The geographical range and overall population status of the feral nutria (Myocastor coypus) in the United States was reviewed. The species was released or has escaped in virtually all states, but established permanent, thriving populations only in the more mild climatic portions of the West and South. A detailed population study was made of a nutria population found thriving and rapidly multiplying in dairy cattle sewage lagoons in Florida. Nutria foraged extensively on the introduced water hyacinth (Eichhorina crassipes) which formed massive unlimited floating food supplies in the sewage lagoons. Population densities reached 24.7 nutria per surface hectare of water and breeding occurred on a year-round basis without periods of decline. The mean litter size based on embryo counts for 148 pregnant females was 5.75 ? .51 young (range 3 to 12 and mode 5.0 embryos). Nutria are polyestrous, exhibit post-partum pregnancies, and produce an estimated 2.7 litters per year in the dairy lagoons. It is concluded that the nutria is very adaptable to a wide range of ecological conditions in the United States and notably insensitive to certain types of aquatic pollution.
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