Distribution and abundance patterns of flatfishes in the Sado Estuary, Portugal

The flatfish community of the Sado estuary was studied based on beam trawl catches in six sampling areas. Temperature and salinity were recorded during surveys and sediment composition was determined at each sampling area. A total of 12 species were identified (1 Bothidae, 1 Pleuronectidae, and 10 Soleidae). Dicologoglossa hexophthalma (Bennett 1831), Microchirus ocellatus (Linnaeus 1758), and Synaptura lusitanica (Capello 1868) were new records to this estuarine system. Monochirus hispidus Rafinesque, 1814, was the most abundant species (about 80% of the total individuals caught). Community structure reflected both spatial and temporal patterns. A longitudinal abundance pattern was noticed with some species much more abundant in outer estuarine areas, namely M. hispidus, Arnoglossus laterna (Walbaum 1792), and Buglossidium luteum (Risso 1810), while others, such as Solea solea (Linnaeus 1758) and Solea senegalensis Kaup, 1858, presented the highest densities in inner areas. Besides temperature and salinity gradients, species distribution was also influenced by sediment composition. Seasonal variation was mainly determined by the different periods of juvenile peak abundance according to the species which emphasize the role of the estuary as a nursery ground for several flatfish species.