Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive <em>Silurus glanis</em> L. in a Deep, Large and Oligotrophic Lake (Lake Maggiore, North Italy)

Abstract

Ecological information of invasive alien species are crucial for their effective management. How-ever, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore where the species is present since 1990 but no scientific infor-mation are available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. NPUE and BPUE (individuals and biomass (g) per unit effort (m2)) of catfish was generally higher in littoral (NPUE &amp;gt; 0.01; BPUE &amp;gt; 96) than pelagic habitats (NPUE &amp;lt; 0.009; BPUE &amp;lt; 114) but catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded belonging to12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad and roach) whilst the diet of littoral catfish was more variable, and was dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake&amp;rsquo;s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake&amp;rsquo;s fishery.