Growth, Morphology And Energetics Of Bowhead Whales (Balaena Mysticetus)

Abstract

This thesis describes investigations on bowhead whales (Balaena mysticetus) conducted over the past three decades, specifically on age, growth, morphology and energetics. The examined whales were harvested by Inupiat Eskimo whale hunters primarily in Barrow, Alaska. Bowheads are robust cetaceans reaching 19 m in length and inhabit the ice-covered waters of the circumpolar Arctic. They have the thickest blubber (? 35 cm) of any cetacean and the longest (>4 m) and most extensive baleen apparatus. Bowheads are ~4 m at birth and grow rapidly to ~8 m in their first year; they then experience a 2-3 year growth pause in both body length and mass. However the baleen continues to grow during this period. Sex differences are minimal but adult females tend to grow longer than males and males have larger pectoral limbs. Based on several lines of evidence, bowheads may routinely live to 150 years and thereby the longest-lived mammal. The recovery of 19 th century stone weapons from recently harvested whales confirms these age estimates. Age was estimated for 48 whales using the aspartic acid racemization technique, based on intrinsic changes of aspartic acid within the eye lens. The age at sexual maturity for bowheads occurs in the mid-20s. All harvested whales examined showed strong thermal gradients through their blubber (dermis and epidermis). A similar thermal gradient was evident through the muscle which is atypical of most terrestrial mammals. The deep body temperature averaged 33.8�C (SD=0.83, N = 28) which is lower than in other non-hibernating eutherian mammals. I did not see elevation of body temperatures in chased whales -- in fact these whales had slightly lower core temperatures. Resting metabolic rates for whales were estimated using a heat-loss technique. The thermal conductivity of the blubber for 5 whales averaged about 0.23 Wm-1K-1; similar to that of other whales and marine mammals. Heat flux rates varied highest to lowest as follows: palatal rete, flukes, tongue and lowest for the thorax and flippers. The resulting metabolic rates were much lower (~ 1/3) than predicted by the Kleiber regression. These investigations suggest that bowhead whales are unique among mammals in several respects such as: (a) following weaning they appear to lose weight over a period of 2-3 years and grow little in body length, (b) resting metabolic rates and body temperatures are lower than in other cetaceans. Their extensive blubber likely buffers bowheads against high variability in primary and secondary productivity in arctic seas.