Introduced vertebrates can cause massive environmental damage but most attempts to remove feral populations have failed. This paper discusses the eradication campaigns against feral muskrats, Ondatra Zibethicus and coypus, Myocastor coypus in Britain. Both specks were introduced in the 1920s to be farmed for pelts and feral populations became established following escapes. The risk of environmental damage by muskrats was well known from Europe and;in eradication campaign started promptly in 1932 making use of overseas expertise and a control strategy designed by pest control specialists. The campaign was brought to a successful conclusion in 1939 when at least 4388 muskrats had been killed.
In the 1930s, few believed that coypus would cause significant environment damage and early trapping efforts were inadequate. An early campaign achieved only limited success partly because of the lack of biological information. The eradication campaign which started in 1981, was based on a long tem study of population ecology. The effect of trapping and cold weather was quantified and detailed population simulations were used to plan the numbers of trappers, the time needed for eradication arid thus the likely cost of the campaign. An incentive bonus scheme was designed to overcome the problem that trappers would be reluctant to work themselves out of a job. Trapper deployment was planned using capture/trapping effort ratios and progress was checked by Ministry of Agriculture field staff.
The muskrat campaigns succeeded because technical information to help plan the work was available and because action was taken quickly. Where an introduced population is well established, as with coypus in Britain, a closely integrated programme involving applied population ecology and a well-planned control organization may he essential for succesful removal.