speeds reaching 6 knots.
This species usually swims in pods containing two to six individuals, although groups of five to fifteen individuals have been observed. Within these social pods, individual whales vary in size, sex, and age. They swim abreast in the pods, touching one another, and they surface and submerge simultaneously.
A common pattern of several shallow dives followed by a longer dive of about 10 to 15 minutes has been noted.
Also while in these pods, members of this species take 2 to 3 low blows in unison, which are proceeded by sounds described as "roars, lowing and sobbing groans." (Loughlin and Perez, 13 December 1985)
Key Behaviors: natatorial; diurnal; motile; nomadic; social
Little recorded information is known about the reproduction of Stejneger's beaked whale, although it is speculated that litter size is one and parturition occurs in the spring and summer. (Loughlin and Perez, 13 December 1985)
Key Reproductive Features: Iteroparous; Seasonal breeding; Gonochoric/gonochoristic/dioecious (sexes separate); Sexual; Fertilization; Viviparous
Although parental investment in this species has not been documented, because these animals are mammals we can infer that females provide a great deal of parental care. They are likely to provide their young with protection as well as food, in the form of milk, until the calves are able to care for themselves.
Distribution and Movements
Stejneger's beaked whale ranges from the Bering Sea to California and Japan, inhabiting only the cool temperate waters of the Northern Pacific Ocean. (Nowak, 1999)
Stejneger's beaked whales, inhabit the deep waters of the ocean far from the shorelines. These animals are rarely seen at sea. They prefer a habitat with cool water.
Stejneger's beaked whale has been observed living sympatrically with Hubb's beaked whale where the ranges of the two species overlap off the coast of northern Japan to Oregon and British Columbia. (Loughlin and Perez, 13 December 1985)
Habitat Regions: Temperate; Saltwater or marine
Aquatic Biomes: Pelagic
Stejneger's beaked whale feeds primarily on deep-water squid. The diet includes cephalopods, mollusks and fish.
A school of salmon was observed being chased by Stejneger's beaked whale off the coast of Japan, and this species is sometimes trapped in salmon driftnets. (Loughlin and Perez, 1985)
Economic Importance for Humans
The meat of Stejneger's beaked whale is considered palatable when cooked, but the Makah Indians of Washington reported cases of diarrhea after eating the blubber and flesh. Commercial fisheries, primarily in Japan, take a number of M. stejnegeri yearly. (Loughlin and Perez, 1985)
Positive Impacts: food
Threats and Conservation Status
The IUCN Red List reports:
Stejneger's beaked whales were hunted in a Japanese fishery, along with Cuvier’s beaked whales. They are not presently the main targets of any hunt.
In the past, some individuals were taken in the Japanese salmon driftnet fishery in the Sea of Japan and in driftnets off the west coast of North America. Entanglement in fishing gear, especially gillnets in deep water, is probably the most significant threat.
This species, like other beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006).
As a cold water species, Stejneger’s beaked whale may be vulnerable to the effects of climate change as ocean warming may result in a contraction of the species range as it tracks the occurrence of its preferred water temperatures (Learmonth et al. 2006). The effect of such changes in range size on this species is unknown.
Evidence from stranded individuals of several similar species indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001); this species may also be at risk.
These whales are a conservation concern. They are listed as Appendix II by CITES, and Data deficient by IUCN.
IUCN Red List: Data Deficient
US Federal List: No special status
CITES: Appendix II
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