Predation Risk and Depth Use During Migration of Atlantic Salmon Smolts Through a Fjord Impacted by Hydropower Discharge

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Hydropower-regulated river discharge influences the fjord migration routes of Atlantic salmon smolts, with predation mortality concentrated at river mouths and physical bottlenecks, and smolts exhibiting diel depth-use patterns. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

Robert J. Lennox; Knut Wiik Vollset; Saron Berhe; Tormod Haraldstad

doi:10.1111/eff.70062

September 9, 2026Ecology Of Freshwater FishOpen Access

Predation Risk and Depth Use During Migration of Atlantic Salmon Smolts Through a Fjord Impacted by Hydropower Discharge

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Key Points

To determine how hydropower-regulated water discharge influences migration routes, depth use, and predation mortality in Atlantic salmon smolts transitioning from river to fjord habitats.
Monitored wild and hatchery Atlantic salmon smolts across 2023 and 2024 migrating from the River Suldalslågen into a fjord system in southern Norway.
Equipped smolts with acoustic transmitters, depth sensor tags, and predation sensors before releasing them in the river or towing them to the fjord.
Smolts navigated outward rapidly, but low river discharge constrained route choice by significantly reducing movement through the northern fjord route.
Mortality clustered at the river mouth and a fjord bridge bottleneck, with sensor data indicating substantial predation by aquatic predators such as brown trout.
Fish traveled predominantly near the surface with minimal spatial variation, exhibiting clear diel vertical movements into deeper waters during daylight hours.

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Implication

Acoustic telemetry study reveals route selection and predation bottlenecks in migrating Atlantic salmon smolts, highlighting the impact of hydropower flow regulation on early marine survival.

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Lennox et al. (2026) studied this question.

synapsesocial.com/papers/6aa27b8858559d80afc74c01 https://doi.org/10.1111/eff.70062

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Predation Risk and Depth Use During Migration of Atlantic Salmon Smolts Through a Fjord Impacted by Hydropower Discharge

Key Points

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Implication

Discussion

Cite This Study

Predation Risk and Depth Use During Migration of Atlantic Salmon Smolts Through a Fjord Impacted by Hydropower Discharge

Key Points

No abstract yet

Implication

Discussion

Cite This Study

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