Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and diffe... more Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g., wetland, urban, wooded, and agricultural) in the River Klarälven and its 30 permanently flowing tributaries. We hypothesized that these environmental attributes would differ between tributary and main stem habitat and that these differences would be driven by landscape attributes including land use. We found considerable intertributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associa...
Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and diffe... more Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g. wetland, urban, wooded and agricultural) in the River Klarälven and its 30 permanently-flowing tributaries. We found considerable inter-tributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associated with coldwater tributaries. We also found an inverse relationship between water quality and anthropogenic land use. Protecting tributaries with low anthropogenic impact will likely become i...
Over the past several decades recreational fisheries have grown substantially throughout the worl... more Over the past several decades recreational fisheries have grown substantially throughout the world. Until recently, however, recreational catch has been ignored in the management of many important fisheries. The studies presented in this thesis examine different approaches to monitoring recreational trolling fisheries’ catch and effort in Lake Vanern, Sweden, the largest lake in the European Union. Paper I presents results from a complemented roving/mail-in survey, designed to estimate recreational effort and catch of Atlantic salmon (Salmo salar) and brown trout (S. trutta). The results show that the recreational trolling fishery today harvests more salmon and trout annually than the commercial and subsistence fisheries combined, and that there are seasonal patterns in effort and catch. Paper II evaluates different angler catch reporting methods (mail-in, tournament reports, and face-to-face interviews), compares catch rates within and among spring and fall fishing periods and exam...
Predation on fish by mammals and birds may be high during winter in boreal streams, and juvenile ... more Predation on fish by mammals and birds may be high during winter in boreal streams, and juvenile salmonids respond by reducing their daytime activity to minimize exposure. Surface ice may offer protection from terrestrial predators, and salmonids under ice cover should spend less time on anti-predator behaviors and increase their activity. Using brown trout as a test species, these predictions were tested in laboratory and field experiments.In an artificial laboratory stream, the presence of ice cover reduced stress and increased swimming activity, foraging and aggression. The effect of ice cover on activity was greatest for trout with high resting metabolic rates, suggesting that individual intraspecific differences in metabolism may influence the strategies used to cope with different winter conditions. In a boreal forest stream, we simulated ice by suspending plastic sheeting over five 30-m-long stretches, and trout that spent winter under this simulated ice cover grew better tha...
There are many obstacles in rivers that prevent or hinder passage of fish past barriers. Here, we... more There are many obstacles in rivers that prevent or hinder passage of fish past barriers. Here, we present a specially designed solution for juvenile and adult brown trout so that they may to swim past discharge-regulating weirs in the upper Caraş River in both the upstream and downstream directions. The proposed solution relies on gravity flow and will have current velocities that will not inhibit weak swimmers swimming upstream to pass the weirs. Corrosion-resistant materials and the absence of components that could potentially injure the fish will be used in the construction of these technical solutions. Although testing of the functionality of this solutions for upstream - downstream and downstream - upstream passage of weirs is needed, we believe that if implemented, it should improve connectivity especially for brown trout and consequently conserve within-stream genetic diversity in the Caraş River and where appropriate in alike other Carpathian lotic systems with similar types...
sStudying fish behaviour at hydropower dams is needed to facilitate the design and improvement of... more sStudying fish behaviour at hydropower dams is needed to facilitate the design and improvement of fish passage solutions, but few studies have focused on Atlantic salmon kelts. Here, we used radio telemetry (n = 40, size range = 50–81 cm) and acoustic sonar to study kelt movements in the forebay as well as their dam passage survival and subsequent migration success past multiple dams. We also compare radio telemetry and acoustic sonar observations of fish behaviour and used acoustic sonar to measure the depth distribution of fish approaching the turbine intake zone. Passage success at the dam was 41%, and mortality was largely associated with turbine passage (62%). The two fish that passed via the spill gates survived and continued their downstream migration. At the dam, all but one radio‐tagged kelt approached the intake zone shortly after arrival to the forebay, and sonar data showed that approaching fish were predominantly surface oriented (72%, 88% and 96% of the observations we...
Summary In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the... more Summary In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators. We tested the effects of burbot (Lota lota) on the winter sheltering behaviour of PIT‐tagged 0+ brown trout (Salmo trutta) in daylight and darkness. Sheltering in the streambed by trout was studied in the presence and absence of fine wood bundles. We found that the use of streambed and fine wood was lower in darkness than in daylight. Availability of fine wood significantly decreased sheltering in the streambed, and this effect was more pronounced in daylight than in darkness. The presence of a burbot significantly decreased sheltering in the streambed, had no effect on use of fine wood and resulted in a higher number of exposed trout. Our resu...
The River Ätran is an important river for diadromous fish species on the Swedish west-coast. Wild... more The River Ätran is an important river for diadromous fish species on the Swedish west-coast. Wild populations of wild Atlantic salmon, trout, European eel and sea lamprey enter the river for spawning and growth. The conditions for migratory fish species are improving in the river since rehabilitation efforts now address the needs of all diadromous species and life-stages, and not only upstream moving salmonids. This presentation gives examples of rehabilitative measures and their feasibility for diadromous fish at two hydroelectric plants (HEPs 1-2) in the River Ätran. Attempts to decrease the mortality among downstream moving fish are now being tested in the River Ätran. A surface spill gate at HEP1 was not an effective measure for downstream passage for silver eels and smolts, but instead they passed rapidly through the racks and turbines. Kelts spent a long time searching for a passageway downstream, and several of them were lost in doing so. By reducing the slope and the gap wid...
Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and diffe... more Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g., wetland, urban, wooded, and agricultural) in the River Klarälven and its 30 permanently flowing tributaries. We hypothesized that these environmental attributes would differ between tributary and main stem habitat and that these differences would be driven by landscape attributes including land use. We found considerable intertributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associa...
Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and diffe... more Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g. wetland, urban, wooded and agricultural) in the River Klarälven and its 30 permanently-flowing tributaries. We found considerable inter-tributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associated with coldwater tributaries. We also found an inverse relationship between water quality and anthropogenic land use. Protecting tributaries with low anthropogenic impact will likely become i...
Over the past several decades recreational fisheries have grown substantially throughout the worl... more Over the past several decades recreational fisheries have grown substantially throughout the world. Until recently, however, recreational catch has been ignored in the management of many important fisheries. The studies presented in this thesis examine different approaches to monitoring recreational trolling fisheries’ catch and effort in Lake Vanern, Sweden, the largest lake in the European Union. Paper I presents results from a complemented roving/mail-in survey, designed to estimate recreational effort and catch of Atlantic salmon (Salmo salar) and brown trout (S. trutta). The results show that the recreational trolling fishery today harvests more salmon and trout annually than the commercial and subsistence fisheries combined, and that there are seasonal patterns in effort and catch. Paper II evaluates different angler catch reporting methods (mail-in, tournament reports, and face-to-face interviews), compares catch rates within and among spring and fall fishing periods and exam...
Predation on fish by mammals and birds may be high during winter in boreal streams, and juvenile ... more Predation on fish by mammals and birds may be high during winter in boreal streams, and juvenile salmonids respond by reducing their daytime activity to minimize exposure. Surface ice may offer protection from terrestrial predators, and salmonids under ice cover should spend less time on anti-predator behaviors and increase their activity. Using brown trout as a test species, these predictions were tested in laboratory and field experiments.In an artificial laboratory stream, the presence of ice cover reduced stress and increased swimming activity, foraging and aggression. The effect of ice cover on activity was greatest for trout with high resting metabolic rates, suggesting that individual intraspecific differences in metabolism may influence the strategies used to cope with different winter conditions. In a boreal forest stream, we simulated ice by suspending plastic sheeting over five 30-m-long stretches, and trout that spent winter under this simulated ice cover grew better tha...
There are many obstacles in rivers that prevent or hinder passage of fish past barriers. Here, we... more There are many obstacles in rivers that prevent or hinder passage of fish past barriers. Here, we present a specially designed solution for juvenile and adult brown trout so that they may to swim past discharge-regulating weirs in the upper Caraş River in both the upstream and downstream directions. The proposed solution relies on gravity flow and will have current velocities that will not inhibit weak swimmers swimming upstream to pass the weirs. Corrosion-resistant materials and the absence of components that could potentially injure the fish will be used in the construction of these technical solutions. Although testing of the functionality of this solutions for upstream - downstream and downstream - upstream passage of weirs is needed, we believe that if implemented, it should improve connectivity especially for brown trout and consequently conserve within-stream genetic diversity in the Caraş River and where appropriate in alike other Carpathian lotic systems with similar types...
sStudying fish behaviour at hydropower dams is needed to facilitate the design and improvement of... more sStudying fish behaviour at hydropower dams is needed to facilitate the design and improvement of fish passage solutions, but few studies have focused on Atlantic salmon kelts. Here, we used radio telemetry (n = 40, size range = 50–81 cm) and acoustic sonar to study kelt movements in the forebay as well as their dam passage survival and subsequent migration success past multiple dams. We also compare radio telemetry and acoustic sonar observations of fish behaviour and used acoustic sonar to measure the depth distribution of fish approaching the turbine intake zone. Passage success at the dam was 41%, and mortality was largely associated with turbine passage (62%). The two fish that passed via the spill gates survived and continued their downstream migration. At the dam, all but one radio‐tagged kelt approached the intake zone shortly after arrival to the forebay, and sonar data showed that approaching fish were predominantly surface oriented (72%, 88% and 96% of the observations we...
Summary In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the... more Summary In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators. We tested the effects of burbot (Lota lota) on the winter sheltering behaviour of PIT‐tagged 0+ brown trout (Salmo trutta) in daylight and darkness. Sheltering in the streambed by trout was studied in the presence and absence of fine wood bundles. We found that the use of streambed and fine wood was lower in darkness than in daylight. Availability of fine wood significantly decreased sheltering in the streambed, and this effect was more pronounced in daylight than in darkness. The presence of a burbot significantly decreased sheltering in the streambed, had no effect on use of fine wood and resulted in a higher number of exposed trout. Our resu...
The River Ätran is an important river for diadromous fish species on the Swedish west-coast. Wild... more The River Ätran is an important river for diadromous fish species on the Swedish west-coast. Wild populations of wild Atlantic salmon, trout, European eel and sea lamprey enter the river for spawning and growth. The conditions for migratory fish species are improving in the river since rehabilitation efforts now address the needs of all diadromous species and life-stages, and not only upstream moving salmonids. This presentation gives examples of rehabilitative measures and their feasibility for diadromous fish at two hydroelectric plants (HEPs 1-2) in the River Ätran. Attempts to decrease the mortality among downstream moving fish are now being tested in the River Ätran. A surface spill gate at HEP1 was not an effective measure for downstream passage for silver eels and smolts, but instead they passed rapidly through the racks and turbines. Kelts spent a long time searching for a passageway downstream, and several of them were lost in doing so. By reducing the slope and the gap wid...
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Papers by Larry Greenberg