DEMOGRAPHY OF THE PORCUPINE CARIBOU HERD, 1983-1992

Population size, parturition rates, and sex- and age-specific survival rates were determined for the Porcupine caribou herd (Rangifer tarand us granti) in northeastern Alaska and northwestern Canada between 1983 and 1992. The herd increased at an annual rate of r = 0.0467 between censuses in July 1983 (n = 135 000), July 1987 (n = 165 000), and July 1989 (n = 178 000). The mean parturition rate for 225 radio-collared cows aged greater than or equal to 3 years monitored for 603 reproduct ive attempts between 1982 and 1992 was 80% and did not differ among ye ars. First-year survival of calves was 51%. The survival rate of calve s through their first month differed among years (range 57-90%). The m ean annual survival rate for greater than or equal to 3-year-old carib ou was 84.2% for 225 females and 82.6% for 42 males. Hunting mortality for the herd averaged 2-3% annually. Population estimates generated b y a computer model using parturition and survival rates for the herd c losely tracked population trends determined from photocensus data. Gro wth of the herd is most sensitive to the survival of females 3 years o f age and older, followed by calf production and survival.