Vertical, lateral and diurnal drift patterns of fish larvae in a large lowland river, the Elbe

A ringnet was used to sample drifting fish quantitatively at distinct depth strata. This method was chosen to examine the lateral, vertical and diurnal drift patterns of fish fry during four sampling campaigns in May 1998 and 1999 in the middle Elbe River, close to the city of Schnackenburg (stream kilometre 475). It became apparent that the fish larvae concentrated mainly at the surface of the right side of the main channel. Fourteen fish species of the four taxonomic families Percidae, Cyprinidae, Osmeridae and Gadidae were caught. Percid fishes (pike-perch and perch) dominated the caught fish fry assemblage. Several environmental parameters were included in a direct gradient analysis in order to detect influencing variables. The main significant qualities were a temporal aspect and the shore distance. Other important influencing variables were suspended particular matter (SPM), fishing depth, time of the day, current velocity and the filtered volume. Negative correlations of abundance and shore distances and concentrations of SPM were found for several species as well as for the total abundance.