Abstract
Anadromous brown trout (sea trout), Salmo trutta, is currently in decline throughout its range, largely due to anthropogenic stressors in freshwater and marine habitats. Acoustic telmetry was utilized to study the marine migration of sea trout post-smolts from three populations in a relatively pristine subarctic fjord system. While at sea, the sea trout spent a substantial part of their time close to their natal river, preferred near shore over pelagic habitats and were strongly surface oriented. Despite a fidelity towards local areas, the sea trout utilized various parts of the fjord system, with maximum dispersion >30 km and total migration distance >300 km. Almost half of the sea trout (44%) migrated between river outlets, indicating that a metapopulation approach may be appropriate when managing neighbouring sea trout populations at high latitudes. Furthermore, the different populations displayed different migratory behaviours in terms of distance migrated, dispersion from origin and the likelihood of leaving their home area. This variation in migratory behaviour is likely influenced by spatiotemporal differences in habitat quality between sites, indicating that local habitat variations may promote population-specific behavioural responses even in relatively confined fjord systems.
Highlights
Describing migration is challenging for aquatic animals, and for many species improved knowledge of the spatiotemporal distribution and habitat use is of great importance for management and conservation (e.g., Mazor et al, 2016; Walli et al, 2009)
This study describes the marine migratory behaviour of sea trout post-smolts from three populations within a subarctic Norwegian fjord system, using acoustic telemetry
Sea trout post-smolts displayed a certain affinity towards areas close to their natal river, large variation in migratory behaviour was present both within and among populations
Summary
Describing migration is challenging for aquatic animals, and for many species improved knowledge of the spatiotemporal distribution and habitat use is of great importance for management and conservation (e.g., Mazor et al, 2016; Walli et al, 2009) This is emphasized for fishes that migrate over large areas and encounter a variety of stressors (Campana et al, 2010; Walli et al, 2009), but is highly relevant for species with smaller distribution ranges (Aspillaga et al, 2016; Thorbjørnsen et al, 2019), as they can be more vulnerable to negative impacts at local and regional scales. Examples of sea trout migrating several hundred kilometres from their origin have been documented throughout large parts of their distribution range (Birnie-Gauvin et al, 2019; Thorstad et al, 2016)
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