Diel differences in the exploitation of shallow inshore habitats by three small bottom-dwelling fishes with implications for their monitoring in a large lowland river

Sampling small-bodied fish species in large lowland rivers poses numerous difficulties often resulting in the underestimation of their true distribution and abundance. Some of these drawbacks might be overcome by using additional sampling gears and adapting sampling strategies to the biological specifications of the target species. The results of a two-year, repeated survey on a single location on the Vistula River (southern Poland) revealed that nighttime beach seining proved to be very effective in collecting specimens of three imperiled species: Romanogobio belingi, Romanogobio kesslerii, and Sabanejewia baltica. It was found that these species were 4.3-8.8 times more abundant in nighttime than in daytime collections. The abundance of all three species peaked at dusk and gradually decreased in subsequent hours. In conclusion, nighttime beach seining is recommended as a supplementary sampling technique for small bottom-dwelling fish species in large lowland rivers.