The 0+ fish community structure in a large lowland river: first results of a study from the River Oder

Abstract

The 0+ fish community structure of the River Oder was studied in the Polish-German National Park 'Unteres Odertal' near Schwedt (Germany) during the summer of 1997. Fish were sampled in five different types of mesohabitat ('Riprap', 'Connected Backwater', 'Navigable Side-canal', 'Deep Groynefield', 'Meander Inside Groynefield') using Point Abundance Sampling by electrofishing. In each mesohabitat, 50 random point samples were taken during each sampling period. Although a total of 23 species of 0+ fishes and one hybrid were caught during this study, only a few eurytopic species occurred in high abundances. The German stretch of the Polish-German National Park provides a large number of poorly structured mesohabitats and only very few adequate nursery habitats for rheophilic species. Thus the progeny of these species was restricted to structurally more complex groynefield-mesohabitats characterized by sandy substrates and a gentle slope. In order to improve the conditions for the early life stages of fish in the National Park, the re-establishment of a natural flood regime on the German side is highly desirable.