Muskrats are considered a pest species in The Netherlands, and a year-round control programme is in effect. The Muskrat control programme offers excellent opportunities for applied biological studies. Temporally and spatially, there is great variation in the number of Muskrat harvested. This is attributable to landscape factors and –presumably- historical Muskrat control effort. Together with other partners (University of Amsterdam, Mammal Society, Wageningen University, Alterra), and commissioned by the Dutch Waterboard Union, A&W worked more than 3 years on a study to better understand the ecology, population dynamics and the population control of the muskrat in The Netherlands.
Part of the study was a unique large scale management experiment in The Netherlands to study the effect of manipulating harvest intensity of Muskrat (time invested in trapping) on potential and actual damage of dikes and waterfronts. The experiment took place in 117 atlas squares of 5*5 km, selected in a stratified random way. There was a strong positive relation between time spent trapping and number of animals caught, substantiating that catch is determined by effort. Catch rate was lower in summer and winter than in other seasons. The development of catch rate over time differed between experimental 5 km-squares, but could not be related to experimental treatments, or any of the environmental variables identified before. The implementation of the time-differentiated treatment was in practice not different from the year-round treatment.
We identified several mechanisms that may have attenuated differences in trapping effort on local Muskrat populations studied. We suggest that the effectiveness of time spent trapping, in interaction with spatial context is more important than previously thought. However, we have not yet fully grasped the details of the developments and there still is room for improvement of analyses performed.