Effects of pulsed discharges from a hydropower station on summer diel feeding activity and diet of brown trout (Salmo trutta Linnaeus, 1758) in an Iberian stream

Abstract

SummaryThe influence of pulsed discharges associated with hydroelectric power generation (i.e. hydropeaking) on feeding activity and diet composition of adult brown trout (Salmo trutta) was studied during summer by comparing two sites: upstream (control site) and downstream from a power plant (hydropeaking site). Twenty fish were captured from each study site by electrofishing at four-hour intervals for two consecutive days and stomach contents were collected with pulsed gastric lavage. Hydropeaking events affected brown trout feeding behaviour as well as prey availability. Feeding intensity, measured by the stomach Fullness Index, showed pronounced variations with maximum values after flow pulses, which were linked to variations in prey availability because of increased drift rates of invertebrates. In contrast, brown trout living at the control site showed smoother variations of feeding activity not linked to invertebrate drift. Overall, brown trout at the hydropeaking site had higher food consumption rates and a more generalist and heterogeneous diet than trout from the control site, indicating an opportunistic feeding behaviour during flow pulses. Therefore, the hydrological disturbance caused by hydropeaking did not appear to cause direct negative impacts on feeding of adult brown trout. However, reduced trout density and imbalanced size structure in the hydropeaking site were detected, requiring further research to clarify the spatial influence of hydropeaking on other factors that could negatively affect brown trout populations.

Hydropeaking effects on movement patterns of brown trout (Salmo trutta L.)

“…There were no significant differences in trout diel activity, thus suggesting that brown trout individuals were active during the day and night. These results agree with a recent study showing an absence of diel cycling in the summer feeding activity of brown trout in the study area (Rocaspana et al, ), and other works reporting that brown trout individuals are active during the day and night in summer (Clapp et al, ; Young, Wilkison, Phelps, & Griffith, ).…”

“…Because flow fluctuations caused by hydropeaking exceed those observed naturally (Poff et al, ), negative impacts on riverine organisms such as benthic invertebrates and fish are expected. For example, the resulting rapid changes in river discharge affect the invertebrate drift (Bruno, Siviglia, Carolli, & Maiolini, ; Gibbins, Vericat, & Battala, ; Lauters, Lavandier, Lim, Sabaton, & Belaud, ; Rocaspana, Aparicio, Vinyoles, & Palau, ) and reduce both the quantity and quality of habitat available to fish (Liebig, Cereghino, Lim, Belaud, & Lek, ; Person, ; Young, Cech, & Thompson, ).…”

Impact of river regulation and hydropeaking on the growth, condition and field metabolism of Brook Trout (Salvelinus fontinalis)

“…Dedual & Collier, ). Studies with brown trout ( Salmo trutta ) have shown higher food consumption rates during hydropeaking flow pulses as an opportunistic response to increased prey availability (Rocaspana, Aparicio, Vinyoles, & Palau, ), effectively coupling the two opposing impacts of increased food supply, and increased energy expenditure driven by hydropeaking. However, regulation‐derived increases in activity (metabolic demands) may not always be offset by increases in food supply, making generalisations about dam impacts difficult.…”

Diel activity and foraging mode of juvenile Arctic charr in fluctuating water flow

“…Rapid fluctuations in water flow can also affect temporal aspects of stream fishes behaviour, for example, small and large‐scale movements, relocation, and habitat use (Korman & Campana, ; Krimmer, Paul, Hontela, & Rasmussen, ; Riley, Maxwell, Pawson, & Ives, ; Scruton et al, ; Taylor et al, ). Other studies have suggested that salmonids also alter their diel feeding activity in response to hydropeaking (e.g., Rocaspana, Aparicio, Vinyoles, & Palau, ). Salmonids show extensive flexibility in diel activity (Reebs, ) and can adjust it in response to daily variations of food availability and predation risk (Larranaga & Steingrímsson, ; Orpwood, Griffiths, & Armstrong, ).…”

“…Rapid fluctuations in water flow can also affect temporal aspects of stream fishes behaviour, for example, small and large-scale movements, relocation, and habitat use (Korman & Campana, 2009;Krimmer, Paul, Hontela, & Rasmussen, 2011;Riley, Maxwell, Pawson, & Ives, 2009;Scruton et al, 2005;Taylor et al, 2014). Other studies have suggested that salmonids also alter their diel feeding activity in response to hydropeaking (e.g., Rocaspana, Aparicio, Vinyoles, & Palau, 2016).…”