F. Økland

Norwegian Institute for Nature Research | NINA · Department of Aquatic Ecology

The Atlantic salmon (Salmo salar) is an iconic species of significant ecological and economic importance. Their downstream migration as smolts represents a critical life-history stage that exposes them to numerous challenges, including passage through hydropower plants. Understanding and predicting fine-scale movement patterns of smolts near hydrop...

The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised...

The aim of this study was to assess whether activity and heart rate sensor implants can be used to measure stress and thus estimate one important welfare indicator for fish in aquaculture pens, and if such measurements correlate to physiological factors measured through blood sampling. The experiment consisted of two parts: i) a bio-logger study wh...

European rivers are obstructed by more than one million barriers that have resulted in excessive loss of river continuity (Belletti et al. 2020). On the main course of the Danube River there are 83 longitudinal continuity interruptions, out of which 65 dams are used for hydropower (ICPDR 2022a). The Iron Gate Hydropower and Navigation System is one...

Introduction River infrastructures, such as hydropower plants Iron Gate I (IG; rkm 943) and II (rkm 863) represent major obstructions to fish migration in the Danube River. Knowledge about fish behaviour and movements in the vicinity of major river structures is required to build effective fish passages to protect migratory fish species, with acous...

Behaviour observations of the endangered native marble trout (Salmo marmoratus, Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in the laboratory and in a tributary to the Idrijca River in Slovenia were combined to study the movements and dominance relationships between individuals of the two species in an open field...

The global population of European eel (Anguilla anguilla) is rapidly declining, and migration barriers in rivers are believed to be one of several key causes. While progress has been made in the development of bypass solutions, they are often constructed based on a limited knowledge of swimming behaviour. A bypass close to the stream bed is often r...

Little is known about the exact movement parameters of migratory cyprinids listed as conservation priorities. A northern population of predatory asp, listed on the Bern Convention Appendix III, was studied in a near natural lake–river ecosystem by tracking adult fish tagged with acoustic transmitters for 32 months. Activity levels in terms of swimm...

Marine aquaculture of Atlantic salmon (Salmo salar) is a relatively new industry where breeding programs have led to rapid genetic change in the captive populations that were built up alongside conspecific wild individuals. Throughout its 50-years history, marine aquaculture of Atlantic salmon has been associated with escapes, and studies have show...

Background Welfare challenges in salmon farming highlights the need to improve understanding of the fish’s response to its environment and rearing operations. This can be achieved by monitoring physiological responses such as heart rate (HR) for individual fish. Existing solutions for heart rate monitoring are typically based on Electrocardiography...

The dam's construction without fish passes had a major impact, obstructing migratory fish populations from moving between different parts of the river systems and utilize they key habitats. Fish species and fish populations are depending on long migrations are most seriously affected by river fragmentation. Building well-functioning fish passage sy...

The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river...

The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river...

Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake—LSC; high structural complexity—HSC) was associated with contrasting behaviour in...

Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulation (PPM) is an acoustic telemetry method that allows multiple unique identification codes to be transmitted at a single acoustic frequency, typically in the 69 kHz range. However, because the potential number of unique identification codes (i.e. tags) i...

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured...

Fish swimming performance is strongly influenced by flow hydrodynamics, but little is known about the relation between fine-scale fish movements and hydrodynamics based on in-situ investigations. In the presented study, we validated the etho-hydraulic fish swimming direction model presented in the River Mandal from Southern Norway, using similar be...

Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators has received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake – LSC; high structural complexity - HSC) was associated with contrasting behaviour...

Background Fish telemetry using electronic transmitter or data storage tags has become a common method for studying free-swimming fish both in the wild and in aquaculture. However, fish used in telemetry studies must be handled, anaesthetised and often subjected to surgical procedures to be equipped with tags, processes that will shift the fish fro...

Ferox trout are large, long‐lived, piscivorous trout normally found in deep lakes; they are highly prized by trophy anglers. Lough Corrib and Lough Mask, Western Ireland, have recorded the majority of Irish specimen ferox trout since angling records began. Little was known regarding the spawning location of ferox trout relative to sympatric brown t...

Repeat spawners constitute an important component of Atlantic salmon populations, but survival of post-spawning individuals (kelts) are often compromised by anthropogenic structures such as hydropower plants (HPPs). Potential effects of HPPs include migration delays and associated increased energy depletion, which potentially results in increased o...

Potamodromous fishes require safe migration routes between spawning, feeding and wintering habitats to complete their life cycle. As knowledge on asp migrations is restricted, this work investigated the movements of adult asp tagged with acoustic transmitters for 3 years in the large Peipsi‐Emajõgi‐Võrtsjärv lake–river system, Estonia, which is fre...

We investigated the relationship between telemetry measurements of heart rate and swimming activity and the physiological status in farmed Atlantic salmon (Salmo salar) to assess the potential to use telemetry measurements as proxies for stress. Sensor tags measuring heart rate and swimming activity were surgically implanted into the peritoneal cav...

Background: Fish telemetry using electronic transmitter or data storage tags has become a common method for studying free-swimming fish both in the wild and in aquaculture. However, fish used in aquatic telemetry studies must be handled, anaesthetised and often subjected to surgical procedures to be equipped with tags, processes that will shift the...

Background: Fish telemetry using electronic transmitter or data storage tags has become a common method for studying free-swimming fish both in the wild and in aquaculture. However, fish used in telemetry studies must be handled, anaesthetised and often subjected to surgical procedures to be equipped with tags, processes that will shift the fish fr...

Background: Fish telemetry using electronic transmitter or data storage tags has become a common method for studying free-swimming fish both in the wild and in aquaculture. However, fish used in telemetry studies must be handled, anaesthetised and often subjected to surgical procedures to be equipped with tags, processes that will shift the fish fr...

Weirs are barriers built across rivers for a wide range of other purposes than hydropower production. Like hydropower installations, weirs can negatively impact fish migrations. Downstream migration and mortality of Atlantic salmon smolts were studied during passage of a weir and power station by tagging 227 smolts with radio transmitters. Extra lo...

The R package yaps was introduced in 2017 as a transparent open source alternative to closed source manufacturer-provided solutions to estimate positions of fish (and other aquatic animals) tagged with acoustic transmitters. Although yaps is open source and transparent, the process from raw detections to final tracks has proved to be challenging fo...

Anthropogenic structures in rivers are major threats for fish migration and effective mitigation is imperative given the worldwide expansion of such structures. Fish behaviour is strongly influenced by hydrodynamics, but little is known on the relation between hydraulics and fish fine scale-movement. We combined 3D Computational fluid dynamics mode...

Salmon smolts were released upstream of a run‐of‐river hydropower site and recaptured downstream for inspection. Descending fish behaviour through three possible migration routes (turbines, fishway, spillway) was analysed using telemetry, fyke nets and diving. Tagged smolts did not follow the main water flow; over 70% used the fishway, which receiv...

There is no generic solution to establish safe passage of downstream migrating fish passed hydropower facilities and mitigation measures are species‐ and site‐specific. Development of solutions is thus often based on “trial and error” and modelling based approaches may significantly reduce cost and time to arrive at successful mitigation. Here we e...

The abundance of European eel has seriously declined during recent decades. Hydropower production is one of the main threats, and solutions at power stations are needed to reduce mortality of downstream migrating silver eel. We examined mortality, migration routes and behavior of silver eel at a power station in Germany, after the power station was...

We report on the data from an extensive monitoring programme for the occurrence of escaped farmed Atlantic salmon (Salmo salar) in Norwegian rivers for 25 years. This monitoring started as a 3-year research programme in 1989 and was followed by management authorities to cover the proportional occurrence of escaped farmed Atlantic salmon in rivers d...

The interaction between hydrodynamics and the upstream migration of fish has been investigated in several studies over the past few years, but there has been a relative lack of investigation into the effects of hydraulics on the downstream migration of fish. In Norway, mortality associated with downstream migration is strongly related to hydropower...

There are substantial benefits to potential fitness conferred to animals that undertake migrations. However, animals must make compromises to maximize survival and compensate for the risks associated with long-distance movement. European eel (Anguilla anguilla), a migratory ca-tadromous fish, has undergone population declines owing to changes in ma...

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temper...

We studied downstream migration of 256 radio-tagged Atlantic salmon smolts passing a low-head power station where technical facilities have been improved to allow safe migration via several bypass routes. Extra mortality was 7 and 17% (two years) in the power station reservoir, and a minimum of 10 and 13% at the power station compared to in a contr...

Aquatic positional telemetry offers vast opportunities to study in vivo behaviour of wild animals, but there is room for improvement in the data quality provided by current procedures for estimating positions. Here we present a novel positioning method called YAPS (Yet Another Positioning Solver), involving Maximum Likelihood analysis of a state-sp...

Downstream migration of 112 radio-tagged Atlantic salmon smolts was studied in the Diemel, Germany, to examine 1) mortality and migration speeds during riverine migration and at a hydropower station, 2) choice of migration routes at the power station, and 3) survival and transit speed through Archimedes screw and Francis turbines. Mortality was not...

Background The aim of telemetry studies is often to determine the fate and mortality rates of fish. A moving fish is usually regarded as alive and a long-term stationary fish as dead—and the site where it became stationary as the site where it died. Downstream transport of dead fish in rivers can lead investigators to mistake dead fish for live fis...

Background Development of miniature acoustic transmitters and data-storage tags has provided new insights into ecology of free-ranging aquatic animals. In this study, we used a data-storage-type and a conventional acoustic transmitter, both equipped with a salinity sensor, to measure the in situ salinity experienced by Atlantic salmon post-smolts d...

Downstream migration of radio-tagged Atlantic salmon smolts, Salmo salar L., was studied in the Kinzig, Germany, to examine effects of passing a run-of-river hydropower station with a movable bulb turbine. Immediate mortality for smolts passing the power station was low (3%–6%), probably facilitated by a curved rack in front of the turbine and the...

The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic taggi...

The aim of this study was to examine migration routes and losses of Atlantic salmon smolt past three hydropower stations, which were the Unkelmühle (River Sieg), Gengenbach (River Kinzig), and Kuhlemühle (River Diemel) power stations. These three power stations represent the use of different technologies to reduce negative impact on downstream migr...

Catadromous anguillid eels (genus Anguilla) migrate from their freshwater or estuarine habitats to marine spawning areas. Evidence from satellite tagging studies indicates that tropical and temperate eel species exhibit pronounced diel vertical migrations, from between 150-300 m nighttime depths to 600-800 m during the day. Collections of eggs and...

While fine mesh trash racks constitute a safe barrier for downstream migrating smolts, such racks can be expensive and technically difficult to retrofit at hydropower intakes. Alternatively, a combination of attraction and repulsion measures can successfully pass fish by the intake and into safe corridors. At the Laudal hydropower plant in the rive...

Little is known about migratory routes and habitat use of anadromous brown trout Salmo trutta at sea. We therefore conducted a 2 yr study (2011-2012) on sea trout in the River Himleån system (a river, an estuary, and a coastal sea environment) in western Sweden. The main objectives were to investigate migration speed, migration routes, and mortalit...

The spawning areas of tropical anguillid eels in the South Pacific are poorly known, and more information about their life histories is needed to facilitate conservation. We genetically characterized 83 out of 84 eels caught on Gaua Island (Vanuatu) and tagged 8 eels with pop-up satellite transmitters. Based on morphological evidence, 32 eels were...