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Tambets M, Kärgenberg E, Järvalt A, Økland F, Kristensen ML, Koed A, Bernotas P. Migrating silver eels return from the sea to the river of origin after a false start. Biol Lett 2021; 17:20210346. [PMID: 34493065 PMCID: PMC8424351 DOI: 10.1098/rsbl.2021.0346] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/16/2021] [Indexed: 11/12/2022] Open
Abstract
The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river of origin after spending up to a year in the marine environment. After migrating to the Baltic Sea, 21% of the silver eels, tagged with acoustic transmitters, returned to the Narva River. Half returned 11-12 months after moving to the sea, with 15 km being the longest upstream movement. The returned eels spent up to 33 days in the river and migrated to the sea again. The fastest specimen migrated to the outlet of the Baltic Sea in 68 days after the second start-roughly 1300 km. The surprising occurrence of returning migrants has implications for sustainable management and protection of this critically endangered species.
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Affiliation(s)
| | - Einar Kärgenberg
- Wildlife Estonia, Veski 4, Tartu 51005, Estonia
- Estonian Marine Institute, University of Tartu, Vanemuise 46, Tartu 51014, Estonia
| | - Ain Järvalt
- Chair of Hydrobiology and Fishery, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 5, Tartu 51006, Estonia
| | - Finn Økland
- Norwegian Institute for Nature Research NINA, PO Box 5685, Trondheim No-7485, Norway
| | - Martin Lykke Kristensen
- Technical University of Denmark, National Institute for Aquatic Resources, Silkeborg 8600, Denmark
| | - Anders Koed
- Technical University of Denmark, National Institute for Aquatic Resources, Silkeborg 8600, Denmark
| | - Priit Bernotas
- Estonian Marine Institute, University of Tartu, Vanemuise 46, Tartu 51014, Estonia
- Chair of Hydrobiology and Fishery, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 5, Tartu 51006, Estonia
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Combining disciplines: Dealing with observed and cryptic animal residencies in passive telemetry data by applying econometric decision-making models. Ecol Modell 2020. [DOI: 10.1016/j.ecolmodel.2020.109340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Teichert N, Tétard S, Trancart T, Feunteun E, Acou A, de Oliveira E. Resolving the trade-off between silver eel escapement and hydropower generation with simple decision rules for turbine shutdown. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2020; 261:110212. [PMID: 32148282 DOI: 10.1016/j.jenvman.2020.110212] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 12/19/2019] [Accepted: 01/27/2020] [Indexed: 06/10/2023]
Abstract
Hydropower plants are commonly reported as a major cause of the worldwide decline of freshwater eels (Anguillidae), so that management solutions are urgently needed to mitigate their impacts. Where downstream passage solutions are complex to develop, turbine shutdown appears as an effective management solution to protect silver eels during their river migration toward spawning areas. However, the definition of operational decision rules for turbine shutdown is challenging due to the duality between the benefit for eel conservation and the concomitant cost in term of hydropower production. Here, we proposed a decision framework for turbine shutdown based on simple hydrological criteria to guide negotiations between stakeholders toward a trade-off between silver eel escapement and hydropower generation. Eel migration was assumed to be triggered by a minimum river flow associated with a minimum discharge pulse, so that threshold values can be directly implemented as decision rules for turbine shutdown. To estimate relevant thresholds, a generic methodological framework was developed to generate alternative decision rules from data collected at hydropower plants, which can include telemetry surveys and estimates of eel abundance. A multiple-criteria decision analysis was then conducted to rank alternatives and to determine the best compromise between promoting silver eel escapement and limiting turbine shutdown duration. Graphic outputs can help stakeholders to understand the competitive interests between eel conservation and hydropower production, while visually identifying a range of consensual alternatives to support negotiations in the choice of operational thresholds. The method was illustrated for three river systems in Europe featured by distinct hydrological conditions and can be applied in other areas, providing that eel monitoring surveys and flow data are available.
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Affiliation(s)
- Nils Teichert
- Laboratoire de Biologie des Organismes et Ecosystèmes Aquatiques (BOREA) MNHN, CNRS, IRD, SU, UCN, UA, Station Marine de Dinard - CRESCO, 38 rue du Port Blanc 35800 Dinard, France.
| | - Stéphane Tétard
- EDF R&D LNHE - Laboratoire National d'Hydraulique et Environnement, 6 Quai Watier, 78401, Chatou, Cedex, France
| | - Thomas Trancart
- Laboratoire de Biologie des Organismes et Ecosystèmes Aquatiques (BOREA) MNHN, CNRS, IRD, SU, UCN, UA, Station Marine de Dinard - CRESCO, 38 rue du Port Blanc 35800 Dinard, France
| | - Eric Feunteun
- Laboratoire de Biologie des Organismes et Ecosystèmes Aquatiques (BOREA) MNHN, CNRS, IRD, SU, UCN, UA, Station Marine de Dinard - CRESCO, 38 rue du Port Blanc 35800 Dinard, France
| | - Anthony Acou
- Agence Française pour la Biodiversité, UMS AFB-CNRS-MNHN PatriNat, Station Marine du MNHN, Dinard, France; Pôle R&D AFB-INRA-Agrocampus Ouest-UPPA pour la Gestion des Migrateurs Amphihalins Dans Leur Environnement, Rennes, France
| | - Eric de Oliveira
- EDF R&D LNHE - Laboratoire National d'Hydraulique et Environnement, 6 Quai Watier, 78401, Chatou, Cedex, France
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Sandlund OT, Diserud OH, Poole R, Bergesen K, Dillane M, Rogan G, Durif C, Thorstad EB, Vøllestad LA. Timing and pattern of annual silver eel migration in two European watersheds are determined by similar cues. Ecol Evol 2017; 7:5956-5966. [PMID: 28808557 PMCID: PMC5551103 DOI: 10.1002/ece3.3099] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 04/27/2017] [Accepted: 05/02/2017] [Indexed: 11/24/2022] Open
Abstract
Many animals perform long‐distance migrations in order to maximize lifetime reproductive success. The European eel migrates several thousand kilometers between their feeding habitats in continental waters (fresh‐, brackish, and sea water) and their spawning area in the Sargasso Sea. Eels residing in freshwaters usually initiate their spawning migration as silver eels during autumn, triggered by diverse environmental cues. We analyzed the time series of silver eel downstream migration in Burrishoole, Ireland (1971–2015), and Imsa, Norway (1975–2015), to examine factors regulating the silver eel migration from freshwater to the sea. The migration season (90% of the run) generally lasted from 1 August to 30 November. Environmental factors acting in the months before migration impacted timing and duration of migration, likely through influencing the internal processes preparing the fish for migration. Once the migration had started, environmental factors impacted the day‐to‐day variation in number of migrants, apparently stimulating migration among those eels ready for migration. Both the day‐to‐day variation in the number of migrants and the onset of migration were described by nearly identical models in the two rivers. Variables explaining day‐to‐day variation were all associated with conditions that may minimize predation risk; number of migrants was reduced under a strong moon and short nights and increased during high and increasing water levels. Presence of other migrants stimulated migration, which further indicates that silver eel migration has evolved to minimize predation risk. The onset of migration was explained mainly by water levels in August. The models for duration of the migration season were less similar between the sites. Thus, the overall migration season seems governed by the need to reach the spawning areas in a synchronized manner, while during the actual seaward migration, antipredator behavior seems of overriding importance.
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Affiliation(s)
| | - Ola H Diserud
- Norwegian Institute for Nature Research (NINA) Trondheim Norway
| | | | | | - Mary Dillane
- Marine Institute Furnace, Newport Co. Mayo Ireland
| | - Gerard Rogan
- Marine Institute Furnace, Newport Co. Mayo Ireland
| | | | - Eva B Thorstad
- Norwegian Institute for Nature Research (NINA) Trondheim Norway
| | - Leif Asbjørn Vøllestad
- Centre for Ecological and Evolutionary Synthesis Department of Biosciences University of Oslo Oslo Norway
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