Fish migration may be hampered by a range of physical barriers. That non-physical barriers such as sudden changes in water quality may also serve as barriers is often stated, but only very few studies address this issue. This study focusses on linking the behavioural response of silver eel and river lamprey when encountering a waste water plume (effluent) in field situations. Individual fish movements were tracked by means of acoustic telemetry in 2D (in 2009) and in 3D (in 2010) at a location surrounding a waste water outlet in the Eems-canal near Groningen. Plume dynamics were modelled and calibrated by Deltares and used to directly link to individual movement patterns of fish. In both years, 20 silver eels (downstream migration) were tagged and in 2009 also 13 rvier lamprey (upstram migration) were tagged. In total, 37 out of 40 silver eels entered the 2D – 3D study site. Of these, 57 % showed avoidance behaviour when encountering the plume, 43 % were indifferent to the plume and no attraction to the plume was observed. Avoidance behaviour varied from moving away from the plume but continuing the migration, to returning and not be detected again, thereby possibly ceasing their migration (3 out of 37). This indicates that waste water plumes may serve as non-physical barriers to migrating silver eel. Given the very dynamic nature of the plume in Groningen, even if waste water plumes serve as non-physical barriers for some of the migrating eels, numerous migratory windows are available in time and in water depths, when the plume is minimal or limited to one shore. Therefore it is estimated that the barrier effect of waste water plumes might be small, although delays in migration are likely to occur. Our findings may be used for management purposes. The occurrence of a behavioural avoidance response of approximately half of the eels opens up the possibility to manipulate plumes in order to ‘steer’ silver eels to a preferred direction, e.g. away from potential hazardous locations.
|Place of Publication||IJmuiden|
|Number of pages||57|
|Publication status||Published - 2011|
|Name||Report / IMARES Wageningen UR|
- sewage effluent
- animal behaviour
- fish migration