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

Abstract

The ecological features of invasive alien species are crucial for their effective management. However, 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 information is 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. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m2), respectively) of catfish were generally higher in littoral (NPUE > 0.01; BPUE > 96) than in pelagic habitats (NPUE < 0.009; BPUE < 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 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 dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.

One Year Monitoring of Ecological Interaction of Silurus glanis in a Novel Invaded Oligotrophic Deep Lake (Lake Maggiore)

“…A total of 60 fish species, of which cyprinids are predominant, were identified in the diet of S. glanis [2,7,9], and this study added two more fish species, P. bonelli and S. fluviatilis, as well as Corbicula sp. The diet of S. glanis in the Lake Maggiore described here was based on six fish species (A. agone, A. alburnus, P. bonelli, P. fluviatilis, S. fluviatilis and R. rutilus), and Coregonus sp.…”

“…The first certain catch of an individual S. glanis was reported in the late 1960s in the River Po basin [3], of which catches became more frequent from the following decades. From the 1980s, the presence of S. glanis can be considered common and continuous in the Po valley, artificial channels included [5], and nowadays it is well-established in the eutrophic sub-alpine lakes, such as Lake Varese, Lake Comabbio, and Lake Monate [6,7]. The first reports of its presence in the oligotrophic and deep Lake Maggiore dated back to the early 1990s [8], which is now successfully colonised by S. glanis, demonstrating its remarkable ecological plasticity.…”

“…Notably, very little is known about oligotrophic and deep lakes (such as the Lake Maggiore), an ecosystem very different from its original (big rivers), and only about a limited period (wintertime) [7]. Difficulties of sampling lentic ecosystems, especially big lakes, has led to a scarcity of data, with only one recent study which started to fill the gap on the ecology of S. glanis in this novel environment [7].…”

“…Notably, very little is known about oligotrophic and deep lakes (such as the Lake Maggiore), an ecosystem very different from its original (big rivers), and only about a limited period (wintertime) [7]. Difficulties of sampling lentic ecosystems, especially big lakes, has led to a scarcity of data, with only one recent study which started to fill the gap on the ecology of S. glanis in this novel environment [7]. Taking advantage of support by professional fishermen, and the experimental usage of large mesh gillnets suitable for catching S. glanis, the authors provided a first glimpse into the trophic interaction of S. glanis with the lake community, but only over a limited period of time (wintertime) [7].…”

“…Difficulties of sampling lentic ecosystems, especially big lakes, has led to a scarcity of data, with only one recent study which started to fill the gap on the ecology of S. glanis in this novel environment [7]. Taking advantage of support by professional fishermen, and the experimental usage of large mesh gillnets suitable for catching S. glanis, the authors provided a first glimpse into the trophic interaction of S. glanis with the lake community, but only over a limited period of time (wintertime) [7]. Thus, for setting management plans, it is essential to understand how the species is able to exploit the new ecosystem in its entirety with regard to both the pelagic and littoral habitat throughout the year.…”