Response of seaward-migrating European eel (Anguilla anguilla) to manipulated flow fields.
Bottom Line: Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures.This study highlights the importance of hydrodynamics in informing eel behaviour.This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.
Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modeled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory 'search' behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.
No MeSH data available.
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Mentions: In the CH treatment, switch points were distributed throughout the intake channel and area immediately upstream, whereas under the UL treatment they tended to be concentrated within a narrow band across the channel width (figure 4). Mean depth-averaged flow velocities at the points of behavioural switch ranged from 0.034 to 0.72 and from 0.14 to 0.67 m s−1 for UL and CH treatments, respectively. The median depth-averaged water velocity at the point of switch was higher in the UL compared with the CH treatment (0.67 and 0.57 m s−1, respectively; Mann–Whitney U = 2.68, p = 0.006). Velocity acceleration at the point of switch ranged from 0.001 to 0.051 and from 0.002 to 0.083 for UL and CH treatments, respectively, and did not vary among treatments (Mann–Whitney U = 1.28, p = 0.21).Figure 4.
No MeSH data available.