ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Marine Biology
This article is part of the Research TopicFactors Influencing Diadromous Fish Migration and their Fitness ConsequencesView all 3 articles
Diel patterns and migration behaviour of sympatric Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta) smolts during seaward migration
Provisionally accepted
- DNV GL (Norway), Sandvika, Norway
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Migrations between different habitats to maximise fitness is well documented in many organisms, although such migrations include potentially great risk when moving between habitats. For anadromous salmonids these migrations occur between the freshwater stage in their natal rivers in coastal waters during spring/summer, where they can potentially experience high mortality rates. This study investigated the riverine migration dynamics for Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) smolts with a multiple camera array over three consecutive years (2021-2023). A total of 19 238 individuals were observed, and dynamics of schooling behaviour and diel patterns were analysed concerning both intra-and interspecific behavioural traits concerning migration patterns. The observed pattern describes the migration dynamics for sympatric natural stocks of Atlantic salmon and sea trout over a three-year period with little-to-no interferences with natural behaviour. Results indicate a clear diel pattern in schooling behaviour, governed by the influx of natural light, with clear species-specific differences in migratory behaviour. The observed diel pattern was less dominant later in the migration period, revealing daylight-length as a factor altering migratory behaviour during the smolt-run. The observed changes in migration dynamics could possibly be adapted as an anti-predator behaviour during river migration, where night/dark offer protection from visual predators, whereas the safety in numbers aid predator detection and avoidance during daytime
Keywords: Smolt migration, schooling behaviour, Seasonal patterns, Fish behaviour, Migration, dynamics, Camera surveillance
Received: 30 Sep 2025; Accepted: 17 Nov 2025.
Copyright: © 2025 Ulvund, Smalås, Strand and Lamberg. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: John Birger Ulvund, john.birger.ulvund@dnv.com
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