Invasive species are one of the greatest threats to biodiversity worldwide, and to successfully manage their introductions is a major challenge for society. Knowledge on the impacts of an invasive species is essential for motivating decision makers and optimally allocating management resources. We use a prominent invasive fish species, the round goby (Neogobius melanostomus) to objectively quantify the state of scientific knowledge on its impacts. Focusing on how native fish species are affected by round goby invasions, we analyzed 113 peer-reviewed papers and found that impacts are highly ecosystem and time scale dependent. We discovered round goby impacts to be profound, but surprisingly complex. Even if identical native species were affected, the impacts remained less comparable across ecosystems than expected. Acknowledging the breadth but also limitations in scientific knowledge on round goby impacts would greatly improve scientists' ability to conduct further research and inform management measures.

Non‐native invasive species are a major threat to biodiversity, especially in freshwater ecosystems. Freshwater ecosystems are naturally rather isolated from one another. Nonetheless, invasive species often spread rapidly across water sheds. This spread is to a large extent realized by human activities that provide vectors. For example, recreational boats can carry invasive species propagules as “aquatic hitch‐hikers” within and across water sheds. We used invasive gobies in Switzerland as a case study to test the plausibility that recreational boats can serve as vectors for invasive fish and that fish eggs can serve as propagules. We found that the peak season of boat movements across Switzerland and the goby spawning season overlap temporally. It is thus plausible that goby eggs attached to boats, anchors, or gear may be transported across watersheds. In experimental trials, we found that goby eggs show resistance to physical removal (90 mN attachment strength of individual eggs) and stay attached if exposed to rapid water flow (2.8 m·s−1for 1 h). When exposing the eggs to air, we found that hatching success remained high (>95%) even after eggs had been out of water for up to 24 h. It is thus plausible that eggs survive pick up, within‐water and overland transport by boats. We complemented the experimental plausibility tests with a survey on how decision makers from inside and outside academia rate the feasibility of managing recreational boats as vectors. We found consensus that an installation of a preventive boat vector management is considered an effective and urgent measure. This study advances our understanding of the potential of recreational boats to serve as vectors for invasive vertebrate species and demonstrates that preventive management of recreational boats is considered feasible by relevant decision makers inside and outside academia.

Managing invasive species is a major challenge for society. In the case of newly established invaders, rapid action is key for a successful management. Here, we develop, describe and recommend a three-step transdisciplinary process (the ''butterfly model'') to rapidly initiate action for invasion management. In the framing of a case study, we present results from the first of these steps: assessing priorities and contributions of both scientists and decision makers. Both scientists and decision makers prioritise research on prevention. The available scientific knowledge contributions, however, are publications on impacts rather than prevention of the invasive species. The contribution of scientific knowledge does thus not reflect scientists' perception of what is essentially needed. We argue that a more objective assessment and transparent communication of not only decision makers' but also scientists' priorities is an essential basis for a successful cooperation. Our three-step model can help achieve objectivity via transdisciplinary communication.

The vast majority of global freshwater ecosystems are small lakes with less than 100 m2 surface area. These lakes are often unconnected to other water bodies but frequently host fish populations. Existing explanations for how fish colonize such remote habitats often involve birds as vectors transporting fish eggs as propagules. In this study, we aim to quantify the prevalence of these explanations among relevant societal groups as well as their scientific knowledge basis. We analyzed entries in online blogs and forums and surveyed the opinions of local stakeholders and decision makers using a questionnaire. To collect published scientific knowledge, we conducted a structured literature review. Our results reveal a discrepancy between commonly found beliefs and the empirical knowledge supporting those beliefs: Dispersal of fish eggs by water birds was overall the most frequent explanation online and in the questionnaire. In the scientific literature, however, we found hardly any empirical research on passive fish egg dispersal. We propose research directions for how to close this gap of knowledge and suggest that future empirical studies on passive fish egg dispersal may be inspired by existing work on passive dispersal in aquatic invertebrates. Mitigating the belief‐evidence discrepancy on fish dispersal will be essential to better understand the patterns of fish biodiversity across landscapes, to counteract its losses, and inform management strategies for invasive fish species.

Abstract1. When prevention of invasive species' introductions fails, society faces the challenge to manage invasive species in an effective and efficient way. The success of this depends on biological aspects and on cooperation between decision makers and scientists.Using the case of the round goby Neogobius melanostomus, one of Europe's "worst invasive species", we propose an approach guiding scientists to co-produce effective and efficient population control measures in collaboration with decision makers.2. We surveyed the effectiveness, urgency and simplicity perceived by decision makers as well as the support of two population control options: removal of eggs and/ or adults. Using a field study and a dynamical population model, we investigated the effectiveness and efficiency for both options in different population contexts.3. Decision makers initially seemed to lack a clear preference for either control option.After being presented with preliminary field and modelling results, decision makers mostly approved measures being developed to implement the two control options.4. Starting population control early after detecting the species requires in total fewer years for eradication than controlling an established population: to reach an eradication success rate of 95%, 13 years for early start vs. 18 years for late start are needed when removing eggs and adults; when removing adults only, 20 vs. 29 years are needed. Removing eggs and adults combined results in a yearly effort of 5.01 h/m 2 , while removing adults only results in a yearly effort of 1.76 h/m 2 . Thus, removing adults only proves to be the most efficient option to eradicate the population. Nonetheless, considerable effort is needed: when removing less than 57% of the adult population, eradication is not feasible, even assuming low survival and fecundity rates for the population. Furthermore, inflow of new propagules renders eradication efforts ineffective. Synthesis and applications.Scientists who aim to support decision makers in finding an optimal control strategy for invasive species need to be able to provide scientific knowledge on effectiveness and efficiency of different options. For round goby and most non-native species, eradication is only feasible if started early in recently arrived populations and if inflow of new propagules can be prevented.