An Attempt to Remove Coypus (Myocastor coypus) from a Wetland Habitat in East Anglia

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Abstract
(1) Coypus, Myocastor coypus Molina, are introduced semi-aquatic rodents. They cause serious damage to crops, drainage systems (through burrowing) and native plant communities in the East Anglian wetlands. (2) A trial was carried out to test whether it was possible to eradicate coypus from an area of wetland in Norfolk using cage trapping. The area was a 30-km stretch of the flood plain of the River Yare between Norwich and Reedham. Three trappers worked full-time for 6 years in 1975-81. Trapping intensity was 59% higher than in control trapping elsewhere in East Anglia. (3) Coypus were completely removed from the western part of the study area, none being caught for the last 2.5 years. Some coypus continued to be caught in the east and particularly near the eastern perimeter. A number of lines of evidence, including the movements of tagged animals, showed that the animals in the east were immigrants from extensive marshland outside the area, where trapping was carried out at a lower intensity by the Coypu Control organization. The absence of field evidence of coypus, especially their faeces, in areas that seemed to have been cleared, suggested that there were no ''trap shy'' animals. (4) Non-target species were released when the traps were inspected each day and included moorhens, mallards, water rails, water voles, and common rats. Capture rates during and after the trapping exercise showed that trapping had no significant effect on any non-target populations; most species increased over the first 4 years of intense trapping. Cold winters may sometimes have reduced numbers, particularly those of water rails. Some non-target populations also declined in 1979 and 1980 for unknown reasons. (5) The results obtained were part of the evidence considered by the Coypu Strategy Group, which recommended an attempt to eradicate coypus from Britain. This recommendation was accepted and a 10-year campaign was started in 1981. Coypus are not endangered in South America although their numbers and range have been reduced.