An integrated evaluation of the invasiveness risk posed by non-native crayfish in Lake Maggiore (Northwest Italy)

Risk analysis of non-native species invasions is one of the main challenges currentlyfaced by both scientists and environmental managers. In this study, the three riskscreening toolkits Harmonia+, Aquatic Species Invasiveness Screening Kit (AS-ISK)and Canadian Marine Invasive Screening Tool (CMIST) were used in conjunctionto evaluate the risk of invasiveness of eight non-native crayfish species (three extantalready present in the risk assessment area and five horizon, not yet reported, butlikely to arrive in the near future) for Lake Maggiore (Northwest Italy). Based onthe toolkit-specific risk scores for each species and their final ranking according tothe thresholds set for each toolkit: 1) Harmonia+ ranked five species with amedium-risk level of invasiveness and three with a low-risk level; 2) AS-ISKranked all species as high risk; 3) CMIST ranked six species as high risk and two asmedium risk. By combining the risk scores from the three toolkits and setting anad hoc threshold, extant horizon calico crayfish Faxonius immunis, spinycheekcrayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swampcrayfish Procambarus clarkii and marbled crayfish Procambarus virginalis were rankedas high risk, whereas horizon Australian red claw crayfish Cherax quadricarinatus,yabby Cherax destructor and Danube crayfish Pontastacus leptodactylus wereranked as medium risk. It is anticipated that the findings of this study will helpinform managers about the proper implementation of non-native speciesmanagement strategies for the Lake Maggiore watershed