Potential effects of navigation-induced wave wash on the early life history stages of riverine fish

Navigation alters the ecology of large inland waterways via engineering and more directly by emission of hazardous substances and wave wash. We investigated the potential effects of the latter on the early life history stages of riverine fish, which have their nursery zones generally located in shallow areas with low current and higher water temperatures. Ship induced wave wash causes the following impacts on fish during their early life history stages: i) short-term dislocation of suitable larval and juvenile fish habitats due to wake and splash; ii) water velocities during ship passages frequently exceed maximum swimming performances of 0+fish; and iii) suspended solids concentrations in the inshore habitats increase dramatically and limit the foraging efficiency of young of the year fish (YOY). In situ conditions during ship passages were investigated in three different inshore zones of the Austrian Danube with respect to wake and splash patterns, changes in water velocity and turbidity. These navigation induced conditions in the main nursery zones of riverine fish were set in comparison to results on swimming performances and capacities of larval and juvenile fish obtained in experimental studies. Engineering in large river systems in Europe and USA has resulted in a strong reduction of natural shoreline structures. Within this altered situation, navigation induced wave wash has a strong and cumulative effect on riverine fish recruitment and, hence, contributes to the general ongoing decline of native fish stocks in inland waterways. These aspects require particular consideration in river restoration programs to mitigate the effects of navigation, especially with respect to the intended expansion of European water ways within EC projects like TEN-T and NAIADES.