Physical Description of Belugas
The beluga (Delphinapterus leucas), or “white whale,” is a small odontocete (toothed- whale). Known for the striking white coloration of the adults, the word “beluga” is derived from the Russian word for white, and the specific name leucas is the Latin word for white. The Latin “apterus” refers to the lack of a dorsal fin, another prominent characteristic. Belugas have a stocky body, flexible neck, small rounded head, short beak, and conical teeth. The flippers are relatively small but broad and spatulate with edges that tend to curl with age. Their flukes are broad and notched with convex trailing edges. Physical characteristics that distinguish belugas from most other cetaceans include unfused cervical vertebrae accompanied by increased head mobility, a very bulbous flexible melon in the forehead region, the lack of a dorsal fin, and presence of a tough dorsal ridge. Belugas are relatively slow swimmers that often roll slowly at the surface, and their blow is often inconspicuous.
Calves are born dark gray to brownish gray and become lighter colored with age. Adults may become white to yellow-white at sexual maturity, although Burns and Seaman (1986) report females may retain some gray coloration for as long as 42 years (assuming one dentinal layer per year). McGuire et al. (2008) reported several photo-identified mothers that were still gray when they had calves, suggesting that coloration is not a definitive indicator of maturity. Beluga researchers commented that the gray belugas they observed in Cook Inlet (during August 2016) appeared larger than the gray belugas found in the St. Lawrence Estuary (R. Michaud, GREMM, pers. comm. to Mandy Migura, NMFS).
Belugas are sexually dimorphic, with length averaging 355 centimeters (cm) (11.6 ft) in adult females and 415 cm (13.6 ft) in adult males (Burns and Seaman 1986). Males weigh up to 1,500 kg (3,307 pounds [lb]) and females 1,360 kg (2,998 lb) (Nowak 1991). Beluga calves in Alaska have been reported to average 150 cm (4.9 ft) in length and 72 kg (159 lb) at birth (Burns and Seaman 1986
Taxonomy, Geographic and Genetic Variation
The beluga is a member of the Monodontidae, the taxonomic family it shares with the narwhal. The earliest fossil record of the Monodontids is an extinct beluga (Denebola brachycephala) from late Miocene deposits in Baja California, Mexico, indicating that this family once occupied temperate ecozones (Barnes 1984). Fossils of belugas found in Pleistocene clays in northeastern North America reflect successive range expansions and contractions of this species associated with glacial maxima and minima. The beluga is a northern hemisphere species, ranging primarily over the Arctic Ocean and some adjoining seas and inhabiting fjords, estuaries, and shallow waters in Arctic and subarctic oceans, except for a small population in the Gulf of St. Lawrence, Canada. Some belugas seek out shallow coastal waters in summer and remain near the ice edge in winter.
In Alaska, there are five recognized beluga stocks (Figure 5) delineated based on summer range: the Beaufort Sea, eastern Chukchi Sea, eastern Bering Sea, Bristol Bay, and Cook Inlet stocks (Allen and Angliss 2012). Murray and Fay (1979) suggested the CI beluga stock has been isolated from the other stocks for several thousand years. The lack of CI beluga observations along the southern side of the Alaska Peninsula (Laidre et al. 2000) and genetic data (O’Corry-Crowe et al. 1997, 2002, 2010) have corroborated Murray and Fay’s (1979) suggestion of distinction from the other stocks.
Sightings of belugas in the Gulf of Alaska are rare outside of Cook Inlet (Laidre et al. 2000). The degree of genetic differentiation between the Cook Inlet stock and the other four Alaska beluga stocks indicates the Cook Inlet stock is the most isolated (O’Corry-Crowe et al. 1997, 2002, 2010). This suggests that the Alaska Peninsula has long been an effective physical barrier to genetic exchange and that migration of whales into Cook Inlet from other stocks is unlikely.
The exception to the rarity of belugas in the Gulf of Alaska outside of Cook Inlet may be a very small group of belugas that appear to reside year-round in Yakutat Bay (Fiscus et al. 1976; Consiglieri and Braham 1982; Hansen and Hubbard 1999; O’Corry-Crowe et al. 2006). Genetic samples collected from whales in Yakutat Bay are more closely related to each other than they are to whales sampled in other areas of Alaska (O’Corry-Crowe et al. 2006), and are unlikely to represent whales traveling from the Cook Inlet population. Since there is no evidence of interaction between CI belugas and belugas found in other areas of the Gulf of Alaska, including the Yakutat Bay area, this recovery plan focuses only on the belugas inhabiting Cook Inlet.