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

The food of harp seals inhabiting the northwest Atlantic consists chiefly of pelagic fish, especially capelin, Mallotus villosus, and pelagic and benthic Crustacea (Euphausiacea, Mysidacea, Amphipoda, Decapoda), with smaller quantities of benthic fish. Feeding has been observed to take place on individual items by suction, and small fish are taken tail first. Feeding is intensive in winter and (by deduction) in summer, less intensive during spring and autumn migration, and in spring during whelping and moult. A weight loss in spring due chiefly to loss in thickness of subcutaneous fat (blubber) is most intensive in adult females as a result of lactation. This loss is made up slowly in summer. The preparturient females are partly segregated in midwinter on what may be the best feeding grounds. During lactation, and immediately following it when they are again segregated from other age-sex groups, adult females tend to feed on decapod Crustacea. In spring, the only time when all age classes are in the same geographic area, there is a stratification of feeding by size of organism and by depth, from chiefly Euphausiacea taken in surface waters by the weaned young, through capelin taken probably at intermediate depths by the immature animals, to herring, cod, and other groundfish taken by the moulting adults to depths of perhaps 150–200 m. Social feeding begins at about 1 year of age with the change from Crustacea to pelagic fish. From knowledge of the rate of feeding, body weights, and reproductive rates, the ecological efficiency of harp seals (i.e. weight of annual increment of population/weight of annual food eaten) is calculated at 0.005, a low figure. Annual weights of food items eaten by the northwest Atlantic population of harp seals are roughly estimated as: all organisms, 2 × 106 metric tons; capelin, 0.5 × 106 tons; and herring, 2 × 104 tons. Predation by harp seals on capelin stocks off eastern Canada occurs only during the winter months when pack ice is present as a resting substrate, the same resource being consumed in the summer months by the great whales (Balaenopteridae).

Measurements of length, girth, and weight show that male white whales grow larger than females. The smallest white whales come from western Hudson Bay, the White Sea, and Bristol Bay, Alaska. Animals of intermediate size inhabit all other arctic Canadian localities sampled and also the St. Lawrence River and the Kara and Barents seas. The largest white whales inhabit West Greenland waters, the Okhotsk Sea, and the coast of Sakhalin. Extreme differences in body weight of adult males are about threefold. Nonoverlapping differences in size indicate isolation of some adjacent populations of white whales; equal or overlapping sizes suggest, but cannot prove, mixing of other populations. Size can be positively correlated with marine productivity, being lowest in the arctic and in estuaries and highest in subarctic seas. Since white whales most often grow largest at the southern ends of their range, their restriction to the arctic is attributed either to competition with certain of the Delphinidae or to predation from killer whales, Orcinus orca L., or to both. Both putative competitors and predator lack adaptations for arctic life.

No abstract

1983. Validation of age estimation in the harp seal, Phoca groenbandica, using dentinal annuli. Can. J . Fish. Aquat. Sci. 40: 1430-1441. We investigated the validity and accuracy of age estimation in harp seals, Phoca grosra1~ndic.a~ using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG). representing1st-year growth, consists of two IGLs: an outer layer sf opaque dentine, bounded by the neonatal Iine, and an inner layer of translucent dentine. Subsequent GLGs. each representing 1 yr of growtla, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May-June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4q0 of estimates of 0-group seals were correct basing only transverse sections. These errors were virtually eliminated (489.0% ~O P P B :~~ age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages I. 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, k i n g 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.