Migration problems of Atlantic salmon (Salmo salar L.) in flow regulated rivers

Migration patterns of adult Atlantic salmon (Salmo salar) and smolts of salmon and brown trout (Salmo trutta) were studied in the flow controlled areas of two northern Swedish rivers. Fish behaviour and migration success at passages of various hydropower facilities were evaluated in different flow regimes. In addition, the impacts of the power-stations on the salmon populations were modelled. On average, 30% (annual mean 0-47%) of the upstream migrating salmon that were captured at the mouth of Umeälven and marked with radio-, PIT- or Carlin-tags in 1995-2005 (n = 2651), reached the fish-ladder 32 km upstream. The migration took, on average, 44 days from the river mouth to the fish-ladder. Salmon were hindered or delayed at the power-station outlet, waterfalls and the fish-ladder area. At the turbine outlet area, salmon generally responded to increased bypass flows by upstream migration. In total, a 70 % average loss of potential spawners to the catchment area was estimated. Predictions based on population modelling showed that if 75 % of the females passed the regulated section successfully and reached spawning areas in the tributary Vindelälven, the population could increase by about 500 % over a ten-year period. Radio-tagged smolts (n = 206) of Atlantic salmon and brown trout released upstream of the power-stations at Umeälven and Piteälven in 2002-2004 migrated downstream in the main flows at a speed of about 2 body length s-1, eventually leading them to the turbine intakes. Migrating smolts were observed surface oriented at depths of 1-3 m. Flow modelling estimated relatively low fish guidance efficiencies for the spillways at natural flows. About 13 % of the smolts at Piteälven were hindered as they approached the power-station, and mortality of smolts at turbine passage was positively related to body size. By using the data for radio-tagged smolts and data from Carlin-tagged smolts (n = 7450) in 1998-1999, the overall average mortality for smolts at the power-station was estimated to 17%. Population modelling predicted a potential increase in the escapement return from 5-30 % to 70-120 % in ten years if the smolts had no losses as they passed the power-station

Influence of flow on migratory behaviour of salmon smolts

A study on the effect of flow velocity on the downstream migration of smolts, i.e. juvenile salmon and trout, in a major northern Swedish river, Ume \ue4lv, is presented. Few studies have been done on Swedish smolt migratory behaviour. This study comprises telemetric studies of downstream migrating smolts and flow velocity measurements in field. To achieve more comprehensive information about the flow field numerical simulations are carried out. This is done by solving the three dimensional Reynolds-averaged Navier-Stokes equations using the Fluent computational fluid dynamics (CFD) package. The field measurements are also used to validate the numerical flow simulation. The river Ume \ue4lv, where the study is preformed, is fully used for power production. However, its largest tributary river, Vindel\ue4lven, is unregulated and holds important spawning grounds for salmon (Salmo salar) and trout (Salmo trutta), and downstream of the confluence of the two rivers there is only one hydropower plant, the Stornorrfors power plant. This constitutes a major hindrance for fish migrating between the Bothnian Sea and the spawning grounds of the river Vindel\ue4lven. The juvenile fish leaving the Vindel\ue4lven downstream towards the ocean can migrate either through the turbines and deep rock tunnels of the power plant or through the surface weirs at the regulating dam. Because of the flow regime during the migration period of smolts most smolts are believed to follow the main stream through the turbines leading to a mortality of approximately 25 %.The objective of the study is to determine the migration paths of salmon and trout smolts and relate their behaviour to hydraulic factors. The results from the study can be used to improve smolt survival by taking appropriate measures to divert the smolts from the turbines, e.g. by changing spill rules or installing diversion systems.In spring 2002 22 salmon and 22 trout smolts were tagged with internal, individually coded radio transmitters (ATS). After the release approximately five kilometres upstream of the dam at Stornorrfors power plant their passages were registered at three plantary loggers and their movements tracked manually along their swimming paths. Simultaneously, flow velocities were measured in three dimensions using an Acoustic Doppler Profiler (ADP).Results from the tracking, flow measurements and flow simulation indicate that the smolts move along the main stream of the river. Since the tracking data only yield information on the smolt positions in the horizontal plane it cannot directly be concluded whether the smolt migration is passive or active. However, results from American studies on local salmon have shown that smolt migration occurs in the upper part of the flowing water. Combined with the fact that the water velocities in the upper part of the water column along the smolts migration paths are close to the mean transport velocity of the smolts it indicates that the downstream migration is passive.This study is part of a more extensive project that comprises studies of both upstream and downstream migration of fish. The objective of the project is to study the effect of flow hydraulics on fish migratory behaviour

Influence of flow on migratory behaviour of salmon smolts

A study on the effect of flow velocity on the downstream migration of smolts, i.e. juvenile salmon and trout, in a major northern Swedish river, Ume \ue4lv, is presented. Few studies have been done on Swedish smolt migratory behaviour. This study comprises telemetric studies of downstream migrating smolts and flow velocity measurements in field. To achieve more comprehensive information about the flow field numerical simulations are carried out. This is done by solving the three dimensional Reynolds-averaged Navier-Stokes equations using the Fluent computational fluid dynamics (CFD) package. The field measurements are also used to validate the numerical flow simulation. The river Ume \ue4lv, where the study is preformed, is fully used for power production. However, its largest tributary river, Vindel\ue4lven, is unregulated and holds important spawning grounds for salmon (Salmo salar) and trout (Salmo trutta), and downstream of the confluence of the two rivers there is only one hydropower plant, the Stornorrfors power plant. This constitutes a major hindrance for fish migrating between the Bothnian Sea and the spawning grounds of the river Vindel\ue4lven. The juvenile fish leaving the Vindel\ue4lven downstream towards the ocean can migrate either through the turbines and deep rock tunnels of the power plant or through the surface weirs at the regulating dam. Because of the flow regime during the migration period of smolts most smolts are believed to follow the main stream through the turbines leading to a mortality of approximately 25 %.The objective of the study is to determine the migration paths of salmon and trout smolts and relate their behaviour to hydraulic factors. The results from the study can be used to improve smolt survival by taking appropriate measures to divert the smolts from the turbines, e.g. by changing spill rules or installing diversion systems.In spring 2002 22 salmon and 22 trout smolts were tagged with internal, individually coded radio transmitters (ATS). After the release approximately five kilometres upstream of the dam at Stornorrfors power plant their passages were registered at three plantary loggers and their movements tracked manually along their swimming paths. Simultaneously, flow velocities were measured in three dimensions using an Acoustic Doppler Profiler (ADP).Results from the tracking, flow measurements and flow simulation indicate that the smolts move along the main stream of the river. Since the tracking data only yield information on the smolt positions in the horizontal plane it cannot directly be concluded whether the smolt migration is passive or active. However, results from American studies on local salmon have shown that smolt migration occurs in the upper part of the flowing water. Combined with the fact that the water velocities in the upper part of the water column along the smolts migration paths are close to the mean transport velocity of the smolts it indicates that the downstream migration is passive.This study is part of a more extensive project that comprises studies of both upstream and downstream migration of fish. The objective of the project is to study the effect of flow hydraulics on fish migratory behaviour

Hydraulic modelling and validation for the study of smolt migration

In order to assess the prerequisites for downstream migration of smolt the flow field upstream two hydropower stations in two large Swedish rivers have been made, and the simulations have been validated against stream velocities measured on site. The validated models have been used to compare the flow paths with the measured swimming paths of smolts. The simulations were done by solving the three dimensional Reynolds-averaged Navier-Stokes equations using the Fluent computational fluid dynamics (CFD) package. One of the studied rivers, Ume \ue4lv, whose main course is completely regulated, has a large unregulated tributary river, Vindel\ue4lven, which holds important spawning grounds for salmon (Salmo salar) and trout (Salmo trutta), and downstream of the confluence of the two rivers there is only one hydropower plant, the Stornorrfors power plant. This constitutes a major hindrance for fish migrating between the Bothnian Sea and the spawning grounds of the river Vindel\ue4lven. The juvenile fish, smolt, leaving the Vindel\ue4lven downstream towards the ocean can migrate either through the turbines and deep rock tunnels of the power plant or through the surface weirs at the regulating dam. Because of the flow regime during the migration period of smolts most smolts are believed to follow the main stream through the turbines leading to a mortality of approximately 25 %. The other studied river, Pite \ue4lv, also contain some spawning grounds in smaller tributaries upstream its first power plant. Although this plant is more like a-run-of-the-river plant most smolt passes the turbines instead of going over the spillways.The objective of the study is to determine the migration paths of salmon and trout smolts and relate their behaviour to hydraulic factors. The results from the study could then be used to improve smolt survival by taking appropriate measures to divert the smolts from the turbines, e.g. by changing spill rules or installing diversion systems.In Ume \ue4lv in Spring 2002, 22 salmon and 22 trout smolts were tagged with internal, individually coded radio transmitters (ATS). After the release approximately five kilometres upstream of the dam at Stornorrfors power plant their passages were registered at three stationary recorders and their movements tracked manually in the horizontal plane along their swimming paths. Simultaneously, velocity profiles were measured in selected cross-sections using an Acoustic Doppler Profiler (ADP). In spring 2003 16 smolt were tagged, released and tracked in the same way in Pite \ue4lv. In 2004 also the swimming depth was recorded.Results from the tracking, flow measurements and flow simulation indicate that the smolts move along the main stream of the river. In Ume \ue4lv the tracking data only yielded information on the smolt positions in the horizontal plane but it was found that the water velocities in the upper part of the water column along the smolts migration paths were close to the mean transport velocity of the smolt. In Pite \ue4lv Spring 2004 the swimming depth was measured to between 0.5 to 2 m below the surface. It can thus be concluded that the smolt migration is passive i.e. the smolt drift passively with the water.This study is part of a more extensive project that comprises studies of both upstream and downstream migration of fish. The objective of the project is to study the correlation between flow hydraulics and fish migratory behaviour. The ultimate goal is to create numerical fish models that are programmed to act as real fish in the CFD model. To get realistic models it is then first necessary to map real fish migratory behaviour to get to know the rules of the fish behaviour

Downstream migration of Salmo salar and S. trutta smolts in two regulated northern Swedish rivers

The downstream migration of Atlantic salmon and anadromous brown trout smolts was studied in two flow controlled northern Swedish rivers. The annual mean flow in Umeälven and Piteälven is c. 430 m3/s and c. 150 m3/s, respectively. Water power constructions located in the lower parts of these rivers may hinder or kill downstream migrating fish. Naturally produced salmon smolts in these rivers have two alternatives for passage of the water power constructions when they undertake their seasonally timed seaward migration in may-june: a) passing the turbines, or b) pass through the spill-way over the dam. Existing power-stations in Stornorrfors (Umeälven) use Francis turbines while Sikfors (Piteälven) use Kaplan turbines. In spring 2002 and 2003 a total of 90 Atlantic salmon and 56 brown trout two-year old hatchery-reared smolts were radio tagged with internal esophageal, individually coded radio transmitters (ATS). Trout were significantly larger (average length: 23.8 cm) than salmon (19.7 cm) (t-test, p<0.01). One to two days post-tagging the fish were released upstream the dammed areas, c. 5.0 km above Stornorrfors dam and c. 2.5 km above Sikfors dam, respectively. Their downstream migration routes were tracked both manually and with automatic listening stations in the horizontal plane (2-dimensional). Simultaneously, velocity profiles were measured in selected cross-sections using an Acoustic Doppler Profiler (ADP) applied to depth measurements giving a digitalised GIS-map over the dammed areas. Our main findings from the telemetry trackings, depth- and flow-measurements, and flow simulation show that the downstream migrating smolts move in the main flow in the river where the highest water velocities were registered. This subsequently resulted that fish entered the power-station, and did not pass downstream over spillways via dams or the fish ladders. The discharge ratio between power-station and spillway, with excess of water passing the power-station, guided fish to pass the turbines giving an extra mortality. Comparing the water velocities in the upper part of the water column with the estimated speed of smolts indicate that the downstream migration is passive. The average migration speed for downstream migrating smolts for the two species tested was found to be c. 0.4 m/s (c. 2 bodylengths/sec). Of the fish that passed trough the Sikfors power-station 83 % was registered downstream the turbine outlet. Remaining fish (17 %) that was not registered could have died or lost their tags in the power-station. Data from a Carlin-tagging study made during the years 98-99 in Piteälven (7450 tagged salmon smolts) is analysed and indicate a mortality of 20-30 % caused by the power-station. These results are discussed and compared to previously conducted studies at Umeälven and other regulated rivers