Abstract
Individual repeatability is a common phenomenon in behavioural ecology. Behavioural data from 38 anadromous brown trout (Salmo trutta), tracked by acoustic telemetry in 2 – 3 consecutive marine feeding migrations in two Norwegian fjord systems, were analysed for intra-individual repeatability in key aspects of their marine migration. Individual brown trout displayed significant inter-annual consistency in marine area use and in the timing of marine exit (i.e. when they returned to spawning rivers), but not in the timing of marine entry or the time spent in the marine environment each year. Intra-individual repeatability linked to changing environmental conditions should therefore be a focus for future studies, as our study raises new questions about how anadromous brown trout respond to changing conditions and anthropogenic factors in the marine environment.
Highlights
The post-spawning feeding migrations of iteroparous fish species have evolved to allow nutritionally depleted individuals the opportunity to exploit richer feeding habitats in an effort to recondition for future reproductive events
This study revealed that some key aspects of the annual marine feeding migration of anadromous brown trout tend to be repeatable between years
Repeatable behavior is a common phenomenon in nature, but this is to our knowledge the first study to illustrate repeatable behavior by anadromous brown trout, and is among the few to evaluate behavioral repeatability in salmonid fishes more generally (Taylor and Cooke, 2014)
Summary
The post-spawning feeding migrations of iteroparous fish species have evolved to allow nutritionally depleted individuals the opportunity to exploit richer feeding habitats in an effort to recondition for future reproductive events. The mechanisms and patterns of migration can vary widely both within and among populations, as may the degree of individual flexibility and/or repeatability of migratory behavior in response to environmental fluctuations. Anadromous brown trout can undertake multiple annual marine feeding migrations during its lifetime (L’Abee-Lund et al, 1989; Thorstad et al, 2016), where the freshwater residency between marine migratory seasons is usually characterized by spawning and overwintering with opportunistic feeding (Davidsen et al, 2017) that have limited importance for somatic growth (Knutsen et al, 2001). Due to logistical constraints imposed by battery life of acoustic transmitters, and relatively high mortality between spawning events (Fleming and Reynolds, 2004), no previous studies have yet assessed the inter-annual flexibility in the marine migrations of brown trout tracked through multiple years
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