Revealing the full ocean migration of individual Atlantic salmon

John Fredrik Strøm,Richard David Hedger,Eva Bonsak Thorstad,Audun Håvard Rikardsen

doi:10.1186/s40317-018-0146-2

John Fredrik Strøm, Richard David Hedger + Show 2 more

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https://doi.org/10.1186/s40317-018-0146-2

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Abstract

BackgroundKnowledge of the complete horizontal migration and vertical movements of Atlantic salmon (Salmo salar L.) during the marine phase is important for understanding the link between individual processes and population recruitment. We studied the detailed migration behaviour of six post-spawned adult Atlantic salmon from a North Norwegian river, during the entire ocean migration, by using high-resolution light-based geolocation archival tags.ResultsThe fish performed long-distance migrations and utilized Arctic areas from the eastern Barents Sea, to areas of Jan Mayen Island, and north to Svalbard. Four of six individuals exhibited a strong fidelity towards Jan Mayen Island, particularly during winter, which may suggest that the ecological conditions in these waters may be important for overwintering. One fish displayed exclusive utilization of the Barents Sea, indicating that growth and survival of some individuals are entirely dependent on these waters. The fish displayed a pelagic behaviour and all individuals spent more than 83% of the time in the uppermost 10 m of the water column. There was a strong seasonal trend in diving intensity, with the number of dives increasing with day length, independent of individuals’ spatial distribution. Diving depth was positively correlated with the depth of the mixed layer.ConclusionsThe Atlantic salmon displayed large individual variation in horizontal migrations, utilizing different ocean areas north of the Arctic Circle. This means that, despite the overall fidelity towards northern latitudes, individuals from the same population may experience highly different ecological conditions, potentially contributing to within-population variation in growth and survival. The seasonal correlation between diving intensity and day length, and spatial correlation between diving depth and depth of the mixed layer, indicate that the overall depth use of the Atlantic salmon depends on both spatially independent seasonal factors, and dynamic oceanographic conditions that facilitate food aggregations. This is the first study of Atlantic salmon to present detailed information about individuals’ continuous horizontal migration and simultaneous vertical movements during the entire ocean migration, thus providing novel information on how habitat use change throughout the ocean residency.

Highlights

Knowledge of the complete horizontal migration and vertical movements of Atlantic salmon (Salmo salar L.) during the marine phase is important for understanding the link between individual processes and population recruitment
The tags had a high failure rate, and of the fish recaptured on their return migration, data were only retrieved from six tags, with the remaining four tags malfunctioning due to technical failures. These six fish exited the river between May 24 and June 15, spent between 375 and 414 days at sea, and had a maximum displacement from the river according to the mean track of 709–1308 km (Table 1)
Horizontal movements The mean track and seasonal residency distributions (RDs) of the six Atlantic salmon revealed an overall utilization of waters spanning from the eastern Barents Sea, to the Greenland Sea, with the northernmost-oriented individuals migrating towards areas of the coast of the Svalbard archipelago (Figs. 2, 3, 4, and Additional file 4: Figure S4)

Summary

Introduction

Knowledge of the complete horizontal migration and vertical movements of Atlantic salmon (Salmo salar L.) during the marine phase is important for understanding the link between individual processes and population recruitment. Atlantic salmon (Salmo salar L.) is an anadromous species distributed across the North Atlantic Ocean, with both juveniles and post-spawned adults undertaking long-distance ocean feeding migrations [1] Throughout their distribution range, many Atlantic salmon. During the past few decades, advances in animal biotelemetry have promoted new insights into the behaviour of aquatic organisms by enabling researchers to track the movement of free-ranging individuals using a variety of electronic tags [4]. Information on the continuous horizontal migration of individual Atlantic salmon during the entire ocean residency is lacking

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