1. The analysis of the introduction pathways of ten alien invasive species
The risk of introduction, survival and spread of ten alien invasive species, that are of concern in the European Union, was assessed in the analysis. These species were: Andean pampas grass (Cortaderia jubata), Finlayson’s squirrel (Callosciurus finlaysonii), Pumpkinseed (Lepomis gibbosus), Himalayan knotweed (Koenigia polystachya), Japanese hop (Humulus japonicus), Japanese climbing fern (Lygodium japonicum), Tree of heaven (Ailanthus altissima), Box tree moth (Cydalima perspectalis), Rusty crayfish (Faxonius rusticus), and New Zealand flatworm (Arthurdendyus triangulates).
2. Researching the usefulness of different eradication methods that take into account the specificities of alien species and their habitats, and evaluating the eradication effectiveness
At the beginning of the project, the spread and abundance of alien crayfish was mapped at each location with test fishing. While researching different eradication methods, intensive trapping was deemed the only feasible option to be used in the studied water bodies. From literature review, we saw that using biocides is the only 100% effective eradication method, however, it was not used during the project due to environmental protection reasons and high reluctance from the landowners. To supplement the intensive trapping of signal crayfish in Reo Quarry and Ropka Reservoir, hundreds of predatory fish, European eels (Anguilla Anguilla), were stocked to these water bodies. Prior to the stocking a mesocosm study was carried out at the Chair of Aquaculture laboratory to see if eels raised in the fish farm will start to feed on different size crayfish.
First feeding experiment (in Estonian).
Intensive trapping with baited traps was carried out in all water bodies with known or suspected alien invasive crayfish presence using the same methodology that is normally used for annual noble crayfish monitoring. Trapping was more intensive in water bodies where the effect was expected to be the greatest. The efficiency of trapping was calculated by multiplying the number of traps with the number of catching nights (i.e., trapping nights). By the end of the project, 27 429 trapping nights in 28 water bodies were carried out, which resulted in catching and eradicating 24 431 alien invasive crayfish. Most of these (n = 23 835) were signal crayfish. About 20 000 were caught from Riksu Stream and more than 3 000 were caught from Vääna River. From Reo Quarry and Ropka Reservoir, 452 and 116 signal crayfish were caught, respectively, and less than 100 crayfish from the rest of the water bodies. The total catches of other alien invasive crayfish species were relatively small – 335 spiny-cheek crayfish, 244 marbled crayfish, and 17 narrow-clawed crayfish. In the end, different alien invasive crayfish species were caught and eradicated from 20 water bodies. The eradication efficiency was greatest in Reo Quarry, Ropka Reservoir, and Riksu Stream (mainly in parts of the stream where the trapping was more intense).
In addition, another mesocosm feeding experiment with European eel (with narrow and broad head) was carried out to investigate their potential for alien invasive crayfish eradication.
Second feeding experiment (in Estonian).
Eradication of Nuttall’s waterweed (Elodea nutallii) was not possible, because its presence was not confirmed in any of the water bodies surveyed in 2022. Altogether, samples were collected from 27 lakes across Estonia where Elodea species or Nuttall’s waterweed was suspected. However, as Nuttall’s waterweed is morphologically very difficult to distinguish from Canadian waterweed (Elodea canadensis; also present in Estonia), molecular genetic analyses were carried out. However, also these analyses did not confirm the presence of the species.
Nuttall’s waterweed – distribution report (in Estonian).
Nuttall’s waterweed – molecular analysis (in Estonian).
eDNA-based detection of noble crayfish, alien invasive crayfish and crayfish plague was carried out in 16 water bodies across Estonia.
eDNA analysis report (in Estonian).
3. Outreach activities
More outreach activities were carried out during the project than originally planned.
With the start of the project, a webpage (in Estonian and in English) was set up, which was constantly updated about all project-related activities, results, and other information. Also, Instagram account was created (Aquatic_Invasive_Species).
Project started with an opening seminar, where all of the planned activities were presented to the stakeholders and government agencies involved with environmental protection in Estonia. Various outreach activities were aimed at people interested in nature as well as private landowners through various media calls (in cooperation with the Estonian Environment Agency). Through this action, people were encouraged to report to the Estonian Environment Agency any alien crayfish sightings. Similarly, all aquatic invasive species sightings could be reported through a “Report a Sighting” tab on this webpage.
More active media involvement was carried out before the start of the crayfish catching season, spring-summer of 2022 and 2023. Also, to inform the public of any long-term eradication activities, information stands were prepared and placed near those water bodies. In addition, leaflets of different crayfish species in Estonia were printed out in three languages – in Estonian, English and Russian, and handed out at seminars and workshops.
As young people receive most of their information from the web via video, an educational and “Report a Sighting” video was made and distributed through different media channels. Throughout the project, members of the alien crayfish control team participated in various seminars and workshops for school and university students, and alien invasive crayfish were introduced at different festivals (e.g., Wähja Fesival 2022 and 2023). Also, couple of popular science articles were written in Estonian in journals like Kalastaja ja Kalale. Looduses!, and a research paper titled “Distribution of Non-Indigenous Crayfish Species in Estonia and Their Impacts on Noble Crayfish (Astacus astacus L.) Populations“ was published.
Problems related to the alien invasive crayfish species were discussed in TV-shows like Osoon and Terevisioon, and also radio interviews were given. Members of the alien crayfish control team participated in many international conferences and workshops (IAA2023, NEOBIOTA2022, eDNA workshop in Sweden, 5th Croatian Symposium on Invasive Species, Innovation in environmental protection conference). At the end of the project, a conference was held together with researchers form the University of Tartu on March 20th, 2024 to introduce the project results and main conclusions.
4. Training the stakeholders on the problems caused by aquatic invasive species as well as on practical eradication methods
During the project two theoretical and two practical training courses were carried out for all relevant people whose work is related to environmental protection (e.g., Ministry of Environment, Environmental Board, and municipal officials). In theoretical training, participants were given the necessary information on how to prevent the problems caused by the spread of the aquatic invasive species and an overview of different eradication methods. At the end of the course, participants learned how to identify different crayfish species and recognise the Nuttall’s waterweed in the wild. Also, an overview of environmental DNA methodology was given. Altogether, 65 officials participated.
In practical training, participants learned how to use baited traps and identify different crayfish species and how to weigh and measure them. Altogether, 30 officials participated.