Status van de Nederlandse otterpopulatie in 2022 : Nieuwe inzichten in genetische uitwisseling, mortaliteit en verkeerssterfte

Summary

Status of the Dutch otter population in 2023: new insights in genetic exchange, mortality and traffic casualties The Dutch otter population is surveyed each year for the Ministry of Agriculture, Nature and Food Quality, with particular attention to developments in the genetic status of the population and roadkill mortality. To support the long-term maintenance of genetic variation, this year we assessed the potential for genetic exchange with neighbouring otter populations. We investigated the presence and genetic origin of otters in six habitat areas near the Dutch-German border by collecting and analysing otter spraints. In total, 23 individuals were identified, including at least one male and one female per habitat area. In three areas, an otter was identified that carried alleles from the German gene pool. This is the first evidence of cross-breeding between Dutch and German otters to be found in the Netherlands in 10 years. The total number of verified traffic casualties in 2022 was 159 (out of a total of 179 reported dead otters). While this is the highest number since monitoring started, the annual growth in the number of casualties is slowing down, a trend that started in 2020. The surprising reduction in the number of casualties in 2021 remained limited to that year. The main roadkill hotspots were identified for each province in the Netherlands within the distribution area of the otter population. We also inventoried additional measures that could help to reduce the number of traffic casualties. Promising options are switching to a more predictive approach to identifying high-risk locations rather than relying on reported casualties, devoting more attention to the functionality of fauna passages through proper construction and regular maintenance checks, and better internal communication in road maintenance organisations aimed at combining mitigation measures with planned construction or maintenance works.