Effects of Harvest on Annual Survival of Muskrats

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Abstract
Muskrats (Ondatra zibethicus) were marked from 1981 through 1984 and recovered for 5 years in Pool 9, Upper Mississippi River [USA] to determine survival and harvest rates by using banding methodology. Tag reporting rate, estimated from trapper interviews, averaged 83 .+-. 1% and was constant among years. Survival and recovery rates did not vary significantly between sexes but were significantly different between birth-year (BY) and after-birth-year (ABY) animals. Data best fit a model assuming constant age-specific survival and year-specific recovery rates. Constant annual survival rate of BY animals was 15.7 .+-. 2.3%, whereas survival of ABY animals was 5.8 .+-. 1.5%. Harvest rates ranged from 17% in 1982 and 45% in 1981, and averaged 32 .+-. 2% of the fall population in all years and habitats combined. Maximum sustained yield in backwaters was 20% of yield of openwaters although annual survival was not different between habitats. There was a density-dependent increase in nonharvest, birth-to-trapping season survival of juveniles, which compensated for increases in harvest mortality.

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