Genetische monitoring van de Nederlandse otterpopulatie : Ontwikkeling van populatieomvang en genetische status 2016/2017

The yearly survey of the Dutch otter population in terms of size, distribution and genetic status is commissioned by the Ministry of Agriculture, Nature and Food Quality, using DNA isolated from spraints and tissue from dead individuals, and the demographic processes of reproduction, mortality, immigration and emigration. The resulting information is also used to detect changes in the spatial distribution and size of the population. Based on the 2016/2017 survey, the population size is estimated at approx. 200 individuals. For the first time the population appears not to have increased in size. This is a preliminary conclusion because the success rate of DNA analyses of spraints was somewhat lower than in previous years. The number of traffic victims increased in 2016 and showed a linear trend with the total population size in the previous year. The total genetic variation at the population level decreased slightly, as did the average genetic variation within individuals. This small decrease in heterozygosity indicates a gradual increase in the level of inbreeding within the population. It underlines the importance of restocking the population with genetically unrelated individuals and the importance of immigration of otters from German populations, which occurs only incidentally