The opportunistic trophic behaviour of the European catfish (Silurus glanis) in a recently colonised large peri‐alpine lake

Abstract

The European catfish (Silurus glanis) recently colonised large peri‐alpine lakes where its exploitation of the different lake habitats (i.e. littoral, pelagic and deep benthic) may be supported by interindividual trophic variations fostering its establishment. We investigated the prey and lake habitats supporting S. glanis diet in the largest French peri‐alpine lake (Lake Bourget) based on the contents of 231 stomachs combined with 217 individual stable isotope measurements (δ13C and δ15N). The interindividual diet variations in stomachs and isotopes were quantified to identify individual specialisation within the population. The effects of body size on trophic characteristics were also explored. For most individuals, a major reliance on littoral resources was determined based on both stomach contents (86% of prey items) and stable isotopes using Bayesian mixing models (BMMs; 70.3 ± 9.6% contributions of the littoral resources). However, pelagic and deep benthic prey (e.g. whitefish and burbot) were also identified, and BMMs indicated significant contributions of pelagic and deep benthic resources to S. glanis diets (15.8 ± 5.3% and 13.9 ± 5.2% respectively). Interindividual variations based on stomach contents were much higher than those estimated from stable isotopes, supporting an opportunistic trophic behaviour; although the population strongly relied on crayfish, perch and roach. Body size explained a minor fraction of S. glanis trophic characteristics, suggesting that ontogeny does not strongly structure the current population diet. Our results underscore the feeding plasticity of S. glanis, revealing that besides the littoral habitat, this invader exploits resources from all habitats in large peri‐alpine lakes (deep benthic and pelagic). Therefore, its establishment in these ecosystems may represent a growing threat to resident species, especially if the population and individual body size increase in the near future.

Combining food web theory and population dynamics to assess the impact of invasive species

“…Specifically, the decrease in abundance of invertebrate SC (e.g., Ephemeridae) and small fish SC (e.g., Blenniidae) would be caused by S. glanis of 40 cm while the decrease of larger fish SC (e.g., Percidae) and large invertebrate SC (e.g., crayfish) would mostly result from the invasion of larger S. glanis (85 cm and 150 cm). Percidae and crayfish represented consistent fraction of S. glanis diet in empirical studies (Carol et al, 2009;Ferreira et al, 2019) and the presence of S. glanis was suspected to alter their abundance in few ecosystems (Copp et al, 2009;Guillerault et al, 2015;Vagnon et al, 2022), suggesting plausible predictions from our approach. Competition between S. glanis and large fish SC was also suggested to negatively alter fish abundances and particularly dampened the abundance of the resident apex predator (Esocidae; high diet overlaps for S85 and S150) while fish SC with weak diet overlaps (Schoener index < 0.1) were poorly or not impacted.…”

“…These results underline the 10.3389/fevo.2022.913954 ability of S. glanis to cause top-down trophic cascades by regulating mesopredator abundances while suggesting that it may not be a major source of species extinctions, similarly to empirical studies conducted in reservoirs, lakes and rivers (Copp et al, 2009;Vejřík et al, 2017). In fact, the opportunistic feeding behavior of S. glanis (Copp et al, 2009;Cucherousset et al, 2018;Vagnon et al, 2022) could foster its reliance on a diversified prey set limiting strong interaction strengths usually known to induce stronger impacts on resident species populations than weak interactions (Terraube et al, 2011;Wootton and Stouffer, 2016).…”

Global introductions and environmental impacts of freshwater megafish

“…Due to their large body size, these harmful impacts are often the result of predation on smaller freshwater species. Indeed, many freshwater megafish species such as blue catfish, flathead catfish, African catfish, and wels catfish, are predators with a wide prey spectrum enabling them to affect many different taxonomic groups of native species (Carol et al., 2009; Cucherousset et al., 2012; Hammerschlag et al., 2019; He et al., 2024; Martino et al., 2011; Vagnon et al., 2022; Winemiller et al., 2015). For example, wels catfish prey on birds, fish, reptiles, mammals, amphibians, and insects (Carol et al., 2009; Cucherousset et al., 2012; Martino et al., 2011; Vagnon et al., 2022).…”

Interannual variability in the trophic niche of young‐of‐year fish belonging to four piscivorous species coexisting in a natural lake

“…Although these species can frequent multiple habitat types with seasonal variations (e.g. De Santis & Volta, 2021; Vagnon et al, 2022), they have some habitat preferences. Pike are mainly littoral and prefer vegetated areas (Chapman & Mackay, 1984; Craig, 1996; Jepsen et al, 2001) while pikeperch are nocturnal and mainly frequent the pelagic area (Huuskonen et al, 2019; Vehanen & Lahti, 2003).…”

“…In general, pikeperch is a piscivorous specialist (Huuskonen et al, 2019; Kangur & Kangur, 1998) that occupies the highest position in the trophic web (Pérez‐Bote & Roso, 2012), often higher than pike, which is also mainly piscivorous but more plastic (Craig, 2008; Kopp et al, 2009; Pedreschi et al, 2015). By contrast, perch is a generalist species and catfish opportunistic (Dörner et al, 2003; Schulze et al, 2012; Vagnon et al, 2022; Vejřík et al, 2017). These species also undergo some ontogenetic variations in diet.…”