Evaluation of Low-Head Ramped Weirs for a Potamodromous Cyprinid: Effects of Substrate Addition and Discharge on Fish Passage Performance, Stress and Fatigue

Abstract

Requalification of low-head ramped weirs through the addition of substrates (retrofitting) has attracted attention in recent years. However, few studies are available on how this measure affects the negotiation of ramped weirs by fish. This study aimed to assess the performance of an experimental ramped weir (3.00 m long with 10% slope; 0.30 m head-drop) to enhance the passage of a potamodromous cyprinid species, the Iberian barbel (Luciobarbus bocagei). Attention was given to testing the effects of the addition of a substrate, in this case cobbles, to the ramp (Nature) vs. a smooth bottom (Control), and discharge (Q; 55 L·s−1 and 110 L·s−1 (or specific discharge per unit width, q = 92 L·s−1·m−1 and 183 L·s−1·m−1)) on fish passage performance. Fish physiological responses to stress and fatigue, measured by glucose and lactate concentrations in blood samples, were also analysed. Results showed that the Nature design generally increased fish movements and successful upstream passages, and enhanced fish passage performance by enabling faster negotiations. Fish movements were also affected by increasing discharge, registering reductions with 110 L·s−1. Results of the physiological parameters indicate that both glucose and lactate concentrations were also influenced by discharge. The outcomes from this study present important information about fish passage performance across low-head ramped weirs and could provide data needed to help biologists and engineers to develop more effective structures to alleviate small instream obstacles.

Barrier mitigation measures trigger the rapid recovery of genetic connectivity in five freshwater fish species

“…Surprisingly, out of nine obstacles with genetic data in both genera, five showed large discrepancies in genus response to fragmentation, with either only gudgeons or only minnows significantly impacted (Figure 2). These discrepancies illustrate how barrier effects can be highly species- or genus-dependent (Amaral et al, 2021; Blanchet et al, 2010; Prunier et al, 2018), and thus hardly predictable given our limited knowledge about fish movement behavior and capacities (Baudoin et al, 2014; Thurow, 2016). In absence of a dedicated fish pass, individuals are supposed to take advantage of drowned conditions, that is, of periods where water level rises above the height of the dam, to cross the obstacle (Keller et al, 2012).…”