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 currently faced by both scientists and environmental managers. In this study, the three risk screening toolkits Harmonia+, Aquatic Species Invasiveness Screening Kit (AS-ISK) and Canadian Marine Invasive Screening Tool (CMIST) were used in conjunction to evaluate the risk of invasiveness of eight non-native crayfish species (three extant already present in the risk assessment area and five horizon, not yet reported, but likely to arrive in the near future) for Lake Maggiore (Northwest Italy). Based on the toolkit-specific risk scores for each species and their final ranking according to the thresholds set for each toolkit: 1) Harmonia+ ranked five species with a medium-risk level of invasiveness and three with a low-risk level; 2) AS-ISK ranked all species as high risk; 3) CMIST ranked six species as high risk and two as medium risk. By combining the risk scores from the three toolkits and setting an ad hoc threshold, extant horizon calico crayfish Faxonius immunis, spinycheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swamp crayfish Procambarus clarkii and marbled crayfish Procambarus virginalis were ranked as high risk, whereas horizon Australian red claw crayfish Cherax quadricarinatus, yabby Cherax destructor and Danube crayfish Pontastacus leptodactylus were ranked as medium risk. It is anticipated that the findings of this study will help inform managers about the proper implementation of non-native species management strategies for the Lake Maggiore watershed.