Age determination and growth of Baikal seals (Phoca sibirica)

Abstract

Abstract The ages of 75 Baikal seals (Phoca sibirica) were determined in order to study the growth pattern of body length and body weight in this species. Longitudinal decalcified and stained sections of canine teeth were prepared, and growth layer groups (GLGs) in the dentine and cementum were counted. In those specimens with fewer than 10 GLGs, the GLG counts in dentine agreed well with those in cementum. However, in specimens with more than 10 GLGs, the cemental GLGs tended to exceed dentinal ones. Individuals of 4–5 years old were absent from the sample population, suggesting that the recorded mass mortality of Baikal seals in 1987–1988 (4–5 years before sampling) had affected the age composition. Growth of body length, body weight and core weight ceased at around 20 years of age. The growth pattern was similar to that of ringed seals (Phoca hispida), but differed from that of other Phoca species. Asymptotic body length and core weight were significantly different between sexes, but body weight was not. In the spring sampling period, female body weights tended to be heavier than those of males of the same body length, a feature attributed to the thicker blubber of females. Sexual dimorphism, and the large fluctuation in body weight and presence of secondary sexual characters reported in males, suggested the presence of intermale competition in the Baikal seal, presumably for access to females.