Non-native goby species in Switzerland : impacts and management

Non-native invasive species are one of the main reasons for biodiversity decline. They can disrupt ecosystem functioning and cause enormous ecological and economic damage. To manage non-native invasive species is a challenge asking for the cooperation of practice and research. In my thesis, I focus on two recent invaders in the High Rhine, bighead goby (Ponticola kessleri) and round goby (Neogobius melanostomus). These two small bottom-living fish species belong to a group of Ponto-Caspian gobiid species that were introduced probably by ballast water to Europe and North America in the last few decades. In the High Rhine in Basel, they were first detected 2011 and immediately caught the attention of decision makers. Throughout my thesis, I highlight the importance of a transdisciplinary process that can guide researchers in collaboration with decision makers to co-produce measures for an effective and efficient invasive species management. The first step in this transdisciplinary process is to objectively assess priorities and contributions of both scientists and decision makers, followed by an open communication about these priorities and contributions. After such a clarification, ideally, a joint research paradigm for invasive species management can be developed.
By applying this process to invasive gobies, several research priorities have emerged in the first step during a workshop together with decision makers: both scientists and decision makers agree that research on management measures such as prevention is of highest priority. A systematic literature review showed that this priority is met by a lack of scientific knowledge on management measures and by an abundance of scientific knowledge on impacts.
Scrutinising the scientific knowledge on impacts revealed that the strength and the direction of the impacts strongly depend on local conditions. Thus, the knowledge on impacts in other systems is of limited use if stakeholders want to base their management decisions on expected impacts in their ecosystem of concern, because invasive species’ impacts are ecosystem- and time-dependent. More important is knowledge on preventive management such as e.g. cleaning of boats. If such preventive measures are intended, rapid action should be initiated despite incomplete knowledge about an approaching invader’s impacts.
If the preventive approach failed, as is already the case for at least part of the High Rhine, eradication or containment by removing goby eggs and adults can be management alternatives. Using a field study and a population model, I found that eradication is only feasible if started immediately after the introduction of the population and if inflow of new propagules can be stopped. Because measures to control an already established population need an extremely high amount of effort, prevention should be favoured and eradication should only be attempted in very valuable habitats. The findings from my thesis form the basis of a “Goby Action Plan” to implement management measures along the lines of decision makers’ valuation and scientific advice.