34 years of investigation in the Rhine River at Ludwigshafen, Germany – trends in Rhine fish populations

Especially rheophilic fish species such as asp Aspius aspius (L.), barbel Barbus barbus (L.) and nase Chondrostoma nasus (L.) which were rarely found during the first catching period (1976 – 1980) were then caught in increasing numbers and abundance. Starting with 6 to 8 fish species per catch in the 1970s, the number has raised to 25 fish species (including 4 neozoans) in recent catches. Overall 31 species have been monitored in the last 34 years.This indicates good river water quality and an increase in fish biodiversity along the BASF site at Ludwigshafen over the last three decades. However, focussing on the past decade, new invasive fish species such as the sunfish Lepomis gibbosus (L.) and three gobies have been found in high densities along the river banks which might have an impact on the fish population in this area in the future.The Rhine is one of the most “mainstreamed” rivers in Europe, balancing several aspects including transport, drinking water supply, cooling water, energy reservoir, as well as being used for effluent disposal, and providing leisure activities such as fishing (Figure 1). The former structure of the river itself had been dramatically changed as a result of the invasive canalisation project by Tulla at the beginning of the 19th century, affecting the entire river from Rheinfelden (Switzerland) to Rotterdam (The Netherlands) [1]. Based on historical fishing data, it can be concluded that this structural change also influenced the fish fauna of the Rhine [2-9]. However, especially after the Second World War, a drop in both fish species number and abundance was observed due to the contamination of the river as a consequence of increasing industrialisation and further urbanisation of the Rhine valley [10-12]. In the 1970s water quality dropped to its lowest levels resulting in the implementation of various Rhine restoration programs, including the reintroduction of endangered and/or temporarily extinct fish species [13-16]. One of the com