GEOGRAPHIC-VARIATION IN GROWTH OF POLAR BEARS (URSUS-MARITIMUS)

The growth patterns of body length and head size in female and male po lar bears (Ursus maritimus) in western Hudson Bay were compared with t hose of five other populations using the von Bertalanffy equation. Our objective was to determine if differences in growth patterns could ac count for higher reproductive rates reported in female polar bears fro m western Hudson Bay compared to the other populations. Significant di fferences in asymptotic size and growth rate were found in body length and head size. At age of first breeding in western Hudson Bay (4.1 ye ars old), females reached 97% of asymptotic body length, while females in other populations took between 4.5 and 5.5 years to attain the sam e proportion. Body length of three- and four-year-old females in weste rn Hudson Bay declined between the 1960s and 1990s and temporal variat ion in growth rates makes cross-population studies uncertain. Zygomati c breadth and head length may provide the most useful measures to comp are populations because they are simple to measure, non-varying, and g rowth in head length is almost complete (97-98%) by the age of first b reeding in females. We conclude that higher reproductive rates in west ern Hudson Bay were associated with higher growth rates. However, the reason for the higher growth rates remain unknown.