Turbine entrainment and passage of potadromous fish through hydropower dams: Developing conceptual frameworks and metrics for moving beyond turbine passage mortality

Abstract

Potadromous fishes are vulnerable to involuntary entrainment through hydropower turbines. However, turbines can also provide a downstream passage route for potadromous fish. Here, we review evidence for turbine entrainment and passage in potadromous fish, and evaluate the effects of these processes on upstream and downstream populations. We develop conceptual frameworks and metrics to quantify vulnerability to turbine entrainment removals, and to quantify the efficiency of turbines as a downstream passage route. We highlight factors that influence these processes and provide case‐studies demonstrating their applicability. We found that juvenile potadromous fish are being entrained through turbines at rates high enough to impact upstream populations. Given that juvenile passage survival is often high, we argue that turbines provide an important downstream passage route for potadromous fish. We show that entrainment vulnerability is likely a function of interactions between in‐reservoir fish behaviour, habitat configuration and operations and thus not well captured by passage mortality estimates. Similarly, we show that while passage mortality can limit downstream passage efficiency, passage success is also dependent on reservoir and forebay navigation, along with survival and fitness in the downstream river. We advocate for a shift in focus away from estimates of passage mortality and injury, which have previously accounted for the majority of turbine passage research. Instead, we recommend an approach that focusses on quantification of the factors that influence downstream passage efficiency and entrainment vulnerability. Moreover, we highlight the need to better understand the broader scale impacts of these events on upstream and downstream populations.

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

“…Trash racks are placed in front of pumping and hydropower stations to prevent large debris getting into the turbines and are the first physical obstacles fish encounter while approaching these structures. Most studies on the effects of pumping or hydropower stations with trash racks focus on the risk of entrainment, but more focus should be directed to behavioural responses of fish in the vicinity of these structures in relation to entrainment risk (Harrison et al, 2019). An eel approaching these structures perceives multiple cues that might trigger a change in its behaviour, for example, at larger distances underwater sound emitted by the stations (Behrmann‐Godel & Eckmann, 2003) and near the trash rack and pumping stations water flows change in direction and increase in speed (Piper et al, 2015).…”

A comparison of turbine entrainment rates and seasonal entrainment vulnerability of two sympatric char species, bull trout and lake trout, in a hydropower reservoir

“…turbine entrainment mortality is frequently <100%, and often~30% (Pracheil, DeRolph, Schramm, & Bevelhimer, 2016;Wilkes, Webb, Baumgartner, et al, 2018), entrainment survivors can disperse into downstream environments and can augment downstream populations (Harrison et al, 2019). While the vulnerability of anadromous salmonid populations to turbine entrainment has been well studied (e.g., Calles & Greenberg, 2009;Silva et al, 2017), less is known about the turbine entrainment vulnerability of potadromous fish populations (Rytwinski et al, 2017).…”

“…When the number of entrained individuals is high, seasonal patterns of entrainment vulnerability can be quantified directly (Smith & Brown, 2002). However, when the number of observable entrainment events are restricted due to sample size, seasonal patterns of forebay (the area of a reservoir in the vicinity of the dam) occupancy, can be used as proxy for entrainment vulnerability (Harrison et al, 2019;Martins et al, 2013). Furthermore, given that fish that are located close to the dam forebay are likely at higher risk of entrainment than fish that are located a long distance away, fish proximity to the forebay, can also be used a measure of entrainment vulnerability, and to help understand seasonal patterns of entrainment vulnerability (Harrison et al, 2019).…”

Fish Community Interactions with Very Low Head (VLH) Turbine Technology

“…In this case the physical traits of the fish community present at the study site is representative of a range of fishes found across North America and differ from the species tested in Europe. If specific species are at a greater risk of mortality or certain injury types, steps can be taken to mitigate risk to the fish community (Algera et al, 2019). In my investigation into this matter I was able to identify sublethal and lethal injury rates and compare these measures across the treatment groups.…”

“…Most of the previous studies of VLH technology have focused on the consequences of entrainment rather that the likelihood of entrainment. Entrainment risk for resident fish populations is an important metric in understanding the potential ecological consequences of hydropower development (Harrison et al, 2019). Given the lack of research on this topic in small to middle sized rivers with low head dams, this research addresses an important gap in VLH turbine risk assessment and more broadly in fish-hydropower interactions.…”