Biology of White Whales (Delphinapterus leucas) in Western Hudson Bay

Abstract

The number of white whales inhabiting western Hudson Bay is about 10,000. In July and early August the herds are concentrated in river estuaries at 57° to 60° N, but a migration in mid-August through September takes them to between 62° and 66°N. Wintering occurs in the western part of the Bay. In the estuary of the Churchill River feeding, mainly on fish, is not heavy and the herds are believed to enter the river estuaries in this region for reproduction as much as feeding. Further north in late summer feeding is heavier and changes towards a diet of decapod Crustacea. It is believed that two dentinal layers are laid down in the teeth each year, each layer consisting of one opaque and one translucent zone of dentine, with the translucent material laid down during periods of reduced feeding. These may occur either at an autumn and a spring migration or during a summer fast at calving time and during winter deprivation. Females attain sexual maturity at 8–13 (mean 10) growth layers and males at 16–18 layers, i.e. at supposed mean ages of 4–7 (5) and 8–9 years. The skin loses all trace of grey color at 18–22 layers. Maximal duration of life is about 50 layers or a supposed age of 25 years in both sexes. The sexes are probably about equal in numbers. Gestation lasts 14 months and lactation about 20 months. Overlap of pregnancy and the previous lactation is infrequent so that calving occurs about once in 3 years. The annual crude birth rate is estimated at 0.12. Estimation of the maximal number of births from counts of corpora luteal scars is complicated by the frequent presence of accessory corpora lutea and luteinized follicles, estimated at about 32% of the total. The mean maximal number of scars retained in the ovaries during a female’s reproductive lifetime is 14.5. The full reproductive lifetime, on the basis of two growth layers per annum, is 20 years. Thus the mean ovulation rate is about 0.7 per annum. Reducing the number of scars by 32% gives 0.5 true (fertile) ovulations per annum, which would indicate a reproductive rate of one pregnancy in 2 years, and a maximal number of 10 pregnancies in a full reproductive lifetime

Reproduction, Growth and Development in Captive Beluga (Delphinapterus leucas)

“…Gestation estimates of wild beluga have varied from 330 days to a maximum of 441 days [Brodie, 1971;Sergeant, 1973;Heide-Jrgensen and Teilmann, 1994]. This variation seems to depend on population location and methodology used to extrapolate conception dates.…”

Concentrations and patterns of organochlorine contaminants in white whales (Delphinapterus leucas) from Svalbard, Norway

“…Ž . Sergeant, 1973 . Several four to 10 blubber biopsies were sampled from an area just anterior of the mid-dorsal ridge of each whale.…”

Socio-sexual and probable mating behavior of Cook Inlet beluga whales, Delphinapterus leucas, observed from an aircraft

“…Reported age of sexual maturity varies from 4 to 10 years for females and 8 to 15 years for males (Nowak, 1991;Suydam et al 1 ). Gestation is 14.0-14.5 months, with a single calf born in late spring or early summer (Sergeant, 1973). This would suggest mating occurs in early spring.…”

“…This would suggest mating occurs in early spring. In autumn, beluga whale populations migrate toward a few common wintering grounds in Bering Sea offshore waters characterized by unconsolidated pack ice where mating is believed to occur during late winter or early spring (Brodie, 1971;Sergeant, 1973;Brown Gladden et al, 1997).…”