Stranding of larval nase (Chondrostoma nasus L.) depending on bank slope, down-ramping rate and daytime

Abstract

Rapid water level decreases due to hydropeaking are known to negatively affect riverine biota, mainly due to the stranding of organisms in the river bank area that becomes regularly dewatered. Even though studies of the last decades have focused on salmonid fish, also cyprinids may be affected. However, limited knowledge is available of this fish family. Therefore, we conducted mesocosm experiments under semi-natural conditions, simulating single hydropeaking events at two different lateral bank slopes (2% and 5%) with varying down-ramping rates (0.7–3.0 cm min−1) during day and night. As a response parameter, we quantified stranding rates of different larval stages (III-IV and V) of common nase (Chondrostoma nasus L.). The experiments revealed that lower sloped banks exhibited distinctly higher stranding rates than steeper ones. Daytime revealed a similar pattern, with more fish becoming stranded at night than during the day, and this was consistent for all down-ramping rates. The data also indicate increased stranding with higher down-ramping rates, particularly at low sloped riverbanks, and interaction effects between the tested parameters. Overall, this study, for the first time, quantifies the consequences of flow down-ramping on nase larvae, also revealing differences between larval stages. The gained information will, therefore, advance the ongoing discussion on hydropeaking mitigation by providing a deeper understanding of the effects of artificial sub-daily flow fluctuations on the early life stages of cyprinid fish. Our results can inform management and policy to sharpen existing mitigation concepts and fine-tune hydropower operations to reduce negative effects on riverine ecosystems.

Cold thermopeaking-induced drift of nase Chondrostoma nasus larvae

“…Finally, one aspect which was not targeted in this experiment was stranding caused by the fish’s inability to shift from shallow to deeper areas during down-ramping (Führer et al. 2022 ; Hayes et al. 2023 ).…”

“… 2021 ; Führer et al. 2022 ). Particularly for early life stages of fish, such as larvae and juveniles, the impacts of hydropeaking can endanger successful recruitment and, ultimately, their survival, as it may cause fish to become stranded or passively drift, making them unable to reach critical habitats for life cycle requirements (Kupren et al.…”

Effects of cold and warm thermopeaking on drift and stranding of juvenile European grayling (Thymallus thymallus)

“…Water used for experiments is diverted from the nearby Lake Lunz; a surface and bottom outlet allow adjustments of channel water temperature. The reader is referred to Auer et al (2017), Führer et al (2022) and https://hydropeaking.boku.ac.at/ for a more detailed description of the HyTEC facility.…”

“…However, this mode of operation, known as hydropeaking, alters the natural flow regime (Greimel et al, 2016), which may entail diverse consequences for riverine organisms (Bejarano, Jansson, & Nilsson, 2018; Bondar‐Kunze, Maier, Schönauer, Bahl, & Hein, 2016; Greimel et al, 2018; Bruno, Siviglia, Carolli, & Maiolini, 2013; Hauer, Unfer, Holzapfel, Haimann, & Habersack, 2014; Schülting, Feld, & Graf, 2016; Young, Cech, & Thompson, 2011). Regarding fish, it has been well documented that hydropeaking entails stranding and downstream displacement of individual fish (Nagrodski, Raby, Hasler, Taylor, & Cooke, 2012; Young et al, 2011; Hunter, 1992; Saltveit et al, 2001; Halleraker et al, 2003; Auer, Zeiringer, Führer, Tonolla, & Schmutz, 2017; Führer et al, 2022), which, in turn, diminishes population vitality (Hayes et al, 2021; Schmutz et al, 2015).…”

Applying a two‐dimensional hydrodynamic model to estimate fish stranding risk downstream from a hydropeaking hydroelectric station

“…Establishing mitigation measures for hydropeaking is challenging as there are no standardized methods for determining the extent of fish stranding across multiple kilometers of a riverscape, defined as all spatially and temporally heterogenous and/or homogenous areas connected by the river. Fish stranding assessments are typically conducted via observational surveys and/or microcosm and mesocosm experiments used to determine if fish stranding is a concern at a given river reach (Auer et al, 2017; Führer et al, 2022; Nagrodski et al, 2012). Identifying potential stranding locations is achievable through the application of hydrodynamic modelling of the river reach.…”