Differences in growth, size and sexual dimorphism in skulls of East Greenland and Svalbard polar bears (Ursus maritimus)

Abstract

Size, growth and sexual dimorphism of nine skull traits was studied in 300 East Greenland and 391 Svalbard polar bears (Ursus maritimus). Two traits were significantly larger in bears from East Greenland compared to Svalbard bears, and trait size was smaller after 1960 in five traits. For both localities and both age groups (subadult, adult), mean trait size values were higher in males than females (all: P < 0.05). Gompertz growth models showed trait size increasing with age in seven traits. Depending on the trait, males reached 95% asymptotic trait size at age 3–10, females at age 2–6. The females of both localities matured at approximately the same age, whereas the Svalbard males generally matured years later than their East Greenland peers. The differences found in the present study between the two polar bear subpopulations support the notion that East Greenland and Svalbard polar bears probably should be managed as separate units.