Abundant feasts: Favoring the invasion of an American fish species in Europe

Abstract

Abstract The ready availability of abundant food sources can be a key factor in the success of biological invasions. This study provides information about feeding habits, dietary niche, and seasonal and ontogenetic diet changes of the American invasive weakfish Cynoscion regalis in the Gulf of Cádiz, where its population is increasing exponentially since 2011 when its presence was reported in the area. By content analysis of 340 stomachs, we assessed the diet composition, prey diversity and abundance of juveniles and adults present in the Guadalquivir River Estuary. Fish and crustaceans accounted for more than 90% of their diet. Mysids are the main food intake for juveniles and piscivory becomes more important as C. regalis grows in size. Stomachs were significantly fuller during the summer and autumn months, coinciding with the higher abundance of small pelagic fish during that time in the estuary, especially the anchovy Engraulis encrasicolus, the main prey consumed through all months of the year, that showed a consumption peak in September and October. Adults also show significant monthly variations in the diet composition (P < 0.01) respect to Total Length. Juveniles show a specialist behaviour feeding almost exclusively on Mesopodopsis slabberi, while adults show a mixed feeding strategy. This research constitutes a comprehensive study of weakfish diet along the year in the non-native area, including for the first time, juvenile’s stages.