Abstract
Most studies on glass eel (Anguilla anguilla) migration are performed in natural estuaries, where they enter freshwater systems to live there for a period of years before they swim back again to the sea to reproduce. In these natural systems, river flows play a major role in attracting and directing migrating eels. However, coastal areas get urbanized more and more and characterized by anthropogenic barriers and hampered or artificial water flows. The effects of these flows on glass eel migration are poorly understood. Therefore, in this study glass eel were sampled at water pumping stations in a constructed part of the Rhine delta in the Netherlands. A mixed linear-effect model was used to determine effects of freshwater flows from water pumping stations on glass eel catch. We found that freshwater flows from water pumping stations had a significant but small effect on glass eel catch. Pumping activity had no significant effect on glass eel catch at sample locations with a continuous freshwater flow from fish passages. However, a low predictive value of the model and low numbers of individuals per sample prohibited strong conclusions on effects of anthropogenic freshwater flows on glass eel migration. More individual tracking techniques should be used to improve understanding migratory behavior of glass eel.
Highlights
River deltas around the globe are often densely populated areas (Syvitski and Saito, 2007)
We found that freshwater flows from water pumping stations had a significant but small effect on glass eel catch
Based on these results we propose that freshwater flows from both pumping activity and fish passages acts as orienting stimuli for glass eels, and that the continuous flows form the dominant stimulus if present
Summary
River deltas around the globe are often densely populated areas (Syvitski and Saito, 2007). Water storage and flood protection in such areas is regulated by dams and dykes, resulting in the obstruction of fish migration between freshwater and marine ecosystems. These anthropogenic barriers can physically block dispersal movements and affect natural salt- to freshwater gradients which fish need to during migration. The European eel (Anguilla anguilla) is a catadromous species that suffers from such obstructed migration. Some glass eels stay in the coastal areas, many try to enter the freshwater systems to live there for a period of years before they swim back to the sea to reproduce (Van Ginneken and Maes, 2005)
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