Fertility in two West Greenland caribou Rangifer tarandus groenlandicus populations during 1996/97: potential for rapid growth

Estimates of caribou Rangifer tarandus groenlandicus abundance in West Greenland in 2001 were much larger than estimates from the early 1990s. Two caribou populations, the Kangerlussuaq-Sisimiut of the North region and the Akia-Maniitsoq of the Central region, were examined for productivity. In total, 96 female caribou were collected in early and late winter from the subareas Kangerlussuaq and Akia, respectively. Data on reproductive status, reproductive history and animal age were collected. Maximum age observed was 15 years and mean age of death may be 12-13 years, which indicates a natural mortality of approximately 8%. Despite habitat differences in climate and vegetation, the two West Greenland caribou populations had similar pregnancy rates for mature females, i.e. ca 81% (P = 0.93). Likewise, mean fertility (total number of all pregnancies) for the age classes 1-10 years (age at breeding season) was not significantly different at 4.77 ± 2.38 and 4.23 ± 2.57, respectively (P = 0.65). Although West Greenland adult female pregnancy rates in 1996/97 were similar to those of North American caribou, the Greenland sample showed a high percentage of pregnant subadults. Further there was no significant difference between early and late winter pregnancy rates for either population. Fertility among Greenland females was excellent. Maximum potential number of pregnancies for their lifetime was attained by 25%, while 2-4% exceeded the maximum, and at the age of 10 Greenland females can be expected to have had > 7 calves. The high productivity in both populations may occur through first conception in the second autumn or twinning, both of which suggest summer forage of equal and excellent value for several years preceding this study. The potential for rapid growth in abundance of both populations was present in 1996/97 regardless of the dissimilar range characteristics.