Native and non-native fish across aquatic habitats in the Ebro Delta

Abstract

We describe the variability in the composition of fish communities in the Ebro Delta (NE Iberian Peninsula) and report the habitat preferences of the most common species. The Ebro Delta is a large coastal wetland that has been intensively modified, mainly for rice cultivation involving the input of a large amount of low-conductivity waters into an originally brackish and saline system. We de- fined nine main habitat types within the Ebro Delta (the river, inflow channels, rice fields, outflow channels, springs, marshes, lagoons, lagoon mouths and bays) and sampled fish communities in them by establishing 376 sampling sites, in which we set 1431 fyke nets. We captured more than 120,000 fish belonging to 52 species, of which 37 were native and 15 were non-native. The ichthyofauna of the Ebro Delta is strongly structured in relation to habitat type, following variations in water salinity, and there is a clear segregation of native and non-native fish species. Native species are clearly dominant in the more saline habitats, namely bays, lagoons, lagoon mouths and marshes, while non-natives dominate the aquatic habitats related to rice cultivation (inflow and outflow channels as well as rice fields). Freshwater springs are dominated by non-natives in terms of abundance, but not in terms of richness. Since the decline and loss of native fish species in the Ebro Delta seems linked to the massive inflow of low- conductivity waters for rice irrigation, fish conservation must focus in reducing the influence of those outflows on the remaining natural and semi-natural wetlands.