Safe two-way migration for salmonids and eel past hydropower structures in Europe: a review and recommendations for best-practice solutions

Abstract

This review provides a summary of knowledge on two-way fish migration of salmonids and eels past hydroelectric plants in Europe. On the basis of a summary of international literature, general designs and recommendations for best practices for fish-pass facilities are provided. The review is part of the Norwegian SafePass project, which focuses on Atlantic salmon, brown trout, grayling and European eel. According to recent international recommendations, many existing European fishways for upstream migration do not have an optimal design. This is especially evident for denil and pool-and-weir fishways in inland areas with species such as grayling and brown trout. Based on the review, we generally recommend (1) using ramps, nature-like channels and vertical-slot fishways for these species and (2) reducing water drop between the pools in pool-and-weir fishways and reducing energy dissipation compared with the design of traditional Atlantic salmon ladders. There are few well-functioning passages for downstream migration of fish in Europe and significant progress has been made in the past decade to improve technology and knowledge. Several international studies have shown that physical structures, such as fine-mesh trash racks with alternative escape routes and bypass arrangements, provide >90% passage efficiency for downstream migration, especially for brown trout and salmon, and have, in recent years, shown good results also for silver eels.

Size- and stage-dependence in cause-specific mortality of migratory brown trout

“…Roscoe et al (2011) found reduced survival of Sockeye salmon ( Oncorhynchus nerka ) that had traversed a dam relative to those that did not and suggested energetic costs of the dam passage as a possible mechanism for this. Additional energetic costs may also arise if passing the dam results in migration delays (Fjeldstad et al 2018), and particularly if such delays forced individuals to overwinter in the river instead of the lake as has been observed in our population. Since energy reserves scale positively with body size (Peters and Peters 1986) such energetic costs may be heavier for smaller individuals, possibly contributing to the negatively size-dependent background mortality predicted by the model.…”

“…On many hydroelectric dams - including the Hunderfossen dam - racks are installed in front of turbine intakes to prevent downriver migrating fish from entering and being exposed to high turbine mortality ( e.g. Fjeldstad et al 2018, Haraldstad et al 2018). The effectiveness of such racks varies across species and sizes, but they appear to work relatively well for adult salmonids (Calles et al 2012).…”

“…Both surprisingly low fish ladder usage by large individuals and variable effects of hydrological conditions have been documented in other salmonid populations (Caudill et al 2007, Jonsson and Jonsson 2002). However, many characteristics influencing attractiveness and efficiency of fish ladders are site-specific (Fjeldstad et al 2018), and more detailed studies are necessary to explain the patterns observed in this particular system. Since using the fish ladder is prerequisite to accessing the spawning habitat above the dam and may thus have considerable impacts on population dynamics, further studies should also aim to identify additional environmental and individual factors ( e.g.…”

Low light levels increase avoidance behaviour of diurnal fish species: Implications for road culverts

“…Abrupt changes in light intensity such as at the entrance/exits of fishways or culverts can also cause avoidance behaviour in lampreys (Moser and Mesa 2009) and juvenile salmon (Ono and Simenstad 2014). However, other studies have demonstrated that upstream migrating salmon, trout, eels, Topeka Shiner, Fathead Minnow and common galaxias in Australia, are unaffected by reduced light levels in civil structures (Fjeldstad et al 2018; Amtstaetter et al 2017; Kozarek et al 2017; Gowans et al 2003; Rogers and Cane 1979). These conflicting accounts of the effect of light on fish movement suggest a range of species-specific behavioural responses to different lighting conditions (Fjeldstad et al 2018; Amtstaetter et al 2017; Kozarek et al 2017; Gowans et al 2003; Rogers and Cane 1979), with such variability also indicating that our understanding of the effects of altered lighting regimes on fish movement is poor, despite this issue being raised in several fish passage guidelines (e.g.…”

Behavioural responses of eel (Anguilla anguilla) approaching a large pumping station with trash rack using an acoustic camera (DIDSON)

“…In the Netherlands, discharge sluices and large pumping stations have been built for water level control of the catchment areas, protection against the sea and to limit saltwater intrusion. 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 arrival time on spawning grounds affecting reproductive success and fitness (Fjeldstad et al, 2018; Travade, Larinier, Subra, Gomes, & De‐Oliveira, 2010; Verhelst, Baeyens, et al, 2018). The delay in migration could also 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).…”