Abstract
AbstractEuropean eel, Anguilla anguilla L., migrating to the sea encounter many man‐made structures that can hamper and delay migration or induce mortality. Studying small‐scale behavioural movements in front of these man‐made structures could provide insight in further mitigating adverse effects. The behaviour of eel approaching a trash rack in front of a large pumping station was investigated using a dual‐frequency identification sonar (DIDSON). Eels approaching the trash rack swam through the rack (40.5%) but also showed turning behaviour at (44.7%) or in front of the rack (14.7%). Eels approaching the rack had varying body positions, predominantly head or tail first, but also curled up into a ball or drifted sideways. After turning in front or at the trash rack, eels showed upstream and downwards swimming towards the canal bottom. The results suggest a stepwise response to potential cues, when firstly the body position is changed in such a way that secondly, later on, enhances eventual fast upstream escapement when perceived necessary. Implications for management of these behavioural observations are discussed.
Highlights
European eel, Anguilla anguilla L., is in strong decline since the 1970s (ICES, 2018) as a result of various factors, such as migration barriers, fisheries, habitat loss and deterioration, pollution, parasites and changes in oceanic conditions (Buysse, Mouton, Stevens, Neucker, & Coeck, 2014; Drouineau et al, 2018; Feunteun, 2002; Moriarty & Dekker, 1997; Palstra, Heppener, Ginneken, Székely, & Thillart, 2007; Westerberg et al, 2018)
European eel migrates from inland waters to the sea during their adult stage to head for their spawning area in the Sargasso Sea (Tesch, 2003)
Differences in swimming depth of the eels when entering the dual-frequency identification sonar (DIDSON) field of view, at or near the trash rack and leaving the field of view (Figure 3), showed no significant change in swimming depth for eels going through the trash rack towards the turbine or eels approaching the trash rack before turning near or at the trash rack (Table 2)
Summary
Anguilla anguilla L., is in strong decline since the 1970s (ICES, 2018) as a result of various factors, such as migration barriers, fisheries, habitat loss and deterioration, pollution, parasites and changes in oceanic conditions (Buysse, Mouton, Stevens, Neucker, & Coeck, 2014; Drouineau et al, 2018; Feunteun, 2002; Moriarty & Dekker, 1997; Palstra, Heppener, Ginneken, Székely, & Thillart, 2007; Westerberg et al, 2018). European eel migrates from inland waters to the sea during their adult stage (silver eel) to head for their spawning area in the Sargasso Sea (Tesch, 2003). During the migration, they encounter man-made structures such as pumping stations, sluices, weirs and hydropower stations that obstruct their migration route. Fish migration can be hampered by pumping stations by inducing additional mortality when the turbines are not designed in a fish-friendly manner (Buysse, Mouton, Baeyens, & Coeck, 2015; Fjeldstad, Pulg, & Forseth, 2018) or by delaying fish resulting in additional energy loss and potential mismatch in. The delay in migration could result in higher predation and fishing risk, higher risk of contracting diseases (Calles et al, 2010; Jansen, Winter, Bruijs, & Polman, 2007; Lennox, Økland, Mitamura, Cooke, & Thorstad, 2018; Verhelst, Buysse, et al, 2018) or eel could postpone their migration (Durif, Dufour, & Elie, 2005; Jansen et al, 2007; Winter, Jansen, & Bruijs, 2006)
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