Mikko Toivola and co-authors share a summary about their latest study which focuses on the movements of an invasive mesopredator within the Archipelago areas of Finland.
The raccoon dog has been known to occur in the archipelago areas of Finland for a long time. However, the role of the species as part of the archipelago ecosystem is largely unknown. How many individuals live in a certain area? How often do raccoon dogs swim from one island to another? How do raccoon dogs utilize ice cover for dispersal? Ultimately, there is a concern about how raccoon dogs adapting to archipelago habitats affect the native species of the archipelago.
Tracking and monitoring of Archipelago raccoon dogs
The raccoon dog was designated a harmful invasive species at the EU level in 2019. At the time, also in Finland, more attention was directed to the species. Also, more resources were allocated to combat the damage than before. In southwestern Finland this situation led to fruitful cooperation with a local association (Archipelago Nature Conservation and Management Association) and the Finnish Wildlife Agency. The parties launched a project aimed at tracking raccoon dogs and collecting information to support efforts to remove the species from the valuable bird areas of the Archipelago Sea National Park.
When the occurrence of raccoon dogs was mapped, they were found to be concentrated abundantly in some parts of the archipelago. The help of trained dogs proved to be an effective tool in the finding and catching of raccoon dogs. To this day, a total of 40 different individuals of raccoon dogs have been marked. The data became gradually so extensive that it was handed over to the University of Turku for research purposes. The project also included the removal of raccoon dogs. In practice, this meant that some individuals were killed, while some received a GPS collar.
Marking and tracking raccoon dogs during different seasons in various island habitats has provided significant value to the management of the species. How the species can be removed and kept away from the important archipelago bird areas is now understood. The work initially required persistence from those carrying it out to locate all individuals in the problem areas. A key requirement for success is the use of dogs trained for raccoon dog hunting in the archipelago. Experience has shown that the work is not impossible.
Action to protect crucial island bird populations
Between 2019 and 2025, nearly 300 raccoon dogs have been removed from the area of the Archipelago National Park and it’s immediate surrounding. In the early years of the project, there were dense raccoon dog populations found on several island groups. Several hunting trips were made in the worst affected areas. By 2025, the situation has developed to the point where only a few raccoon dog individuals remain in this vast area. Raccoon dogs are no longer found in the most crucial island groups for bird populations.
Based on the monitoring data the raccoon dog appears to prefer archipelagos with larger, lush islands. Individuals of the species reach these areas over the ice and establish permanent populations. Once a population is established, it can become exceptionally dense after the breeding season. This is largely due to the structure of the archipelago and the raccoon dog’s ability to thrive on a diverse range of food. In mild winters, young pups born in spring become trapped in their island habitats, as raccoon dogs are generally reluctant to swim more than a kilometre. As climate change progresses, likelihood of these mild winters increases. This undermines raccoon dogs’ chances of reaching more distant archipelagos. On the other hand, individual survival rates improve, as winters are no longer as severe.
The removal of raccoon dogs from the wild should always be done in such a way that both male and female are killed. If this is not successful, the remaining individual is likely to become more active and may move to new areas that are even more significant for nature. The raccoon dog’s impact is likely most significant on bird populations nesting in larger island groups. The velvet scoter (Melanitta fusca) is a particularly affected species. This species nests late and is still incubating in July when young raccoon dogs are already active.
Takeaways for future conservation and management
The Archipelago Sea is also home to another invasive predator, the mink. In the worst cases, sensitive bird areas have had large populations of both invasive predator species. Fortunately, the situation has continuously improved over the recent years. Once raccoon dogs are removed, efforts can be directed on the mink. The presence of raccoon dogs can be monitored in conjunction with mink hunting, allowing for the quick removal of individuals that have made their way into the archipelago.
Read the full article “Ice cover and partner removal increase movements of invasive mesopredator in the coastal island mosaic” in Journal of Ecological Solutions and Evidence
