Environmental factors influencing downstream migration of European eel (Anguilla anguilla L.) in a free-flowing river system

Environmental factors influencing downstream migration of European eel (Anguilla anguilla L.) in a free-flowing river system | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Environmental factors influencing downstream migration of European eel (Anguilla anguilla L.) in a free-flowing river system Hanna Jaspaert, Pieterjan Verhelst, Jan M. Baetens This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8979692/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Background: To support the recovery of the critically endangered European eel ( Anguilla anguilla ), understanding downstream migration triggers is essential. Unlike well-studied regulated systems, this study investigates migration drivers in a free-flowing river system to provide a needed reference framework. Methods: Using acoustic telemetry we tracked the movement of 39 silver eels starting in the upper reach of the River Grote Nete (Belgium), a free-flowing tributary of the Scheldt basin. Generalized linear mixed models were applied to analyse environmental factors influencing migration onset and pauses. Chi-squared tests were used to investigate cyclic migration patterns (circadian, circatidal and circalunar patterns). Results: In the non-tidal zone, river discharge was the primary trigger. Migration onset coincided with discharge peaks exceeding seasonal averages and migration pauses were significantly correlated with reduced discharge. Next to this, eels prioritized migration during the first part of the night, however these patterns became less clear in the tidal zone. Here, their activity was largely driven by the tidal cycle, as such inducing selective tidal stream transport. We also observed a clear preference towards migration during new Moon. Conclusion: Our findings underscore the critical role of natural flow dynamics and light regimes in regulating eel migration. As removing water regulating structures is not always realistic, water management strategies at these structures could target periods of high discharge, low lunar brightness and the first half of the night, to maximize eel escapement. Acoustic telemetry Migration Diadromous Discharge Lunar effect Selective tidal stream transport Full Text Additional Declarations No competing interests reported. Supplementary Files Additionalfile1.pdf Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 05 May, 2026 Reviews received at journal 28 Apr, 2026 Reviewers agreed at journal 10 Apr, 2026 Reviewers agreed at journal 07 Apr, 2026 Reviewers invited by journal 06 Apr, 2026 Editor assigned by journal 27 Feb, 2026 Submission checks completed at journal 27 Feb, 2026 First submitted to journal 26 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8979692","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":619697997,"identity":"a219dbdf-12e9-4537-a5e8-efb6b9df4532","order_by":0,"name":"Hanna Jaspaert","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBUlEQVRIiWNgGAWjYBACAwjFBuPbQCjGBqK1JKRBNBChBQYSDhPWYs5+9tiDHwx88vKzmx8+rvxxPnG+e+/xB4w7bHBqsezJSzfsYWAz3HDnmLHhmYTbiRvPnEtsYDyThtthB3LMJHgY2Bg3SCSYSTaAtMzIMWxgbDuMW8v5N2aSfxjY7OfPSP/+syHhXOLG+W9AWv7j1nIjx0waaEtiA5DB2JBwIHG+BA9IywE8Wt6YScsYsCVvuHOmWLIhLdl4A0+O4YzEM8l4HJZjJvmm4pjt/NntGz822NjJzm8/Y/Dh4w47nFqgGo8xMEjAAwRIJBDQAAQ1CC3yDYSVj4JRMApGwcgCANTJWlOl9AkMAAAAAElFTkSuQmCC","orcid":"","institution":"Ghent University","correspondingAuthor":true,"prefix":"","firstName":"Hanna","middleName":"","lastName":"Jaspaert","suffix":""},{"id":619697998,"identity":"cf14fa9c-b8f0-4376-b523-9f2696824d7f","order_by":1,"name":"Pieterjan Verhelst","email":"","orcid":"","institution":"Research Institute for Nature and Forest (INBO)","correspondingAuthor":false,"prefix":"","firstName":"Pieterjan","middleName":"","lastName":"Verhelst","suffix":""},{"id":619697999,"identity":"19b2853a-3013-4f80-82d7-ac6c43d568d3","order_by":2,"name":"Jan M. 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Unlike well-studied regulated systems, this study investigates migration drivers in a free-flowing river system to provide a needed reference framework.\u003c/p\u003e\u003ch2\u003eMethods:\u003c/h2\u003e\u003cp\u003eUsing acoustic telemetry we tracked the movement of 39 silver eels starting in the upper reach of the River Grote Nete (Belgium), a free-flowing tributary of the Scheldt basin. Generalized linear mixed models were applied to analyse environmental factors influencing migration onset and pauses. Chi-squared tests were used to investigate cyclic migration patterns (circadian, circatidal and circalunar patterns).\u003c/p\u003e\u003ch2\u003eResults:\u003c/h2\u003e\u003cp\u003eIn the non-tidal zone, river discharge was the primary trigger. Migration onset coincided with discharge peaks exceeding seasonal averages and migration pauses were significantly correlated with reduced discharge. Next to this, eels prioritized migration during the first part of the night, however these patterns became less clear in the tidal zone. Here, their activity was largely driven by the tidal cycle, as such inducing selective tidal stream transport. We also observed a clear preference towards migration during new Moon.\u003c/p\u003e\u003ch2\u003eConclusion:\u003c/h2\u003e\u003cp\u003eOur findings underscore the critical role of natural flow dynamics and light regimes in regulating eel migration. As removing water regulating structures is not always realistic, water management strategies at these structures could target periods of high discharge, low lunar brightness and the first half of the night, to maximize eel escapement.\u003c/p\u003e","manuscriptTitle":"Environmental factors influencing downstream migration of European eel (Anguilla anguilla L.) in a free-flowing river system","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-10 09:55:48","doi":"10.21203/rs.3.rs-8979692/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-05T08:11:40+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-28T09:12:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"234632405443957619651905074633523260454","date":"2026-04-10T09:18:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"171331983866374960451338924004678988659","date":"2026-04-07T12:32:13+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-06T11:00:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-27T05:05:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-27T05:03:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Movement Ecology","date":"2026-02-26T15:45:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"movement-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"move","sideBox":"Learn more about [Movement Ecology](http://movementecologyjournal.biomedcentral.com/)","snPcode":"40462","submissionUrl":"https://submission.nature.com/new-submission/40462/3","title":"Movement Ecology","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5e4a4c22-f40b-4ab5-820e-1ee5ebe40e9b","owner":[],"postedDate":"April 10th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-05T08:11:40+00:00","index":20,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-10T09:55:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-10 09:55:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8979692","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8979692","identity":"rs-8979692","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}