App. D: Natural History Supp.

NOTE TO READER: The text below was developed by the CIBRT and reproduces information readily available in other reports. In Section II.B of this document, we provided natural history information sufficient to justify the recovery criteria and actions. Additional natural history information follows.

Body Size

Geographic variation in body size has been documented across the beluga’s range (Kleinenberg et al. 1969; Sergeant and Brodie 1969) and may be indicative of ecological differences, such as the availability of winter prey. Sergeant and Brodie (1969) documented a positive correlation between beluga size and marine productivity, with belugas in estuarine and Arctic waters being the smallest, whereas belugas in the subarctic were the largest. Furthermore, Native hunters remarked that CI belugas are larger than belugas in other parts of Alaska (Huntington 2000), but a systematic analysis of body size across Alaskan populations has not been completed. However, belugas from Cook Inlet and Bristol Bay (both estuarine areas) and the eastern Chukchi Sea (the high Arctic) were documented to be of similar size (Suydam 2009). An examination of five beluga populations of the Canadian Arctic showed that body length was positively correlated with latitude (Luque and Ferguson 2010), with belugas harvested at the highest latitude attaining the longest adult body lengths. Luque and Ferguson (2010) postulated that this latitudinal variation in body size may result from the seasonality of important environmental resources. From a preliminary analysis of a small number of specimens, Murray and Fay (1979) suspected there may be differences in skull morphology between CI belugas and other beluga populations. Similarly, differences in vocal repertoires and acoustic signatures among CI belugas and other Alaskan populations were investigated by Angiel (1997), but results are inconclusive.

Distribution

A review by Laidre et al. (2000) of cetacean surveys conducted from 1936 to 2000 in the Gulf of Alaska (Unimak Pass to Dixon Entrance) confirmed that beluga sightings are rare outside Cook Inlet. During dedicated surveys covering over 150,000 km (93,205 mi) of the Gulf of Alaska (including Cook Inlet), only five belugas (four sightings) were reported outside of Cook Inlet (four near Kodiak Island and one in Prince William Sound) out of over 23,000 individual cetacean sightings (Laidre et al. 2000). In addition to these dedicated surveys (with records of effort and other cetaceans seen), the NMFS Platforms of Opportunity database (data from surveys without defined effort) contained only 39 individual belugas (from five sightings) out of over 100,000 individual cetaceans sighted (Laidre et al. 2000). Other incidental sightings from 1936 and 2000 (from commercial or recreational fishing boats, tourists, and bird surveys with no information about survey effort or other cetaceans seen) documented over 260 individual belugas (from approximately 19 sightings) (Laidre et al. 2000), with only 28 sightings of belugas outside of Cook Inlet (nine near Kodiak Island, 10 in or near Prince William Sound, eight in Yakutat Bay, and one sighting well south of the Gulf of Alaska).

Age Determination

Figure D1. Photo of beluga tooth cross section. Notes: Photo of a beluga whale tooth cross section showing the pulp cavity at the left and progressive layers of dentin towards the right. The oldest dentin layers are on the outer margins of the tooth with progressively thinner layers of dentin deposited in later years near the central pulp cavity. Each layer is considered a growth layer group and is used for aging the individual. Source: The North Atlantic Marine Mammal Commission; image acquired 24 July 2013 from report of the workshop on age estimation in monodontids.

There has been recent discussion about the deposition rate of growth layer groups (GLGs) in beluga teeth (Figure D1), including questions on whether belugas produce one or two GLG per year. The initial hypothesis was that two GLGs were deposited annually (Sergeant 1959), which was supported by many successive studies (Brodie 1971, 1982; Sergeant 1973; Burns and Seaman 1986; Goren et al. 1987; Brodie et al. 1990; Heide-Jørgensen et al. 1994). This deposition rate was previously assumed for most odontocetes. Although further investigation revealed that other odontocetes deposited only one GLG per year, the notion of two GLGs per year persisted for belugas. After re-evaluation of previous studies, analyses of teeth of two captive belugas, and examination of tetracycline-marked teeth, several studies concluded that belugas deposited only one GLG per year (Hohn and Lockyer 1999; Stewart et al. 2006; Lockyer et al. 2007; Luque et al. 2007; NAMMCO 2011). Deposition of a single GLG per year among belugas would double most of the previous estimates of age, with associated changes to vital rates (such as longevity, age at sexual and physical maturity, age at first birth, etc.). Here, it is assumed that one GLG is deposited annually and some of the estimates in Table 1 have been revised to reflect this change.

Notes: Photo of a beluga whale tooth cross section showing the pulp cavity at the left and progressive layers of dentin towards the right. The oldest dentin layers are on the outer margins of the tooth with progressively thinner layers of dentin deposited in later years near the central pulp cavity. Each layer is considered a growth layer group and is used for aging the individual.