Migration behaviour of Atlantic salmon smolts (Salmo salar L.) in a short and highly fragmented gravel‐bed river stretch

Abstract

The succession of migration barriers and different turbine types during downstream migration impede Atlantic salmon (Salmo salar L.) smolts from reaching the sea in time but is poorly studied. We investigated the isolated and cumulative impacts of 14 consecutive migration barriers (MBs) on downstream migration of 200 radio-tagged smolts over an 18.9 km stretch of gravel-bed river, by equipping five MBs with automated radio listening stations. At the level of isolated barriers, median research times (i.e. time between the first and the last detection upstream of a MB) varied between 0.1 and 0.7 h. The median crossing delays (i.e. time between the first detection upstream and the first detection downstream of a MB) varied between 1 and 2.9 h. Considering successive MBs, median cumulative crossing delays varied between 2.6 and 32.1 h and increased with the number of MBs. We observed a global mortality rate between 33% and 76%, increasing with the distance travelled and the associated number of MBs. Only 48% of the migrating smolts reached the end of the studied river stretch. Results suggest that the dynamics of the smolt downstream migration over this short highly fragmented stretch had a significant effect in terms of delays, mortalities and seaward escapement rate.

What do fish do after passing through a fishway? A radio‐telemetry study on patrimonial holobiotic species

“…Fish were captured in the cage capture of FW1 and FW2 and were anaesthetised with 0.2 mL/L of a solution of 2‐phenoxy‐ethanol, measured (±1 mm, fork length), weighed (±1 g) and sexed. Fish were surgically equipped with a radio transmitter (ATS Inc. 40 MHz trailing whip antenna), whose weight/transmitter index did not exceed 2.5% (Ovidio et al., 2020; Renardy et al., 2022), in their intraperitoneal cavity through a 0.8–2 cm midventral incision, depending on the size of the transmitter, behind their pelvic fin (Ovidio & Philippart, 2002). The incision was closed with two or three independent stitches, using resorbable Vicryl sutures, and disinfected with eosin.…”

Movement behaviour and fishway performance for endemic and exotic species in a large anthropized river

“…Most fish species develop movement behaviours in order to complete their biological activities such as feeding, resting and breeding, in various functional habitats within their home range (Benitez et al, 2015). River connectivity is essential for river dynamics and for the resilience of fish assemblages and populations; reaching good ecological status for river systems is a priority (Ovidio and Philippart, 2008;Sánchez-Pérez et al, 2022). However, the omnipresence of physical barriers reduces watershed longitudinal connectivity in, both upstream and downstream.…”

“…It is, therefore, crucial to improve fishway design and to collect data from a wide range of structural typologies on different fish species in a wide variety of rivers and regions, in order to find more successful, integrative solutions for the future (Cook and Hinch, 2013;Kemp, 2012;Ovidio et al, 2017). Studies on passage efficiency (the percentage of the fish present which entered and successfully moved through a fishway) have increased in the past 10 years and more recent efforts have been made to focus on non-commercial species (Alexandre et al, 2013;Branco et al, 2013;Sanz-Ronda et al, 2016;Silva et al, 2010Silva et al, , 2012Ovidio et al, 2017;Grimmardias et al, 2022;Sánchez-Pérez et al, 2022). In the course of these studies, additional efforts were made to quantify fishway performance at the multispecies level, including the entire fish community, to be as representative as possible (Castro-Santos et al, 2009;Bunt et al, 2012Bunt et al, , 2016.…”

“…In the lower course of the Meuse in Belgium, large fishways have been progressively installed over the last 20 years, strongly stimulated by the Salmon program, aiming to reintroduce this flagship species into Belgium after its extinction in the beginning of the 20th century (Renardy et al, 2022). These fishways were primarily designed for large rheophilic species but it transpires that they are also intensively used by eel, eurytopic and limnophilic species, as well as by exotic species at different times of the year and day (Nzau Matondo et al, 2017;Benitez et al, 2018Benitez et al, , 2022.…”

Assessment of the Attractiveness and Passage Efficiency of Different Fish Passage Solutions at a Hydropower Plant by Combining Fine Scale 2D-Telemetry and Hydraulic Numerical Modelling

“…Migratory species have been highly impacted by river fragmentations due to human activities, such as navigation and hydropower production [1]. These disruptions gradually delay both upstream and downstream migrations [2,3]. River fragmentation has caused drastic reductions, and the extinction of entire populations of several migratory species, such as the Atlantic salmon (Salmo salar L.), by impeding free movements and limiting access to functional habitats between marine and freshwater ecosystems [4,5].…”