Larry Greenberg

Karlstads Universitet · Department of Environmental and Life Sciences

By analyzing otolith microchemistry, we examined the use of freshwater and marine environments by brown trout Salmo trutta L. that spawn in the Swedish River Emån and migrate to the Baltic Sea. We estimated the time juveniles spent in freshwater and the number of times the fish returned to freshwater, presumably to spawn. Twenty-six percent of the...

Changes in the number, structure, and function of mitochondria during the early life stages of animals can play an important role for an organism’s metabolic rate, growth, and health. Previous studies have shown that juvenile brown trout (Salmo trutta) subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduc...

In many rivers, downstream‐migrating salmonid smolts must pass multiple dams often with high losses as a result. Fish experience mortality both in dam and reservoir passage, and spilling water might allow fish to avoid turbine passage and hence increase migration survival. In River Klarälven, Sweden landlocked Atlantic salmon smolts migrate along a...

Winter represents a challenging season for animals in boreal streams and is a period with low temperatures, extremely low levels of primary production, low metabolic rates of ectotherms, and little light. Yet, stabile ice cover provides shelter for salmonids residing in rivers. Despite low light levels in winter, stream salmonids are mainly nocturn...

Forest management operations greatly influence stream habitats. Canopy clearing and subsequent canopy development during succession, site preparation , and ditching alter the light environment, and increase sediment inputs and nutrient exports from upland and riparian soils to streams. These physico-chemical changes affect aquatic biofilms and meta...

Variation in thermal conditions during embryogenesis can have far-reaching impact throughout ontogeny and may give rise to behavioural variation. Many animals, such as salmonids, exhibit behavioural trade-offs related to foraging and predator avoidance. How embryonic temperature affects these behaviours has remained unexplored. Not only abiotic con...

During winter, stream fishes are vulnerable to semi-aquatic predators like mammals and birds and reduce encounters by being active in darkness or under surface ice. Less is known about the behavior of fishes towards instream piscivorous fishes. Here, we examined how surface ice and light affected the anti-predator behavior of juvenile brown trout (...

Personality varies among individuals and is influenced by the environment. Here, we tested the hypothesis that egg incubation temperature had carry-over effects on swimming activity of juvenile brown trout, Salmo trutta. Eggs from different crosses involving anadromous and lacustrine-adfluvial parents were incubated under two temperature regimes, u...

Conditions early in ontogeny can have considerable effects later on in life. Many salmonids spawn during the autumn, and temperature during subsequent embryogenesis may have far‐reaching effects on life‐history traits, especially when considering ongoing climate change. Even biotic conditions during embryogenesis, such as predation threat, may affe...

When fish migrate downstream, they follow bulk flow and unless enough flow is redirected towards a bypass, they need guidance to pass the dam. Guidance relying on behavioural responses by fish are generally less effective but less expensive than physical guidance structures, and hence there is an interest in finding more effective behavioural guida...

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, wo...

Collaboration has the potential to aid the balancing of values and goals that belong to different, sometimes competing, policy fields, such as energy, climate adaptation and nature conservation—a key component of sustainable governance. However, we need to know more of how collaboration can function as integrating (and integrated) components of gov...

Large boreal rivers in Sweden are generally impounded by hydropower dams and a large proportion of main stem shallow flowing habitats have been lost. Tributaries often contain the last undisturbed habitats and could be important for the conservation of species diversity. In particular, tributary mouth areas could be biodiversity hot-spots, due to t...

Vattenkraften är viktig för Sveriges omställning till fossilfri elproduktion. För att öka vattenkraftens hållbarhet som energikälla behövs miljöåtgärder som gör att elproduktionens miljöeffekter minimeras där det är möjligt. Regleringen av vattenflöden leder ofta till att vattendragens ekosystem förändras med förlust av biologisk mångfald och ekosy...

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, woo...

River connectivity is a major environmental factor affecting fish migration through river systems. Anthropogenic barriers cause substantial delays and mortality to long-migrating diadromous fish, such as salmonids. Downstream bypasses have received little attention over the years and can be constructed in several ways, with bypass acceptance by fis...

Large boreal rivers in Sweden are generally impounded by hydropower dams and a large proportion of their main stem shallow flowing habitats have been lost. Tributaries often contain relatively undisturbed habitats and could be important for the conservation of species diversity. Tributary mouth areas could be biodiversity hot-spots, due to the vici...

The present experiment tested if temperature during embryogenesis and parental heritage affected the migratory behaviour of young brown trout Salmo trutta. Two parental forms were used, a freshwater resident form and an anadromous form, both from the same river system but geographically isolated since 1993–95. Four groups of young S. trutta were pr...

ABSTRACT Tumors and infectious agents both benefit from an immunosuppressive environment. Cutibacterium acnes (C. acnes) is a bacterium in the normal skin microbiota, which has the ability to survive intracellularly in macrophages and is significantly more common in prostate cancer tissue compared with normal prostate tissue. This study investigate...

Historically, ecological engineered solutions for fish passage across anthropogenic barriers in rivers has mainly focused on facilitating upstream passage for long-migrating diadromous fish, such as salmonids. More recently, passage solutions have shifted their focus to a more holistic ecological perspective, allowing passage for species with diffe...

Reliable methods for assessing the ecological status of degraded rivers are essential for evaluating restoration efforts in lotic habitats. Several methods are based on biological indicators, such as benthic macroinvertebrates. The Hester–Dendy multi-plate sampler is a commonly used tool for sampling macroinvertebrates, but its performance under di...

Temperature during egg incubation and early development influences later life stages of fishes, potentially influencing survival. Throughout its distribution, Atlantic salmon (Salmo salar Linnaeus, 1758) have experienced population declines, and in view of ongoing global warming, we tested if temperature during the earliest developmental stages mod...

Citation: Durtsche, R. D., B. Jonsson, and L. A. Greenberg. 2021. Thermal conditions during embryogenesis influence metabolic rates of juvenile brown trout Salmo trutta. Ecosphere 12(2): Abstract. The projected climate change and increase in thermal conditions in northern latitudes over the next 60 yr has the potential to alter the metabolic scope...

Managing and conserving threatened migratory salmonid populations in large river–lake ecosystems is challenging not only because of the ecosystems’ large size, but also because there is often more than one anthropomorphic stressor. The River Klarälven – Lake Vänern ecosystem, situated in Norway and Sweden, is a large, highly modified ecosystem, hom...

Passage of hydropower plants by upstream-migrating salmonid spawners is associated with reduced migration success, and the need for knowledge of fish behavior downstream of dams is widely recognized. In this study, we examined fishway passage of landlocked Atlantic salmon (Salmo salar) in River Klarälven, Sweden, and brown trout (Salmo trutta) in R...

Background Temperature affects many aspects of performance in poikilotherms, including how prey respond when encountering predators. Studies of anti-predator responses in fish mainly have focused on behaviour, whereas physiological responses regulated through the hypothalamic-pituitary-interrenal axis have received little attention. We examined pla...

Recreational fishing has grown substantially worldwide; for some recreational fisheries both catch and economic value now exceeds that of commercial fisheries. Monitoring of recreational fisheries effort and catch is therefore important for sustainable fisheries management. We developed and implemented an angler survey to estimate effort and catch...

Low winter temperatures constrain predator‐detection and escape capabilities, making poikilotherms vulnerable to predation. Investigations of temperature effects on predator–prey interactions can therefore be of special importance in light of ongoing climate change, where winter temperatures are predicted to increase substantially at northern latit...

Nonanadromous Atlantic salmon (Salmo salar) exhibit a combination of variation in life history, habitat, and species co-existence matched by few vertebrates. Distributed in eastern North America and northern Europe, habitat ranges from hundreds of metres of river to Europe’s largest lakes. As juveniles, those with access to a lake usually migrate t...

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...

Background Globally, there are a large and growing number of researchers using biotelemetry as a tool to study aquatic animals. In Europe, this community lacks a formal network structure. The aim of this study is to review the use of acoustic telemetry in Europe and document the contribution of cross-boundary studies and inter-research group collab...

Populations of fishes provide valuable services for billions of people, but face diverse and interacting threats that jeopardize their sustainability. Human population growth and intensifying resource use for food, water, energy and goods are compromising fish populations through a variety of mechanisms, including overfishing, habitat degradation a...

The purpose of this study was to investigate behavior and survival of radio-tagged wild- and hatchery-reared landlocked Atlantic salmon smolts as they migrated past three hydropower dams equipped with fish bypass solutions in the Winooski River, Vermont, USA. Among hatchery-released smolts, those released early were more likely to initiate migratio...

Abstracts Studying 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 s...

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...

Passage of fish through hydropower dams is associated with mortality, delay, increased energy expenditure and migratory failure for migrating fish and the need for remedial measures for both upstream and downstream migration is widely recognised. A functional fish passage must ensure safe and timely passage routes that a substantial portion of migr...

Protection provided by shelter is important for survival and affects the time and energy budgets of animals. It has been suggested that in fresh waters at high latitudes and altitudes, surface ice during winter functions as overhead cover for fish, reducing the predation risk from terrestrial piscivores. We simulated ice cover by suspending plastic...

Prior to out-migration, salmonid fish typically undergo physiological and morphological changes — a process known as smolting. This study indicates that smolting in brown trout (Salmo trutta) is affected by feeding conditions in spring immediately prior to out-migration. This conclusion was reached after experimentally testing the effect of seasona...

Repeat salmonid spawners may make large contributions to total recruitment and long term population stability. Despite their potential importance, relatively little is known about this phase of the life history for anadromous populations, and nothing has been reported for landlocked populations. Here, we studied post-spawning behaviour and survival...

Surface ice in rivers and lakes buffers the thermal environment and provides overhead cover, protecting aquatic animals from terrestrial predators. We tested if surface ice influenced the behavior (swimming activity, aggressive encounters, and number of food items eaten) and stress level (coloration of eyes and body) of stream-living brown trout Sa...

Upstream migration by adult salmonids is impeded by dams in many regulated rivers, as is the case for landlocked Atlantic salmon, Salmo salar, in the River Klarälven, Sweden. There, the salmon cannot reach the spawning grounds due to the presence of eight dams. Hence, hatchery-reared smolts are released downstream of the dams, and upstream migratin...

Periphyton communities of a boreal stream were exposed to different light and nutrient levels to estimate energy transfer efficiency from primary to secondary producers using labeling with inorganic 13C. In a one-day field experiment, periphyton grown in fast-flow conditions and dominated by opportunistic green algae were exposed to light levels co...

Salmonids exhibit considerable variation within and between individuals in growth, diet, foraging strategy and habitat use, but little is known about how these characteristics covary. Previous work has shown that habitat use strongly influences growth rates in brown trout ( Salmo trutta ). We examined individual variation in diet of PIT‐tagged Salm...

The migratory behaviour of hatchery-reared landlocked Atlantic salmon Salmo salar raised under three different feeding regimes was monitored through the lower part of the River Klarälven, Sweden. The smolts were implanted with acoustic transmitters and released into the River Klarälven, 25 km upstream of the outlet in Lake Vänern. Early mature male...

The effects of feed quality and quantity on growth, early male parr maturation and development of smolt characteristics were studied in hatchery-reared landlocked Atlantic salmon Salmo salar. The fish were subjected to two levels of feed rations and two levels of lipid content from first feeding until release in May of their second year. Salmo sala...

Changes to the riparian vegetation of forest streams during timber harvesting may have considerable impacts on stream biota, but few studies have attempted to separate the effects of individual factors that are altered during clear‐felling operations. We studied the effects of large wood and terrestrial invertebrate supply, two factors affected by...

Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factor...

The foraging success of predators depends on how their consumption of prey is affected by prey density under different environmental settings. Here, we measured prey capture rates of drift-feeding juvenile brown trout and European grayling at different prey densities in an artificial stream channel at 5 and 11 °C. Capture rates were lower at 5 than...

Preferring one social partner over another can enhance fitness. This paper reports that juvenile grayling were significantly more likely to enter and forage in new, upstream habitats when paired with familiar versus unfamiliar social partners. Fish paired with unfamiliar partners or when alone were more reluctant to enter the new area. The entry ti...

Relatively little is known about the downstream migration of landlocked stocks of Atlantic salmon Salmo salar L. smolts, as earlier migration studies have generally focused on upstream migration. However, in watersheds with many hydroelectric plants (HEPs), multiplicative loss of downstream-migrating salmon smolts can be high, contributing to popul...

1. Winter ice conditions in boreal streams are highly variable, and behavioural responses by fish to river ice may affect overwinter survival rates. One type of ice, surface ice, stabilises water temperatures, reduces instream light levels and may provide overhead cover. 2. Because surface ice is believed to afford protection against endothermic pr...

Drift-feeding salmonids in boreal streams face temperatures below physical optima for extensive periods of the year. Because juvenile salmonids react to low water temperatures by becoming nocturnal, knowledge about their foraging ability at low light intensities in cold water is needed to accurately estimate energy intake during non-summer conditio...

This chapter provides a brief historical review of downstream bypass problems in Sweden. This is followed by a description of the Swedish situation today, with a focus on several case studies that have evaluated rehabilitating downstream bypass efficiency at hydroelectric plants in rivers of different sizes and for several different species. Finall...

Forskargruppen Naturresurs Rinnande Vatten på ämnet biologi vid Karlstads universitet medverkar i det Interregfinansierade projektet Vänerlaxens fria gång. Under två år har vi genomfört projekt i Klarälven i syfte att lära oss mer om laxens biologi i Klarälven. För att kunna genomföra en god förvaltning av ett ekosystem måste man ha goda kunskaper...

Conservation of migratory salmonids requires understanding their ecology at multiple scales, combined with assessing anthropogenic impacts. We present a case-study from over 100 years of data for the endemic landlocked Atlantic salmon (Salmo salar, Salmonidae) and brown trout (Salmo trutta, Salmonidae) in Lake Vänern, Sweden. We use this case-study...

Power plant dams constitute barriers for downstream migration by smolts. The purpose of this study was to measure guidance efficiency of existing trash diverters and the use of overhead cover in combination with trash diverters to guide brown trout (Salmo trutta L.) smolts away from turbine intakes into trash spillway gates at two power plants in t...

Prey capture success and foraging mode were studied in brown trout Salmo trutta at temperatures ranging from 5.7 to 14.0° C. At low temperatures, there was a positive correlation between prey capture success and the proportion of time that the fish spent holding feeding stations. This correlation was not found at temperatures >10° C.

Subsidies of energy and material from the riparian zone have large impacts on recipient stream habitats. Human-induced changes, such as deforestation, may profoundly affect these pathways. However, the strength of individual factors on stream ecosystems is poorly understood since the factors involved often interact in complex ways. We isolated two...

Trout diet. Seasonal changes in the frequency of occurrence (O%) and mean relative biomass (A%) of the most important food items in the diet of young (Y) and old (O) trout in unmanipulated (U), light (L), terrestrial invertebrate reduction (TR) and terrestrial invertebrate reduction and light (TRL) treatments throughout the study period. Chironomid...

1. Changes in riparian vegetation owing to forest harvesting may affect the input of large wood, a major structural element, to streams. Studies of large wood impacts on stream fish have focused on population‐level responses, whereas little attention has been given to how wood affects fish behaviour. 2. In a laboratory stream experiment, we tested...

Intact longitudinal conductivity ensures that fish migrate between habitats. Here, we present our studies of longitudinal connectivity conducted from 2000-2009 as they relate to migration of trout and other species in the regulated River Emån, Sweden. Two nature-like fishways for upstream migration were constructed at Finsjö, approximately 30 km up...

The River Klarälven /Trysilelva/Femundselva is home to the endemic, landlocked and iteroparous Atlantic salmon, which historically migrated up to 400 km between Lake Vänern in Sweden and spawning and nursery areas in Sweden and Norway. Fragmentation and loss of longitudinal connectivity caused by the development of 11 run-of-river power plants over...

Trout foraging in small forested streams is largely affected by the surrounding forest, both by affecting habitat structure and prey availability. In this presentation we focus on trout responses to woody debris and terrestrial invertebrates, two factors influenced by riparian zone structure, potentially affecting streams and foraging of brown trou...

Estimating net energy intake (NEI) of is a key requirement in a new suite of models being developed to assess habitat quality for stream fish. To estimate NEI, habitat quality models use a drift-foraging sub-model, typically based on Hughes and Dill’s (1990, CJFAS) well-known model. The Hughes and Dill model estimates the energetic costs and benefi...

Hydroelectric plants (HEPs), with their dams and turbines, interrupt connectivity in water bodies and constitute barriers and sources of mortality for upstream-migrating spawners and downstream-migrating smolts and kelts. In watersheds with multiple dams the cumulative losses of migrating juvenile salmon can be high, contributing to population decl...

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...

Abstract –  The possibility to increase the proportion of migrating hatchery-reared smolts by reducing their food ration was studied. Lake-migrating, hatchery-reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish-farming industry, or reduced (15–20%) rations. They were rel...

We monitored temporal changes in body size for three cohorts of a partial migratory, lake-migrating brown trout population. We tested if body mass differed between nonmigratory males, migrants, and other members of the cohort (females and immature males). We hypothesized that large-sized individuals would mature as nonmigratory males or migrate at...

1. The European eel population has decreased drastically during recent decades, and new EU‐legislation calls for measures to change this negative trend. This decline has been attributed to a number of factors, including habitat fragmentation by structural barriers that prevent eels moving between freshwater and the sea. The success of downstream mi...

1. Habitat degradation is a major reason for species extinctions. For parasite–host interactions, the decline of a parasite may not only be related to the parasite’s tolerance to habitat degradation but also indirectly through the host’s tolerance to the same disturbance. 2. Our objective was to explore the cause of population declines of the fresh...

IntroductionMaterial and methodsResults and discussionConclusions and implications for managementAcknowledgementsReferences

Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and >= 2+)...