Standard metabolism is estimated for the fin whale, Balaenoptera physalus, from the energy yield of lipid stores consumed while in regions of limited prey availability. The metabolic rate appears better described by a surface rather than a volumetric rule. The larger body size of some Antarctic Balaenoptera compared with those of the Northern Hemisphere is attributed to selection for body proportions that reduce the specific metabolic rate and establish an optimal surface area for deposition of a lipid cache. Such proportions allow short—term forays into areas where prey is extremely dense but of restricted seasonal availability, and permit extended use of lipid stores during exclusion to warmer but less productive waters. Thus, adult body size within species is inversely correlated with the length of the feeding season and directly correlated with prey availability during that period. As differences in diversity of prey and/or their year—round availability become less marked between hemispheres, so do the body—size differences of the lesser rorquals. This is also applied to odontocetes. Thermal homeostasis is considered to be equally dependent upon morphology and behavior. Minimal densities of prey necessary for the maintenance of rorquals could be estimated from certain known parameters.

The beluga or white whale, Delphinapterus leucas (Pallas), was studied in Cumberland Sound, Baffin Island. Layering in teeth and mandibles plus body size were used to determine age. Sexual maturity is attained at 5 years for females and at 8 years for males, with potential life span estimated to be 30 years. Whitening of the skin begins after 6 years.Multiple ovulations and accessory corpora lutea are typical of beluga. The breeding season is in May, and after 14.5 months gestation single births occur in late July or early August. Lactation lasts about 2 years, resulting in a 3-year reproductive cycle. Tooth eruption begins late in the 2nd year with partial eruption by the 3rd. This population appears to have been overexploited by commercial hunting. Productivity estimates for this species are 43% of those implied in previous studies.

The grooved throat wall of fin whales, Balaenoptera physalus, extends tremendously during feeding causing the whale to expand its profile from a cigar shape to the shape of an elongated, bloated tadpole. Ventral groove blubber associated with the engulfing feeding mechanism can be extended reversibly to as much as 4 times its resting length in the circumferential direction, and to 1.5 times its resting length along the long axis of the body. The muscle in the throat wall can be reversibly extended up to 3 times its resting length. Both these tissues have large amounts of the protein elastin in their microstructures that may function in retracting the expanded buccal cavity. Calculations of forces contributing to the expansion of the buccal cavity show that the engulfing process in feeding can be powered solely by the speed of swimming.

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.

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