Recent invasions by non-native gobiid fish species that are ongoing in the Western European rivers Rhine and Meuse,
will lead to interactions with native benthic fish species. Since both non-native gobiids and native benthic species are bottom
dwelling species with a preference for shelter during at least part of their life cycle, it is likely that competition for shelter will
occur between these non-native and native species when shelter is a limiting factor. To investigate the importance of this mechanism
for species replacements, various habitat choice experiments were conducted between two common native benthic fish species
(Cottus perifretum and Barbatula barbatula) and four invasive non-native gobiid species (Proterorhinus semilunaris, Neogobius
melanostomus, N. kessleri and N. fluviatilis). The first series of single specimen experiments determined the habitat choice of
each individual fish species. In a second series of competition experiments, shifts in habitat choice in comparison with the previously
observed habitat choice, were determined when a native benthic fish species co-occurred with non-native gobiid species.
Native C. perifretum displayed a significant shift in habitat choice in co-occurrence with the gobiids N. kessleri or P. semilunaris.
C. perifretum was outcompeted and moved from the available shelter place to less preferred habitat types. During the competition
experiments no change in habitat choice of B. barbatula was shown. Our study therefore suggests that competition for shelter is
likely to occur in rivers invaded by N. kessleri and P. semilunaris at sites where shelter is limiting.