Seasonal changes in distribution and abundance of the fish fauna in the two estuarine systems of Strymonikos gulf (Macedonia, Greece)

Fifty-five fish species representing 20 families were recorded in the two estuarine systems of Strymonikos Gulf. Twelve of them were freshwater, while 43 were estuarine and near-shore marine species. Forty-three species were caught in the Strymon estuarine system, nine of which were freshwater (20.9\%), and 29 in the Rihios estuarine system, five of which were freshwater species (17.5\%). The euryhaline Pomatoschistus marmoratus was the dominant species throughout the whole sampling period in the Strymon system but the highest relative abundance was recorded for Liza ramada in May 1999 (4,738 ind./1,000 m(2)). The highest species richness in the Strymon system was observed in September 1997 with 16 species and the lowest in January 1998 with only two species. In the Rihios system, the freshwater species Rhodeus amarus was the most abundant one during the months of its presence and exhibited the highest CPUE value (38,833 ind./1,000 m2) recorded in this study. Species richness in the Rihios system peaked in July 1998 (18 species). Species richness and total abundance in the two sites were both found to increase during the warm seasons of the year (summer and autumn) following the water temperature fluctuations almost immediately. The seasonality of temperature changes was also found to determine the temporal changes of species composition of the overall fish community.