Invasive Ponto-Caspian gobies in the diet of piscivorous fish in a European lowland river

Abstract

Between 2012 and 2013, we estimated predation of non-native Ponto-Caspian gobies by native piscivores in a European mid-sized lowland river by analysing 268 digestive tracts from six native species: perch Perca fluviatilis, burbot Lota iota, European catfish Silurus glanis, pike Esox lucius, Volga zander Sander volgensis and European zander S lucioperca. Species closely associated with the rip-rap bank had a higher proportion of gobies in their diet (burbot 66 % weight proportion [%m], >= 1+ perch 53 %m, = 1+ perch showed positive selection for tubenose goby Proterorhinus semilunaris, while burbot and pike showed a preference for round goby Neogobius melanostonius, though the values may have been affected by the relatively low sample sizes. We estimate that predators consumed approximately 52 % of goby biomass over our study stretch each year (burbot 41%, <= 2+ European catfish 5 %, pike 3 %, all other predatory species <2 % each), confirming that gobies rapidly become an important component in the aquatic food web of invaded rivers, both by preying on aquatic invertebrates and as prey to native predators (particularly burbot). On the other hand, our data suggest that the long-term impact on European goby populations, at least in our study area, has been limited, as indicated by their ongoing spread.