Sex and age composition of spring-hunted Eurasian beaver in Norway
Journal article, Peer reviewed
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OriginalversjonJournal of wildlife management 66(2002) No. 4, p. 1164-1170
In Norway, Sweden and Finland most Eurasian beaver (Castor fiber) harvested are shot in April and May. As beaver cannot be sexed or effectively aged under spring hunting conditions, hunters normally shoot the first animal seen. The consequences for population management are so far 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, 1997-99, on a 242 km2 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 shot first from colonies than others, the later probably because the increased nutritional demands of late pregnancy exposed them more to hunters. Removal of an estimated 22-26% of the beaver population each year, of which 25% was 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.