A multi-approach study to reveal eel life-history traits in an obstructed catchment before dam removal

Abstract

River fragmentation is expected to impact not only movement patterns and distribution of eels within catchment, but also their life-history traits. Here, we used otolith multi-elemental signatures to reconstruct life sequences of European silver eels within an obstructed catchment, just before the removal of hydropower dams. Beyond providing an initial state, we hypothesized that otolith signatures can provide crucial information on the way eels use the watershed. Indeed, their spatial distribution is expected to shape life-history traits, including condition coefficient, trophic level, growth rate, or infection by metazoan parasites. While Sr:Ca and Ba:Ca ratios were complementary in tracing fish movements between freshwater and estuary, the Ba:Ca variations allowed to discriminate three freshwater sectors. The eels assigned to the midstream sector were more mobile and exhibited lower growth rates, probably in response to higher competition at the vicinity of dams. While most eels are currently produced by downstream and midstream sectors, eels assigned to upper reaches of connected tributaries generally display higher richness in native parasite and higher body condition and lipid reserve, known to promote the success of migration and reproduction. In the near future, the dam removals will represent an outstanding experimental framework for evaluating impacts of catchment reconnection.

Searching for the critically endangered European eel in oceanic islands: A pioneer study in the freshwater systems of Madeira, Macaronesia

“…Water control structures have increased worldwide following the growing demand for energy production and flood control (Belletti et al, 2020). Simultaneously, increasing evidence shows how these obstacles to fish migration – including the less considered small ones – are responsible for habitat fragmentation, limit fish movement, affect their physical condition and impact the life cycles of a wide array of species (Acou et al, 2008; Belletti et al, 2020; Clavero & Hermoso, 2015; OSPAR, 2022; Teichert et al, 2022). Recently, there has been an increase in the removal of obsolete obstacles and the construction of eel passes (some with reduced costs such as bristles and tiles) (Bravo‐Córdoba et al, 2023; Kerr et al, 2015; Laffaille et al, 2005; Sun et al, 2021; Tamario et al, 2019; Vowles et al, 2015).…”

The Influence of Natural and Anthropogenic Environmental Pressures on European Eel Abundances in French Estuaries

“…The restocking sites are mainly in freshwater, several kilometres away from the estuaries (i.e., 7 to 263 km upstream), e.g., 131 km from the sea in the Vilaine. Although eels have a plasticity in habitat use that allows for a wide geographic distribution of the species [100][101][102], most eels rapidly adopt a sedentary lifestyle during the continental growth phase [22,103,104] and may limit their dispersal to a few kilometres upstream and downstream of the restocking locations. The proportion of silver eels reaching estuaries as a result of restocking is unknown.…”

Biogeographical snapshot of life-history traits of European silver eels: insights from otolith microchemistry

“…First, elemental profiles were segmented to produce homogeneous segments that are assumed to represent non-moving phases in specific habitats (Teichert et al 2022). For each eel, the univariate Sr:Ca time series was segmented following the Lavielle's (1999) method as implemented by Patin et al (2020) to infer individual behavioral modes.…”

“…This sex-related difference in length at silvering reflects a size-maximizing strategy for females that optimize their absolute fecundity, whereas males tend to reduce the continental phase duration (Helfman et al 1987;Oliveira 1999;Durif et al 2020). Beyond sexual dimorphism, a great variability in fat condition, size and age at silvering is reported between and within river catchments (Svedäng and Wickström 1997;Vélez-Espino and Koops 2010;Mateo et al 2017;Teichert et al 2022). Eels residing in the upper reaches generally exhibit lower growth rates and metamorphose older than the individuals living downstream (Daverat et al 2012).…”