engleski

Seasonal changes of species occurrence, abundance and diversity in Neretva River delta (Croatia) fish populations

The river mouth environments (estuaries, deltas), as areas of marine and freshwater dynamic contact have a high biological productivity and supports a wide faunal diversity. This areas performs a crucial role in the life-cycle of many fishes. Fish assemblages there are very complex and varied, composed of true estuarine, amphihaline or euryhaline species. The Neretva river delta is among the biggest river mouth environments in the eastern Adriatic Sea and has been recognised as significant in Mediterranean area for its species richness and high degree of endemism of freshwater fishes. Moreower, it is noteworthy that several new fish species have been described from this drainage basin during the last decade. The aim of the present work is to provide an initial reference document on the specific composition of its fish assemblage. Eighty-two fish species representing 32 families were recorded in the Neretva river delta area. Sixty-nine of them (84, 14%) were estuarine and near-shore marine species, while 13 were freshwater species (15, 85%). The Atherinidae was the most abundant family (67.89%), followed by Mugilidae (23.32%), while Sparidae (1.14%), Labridae (1.82 %) and Gobiidae (0.96%) were under-represented. However, Gobiidae represent the most diverse family followed by Sparidae, Mugilidae and Soleidae. Young-of-the-Year fishes (Y-O-Y) in the littoral zone of the investigated area comprises a highly diverse fish community composed of 68 species representing 28 families. Moreover, more than 65% (44 species) of the Y-O-Y species caught are among the species that form the main targets for commercial fisheries in the southern Adriatic. This fact emphasises the importance of the delta shallow water habitats as a nursery ground for the fish. Five most abundant species included euryhaline (Atherina boyeri, Pomatoschistus marmoratus, Liza saliens, L. aurata, L. ramado). A. boyeri was the dominant species throughout the whole sampling period, but the highest relative abundance was recorded for Liza saliens in August-September period (69%). The highest species richness was observed in August with 31 species and the lowest in January with only 8 species. Collected species showed marked seasonal patterns of occurrence with the majority of each usually being caught within two month periods. Species richness and to even greater extent the total abundance of fish, underwent consistent seasonal trends and were found to increase during the warm seasons of the year (summer and autumn) following the water temperature fluctuations. These changes were largely attributable to a sequential immigration and emigration of different species, particulary estuarine-dependent marine species and also partially driven by variations in water temperature as well as salinity of freshwater discharge from the river.

Estuaries fish; Neretva river delta; Seasonality

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