| 1. |
- Andersson, Magdalena, et al.
(author)
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Assessing Movements between Freshwater and Saltwater by Brown Trout (Salmo trutta L.) Based on Otolith Microchemistry
- 2024
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In: Animals. - : MDPI. - 2076-2615. ; 14:14
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Journal article (peer-reviewed)abstract
- 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 fish migrated to sea by 1 year of age. However, 13% spent less than one year in the river. Most brown trout (48%) migrated to the sea between 1 and 2 years of age. On average, brown trout, which averaged 4.4 years in age (range 3–6 years), returned to freshwater 2.3 times, and there was an inverse relationship between time spent in freshwater after hatching and the number of visits to freshwater. Our results do not support the classical life history pattern, where brown trout spend one or more years in freshwater before migrating to the sea. Here, we found evidence that part of the population leaves freshwater during their first year. While the cause for precocial migration in the River Emån is not known, our results from this permanently flowing river do not support the idea proposed for other Baltic Sea populations, where the risk of drought has been suggested to be the cause.
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| 2. |
- Calles, Olle, 1974-, et al.
(author)
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Efficient and timely downstream passage solutions for European silver eels at hydropower dams
- 2021
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In: Ecological Engineering. - : Elsevier. - 0925-8574 .- 1872-6992. ; 170
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Journal article (peer-reviewed)abstract
- The European eel population is critically endangered due to a multitude of human-induced factors such as habitat fragmentation, parasites, fishing, and climate change. In freshwater, downstream migrating silver eels encountering hydroelectric plants often suffer substantial delays and increased mortality from trash-rack impingement and turbine-induced mortality. Downstream passage problems can be ameliorated by implementing different types of downstream passage solutions that show variable but promising results for salmonids, but their performance for silver eels remains largely unknown. To address these knowledge gaps, radio telemetry was used to monitor the downstream migration of silver eels during 2 years past a hydroelectric plant recently equipped with two new fish passage solutions, consisting of an angled bar rack with a full-depth bypass, and a nature-like fishway. No tagged eels passed through the turbines, but bypassed the dam evenly between the two passage solutions, resulting in a 95% impediment passage efficiency and a median passage time of 1 h. Movement patterns and route selection were associated with variation in discharge and most individuals approached both passage solutions before passing, resulting in route-specific efficiencies of 69% for the angled rack and bypass, and 46% for the nature-like fishway. We conclude that the combination of a new bypass, paired with an angled rack, and a large nature-like fishway provided downstream migrating silver eels with a highly effective combination of passage solutions, with high impediment passage success and relatively low passage times.
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| 3. |
- Campbell, J. A., et al.
(author)
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Application of Animal Movement Models to Acoustic Telemetry Positioning
- 2024
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In: Advances in Hydraulic Research. - : Springer Science+Business Media B.V.. ; , s. 29-41
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Book chapter (other academic/artistic)abstract
- Over the past decade, acoustic telemetry has become commonplace in studies on fish movement and behaviour. Over small spatial scales, arrays of acoustic receivers can be used to estimate movement paths in 2- or 3-dimensions with high temporal resolutions. Despite the growing prevalence of acoustic telemetry arrays, guidelines on how to generate robust position estimates—and further utilize this data in animal movement models such as hidden Markov models or step selection functions—are sparse. As animal movement models generally require either true positions or accurately specified spatial error distributions, understanding positioning error is crucial for behavioural inference. Here, current methods of telemetry positioning are reviewed. Simulated case studies are used to highlight the effect of state space model parameter selection on positioning accuracy, and in turn, the fitting of animal movement models.
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| 4. |
- Eggers, Florian, et al.
(author)
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Methods for the Assessment of Fishways (Upstream Fish Passage)
- 2024
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In: Advances in Hydraulic Research. - : Springer Science+Business Media B.V.. - 9783031560927 ; , s. 67-79
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Book chapter (other academic/artistic)abstract
- Fragmentation of rivers by manmade barriers has impeded the ability of riverine fish to move freely. Barriers can be improved by fishways that can partially mitigate the negative impacts by acting as aquatic corridors. Effective fishways require knowledge about the physiological and spatial demands of fish species, but the existing knowledge largely derived from laboratory settings. Evaluating fishway performance is needed for optimisation of their hydraulic design and positioning. Qualitative methods include trapping, electrofishing, and camera observations to estimate the number of individuals passing (effectiveness). For quantitative assessment, the study of individual fish behaviour can identify fishway sections in need of improvement and estimate associated efficiencies. This can be accomplished by telemetric techniques such as PIT tagging, radio, and hydroacoustic telemetry.
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| 5. |
- Hagelin, Anna, 1974-, et al.
(author)
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Upstream fishway performance by Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) spawners at complex hydropower dams – is prior experience a success criterion?
- 2021
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In: Canadian Journal of Fisheries and Aquatic Sciences. - : CANADIAN SCIENCE PUBLISHING. - 0706-652X .- 1205-7533. ; 78:2, s. 124-134
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Journal article (peer-reviewed)abstract
- Passage of hydropower plants by upstream-migrating salmonid spawners is associated with increased mortality, delays, injuries and reduced migration success, and consequently the need for a more comprehensive understanding of fish behavior downstream of dams is widely recognized. Studies of passage typically involve tagging fish, and in many cases, the fish used in these studies are caught in the fishways, and hence have prior experience negotiating them. In this study, we studied fishway passage of tagged landlocked Atlantic salmon (Salmo salar) in the River Klarälven, Sweden and brown trout (Salmo trutta) in the River Gudbrandslågen, Norway, and the influence of prior experience on passage success in 2012 and 2013. In the River Klarälven, fishway efficacy varied from 18 (2012) to 88% (2013). Most salmon (81%) entered the fishway trap on days without spill, and salmon moved from the turbine area to the spill zone when there was spill, with small individuals showing a stronger reaction than large fish. Analysis of fish with and without prior trap experience showed that a higher percentage of the “naïve” fish (70% of salmon and 43% of the trout) entered the fishway traps than the “experienced” ones (25% of the salmon and 15 % of the trout). Delays for fish that entered the trap ranged from 3-70 days for salmon and 2-47 days for trout, and there was no difference in median delay between naïve and experienced fish for each species. Manual positioning of radio-tagged salmon revealed that 11% of the naïve fish and 50% of the experienced fish ceased migration after tagging and release. In addition, a greater percentage of the salmon that were captured, marked and released in the lake attempted to enter the fishway (70%) than lake-caught salmon that were also transported 10km to the stream before release (33%). The data based on manual positioning and lake caught salmon indicate that differences in behavior of naïve and experienced individuals are likely stress-related. Moreover, our results suggest that estimates of fishway efficacy using fish with prior fishway experience may be biased, and based on our study, efficacy is underestimated.
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| 6. |
- Harbicht, Andrew, et al.
(author)
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Environmental and anthropogenic correlates of migratory speeds among Atlantic salmon smolts
- 2021
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In: Rivers Research and Applications. - : Wiley. - 1535-1459 .- 1535-1467. ; 37:3, s. 358-372
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Journal article (peer-reviewed)abstract
- Dams, weirs, and hydropower facilities are often cited as migratory barriers which impart significant reductions in fitness among migratory fish species. Even where upstream and downstream passage options are available, barrier passage can still often result in energetic or physical costs which compound delays or cause mortality. Past studies have identified variables associated with such fitness reductions, though few examine their effects in the context of the whole river scale. To this end, we assessed the migratory rates and downstream passage of radio-tagged Atlantic salmon (Salmo salar) smolts through nine river sections (including two reservoir sections and one dammed section) along a 20 km stretch of river. Migration stoppages were not found to be elevated in reservoir or dammed sections, while migration rates were best described by physical river properties (width), biological traits (smolt total length), and seasonal variables (diel period) rather than anthropogenic factors. These results suggest the negative effect of reservoirs may primarily be due to their influence on river width and may be negligible when width is largely unaffected by an impoundment. Similarly, spilling water during fish migrations as a mitigative measure appears to make delays negligible. These conditions and actions may not completely marginalize the effect of dams, however, as a negative trend was still observed resulting from passage effects at the dam.
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| 7. |
- Harbicht, Andrew, et al.
(author)
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Guiding migrating salmonid smolts : Experimentally assessing the performance of angled and inclined screens with varying gap widths
- 2022
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In: Ecological Engineering. - : Elsevier. - 0925-8574 .- 1872-6992. ; 174, s. 1-8
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Journal article (peer-reviewed)abstract
- The loss of longitudinal connectivity in regulated rivers, both up- and downstream, has been detrimental for biodiversity worldwide. While progress has been made regarding upstream fish passage solutions, many questions remain unanswered regarding downstream passage alternatives. To address these knowledge gaps, we used Atlantic salmon (S. salar) smolts to experimentally assess the guidance efficiency and passage rates produced by several common screen-and-bypass fish guidance systems. Vertical screens with horizontally oriented bars extending across a turbine intake channel at a shallow angle (angled guidance screens), combined with a single, full-depth bypass entrance at their downstream end, were on average 20% more effective and produced passage rates that were 10 times higher than screens which extended perpendicularly across a turbine intake channel with vertically oriented bars that rose gradually towards the surface (inclined guidance screens) and with a bypass at the surface, on either side of the screen. Among inclined screens, gap width was negatively associated with guidance efficiencies and the smallest gap width (15 mm) exhibited a 41% greater guidance efficiency than the largest (30 mm). Among angled screens, performance was more closely linked to construction material as metal racks produced passage rates over three times faster than flexible Kevlar netting. Overall, passage through the guidance screens, and therefore into a tentative turbine intake area, was positively associated with gap width and was twice as prevalent among the inclined relative to angled guidance screens. Ultimately, an angled guidance screen with a 30 mm gap width produced the highest guidance efficiency and passage rates (a 30% improvement over the next best screen), while an inclined screen with a 30 mm gap width produced the lowest guidance efficiencies and passage rates. These results have implications for the suitability and performance of downstream fish passage solutions at both large- and small-scale hydropower plants where passage solutions are currently lacking or inadequate.
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| 8. |
- Kjærås, Halvor, et al.
(author)
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Three-dimensional migratory behaviour of European silver eels (Anguilla anguilla) approaching a hydropower plant
- 2023
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In: Journal of Fish Biology. - : John Wiley & Sons. - 0022-1112 .- 1095-8649. ; 102:2, s. 465-478
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Journal article (peer-reviewed)abstract
- 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 recommended at fish passage facilities to accommodate downstream eel migration. The results of this recommendation are poorly studied, and the few studies that exist show varying bypass efficiencies. The current study used acoustic telemetry with depth sensors to explore the three-dimensional migratory behaviour of downstream-migrating silver eels. The eels were tracked as they approached a hydropower plant with a state-of-the-art angled bar rack and full-depth bypass. Downstream and upstream swimming differed in preferred vertical and lateral positions. During periods of local downstream movement, the density of observations was largest in the upper middle section, away from the river boundaries and in higher velocities. Conversely, when moving upstream, eels tended to avoid the upper layers of the middle part of the river, swimming closer to the riverbed and using the bank areas to a greater extent. Downstream-moving fish swam higher in the water column during night and in turbid conditions (high discharge). When approaching the impassable bar rack and the full-depth bypass, the eels searched most intensely but not exclusively along the bottom third of the rack, often exploring at new depths after changing direction. The impediment passage efficiency was 100% when both bypass solutions were considered. The study provides knowledge of the swimming behaviour of silver eels, which is relevant for the design of bypass solutions for eels at migration barriers.
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| 9. |
- Lund Bjørnås, Kristine, 1991-, et al.
(author)
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Modeling Atlantic salmon (Salmo salar) and brown trout (S. trutta) population responses and interactions under increased minimum flow in a regulated river
- 2021
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In: Ecological Engineering. - : Elsevier. - 0925-8574 .- 1872-6992. ; 162
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Journal article (peer-reviewed)abstract
- Describing and understanding the relationship between streamflow and ecological processes is a classic problem in stream ecology and river management. We applied the individual-based model inSTREAM to describe the relationship between the dynamic river habitat and emergent population responses in sympatric landlocked Atlantic salmon (Salmo salar) and lake-migrating brown trout (Salmo trutta). This application explicitly describes the environmental conditions in the Gullspang Rapids, a residual flow stretch in the hydropower-regulated Gullspang River, Sweden (Svenskt elfiskeregister - SERS, 2019) etween September 2008 and September 2018. We simulated three static minimum flow scenarios and three variable natural flow regimes, contrasting highly artificial conditions with more natural dynamics. Our main response variable was the number of large (>= 12 cm) out-migrants of salmon and trout, a proxy for successful population recruitment. The baseline model predicted an average production of 455 salmon and 532 trout out-migrants per year during 2008-2018 in this 11,700 m(2) spawning and rearing area. The only alternative scenario producing more out-migrants was when the minimum flow was raised by a factor of three, as this led to a modest increase in trout out-migrants. Interestingly, none of the flow alternatives produced more salmon out-migrants than the baseline model, suggesting a competitive disadvantage originating from spawning later than trout. Density-dependent population regulation, a well-known phenomenon in salmonids, was reproduced by the model. Both intra- and interspecific competition was evident. While the number of out-migrants varied with flow regime, sensitivity analyses showed that other model input, specifically velocity shelter availability and stream temperature, were just as important. Increased availability of velocity shelters (in-stream structures that reduces the swimming speed of drift-feeding fish) was the only environmental factor that increased production of both salmon and trout in silico. We conclude that in this system, flow restoration based on simplistic flow scenarios will have limited effect, unless complemented by an increase of instream structural complexity.
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| 10. |
- Lund Bjørnås, Kristine, 1991-
(author)
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Modeling Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) responses to river habitat alteration
- 2020
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Licentiate thesis (other academic/artistic)abstract
- Half the world’s river volume is affected by flow alterations and/or fragmentation, a figure that is likely to increase with the current global surge in hydropower development. At the same time, freshwater biodiversity is in rapid decline. In fluvial ecosystems, streamflow is a master variable, shaping riverine species’ habitat over space and time. Atlantic salmon (Salmo salar) and brown trout (S. trutta) are examples of species that need fluvial habitats for reproduction and juvenile rearing, and whose flow needs can come in conflict with hydropower production objectives. This necessitates tools for predicting the effect of fluvial habitat alteration on fish production.In this thesis, I applied the individual-based model inSTREAM to simulate salmon and trout in the Gullspång Rapids, a residual flow stretch of the Gullspång River, Sweden, over a ten-year period. InSTREAM uses sub-daily time steps to simulate individual fish interacting with their biotic and physical environment, and tracks the fitness consequences of their main actions: habitat and activity selection. For inSTREAM input, I had to describe key habitat features, create a 2D hydraulic model of the rapids, model river temperature, and gather data on salmon and trout eco-physiology and life history characteristics in the Gullspång River. I ran simulation experiments varying either flow input, the number of spawners, spawning gravel, shelter and boulder availability, or temperature. Flow alterations had limited benefit. Only the scenario where the current minimum flow was set three times higher yielded increased production, and only for trout. Trout dominated salmon in competition, and production was density dependent. The model predicted that the only way to increase production of both species at current spawner numbers was to add instream structures offering more energetically profitable feeding positions.
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