Mass and body-dimension relationships of polar bears in northern Alaska

Models developed from morphometric parameters are useful for estimating body mass (M) of captured wild ursids. The accuracy of those models, however, may depend on sex, season, and geographic location of the population. We tested the suitability of reported models to predict mass of polar bears (Ursus maritimus) captured in northern Alaska, but found that models developed for other populations performed poorly. Hence, we derived new models from field measurements of axillary girth (AG), straight-line body length (SLBL), condylobasal length (CL), and zygomatic width (ZW). Our equations accurately predicted body mass for polar bears captured during spring and autumn. The equation for spring-captured polar bears was M = 0.000078 * AG^1.6026 * SLBL^1.3579 (R²=0.97), while the equation for autumn-captured polar bears was M = 0.000250 * AG^1.4967 * SLBL^1.2468 (R²=0.97). Our results suggest that investigators should verify the accuracy of reported equations when applied to each situation and if necessary, develop models specific for the population in question.