| 1. |
- Degerman, Erik, et al.
(författare)
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Fysisk restaurering av sjöar.
- 2017
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Rapport (refereegranskat)abstract
- Denna rapport beskriver översiktligt omfattningen av antropogen påverkan på våra sjöar och vilka effekter detta fått på biologisk mångfald, ekosystemets funktion och på ekosystemtjänster. Fokus ligger på att beskriva möjliga fysiska restaureringsåtgärder. Vi går igenom exempel från ett antal genomförda sjörestaureringar, både nationellt och internationellt, och försöker ge generella rekommendationer för olika åtgärder. Det kan dock inledningsvis konstateras att det finns mycket få redovisade arbeten om fysisk sjörestaurering, frånsett olika åtgärder i eutrofierade vatten. Det gör att detta inte är en litteratursammanställning eftersom en sådan hade dominerats helt av olika typer av påverkan och endast motåtgärder mot övergödning. Utav de cirka 4000 restaureringsåtgärder som finns redovisade i databasen ”Åtgärder i Vatten” berör endast ett tiotal sjörestaurering. De problemområden som tas upp är reglerade sjöar, sänkta sjöar, övergödning, förlorad funktion av strandzon och kantzon samt förlorad konnektivitet. Många av dessa problem hänger ihop, till exempel sänkta och övergödda sjöar, och det är komplexa samband som styr möjligheter och effekter av restaurering. Det finns flera exempel på hur man trots omfattande insatser inte nått ända fram. Varje restaureringsprojekt är unikt och har egna förutsättningar. Eftersom det är komplexa samband som ger negativ påverkan är det inte enkelt att sätta tydliga mål för restaureringen. Detta försvåras ytterligare av att det inte finns statiska tillstånd i naturen. Restaureringsåtgärderna måste ses i ett holistiskt perspektiv, både över tid, inom avrinningsområdet och med beaktande av olika ekosystemtjänster och andra verksamheter. De exempel som finns visar ofta att vi inte lyckats fullt ut därför att åtgärderna inte tillåts vara omfattande nog. För reglerade sjöar rekommenderas att regleringen så långt möjligt följer den naturliga flödesregimen, att regleringen i mindre sjöar inte får överstiga den naturliga variationen ett normalår. Som ett riktvärde högst en meters amplitud. För sänkta sjöar finns tre möjliga vägar, att höja vattennivån, att muddra djupare (endast lämpligt i vissa sjöar) eller en kombination av de båda. Ofta är det svårt att få utrymme för en höjning av sjön, varför olika typer av muddring blir aktuellt, ofta efter en inledande eliminering av överflöd av växter. För övergödda sjöar är det avgörande att avlasta extern- och internbelastning. Det senare innebär att muddring av de närsaltrika översta sedimenten krävs. Alternativ kan vara att kemiskt binda fosforn i sedimenten. Muddringen har dock fördelen att även öka vattendjupet och i bästa fall kan fosforn komma till användning på landbacken. Lågflödesmuddring ser ut att vara det bästa alternativet i lite större och djupa vatten, medan mer igenväxta små och grunda sjöar kan pontonmuddras. Sjöars konnektivitet och behovet av att återfå en kant- och strandzon med naturliga processer berörs också.
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| 2. |
- Degerman, Erik, et al.
(författare)
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Occurrence and habitat use of European eel (Anguilla anguilla) in running waters : lessons for improved monitoring, habitat restoration and stocking
- 2019
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Ingår i: Aquatic Ecology. - : Springer. - 1386-2588 .- 1573-5125. ; 53:4, s. 639-650
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Tidskriftsartikel (refereegranskat)abstract
- To improve the management of the European eel (Anguilla anguilla) in freshwater, it is essential to define important lotic habitats. Electrofishing data from 289 wadeable, hard-bottom sites in 69 Swedish coastal rivers and streams, originally surveyed for salmonid monitoring, were used to evaluate the effects of sampling- and habitat-related factors on eel occurrence. Probability of eel occurrence, as influenced by sampling procedure (sampled area, number of consecutive runs and ambient water temperature) and habitat characteristics (size of catchment, dominating bottom substrate, shade, water velocity, mean depth), was evaluated for small (total length <= 150 mm) and large (>150 mm) yellow eels. Data were analysed in a mixed presence/absence generalized linear model with dispersal (distance to mouth from sampled site), habitat and sampling-related variables as covariates. The two models explained variation in occurrence to 81.5% for small eel and 76.2% for large eel. Probability of eel occurrence decreased with distance from the river mouth, and increased with sampled area, number of runs, water temperature, coarser substrate and size of river. We suggest that future eel habitat restoration should focus on lower reaches of larger rivers with suitable coarse bottom habitats. Stocking of young eel should be carried out in comparable accessible habitats in the upper reaches where eel densities are low. The results also strongly indicate that eel may be sampled together with young salmonids with DC electrofishing in wadeable habitats.
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| 3. |
- Donadi, Serena, et al.
(författare)
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Country-wide analysis of large wood as a driver of fish abundance in Swedish streams : Which species benefit and where?
- 2019
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Ingår i: Aquatic conservation. - : John Wiley & Sons. - 1052-7613 .- 1099-0755. ; 29:5, s. 706-716
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Tidskriftsartikel (refereegranskat)abstract
- Rivers are heavily affected by human impacts that threaten many fish species. Among restoration measures, the addition of large wood (LW) in streams has been shown to increase fish abundance, yet which species benefit from LW, to what extent relative to other drivers, and which factors influence LW quantity is not clear, and these uncertainties limit our ability to use LW as an effective restoration measure. Here, a time series (from 1993 to 2016) of electrofishing data, including 3641 streams across Sweden, was used to investigate the beneficial effects of LW on the abundance of juvenile brown trout, Salmo trutta, juvenile Atlantic salmon, Salmo salar, and juvenile and adult sculpins, Cottus gobio and Cottus poecilopus, while accounting for other abiotic and biotic factors, and the drivers of LW abundance at a country-wide scale. Large wood benefitted brown trout, and the effects were greater with decreasing shaded stream surface. LW effects were comparable in magnitude to the positive effects of average annual air temperature and the negative effects of stream depth and predator abundance - factors where the influence was second only to the negative effects of stream width. LW did not benefit salmon abundance, which was correlated positively with stream width and negatively with altitude, nor did it benefit sculpin abundances, which mainly decreased with annual average air temperature and altitude. The quantity of LW strongly diminished with stream width, and, to a lesser extent, with stream depth, altitude, annual average air temperature, and forest age, whereas it increased with stream velocity, slope, and forest cover. The results suggest that LW can be used as an effective restoration tool for brown trout in shallow and narrow streams, especially in areas with little shade. Here, the addition of LW may help to alleviate the impacts of forest clearance and climate change.
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| 4. |
- Göthe, Emma, et al.
(författare)
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Flow restoration and the impacts of multiple stressors on fish communities in regulated rivers
- 2019
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Ingår i: Journal of Applied Ecology. - : John Wiley & Sons. - 0021-8901 .- 1365-2664. ; 56:7, s. 1687-1702
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Tidskriftsartikel (refereegranskat)abstract
- River regulation for hydropower is undertaken worldwide, causing profound alterations to hydrological regimes and running water habitats. Regulated catchments are often subjected to additional stressors, arising inter alia from agriculture, forestry and industry, which are likely to interact with impacts of river regulation on fish and other biota. Such interactions are poorly understood, hindering planning of effective mitigation and restoration. We investigated fish responses to increased discharge (as a restoration measure) in regulated rivers in Sweden. We compiled electrofishing data from river channels downstream of hydropower dams, each of which either has or lacks a mandated minimum discharge corresponding to c. 5% of pre-regulation discharge. We further analysed interactions between flow restoration and co-occurring local and regional stressors. River channels without a mandated minimum discharge were characterized by a low diversity of fish species with traits favouring persistence under unpredictable environmental conditions, including omnivory, short life cycles and small size. Additional stressors further reduced diversity and increased dominance by broad-niched, opportunistic species. Both the presence and magnitude of a mandated minimum discharge were positively related to fish diversity and density, and the relative density of three economically and recreationally valuable species. However, the size of these relationships frequently varied with the presence of additional stressors. Increasing levels of hydrological degradation and reduced connectivity at the catchment scale reduced positive flow-ecology relationships and hindered the restoration of fish communities towards reference conditions. However, application of a mandated minimum discharge also assisted in mitigating impacts of some co-occurring stressors, especially reduced riparian integrity. Synthesis and applications. Additional stressors can strongly influence the outcomes of flow restoration for fish community diversity and composition. Our approach combining fish species and trait data from multiple flow restoration projects with information on additional stressors yielded valuable insights into factors affecting flow restoration success, useful for (a) identifying the systems most likely to benefit from mandated minimum flows, (b) modelling influences of multiple stressors on flow-ecology relationships, (c) prioritizing additional measures to manage co-occurring stressors and enhance outcomes from flow restoration.
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| 5. |
- Nilsson, Per Anders, 1968-, et al.
(författare)
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Substrate-size choice in European eel (Anguilla anguilla) elvers is not altered by piscivore chemical cues
- 2020
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Ingår i: Journal of Fish Biology. - : John Wiley & Sons. - 0022-1112 .- 1095-8649. ; 96:6, s. 1534-1537
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Tidskriftsartikel (refereegranskat)abstract
- The European eel Anguilla anguilla Linnaeus 1758 is critically endangered with recruitment estimated at 5-10% of historical levels. Enhancing survival of recruits is pivotal for conservation, and restoration should consider habitat choice of elvers ascending river systems. We experimentally show that newly ascended elvers choose small pebble habitat over finer and larger substrates, regardless of the presence or absence of piscivore chemical cues, indicating no predator-induced change in substrate choice. Enriching habitats with this substrate fraction should enhance eel recruitment as well as biodiversity at large.
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| 6. |
- Polic, Daniela, et al.
(författare)
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Movements and occurrence in two closely related fritillary species
- 2021
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Ingår i: Ecological Entomology. - : John Wiley & Sons. - 0307-6946 .- 1365-2311. ; 46:2, s. 428-439
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Tidskriftsartikel (refereegranskat)abstract
- Mobility may affect species' distribution patterns in heterogeneous landscapes, and it might impact fitness by influencing mating success, predation avoidance, and foraging success. Here, we studied causes and consequences of mobility patterns in butterflies: Argynnis adippe, a specialist constrained to warm microhabitats within woodland landscapes, and A. aglaja, a relative generalist that also inhabits grasslands, and tolerates lower temperatures. We explored associations of movement and occurrence patterns, population size and density, niche breadth, wing size, and different types of behaviour prior to capture by conducting a mark-release-recapture study on the Swedish island oland. We marked 1 935 A. aglaja and 123 A. adippe and achieved recapture rates of 9.5% (A. aglaja), and 8.9% (A. adippe). Estimated population densities were 5 066 and 814 individuals per km(2), for A. aglaja and A. adippe, respectively. Argynnis aglaja was less likely to perform long-distance flights according to estimated dispersal kernels, hinting at negative density-dependent dispersal in these species. Although we detected the longest flight distances ever in these species in MRR studies (11.9 km for A. aglaja and 3.7 km for A. adippe), most butterflies were recaptured within 200 meters (60-80%). Low recapture rates along with low estimated residence times and the potential for long movement might indicate that many individuals left the study area, and that the species form open populations, stretching over large areas. Despite significant differences in wing size and behaviour types, mean observed flight distances were similar in these species.
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| 7. |
- Sunde, Johanna, et al.
(författare)
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Variation in salinity tolerance between and within anadromous subpopulations of pike (Esox lucius)
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Environmental heterogeneity is a key determinant of genetic and phenotypic diversity. Stable andhomogenous environments tends to result in evolution of specialism and local adaptations, whiletemporally unpredictable environments may maintain a diversity of specialists, promote generaliststrategies, or favour diversified bet hedging strategies. We compared salinity tolerance between twoanadromous subpopulations of pike (Esox Lucius) that utilize freshwater spawning sites with differentsalinity regimes. Eggs from each population were artificially fertilized and incubated in a salinitygradient (0, 3, 5, 7, and 9 psu) using a split-brood design. Effects on embryonic development, hatchingsuccess, survival of larvae, and fry body length were compared between populations and families.The population naturally spawning in the stable freshwater habitat showed signs of specialization forfreshwater spawning. The population exposed to fluctuating selective pressure in a spawning area withoccasional brackish water intrusions tolerated higher salinities and displayed considerable variation inreaction norms. Genetic differences and plasticity of salinity tolerance may enable populations to copewith changes in salinity regimes associated with future climate change. That geographically adjacentsubpopulations can constitute separate units with different genetic characteristics must be consideredin management and conservation efforts to avoid potentially negative effects of genetic admixture onpopulation fitness and persistence.
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| 8. |
- Tamario, Carl, et al.
(författare)
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Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.) : Implications for conservation strategies regarding fish-passage solutions
- 2019
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Ingår i: Aquatic conservation. - : John Wiley & Sons. - 1052-7613 .- 1099-0755. ; 29:4, s. 612-622
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Tidskriftsartikel (refereegranskat)abstract
- Many diadromous fish populations are declining and at risk of collapse. Lack of river connectivity is a major contributor to these declines, as free migration routes between marine and freshwater habitats are crucial for life-history completion. For the conservation and ultimately recovery of such species, it is imperative that remedial measures aimed at increasing connectivity are effective. This study investigated the distribution patterns of ascending juvenile European eel (Anguilla anguilla L.) in rivers in south-western Sweden, with a focus on the effects of barriers and measures that aim to reduce the impact of barriers, i.e. fish-passage solutions (FPSs). Eel occurrence data were spatially and temporally integrated with the national databases of dams and FPSs in a Geographic Information System (GIS) environment to evaluate their effect on ascending eel distribution. The types of barriers assessed were: (i) dams with nature-like fishways; (ii) dams with eel ramps; (iii) dams with technical fishways; and (iv) dams without FPSs. Dams fitted with eel ramps or technical fishways, as well as dams without FPSs, produced a significant negative effect on the probability of eel occurrence upstream. This negative effect was not found for dams fitted with nature-like fishways, indicating that these solutions may function better than the other FPS types in this study. The probability of eel occurrence decreased with distance from the sea and increased with area sampled, number of electrofishing runs, water temperature, and with the size of the bottom substrate. We suggest that future conservation strategies for improving the natural immigration of juvenile eels should include optimizing FPS function (e.g. placement and design), the continued maintenance of FPSs, the construction of nature-like fishways, and preferably the removal of dams, which will also benefit the downstream migration of maturing eels as well as restoring other ecosystem services.
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| 9. |
- Tamario, Carl, et al.
(författare)
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Ecological and Evolutionary Consequences of Environmental Change and Management Actions for Migrating Fish
- 2019
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 7, s. 1-24
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Forskningsöversikt (refereegranskat)abstract
- Migration strategies in fishes comprise a rich, ecologically important, and socioeconomically valuable example of biological diversity. The variation and flexibility in migration is evident between and within individuals, populations, and species, and thereby provides a useful model system that continues to inform how ecological and evolutionary processes mold biodiversity and how biological systems respond to environmental heterogeneity and change. Migrating fishes are targeted by commercial and recreational fishing and impact the functioning of aquatic ecosystems. Sadly, many species of migrating fish are under increasing threat by exploitation, pollution, habitat destruction, dispersal barriers, overfishing, and ongoing climate change that brings modified, novel, more variable and extreme conditions and selection regimes. All this calls for protection, sustainable utilization and adaptive management. However, the situation for migrating fishes is complicated further by actions aimed at mitigating the devastating effects of such threats. Changes in river connectivity associated with removal of dispersal barriers such as dams and construction of fishways, together with compensatory breeding, and supplemental stocking can impact on gene flow and selection. How this in turn affects the dynamics, genetic structure, genetic diversity, evolutionary potential, and viability of spawning migrating fish populations remains largely unknown. In this narrative review we describe and discuss patterns, causes, and consequences of variation and flexibility in fish migration that are scientifically interesting and concern key issues within the framework of evolution and maintenance of biological diversity. We showcase how the evolutionary solutions to key questions that define migrating fish-whether or not to migrate, why to migrate, where to migrate, and when to migrate-may depend on individual characteristics and ecological conditions. We explore links between environmental change and migration strategies, and discuss whether and how threats associated with overexploitation, environmental makeovers, and management actions may differently influence vulnerability of individuals, populations, and species depending on the variation and flexibility of their migration strategies. Our goal is to provide a broad overview of knowledge in this emerging area, spur future research, and development of informed management, and ultimately promote sustainable utilization and protection of migrating fish and their ecosystems.
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| 10. |
- Tamario, Carl, et al.
(författare)
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Ecological marginality and recruitment loss in the globally endangered freshwater pearl mussel
- 2022
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Ingår i: Journal of Biogeography. - : John Wiley & Sons. - 0305-0270 .- 1365-2699. ; 49:10, s. 1793-1804
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Tidskriftsartikel (refereegranskat)abstract
- Aim Ecological marginality is the existence of species/populations in the margins of their ecological niche, where conditions are harsher, and the risk of extinction is more pronounced. In threatened long-lived species, the disparity between distribution and population demography may provide understanding of how environmental heterogeneity shapes ecological marginality, potential extinction patterns and range shifts. We set out to evaluate this by combining a species distribution model (SDM) with population-specific demography data. Location Sweden, 450,000 km(2). Major Taxa Studied Freshwater pearl mussel (FPM, Margaritifera margaritifera) and two salmonid fish species. Methods A SDM for the mussel was constructed with MaxEnt using salmonid host fish (Salmo trutta plus S. salar) density, extreme low and high temperatures, precipitation, altitude, and clay content as explanatory variables. The output was used to test the ecological marginality hypothesis by evaluating whether lowly predicted populations had higher loss of recruitment. Logistic regression was used to explicitly test the factors involved in recruitment loss. Results Host fish density contributed the most (50.3%) to the mussel distribution, followed by lowest temperature the coldest month (34.3%) and altitude (10.3%), while the remaining explanatory variables contributed minimally (<3.3%). Populations with lower SDM scores lacked recruitment to a significantly higher degree. Populations inhabiting areas at low altitude, with lower densities of host fish, and warmer winter temperatures have lost recruitment to a higher degree. Main Conclusions We found support for the ecological marginality hypothesis. The patterns indicate that FPM habitat niche may shift northwards over time. Salmonid host fish density seems to be a driving factor for both historical distribution and recent demographic performance. Finally, we emphasize the value of combining SDMs with independent data on population demography as it both lends rigidity to model validation and understanding of how ecological marginality affects species distribution and viability.
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| 11. |
- Tamario, Carl, et al.
(författare)
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Effects of river fragmentation on spatial synchrony of fish and its consequences for population performance in fragments
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The spatial synchrony framework has shown that population asynchrony among branches in river networks tends to stabilize global populations. However, how river fragmentation by damming affects this framework remains largely unknown. Given that population synchrony is said to arise from dispersal and environmental similarity, both of which are affected by dams, we here empirically evaluate the effects of dams on fish population synchrony, and subsequently the effects of synchrony on global population persistence, productivity, stability, and trajectory in the remaining fragments. We found that dams demographically decouple populations by decreasing synchrony in two out of the three investigated fish species, emphasizing the need to account for barriers in future studies. We did not find any convincing evidence that within-fragment synchrony bears consequences for the performance of the global fragment population. We conclude that the processes generating the link between within-fragment synchrony and population performance remain elusive.
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| 12. |
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| 13. |
- Tamario, Carl, et al.
(författare)
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Nature-like fishways as compensatory lotic habitats
- 2018
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Ingår i: River Research and Applications. - : Wiley. - 1535-1459 .- 1535-1467. ; 34, s. 253-261
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Tidskriftsartikel (refereegranskat)abstract
- Damming of rivers disrupts migration of fish and results in lotic habitats being both scarcer and spaced further apart, ultimately affecting riverine fish communities. Nature-like fishways are often designed as bypass channels, constructed with natural materials that reroute part of the water around weirs and dams, restoring longitudinal connectivity as well as forming nature-mimicking habitats. We evaluated the potential of such bypasses to function as compensatory lotic habitats by comparing fish fauna in 23 bypasses to adjacent lotic stream habitats in a same-river pairwise design. Bypasses were narrower, shallower, and less shaded than adjacent stream habitats, but very few significant differences could be detected in the fish communities, indicating the potential of such nature-like fishways to constitute compensatory lotic habitats for fish. Analyses also indicated how bypass design may be altered to favour or disfavour certain target species. Generally, narrower and shallower bypasses with high gradient favoured brown trout (Salmo trutta), whereas European eel (Anguilla anguilla) were more abundant at sites with lower gradient. Finally, to increase the impact of these compensatory habitats on running water ecosystems, we suggest that the size of bypasses should be maximized in areas where natural stream habitats have been lost.
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| 14. |
- Tamario, Carl
(författare)
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On the abundance and distribution of organisms in fragmented riverscapes : Insights From Studies On Different Species And Spatiotemporal Scales
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dams in rivers modify the habitats and hinder dispersal and migration. Since moving around is an essential part of most organisms’ life histories, this represents a new regime for life in freshwater. This thesis addresses several issues that are either directly or indirectly related to fragmentation and aims to contribute to our understanding of living and coping in fragmented riverscapes. It contains studies conducted on different study species and several spatial, temporal, and ecological scales.I first show that individuals in spawning migrating populations of cyprinid fish are phenotypically sorted along the length of a river with culverts. Results support the spatial sorting hypothesis, and are consistent between species, between sexes, and among individuals within sex; smaller and slimmer fish migrate further. I next show that eel ladders, which are passage solutions at dams aimed at increasing the distribution of European eel, did not remove the negative barrier effect of the dam.Next, I show that the spatial configuration of distinct rapid-flowing habitats has significant impacts on the well-being of brown trout populations. Subpopulations in larger and closer located habitats were significantly denser and more stable, likely because of lower extinction rates and higher immigration rates. I further evaluated the effects of dams on spatial synchrony in populations of trout, Eurasian minnow, and northern pike; dams contributed to demographic isolation by decreasing synchrony in the two former species, but the effects of population synchrony on global population viability were weak.Lastly, I show how the distribution and demography of the threatened freshwater pearl mussel is influenced by environmental heterogeneity and viability of host fish populations. Mussel populations residing in colder regions, and in locations with more viable host fish populations, had retained recruitment to a higher degree. The long-lived mussels exemplify how stress in aquatic environments can accumulate and manifest over time.This thesis emphasizes in different ways that the spatial context in which individuals, populations and species move, distribute, and interact matters. Each study has important conservation implications regarding its study species, study system, or for the environmental aspect under scrutiny.
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| 15. |
- Tamario, Carl, et al.
(författare)
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Size, connectivity and edge effects of stream habitats explain spatio-temporal variation in brown trout (Salmo trutta) density
- 2021
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : Royal Society. - 0962-8452 .- 1471-2954. ; 288:1961
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Tidskriftsartikel (refereegranskat)abstract
- Ecological theory postulates that the size and isolation of habitat patches impact the colonization/extinction dynamics that determine community species richness and population persistence. Given the key role of lotic habitats for life-history completion in rheophilic fish, evaluating how the distribution of swift-flowing habitats affects the abundance and dynamics of subpopulations is essential. Using extensive electrofishing data, we show that merging island biogeography with meta-population theory, where lotic habitats are considered as islands in a lentic matrix, can explain spatio-temporal variation in occurrence and density of brown trout (Salmo trutta). Subpopulations in larger and less isolated lotic habitat patches had higher average densities and smaller between-year density fluctuations. Larger lotic habitat patches also had a lower predicted risk of excessive zero-catches, indicative of lower extinction risk. Trout density further increased with distance from the edge of adjacent lentic habitats with predator (Esox lucius) presence, suggesting that edge- and matrix-related mortality contributes to the observed patterns. These results can inform the prioritization of sites for habitat restoration, dam removal and reintroduction by highlighting the role of suitable habitat size and connectivity in population abundance and stability for riverine fish populations.
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| 16. |
- Tamario, Carl, et al.
(författare)
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Spatial sorting according to body size and shape explains variation in spawning migration distance between species, sexes and individuals of cyprinid fish
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Spatial sorting is a process in which individuals in a moving population are sorted in space according to phenotypic traits that influence their dispersal capabilities. Although the spatial sorting hypothesis was originally developed to explain patterns in the distribution of phenotypes within populations and species, we propose that under certain conditions, differences in dispersal capacity due to phenotypic traits may also contribute to spatial arrangement of different species. Dispersal capacity in fish is often related to size and slimness. Here, we evaluate the hypothesis that spawning migrating fish will be spatially sorted along the length of a river according to species, sex, and individual phenotype. We marked 457 and 493 spawning migrating ide (Leuciscus idus) and roach (Rutilus rutilus) individuals with PIT-tags and followed their migration along a stream using multiple PIT-reader stations. All marked ide individuals remained in the lower reaches of the stream. Roach, which are smaller and slimmer than ide, migrated further. Roach males, which are slimmer than females, migrated further. Among female roaches, slimmer individuals migrated further than stouter individuals. Although alternative mechanisms are possible, all these patterns are accounted for with a non-adaptive spatial sorting regime. This study illustrates that individuals in migrating populations distribute non-randomly in rivers, which has important implications regarding modifications to connectivity.
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| 17. |
- Törnblom, Johan, et al.
(författare)
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Prioritizing dam removal and stream restoration using critical habitat patch threshold for brown trout (Salmo trutta L.): a catchment case study from Sweden
- 2017
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Ingår i: Écoscience. - : Informa UK Limited. - 1195-6860 .- 2376-7626. ; 24, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- Catchments form an important terrestrial-aquatic habitat complex for biodiversity conservation and human well-being. Riparian and stream components are debated about how much habitat need to be maintained or restored in rivers subject to habitat degradation and fragmentation. Using brown trout as a focal species we tested the hypothesis that presence of suitable habitat in lotic stream sections can be predicted using habitat modelling. We modelled brown trout habitat at the catchment scale in terms of quality, size, juxtaposition of stream segments using digital elevation data, and presence of dams. The habitat models were validated against presence-absence data for local brown trout populations. A self-reproducing brown trout population was defined as having three year-classes. We identified the required minimum length (270 m) of a lotic stream section hosting a local brown trout population, corresponding to 3500 m(2). Adjacent areas of lotic stream habitat between dams had a significant positive effect on brown trout presence. The abundance of brown trout was significantly positively correlated to habitat quality, and negatively to hydropower water regulation. Critical habitat loss thresholds can be used for gap analysis regarding selection of dams to be removed and where restoration measures will be most effective in a catchment.
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| 18. |
- Watz, Johan, 1977-
(författare)
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Climbing the ladder : an evaluation of three different anguillid eel climbing substrata and placement of upstream passage solutions at migration barriers
- 2019
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Ingår i: Animal Conservation. - : John Wiley & Sons. - 1367-9430 .- 1469-1795. ; 22:5, s. 452-462
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Tidskriftsartikel (refereegranskat)abstract
- Conservation programmes for endangered, long-lived and migratory species often have to target multiple life stages. The bottlenecks associated with the survival of juvenile anguillid eels migrating into inland waters, the survival and growth of the freshwater life stage, as well as the recruitment and survival of silver eels, migrating back to the ocean to spawn, must be resolved. In this study, we focus on the efficiency of passage solutions for upstream migrating juveniles. Such solutions can consist of inclined ramps lined with wetted climbing substrata. We evaluated different commonly used substrata in a controlled experiment, recorded eel behaviour at the entrance of the ramp with infrared videography and validated the experimental results at a hydropower dam, where we also investigated the effects of ramp placement on performance. In the experiment on eel substratum selection, 40 % of the eels passed in lanes with studded substratum, whereas only 21 and 5 % passed using open weave and bristle substrata, respectively. Video analysis revealed that the studded substratum attracted more approaches and initiated climbs than the other substrata, but once a climb had been initiated, passage success rates did not differ between substrata. Eels using the studded substratum climbed 26 % faster than those using the bristle substratum and almost four times as fast as those climbing in the open weave. The superior performance of the studded substratum was supported by data from the field validation. Moreover, ramps positioned by the bank with low water velocities caught the most eels, but proximity to the dam had no effect on performance. To strengthen the European eel population, more juveniles need to reach their freshwater feeding grounds. A critical step to achieve this increase is to equip upstream passage solutions with suitable substrata and to optimize ramp placement at migration obstacles.
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| 19. |
- Watz, Johan, 1977-, et al.
(författare)
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Enhancing upstream passage solutions for juvenile eels : Effects of climbing substrate and ramp placement
- 2018
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Konferensbidrag (refereegranskat)abstract
- Juvenile anguillid eels migrating into inland waters often face migration barriers. Upstream passage solutions normally consist of inclined ramps lined with a wetted climbing substrate. In this study, we compared the performance of three commonly used substrate types in a controlled experiment, using European eel as the test species. We also analyzed climbing behavior with videography and validated the experimental results under natural conditions at a hydropower plant. In addition, we investigated the effects of ramp placement. Studded substrate attracted more approaches and climbs and passed more eels at a higher climbing velocity than open weave and bristle substrates, results that were confirmed by the field validation. Moreover, ramps placed in the tailrace caught more eels in low than in high water velocities. To conserve anguillid eels, both safe routes for downstream-migrating adult silver eels and improved recruitment at the freshwater feeding life stage must be achieved. Optimizing ramp position and equipping upstream passage solutions with functioning climbing substrate are key factors to enhance the performance of eel ramps.
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