Abstract
Unambiguous evidence for the effectiveness of muskrat (Ondatra zibethicus L.) control in well-established populations in
mainland Europe is lacking. Yet, this evidence is important given ongoing public challenges to the need for muskrat control
and the expressed political aim of the European Union to eradicate invasive alien species, including the muskrat. In this study,
indices of muskrat abundance based on livetrapping were compared among (i) sites at which muskrat control had been suspended
for 3 years (suspended trapping), (ii) sites with ongoing control by kill trapping (ongoing trapping) and (iii) a site at which control
efforts had ceased more than 8 years previously (no trapping). In the no trapping site, the muskrat abundance index was variable
but consistently high, while in the ongoing trapping sites, the muskrat abundance index was consistently low. In the suspended
trapping sites, the index of muskrat abundance increased from a level near that of the ongoing trapping sites to that of the no
trapping sites. The findings are corroborated by population estimates based on data from robust design mark-recapture models
and data from kill trapping. The results are interpreted as compelling proof for an effect of control on muskrat numbers, a basic
premise of the control programme.