Productivity of beavers (Castor canadensis) from northeastern Ohio was calculated from analysis of 219 specimens (114 males, 105 females) collected in the 1966 and 1967 trapping seasons (Feb. 1-15). Beavers were aged by characteristics of eruption, closure of basal openings, and cementum layering of molar teeth. Seventy-four percent of breeding-age females (1.5 years or older) had ovulated, but only 40 percent of 1.5-2-year-olds had ovulated. The mean ovulation rate for ovulating females was 4.3, and mean placental scar count was 3.8. Signs of implantation were present in 62 percent of breeding-age females. Mean ovulation rate, conception rate, and placental scar count increased to age 5.5-6 years. Estimated prenatal mortality was 11-16 percent. First-year trapping and natural mortality was calculated to be 41.6 percent. Estimated rate of annual population increase, including prenatal and juvenile mortality, was 49 percent. On this basis, a harvest rate of 32 percent would maintain a stable beaver population.
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