Frontiers in Marine Science (Dec 2015)
Seasonal changeover of fish assemblages in a medium-sized temperate lowland river
Abstract
Seasonal variations in the structure of riverine ichthyofaunas are widely known and have been often commercially exploited. Though, there is only little quantitative data on the community level. We performed a 3-year-long study on the Nida River, a 154-km-long (drainage area of 3844 km2, mean discharge of 22 m3s-1) lowland tributary of the Upper Vistula (SE Poland). Fish were sampled by continuous boat electrofishing at 21 sites within the 100-km-long middle and lower stretch of the river. Surveys were performed every April, July and October in 2012–2014 period. A total of 20399 specimens of 38 species and 2 intergeneric hybrids were caught. Species richness for single survey varied from 24 (summer 2014) up to 32 (spring 2012 and 2013, summer 2012). Abundance varied from 1042 (autumn 2014) up to 3571 specimens (summer 2012). Fauna exchange index among the seasons amounted 0.05–0.21. The composition of the ichthyofauna was most similar between spring and autumn 2013 (T = 0.05) and between spring 2012 and autumn 2013 (0.08). The largest differences occurred between summers of 2012 and 2014 and between spring and summer of 2014 (0.21 in both cases). Composition of the fish fauna was most stable in 2013 (T < 0.10), whereas the largest variation was recorded in 2014 (0.16–0.21). DCA results suggested that full changeover of the fish assemblage did not occurred at any site. NMDS distinguished most spring and autumn samplings from results obtained during the summer expeditions. It seems that water temperature (related to oxygen level) and water discharge (availability of various habitats) are the most important factors shaping the structure of fish assemblages in the Nida River. This study was supported by the project no. 2011/01/N/NZ9/02367 of the National Science Centre of Poland.
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