. The Canadian field-naturalist. 1984 Parker and Maxwell: Trapping Seasons for Muskrats 303 had little impact upon population change. We believe that the initial decline in the autumn-only harvest resulted from low harvest levels prior to the study, an initial surplus was quickly removed followed by population stability. We suggest that the apparent numerical decline in population SA was real and resulted from sustained overharvest. We estimated a constant seasonal removal rate of 60% of the initial populations, a rate which should not create declines in annual levels, especially in popul
. The Canadian field-naturalist. 1984 Parker and Maxwell: Trapping Seasons for Muskrats 303 had little impact upon population change. We believe that the initial decline in the autumn-only harvest resulted from low harvest levels prior to the study, an initial surplus was quickly removed followed by population stability. We suggest that the apparent numerical decline in population SA was real and resulted from sustained overharvest. We estimated a constant seasonal removal rate of 60% of the initial populations, a rate which should not create declines in annual levels, especially in popula- tions with proven high levels of productivity (Smith and Jordan 1976). However, the additional 60% loss of the spring population following an autumn harvest in addition to expected overwinter losses does appear to surpass the limits of removal which allow sustained yield. Although densities declined with overharvest, our data suggest that the reproductive potential and productivity increased concurrent with increased mortality. Although our data do not show that popu- lation SA produced more young per female (placental scars) the proportions of juveniles in the autumn harvests were greater than for the other two popula- tions. Conversely, the proportions of juveniles in the spring harvests were lower than the other two popula- tions, especially following the initial year of trapping. In contrast to juvenile male:female ratios of 72:50 and 65:50 in harvests from populations A and S respectively, the comparative ratio in harvests from population SA was 50:50. Not only was the represen- tation of juvenile females greater in population SA, but also the only incidences of precocial breeding occurred in that population. Forty-two percent of females from SA bearing placental scars were juve- niles; 5% of all juvenile females harvested from SA were pregnant or had given birth. Thus, increased productivity (% juveniles in the harvest) was a func- tion of precocial breeding by juvenil
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