Mesoplodon stejnegeri True, 1885

English: Stejneger's beaked whale
German: Stejneger-Zweizahnwal
Spanish: Zifio de Stejneger, ballena picuda de Stejneger
French: Mésoplodon de Stejneger, baleine à bec de Stejneger

Family Ziphiidae

Mesoplodon stejnegeri © Wurtz-Artescienza (see links).

1. Description

Stejneger's beaked whale appears to be dark above and pale below, with the beak and neck areas being paler. However, a dark cap extending from both eyes over the top of the head appears to be characteristic. In adult males two large erupted teeth point forwards near the peak of the arched lower jaw, about halfway from the gape . The largest male measured 5.7 m and 1,600 kg (Jefferson et al. 2008). Females and young males have no erupted teeth and, at sea, are probably impossible to distinguish from other Mesoplodon species (Carwardine, 1995).

2. Distribution

Stejneger's beaked whale ranges in subarctic waters of the North Pacific from the Bering Sea south to Japan and central California (Loughlin and Perez, 1985; Rice, 1998). The center of its distribution seems to be the Aleutian Islands, where M. stejnegeri has been known to strand in small groups. There are also sighting records from the central Aleutian Islands (Mead, 1989 and references therein).

Distribution of Mesoplodon stejnegeri (Taylor et al. 2008; © IUCN; enlarge map). It lives over
continental slopes and in oceanic waters of the sub-Arctic and temperate North Pacific from
California to Japan (Pitman, 2002).

3. Population size

Unknown.

4. Biology and Behaviour

Schooling: Small groups sometimes travel abreast, almost touching one another, and may surface and submerge in unison. There are reports of 5 or 6 shallow dives, followed by long dives of 10 to 15 minutes. Diving involves a slow, casual roll at the surface. Groups usually include both small and large animals, suggesting a mixing of ages and/or sexes (Carwardine, 1995).

Walker and Hanson (1999) also concluded that Stejneger's beaked whales travel in small groups, as 4 animals stranded within short range of one another at Kuluk Bay, Adak Island (51°54'N, 176°34'W) in August 1994.

Food: Stejneger's beaked whales feed on squid of the family Gonatidae and Cranchiidae in mesopelagic and bathypelagic depths. Fish are also taken (Walker and Hanson, 1999; Jefferson et al. 2008).

5. Migration

There have been numerous strandings from the coasts of Japan with the Sea of Japan, and many fewer along the Pacific coast. The large peak in strandings in this area in winter and spring suggests that the species may migrate north in summer (Mead, 1989). M. stejnegeri in the Bering Sea sometimes bear fresh cookie-cutter shark bites, also suggesting that they probably moved north from warmer waters (Pitman, 2009).

6. Threats

Entanglement in fishing gear, especially gillnets in deep water, is probably the most significant threat (Taylor et al. 2008). Several Stejneger's beaked whales are known to have been taken in salmon driftnets off Japan and on the west coast of North America. There have been occasional direct catches of this species off Japan and possibly elsewhere (Jefferson et al. 1993).

Baker et al. (2006) report on whale meat from M. stejnegeri found in a systematic survey of whalemeat markets in South Korea between 2003 and 2005. The meat originated presumably from by-catch.
Honma et al. (1999) report on one specimen having died after a strike from a jetfoil operating for the Sado Line (Niigata-Ryotsu route) in the Sea of Japan.

7. Remarks

Range states (Loughlin and Perez, 1985 ; Taylor et al. 2008) :
Canada; Japan; Russian Federation; United States of America

IUCN status: "Data Deficient". Not listed by CMS. Listed in Appendix II of CITES.

8. Sources and further information

see "Genus Mesoplodon - Beaked whales: Introduction and Sources"

© Boris Culik (2010) Odontocetes. The toothed whales: "Mesoplodon stejnegeri". UNEP/CMS Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.