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)

Vanessa De Santis,Pietro Volta

doi:10.3390/w13182549

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.

Highlights

2019 to January 2020, in the occasion of a special permit released by the fishing authorities in favor of professional fishermen, which provided the experimental use of large mesh temperature probe, with data registered across multiple depths, at a speed of 1 m/s, and a frequency of 200 milliseconds
The fish ranged in total length between 67 cm and 150 cm and in estimated weight between 1932 and 22,940 g, with the largest fish found in the pelagic habitats and the smallest in the littoral one (Table 1)
In late autumn/early winter 2019, the relative abundance and biomass of pelagic catfish were lower than that of littoral catfish, and generally higher in November than in December and January. These results suggest that there is a potential segregation in habitat occupation between size classes, with larger individuals (>100 cm) prevailing in the open waters and medium-sized ones (

Summary

Introduction

The impacts of biological invasions are highly context-dependent [8,9,10], triggering the predictions of the consequences of successful invasions [11]. This may be true when the invader colonizes habitats that are different than those that are usually occupied both in the native and invaded ranges (i.e., novel habitats). Studies aimed to gain ecological information on invasive populations in novel environments are of great value to create data on which theoretical frameworks and hypotheses may be developed and tested [8], to extend our understanding of IAS impacts and plan their management

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Results

Discussion

Conclusion