Diel pattern of utilization of shallow sandy habitats by fishes in temperate lowland rivers of various size

• Main Authors: Michał Nowak, Ján Koščo
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2015-12-01
• Series: Frontiers in Marine Science
• Subjects: Temporal variations; Fish assemblages; Riparian zones; Lowland rivers; Diel migrations; Riverine system
• Online Access: http://journal.frontiersin.org/Journal/10.3389/conf.FMARS.2015.03.00259/full

Diel changeover of fish assemblages in inshore habitats of lowland rivers is a world-wide phenomenon. Predator avoidance, resources partitioning and differences in food availability are usually given as main drivers of variation observed in fish presence. Researches performed in different European rivers have led to contradictory results, indicating either nocturnal or diurnal increase in species richness and abundance. It has been hypothesized that relative differences in availability of certain type of habitats (inshore vs. offshore) resulting from various size (discharge) of rivers might explain these discrepancies. We performed a series of 24-h samplings at three rivers differing in discharge: Vistula (~120 m3s-1), Nida (~22 m3s-1), and Czarna Nida (~5 m3s-1). Fish were caught by fine-meshed beach seine nets (6 × 2 m or 15 × 3 m) every 3 h in May, July/August and November 2014 and February 2015. We caught 1792 specimens classified into 24 species. In all instances the communities were dominated by small-sized cyprinids (dace, bleak, common gudgeon, whitefin gudgeon, and roach). NMDS ordination indicated a clear distinction between diurnal and nocturnal samples. PERMANOVA supported significance of time of day on the structure of fish assemblages. Despite seasonal modifications, in all three rivers an uniform pattern of diel changes in the composition of fishes occurred. Both species richness and abundance noticeably increased just after the dusk, then consecutively decreased towards the dawn and remained at constantly lower levels during the daytime. This suggests that overall changeover of fish assemblage reflects interspecific interactions ongoing in a given stream section and species composition might explain differences observed between various rivers better than the river discharge.