Sex and age composition of spring-hunted Eurasian beaver in Norway

In Norway, Sweden, and Finland, most Eurasian beaver (Castor fiber) harvested are shot in April and May. Since beaver cannot be sexed or effectively aged under spring hunting conditions, hunters normally shoot the first animal seen. The consequences for population management are unknown. We tested the hypothesis that (1) the age composition and reproductive status of beaver shot did not vary significantly as individuals were removed sequentially from colonies, and (2) the sex ratio of shot beaver did not deviate significantly from a 50:50 distribution. We investigated the sex, age, and reproductive status of 126 beaver shot with rifles between 13 March and 15 May, 1997-1999, on a 242-km 2 land area in southeast Norway. The sex ratio of fetuses and all age groups did not deviate significantly from 50:50. The age ratio of the pooled bag was 14% juveniles, 22% 2 year olds, and 63% adults. Adults and pregnant females were more likely to be the first beaver shot from colonies. Pregnant females were probably vulnerable to hunters because of the increased nutritional demands of late pregnancy. Removal of an estimated 22-26% of the beaver population each year, of which 25% were pregnant females, was seemingly the main cause of the decline in occupied colonies from 57 to 31 (46%) during 3 years. The apparent susceptibility of adults and pregnant females to spring shooting should be considered when designing management plans for beaver.