The reliability of counting cementum annulations in premolar sections was evaluated for age determination in live polar bears (Ursus maritimuls). Structural irregularities in cementum deposits decreased accuracy of age assignments. Displacements of the neonatal line toward the exterior margin of cementum growth resulted in erroneous aging for young animals. Striated, wavered, and doubled growth layers affttected accuracy for older animals. Sixty-eight unlabeled tooth slides representing 57 known-age bears, examined by 3 independent investigators, revealed that only 32-45 percent were correctly aged. Analysis of age-related body measurements of 46 male and 63 female polar bears of known age showed that morphometric regression equations could be used as an age indicator. Reproductive status, general body size, and tooth replacement or wear used as criteria to tentatively age animals in the field, combined with subsequent cementum counts and growth regression analyses, provided reliable age determinations. Differential growth in tooth cementum has been widely used to determine the age of individual animals (Klevezal and Kleinenberg 1969). Cementum annuli were confirmed in known-age brown (Ursus arctos) and black (U. americanus) bears (Rausch 1961, Sauer et al. 1966, Stoneberg and Jonkel 1966) and from teeth taken at different intervals from known-age grizzly bears (U. arctos) (Craighead et al. 1970). Legibility of cementum layers in brown and black bears appeared correlated to retarded growth zones formed during winter denning. Chronological layers formed in cementum of polar bear teeth are much less consistent because activity patterns differ, particularly as related to winter denning. Lentfer (1976) noted that polar bears (except parturient females) were active, or at least intermittently so, throughout the entire year. Harington (1968) reported that the denning period of polar bears varied considerably by age, sex, and physiological state. Rausch (1969) observed structural irregularities in polar bear teeth and cited variation in annual activities as a plausible reason for cementum having little value for determining chronological age. The Alaska Department of Fish and Game and the U.S. Fish and Wildlife Service conducted a polar bear mark-and-recovery program between 1967 and 1976. During this time, 809 polar bears including 286 known-age litter members were captured, marked, and released in the Alaska sector of the polar basin. Eighty-nine of these were recaptured 1 or more times. It became apparent early in this program that structural irregularities of cementum layering posed a serious problem in assigning ages to marked polar bears. The recovery of known-age polar bears led to a partial assessment of this problem.
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