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  • 1.
    Addo, Louis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Hajiesmaeili, Mahboobeh
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Piccolo, John
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Watz, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows2023In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, no 2, p. 282-290Article in journal (Refereed)
    Abstract [en]

    Sub-daily fluctuations in streamflow may have adverse effects on the biota downstream of dams in hydropeaking-regulated rivers. Although the stranding of salmonid fry is one documented effect of hydropeaking, little is known about the species-specific behavioural and subsequent growth effects of sub-daily flow fluctuations. We investigated the effects of sub-daily flow fluctuation on growth, mortality and behaviour of sympatric Atlantic salmon (Salmo salar) and brown trout (S. trutta) fry (29–34 mm) in a laboratory experiment. The fluctuating flow treatment negatively affected growth and increased mortality for trout but not for salmon. The level of aggressive behaviour was similar in the fluctuating- and stable-flow treatments. Within the fluctuating flow treatment, there was a trend that more fishes were visibly active above the substrate during low than high flow. These findings suggest that hydropeaking-induced flow fluctuations may affect fry of different salmonid species in different ways and that brown trout fry may be more vulnerable to hydropeaking effects than Atlantic salmon fry. It can therefore be important to consider the possibility of divergent reactions by different fish species under hydropeaking situations and to incorporate species-specific strategies to conserve culturally and economically relevant riverine fish species.

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  • 2.
    Ahlbeck, Ida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlöf, Oliver
    Sedentarity in Eurasian perch (Perca fluviatilis) in a coastal Baltic Sea areaIn: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633Article in journal (Refereed)
  • 3.
    Andersson, Anastasia
    et al.
    Stockholm Univ, Dept Zool, Div Populat Genet, Stockholm, Sweden..
    Johansson, Frank
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Sundbom, Marcus
    Stockholm Univ, Dept Environm Sci & Analyt Chem, Stockholm, Sweden..
    Ryman, Nils
    Stockholm Univ, Dept Zool, Div Populat Genet, Stockholm, Sweden..
    Laikre, Linda
    Stockholm Univ, Dept Zool, Div Populat Genet, Stockholm, Sweden..
    Lack of trophic polymorphism despite substantial genetic differentiation in sympatric brown trout (Salmo trutta) populations2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, no 4, p. 643-652Article in journal (Refereed)
    Abstract [en]

    Sympatric populations occur in many freshwater fish species; such populations are typically detected through morphological distinctions that are often coupled to food niche and genetic separations. In salmonids, trophic and genetically separate sympatric populations have been reported in landlocked Arctic char, whitefish and brown trout. In Arctic char and brown trout rare cases of sympatric, genetically distinct populations have been detected based on genetic data alone, with no apparent morphological differences, that is cryptic structuring. It remains unknown whether such cryptic, sympatric structuring can be coupled to food niche separation. Here, we perform an extensive screening for trophic divergence of two genetically divergent, seemingly cryptic, sympatric brown trout populations documented to remain in stable sympatry over several decades in two interconnected, tiny mountain lakes in a nature reserve in central Sweden. We investigate body shape, body length, gill raker metrics, breeding status and diet (stomach content analysis and stable isotopes) in these populations. We find small significant differences for body shape, body size and breeding status, and no evidence of food niche separation between these two populations. In contrast, fish in the two lakes differed in body shape, diet, and nitrogen and carbon isotope signatures despite no genetic difference between lakes. These genetically divergent populations apparently coexist using the same food resources and showing the same adaptive plasticity to the local food niches of the two separate lakes. Such observations have not been reported previously but may be more common than recognised as genetic screenings are necessary to detect the structures.

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  • 4.
    Andersson, Anastasia
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Johansson, Frank
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ryman, Nils
    Stockholm University, Faculty of Science, Department of Zoology.
    Laikre, Linda
    Stockholm University, Faculty of Science, Department of Zoology.
    Lack of trophic polymorphism despite substantial genetic differentiation in sympatric brown trout (Salmo trutta) populations2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, no 4, p. 643-652Article in journal (Refereed)
    Abstract [en]

    Sympatric populations occur in many freshwater fish species; such populations are typically detected through morphological distinctions that are often coupled to food niche and genetic separations. In salmonids, trophic and genetically separate sympatric populations have been reported in landlocked Arctic char, whitefish and brown trout. In Arctic char and brown trout rare cases of sympatric, genetically distinct populations have been detected based on genetic data alone, with no apparent morphological differences, that is cryptic structuring. It remains unknown whether such cryptic, sympatric structuring can be coupled to food niche separation. Here, we perform an extensive screening for trophic divergence of two genetically divergent, seemingly cryptic, sympatric brown trout populations documented to remain in stable sympatry over several decades in two interconnected, tiny mountain lakes in a nature reserve in central Sweden. We investigate body shape, body length, gill raker metrics, breeding status and diet (stomach content analysis and stable isotopes) in these populations. We find small significant differences for body shape, body size and breeding status, and no evidence of food niche separation between these two populations. In contrast, fish in the two lakes differed in body shape, diet, and nitrogen and carbon isotope signatures despite no genetic difference between lakes. These genetically divergent populations apparently coexist using the same food resources and showing the same adaptive plasticity to the local food niches of the two separate lakes. Such observations have not been reported previously but may be more common than recognised as genetic screenings are necessary to detect the structures.

  • 5.
    Calles, Olle
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, L.A.
    Karlstad University, Faculty of Social and Life Sciences.
    The use of two nature-like fishways by some fish species in the Swedish River Emån: Nature-like fishways2007In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 16, no 2, p. 183-190Article in journal (Refereed)
    Abstract [en]

    We studied the use of two nature-like fishways by 15 fish species (N ¼ 240) in the River Emån in southern Sweden. Use of the fishways for both passage and as a habitat was studied by electrofishing, trap catches and PIT telemetry. Of the 187 PIT-tagged fish, 52 individuals from 10 different species ascended one of the fishways for a total passage efficiency of 74%. For the five species that most frequently ascended the fishways, the passage efficiency was 100% for tench (Tinca tinca L.) and perch (Perca fluviatilis L.), 86% for chub (Leuciscus cephalus L.), 60% for burbot (Lota lota L.) and 50% for roach (Rutilus rutilus L.). Individuals that failed to pass the fishways were typically small cyprinids or species that were assumed to have taken up residence in the fishways, such as juvenile brown trout (Salmo trutta L.) and burbot. The nature-like fishways have re-established longitudinal connectivity for most of the studied species and also functioned as rearing and winter habitat for a number of species.

  • 6.
    Calles, Olle
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Russon, I
    Kemp, P
    Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions2010In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 19, no 2, p. 197-205Article in journal (Refereed)
  • 7. Dahl, J.
    et al.
    Pettersson, E.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Animal Ecology.
    Dannewitz, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution.
    Järvi, T.
    Löf, A-C
    No difference in survival, growth and morphology between offspring of wild-born, hatchery and hybrid brown trout (Salmo trutta)2006In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 15, no 4, p. 388-397Article in journal (Refereed)
    Abstract [en]

    We studied survival, growth and morphological characters in the offspring of native hatchery and wild-born anadromous brown trout (Salmo trutta) and their hybrids (wild-born female x hatchery male and wild-born male x hatchery female) in a 1-year field experiment. We also conducted laboratory studies where we examined social interactions between the offspring of the same hatchery and wild-born trout. All offspring were raised in a hatchery and nose tagged before being released into the stream. In total, 1125 individuals were released into the stream (1999) and a total of 614 individuals were recovered (2000). We found no differences in growth and survival between the offspring of hatchery, wild-born and hybrid trout. Morphology was also similar among groups, where only 38% females and 36% males were classified into the right category, which were only 12% better than random classification. In the laboratory experiment, we compared only the offspring of hatchery and wild-born trout with respect to growth, dominance, aggressiveness, feeding and activity. We found small differences between the offspring of hatchery and wild-born fish with respect to growth but this effect was not found in the field experiment. Our result suggests that the offspring of hatchery trout and hybrids between hatchery and wild-born trout performed equally well to the offspring of wild-born trout.

  • 8.
    Enefalk, Åsa
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Bergman, Eva
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Effect of fine wood on juvenile brown trout behaviour in experimental stream channels2016In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 25, no 4, p. 664-673Article in journal (Refereed)
    Abstract [en]

    In-stream wood can increase shelter availability and prey abundance for stream-living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in-stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small-sized trout. In a laboratory stream experiment, we tested the behavioural response of young-of-the-year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four-fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others. © 2015 John Wiley & Sons A/S.

  • 9.
    Engstedt, Olof
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Engkvist, Roland
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Larsson, Per
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Elemental fingerprinting in otoliths reveals natal homing of anadromous Baltic Sea pike (Esox lucius L.)2014In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 23, no 3, p. 313-321Article in journal (Refereed)
    Abstract [en]

    We examined the element pattern in the otoliths of a migratory fish species that inhabit the coastal areas in the brackish of the Baltic Sea. The northern pike (Esox lucius) show migratory behaviour, spawning in streams and rivers and foraging in the sea. We examined spawning migration in four nearby streams in the south-west part of the Baltic. Otolith analysis by microPIXE revealed unique elemental patterns (Sr, Zn, Br, Co and Mn) for the juveniles in each of the different streams. The strontium signal in the otolith of the juveniles was used as an indicator of freshwater origin and the time spent in the stream. Adult pike in their migrating spawning phase were caught in each of the streams. The elemental composition in otoliths in their freshwater phase (using juvenile pike in the streams as references) was determined. A principal component analysis showed that the elemental fingerprint during the freshwater phase several years back in time was similar for the adult fish and for juveniles inhabiting the stream today. The results indicated natal homing of the adults to a specific stream, a conclusion that was strengthened by the fact that marked fish returned to spawn over consecutive years. Anadromous pike in the Baltic Sea may thus be divided in subpopulations. The results of the study may have implications for fishery management, as pike in the Baltic Sea cannot be seen as homogenous population.

  • 10.
    Engstedt, Olof
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Engkvist, Roland
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Larsson, Per
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Elemental fingerprinting in otoliths reveals natal homing of anadromous Baltic Sea pike (Esox lucius L.)2014In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 23, no 3, p. 313-321Article in journal (Refereed)
    Abstract [en]

    We examined the element pattern in the otoliths of a migratory fish species that inhabit the coastal areas in the brackish of the Baltic Sea. The northern pike (Esox lucius) show migratory behaviour, spawning in streams and rivers and foraging in the sea. We examined spawning migration in four nearby streams in the south-west part of the Baltic. Otolith analysis by microPIXE revealed unique elemental patterns (Sr, Zn, Br, Co and Mn) for the juveniles in each of the different streams. The strontium signal in the otolith of the juveniles was used as an indicator of freshwater origin and the time spent in the stream. Adult pike in their migrating spawning phase were caught in each of the streams. The elemental composition in otoliths in their freshwater phase (using juvenile pike in the streams as references) was determined. A principal component analysis showed that the elemental fingerprint during the freshwater phase several years back in time was similar for the adult fish and for juveniles inhabiting the stream today. The results indicated natal homing of the adults to a specific stream, a conclusion that was strengthened by the fact that marked fish returned to spawn over consecutive years. Anadromous pike in the Baltic Sea may thus be divided in subpopulations. The results of the study may have implications for fishery management, as pike in the Baltic Sea cannot be seen as homogenous population.

  • 11.
    Filipsson, Karl
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Erlandsson, Ann
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Greenberg, Larry
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Österling, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Watz, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Bergman, Eva
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Do predator odours and warmer winters affect growth of salmonid embryos?2023In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, no 1, article id e12747Article in journal (Refereed)
    Abstract [en]

    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 affect later life stages. Here, we examined how predator odours and increased temperatures affect embryonic growth and development of a fish (brown trout Salmo trutta). We found that embryos had lower body mass and greater yolk volume close to hatching when subjected to predator odours. Trout embryos incubated at temperatures representing natural winter conditions were larger than embryos incubated at higher temperatures, although the latter hatched earlier. Fry sizes at emergence did not differ between treatments, perhaps because of compensatory growth during spring. This study shows that predator presence can have similar effects on embryonic growth of salmonids as warming winters, with possible impact later in ontogeny. 

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  • 12.
    Filipsson, Karl
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Göteborgs universitet.
    Petersson, Tina
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Hojesjo, Johan
    Göteborgs universitet.
    Piccolo, John
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Naslund, Joacim
    Göteborgs universitet.
    Wengstrom, Niklas
    Göteborgs universitet; Swedish Anglers Assoc, Gothenburg,.
    Österling, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Heavy loads of parasitic freshwater pearl mussel (Margaritifera margaritifera L.) larvae impair foraging, activity and dominance performance in juvenile brown trout (Salmo trutta L.)2018In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 27, no 1, p. 70-77Article in journal (Refereed)
    Abstract [en]

    The life cycle of the endangered freshwater pearl mussel (Margaritifera margaritifera) includes a parasitic larval phase (glochidia) on the gills of a salmonid host. Glochidia encystment has been shown to affect both swimming ability and prey capture success of brown trout (Salmo trutta), which suggests possible fitness consequences for host fish. To further investigate the relationship between glochidia encystment and behavioural parameters in brown trout, pairs (n = 14) of wild-caught trout (infested vs. uninfested) were allowed to drift feed in large stream aquaria and foraging success, activity, agonistic behaviour and fish coloration were observed. No differences were found between infested and uninfested fish except for in coloration, where infested fish were significantly darker than uninfested fish. Glochidia load per fish varied from one to several hundred glochidia, however, and high loads had significant effects on foraging, activity and behaviour. Trout with high glochidia loads captured less prey, were less active and showed more subordinate behaviour than did fish with lower loads. Heavy glochidia loads therefore may negatively influence host fitness due to reduced competitive ability. These findings have implications not only for management of mussel populations in the streams, but also for captive breeding programmes which perhaps should avoid high infestation rates. Thus, low levels of infestation on host fish which do not affect trout behaviour but maintains mussel populations may be optimal in these cases.

  • 13.
    Frank, Beatrice M.
    et al.
    Belgium.
    Piccolo, John J.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Baret, Philippe V.
    Belgium.
    A review of ecological models for brown trout: towards a new demogenetic model2011In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 20, no 2, p. 167-198Article in journal (Refereed)
    Abstract [en]

    Ecological models for stream fish range in scale from individual fish to entire populations. They have been used to assess habitat quality and to predict the demographic and genetic responses to management or disturbance. In this paper, we conduct the first comprehensive review and synthesis of the vast body of modelling literature on the brown trout, Salmo trutta L., with the aim of developing the framework for a demogenetic model, i.e., a model integrating both population dynamics and genetics. We use a bibliometric literature review to identify two main categories of models: population ecology (including population dynamics and population genetics) and population distribution (including habitat–hydraulic and spatial distribution). We assess how these models have previously been applied to stream fish, particularly brown trout, and how recent models have begun to integrate them to address two key management and conservation questions: (i) How can we predict fish population responses to management intervention? and (ii) How is the genetic structure of fish populations influenced by landscape characteristics? Because salmonid populations tend to show watershed scale variation in both demographic and genetic traits, we propose that models combining demographic, genetic and spatial data are promising tools for improving their management and conservation. We conclude with a framework for an individual-based, spatially explicit demogenetic model that we will apply to stream-dwelling brown trout populations in the near future.

  • 14. Greenberg, L A
    et al.
    Hernnäs, B
    Brönmark, D
    Dahl, J
    Eklöv, A
    Olsén, K Håkan
    Södertörn University, Avdelning Naturvetenskap.
    Effects of kinship on growth and movements of brown trout in field enclosures2002In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 11, no 4, p. 251-259Article in journal (Refereed)
    Abstract [en]

    The effect of kinship on growth and use of space by individually PIT-tagged 1+ brown trout was studied for 11 weeks in eight stream enclosures. Each enclosure consisted of two sections, separated by a region containing PIT-detecting antennae, which enabled us to measure use of sections by all individuals. Two types of sibling groups were tested, a single sibling group, F1, consisting of four individuals that were reared together in hatchery tank 'a' (F1(a)) plus four additional siblings of the same family but raised in hatchery tank 'b' (F1(b)), and a mixed sibling group, consisting of four F1(a) individuals plus four siblings from a second family, F2. Based on kin theory and earlier laboratory studies, we expected that growth of the F1(a) individuals in the single sibling group to be greater than that of F1(a) individuals in the mixed family sibling group, but instead we found just the opposite. The variance of growth did not differ between treatments. Nor was there a difference in time F1(a) individuals spent together when they were in mixed versus single sibling groups. We did find that F1(a) individuals changed habitat more frequently than F2 individuals in the mixed sibling group but less frequently than F1(b) in the single sibling groups. Thus, our predictions based on kin theory for growth and behavior of brown trout were not supported by our data, and we suggest that the role of kin recognition for the ecology of salmonids deserves further attention.

  • 15.
    Greenberg, Larry
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Eklöv, Anders
    Effects of Predation and Intraspecific Interactions on Habitat Use and Foraging by Brown Trout in Artificial Streams1997In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 6, no 1, p. 16-26Article in journal (Refereed)
    Abstract [en]

    We studied habitat use, foraging rates and behavior of 10 cm and 12 cm long brown trout, Salmo trutta, at two densities, 1.5 and 3.0 fish. m−2, in artificial streams that contained either the amphipod, Gammarus pulex, alone or G. pulex together with the piscivore, northern pike, Esox lucius. Gammarus were stocked in and largely restricted to the pools at a density of 128 Gammurus. m−2. pool−1 Large trout (12 cm) used pools more and riffles less when small trout (10 cm) were present than when small trout were absent. Small trout consumed fewer Gammarus when together with large trout than when alone, but showed no difference in habitat use in the presence and abscnce of large trout. Habitat use and number of Gammarus consumed per trout were not affected by trout density for either size-class when alone. For both size-classes of trout, use of pools and foraging rates were higher in the absence than in the presence of pike, and pike primarily resided in the pools. The number of aggressive interactions by both size-classes of trout decreased when pike was present. Our results indicate that for habitats that differ in food resources and predation risk, size structure may affect habitat use and foraging by brown trout.

  • 16.
    Gustafsson, Pär
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)2010In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 19, no 2, p. 170-177Article in journal (Refereed)
    Abstract [en]

    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+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics.

  • 17.
    Jönsson, Mikael
    et al.
    Lund University.
    Ranåker, Lynn
    Lund University.
    Nilsson, P. Anders
    Lund University.
    Brönmark, Christer
    Lund University.
    Prey-type-dependent foraging of young-of-the-year fish in turbid and humic environments2012In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 21, p. 461-468Article in journal (Refereed)
  • 18.
    Lans, Linnea
    et al.
    Department of Biology, Karlstads universitet.
    Greenberg, Larry A.
    Department of Biology, Karlstads universitet.
    Karlsson, Jens
    Calles, Olle
    Department of Biology, Karlstads universitet.
    Schmitz, Monika
    Department of Biology, Karlstads universitet.
    Bergman, Eva
    Department of Biology, Karlstads universitet.
    The effects of ration size on migration by hatchery-raised Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)2011In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 20, no 4, p. 548-557Article in journal (Refereed)
    Abstract [en]

    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 released into the River Klaralven, western Sweden, and followed as they swam downstream to Lake Vanern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.

  • 19.
    Lans, Linnea
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Karlsson, Jens
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Calles, Olle
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Schmitz, Monika
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    The effects of ration size on migration by hatchery-raised Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)2011In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 20, no 4, p. 548-557Article in journal (Refereed)
    Abstract [en]

    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 released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.

  • 20.
    Matetski, Lagle
    et al.
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Rohtla, Mehis
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Svirgsden, Roland
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Kesler, Martin
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Saks, Lauri
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Taal, Imre
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Hommik, Kristiina
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Paiste, Päärn
    Department of Geology University of Tartu Tartu Estonia.
    Kielman-Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology. Department of Geosciences Swedish Museum of Natural History Stockholm Sweden.
    Birzaks, Jānis
    Department of Ecology University of Daugavpils Daugavpils Latvia.
    Saura, Ari
    Natural Resource Institute Finland Helsinki Finland.
    Ziņģis, Mārcis
    Aquaculture Research and Education Centre Institute of Food Safety Animal Health and Environment Fish Farm “Tome” Ķegums Latvia.
    Vaittinen, Matti
    Centre of Economic Development, Transport and the Environment for Southeast Finland Kouvola Finland.
    Vetemaa, Markus
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Variability in stream water chemistry and brown trout ( Salmo trutta L.) parr otolith microchemistry on different spatial scales2021In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 31, no 2, p. 438-453Article in journal (Refereed)
  • 21.
    Matetski, Lagle
    et al.
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Rohtla, Mehis
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Svirgsden, Roland
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Kesler, Martin
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Saks, Lauri
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Taal, Imre
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Hommik, Kristiina
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Paiste, Päärn
    Department of Geology University of Tartu Tartu Estonia.
    Kielman-Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Birzaks, Jānis
    Department of Ecology University of Daugavpils Daugavpils Latvia.
    Saura, Ari
    Natural Resource Institute Finland Helsinki Finland.
    Ziņģis, Mārcis
    Aquaculture Research and Education Centre Institute of Food Safety Animal Health and Environment, Fish Farm “Tome” Ķegums Latvia.
    Vaittinen, Matti
    Centre of Economic Development, Transport and the Environment for Southeast Finland Kouvola Finland.
    Vetemaa, Markus
    Estonian Marine Institute University of Tartu Tartu Estonia.
    Variability in stream water chemistry and brown trout (Salmo trutta L.) parr otolith microchemistry on different spatial scales2021In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633Article in journal (Refereed)
  • 22.
    Motyka, Roman
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Calles, Olle
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Lind, Lovisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Watz, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Growth and behaviour of juvenile European eel (Anguilla anguilla) in sandy and stony bottom substrates2023In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 32, no 3, p. 640-647Article in journal (Refereed)
    Abstract [en]

    Understanding how the physical habitat influences growth and behaviour is essential for developing effective habitat restoration programmes of threatened and endangered fish species. In our study, we compared the growth and behaviour of juvenile European eel during 13 weeks in aquaria with either sand (0.8-2 mm) or pebbles (25-40 mm) as bottom substrate. In aquaria with the pebble substrate, eel grew significantly faster than in aquaria with sand (specific growth rate 0.15 vs. 0.11% day(-1)). Moreover, growth rates varied more for individuals inhabiting aquaria with sand than in those with pebbles (coefficient of variation 1.26 vs. 0.67). Habitat-dependent growth rates may partly be explained by the observed differences in behavioural patterns. In aquaria with sand, eel left the substrate more often and moved close to the bottom or freely in water column. In aquaria with pebbles, eel remained hidden in the substrate to a high degree, also during feeding. These results may be important for prioritising connectivity- and habitat-restoring measures and for optimization of restocking programmes.

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  • 23.
    Naslund, Joacim
    et al.
    Univ Gothenburg, Dept Biol & Environm Sci, Box 463, SE-40530 Gothenburg, Sweden..
    Sundström, L. Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Johnsson, Jorgen I.
    Univ Gothenburg, Dept Biol & Environm Sci, Box 463, SE-40530 Gothenburg, Sweden..
    Autumn food restriction reduces smoltification rate, but not over-winter survival, in juvenile brown trout Salmo trutta2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, no 2, p. 205-216Article in journal (Refereed)
    Abstract [en]

    The winter is often considered as a survival bottleneck for stream-living fish. Juvenile salmonids generally become less active during this period, and while food intake continues to some extent, growth rates are typically low. Here we present the results of an over-winter field experiment where energy levels were manipulated in late autumn. Three groups of juvenile (age 1+) brown trout, from an anadromous population, were monitored with respect to over-winter growth rate and survival (as indicated by recapture rates). Two groups were fed either high (HR), or low (LR) food rations in the laboratory for a month (October); the third group remained in the stream (STR). Over-winter growth rates were relatively low in all groups, and no growth compensation could be detected. Compared to HR and LR, STR fish had higher recapture rates after winter, indicating that laboratory housing may have affected the subsequent stream survival negatively. Comparing the two laboratory-housed groups, the LR group reached similar condition as the HR group in early spring, without indications of differences in survival. However, the initiation rate of body silvering (indicating initiation of smoltification) was lower in the LR group. Thus, it appears that food restriction during late autumn affect the onset of smoltification in juvenile brown trout. The results support previous laboratory studies indicating that salmonids modify their over-winter foraging behaviour to avoid too low energy levels at the end of winter. This modification appears to delay smoltification, but may not necessarily be costly in terms of over-winter mortality.

  • 24.
    Nordahl, Oscar
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Koch-Schmidt, Per
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Tibblin, Petter
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Forsman, Anders
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Larsson, Per
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Vertical movements of coastal pike (Esox lucius): on the role of sun basking2020In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 29, no 1, p. 18-30Article in journal (Refereed)
    Abstract [en]

    Knowledge of patterns and drivers of the spatiotemporal distribution of top predatory fish is key to understand ecological dynamics and to successful management. Here, we integrated field and laboratory approaches to study vertical movements of pike (Esox lucius) in relation to season, light regimes and body temperature. We tagged pike from the Baltic Sea with data storage tags during spawning migration and retrieved them during migration the following years to obtain high‐resolution data from full year of movements. The results showed seasonal and diel patterns of activity and body temperature that conformed to distinct patterns of crepuscular activity and diel vertical migrations. The latter manifested as two different patterns, either a stationary phase in the surface water during day followed by night‐time in deeper water or vice versa. The occurrence of these two behaviours varied among individuals and within individuals among seasons. Diel vertical migration has previously not been described for this shallow‐dwelling species, but was a common and consistent behaviour among individuals in this study. We suggest that the function of the daytime surface behaviour in pike is to increase body temperature through sun basking. This thermoregulatory role of surfacing was supported by the laboratory study where individuals sought the surface layer, exposed themselves to infrared light and thereby attained body temperatures in excess of ambient water. These results support sun basking as a mechanism for heat gain and further suggest that access to sunlight in the surface layer could be an important driver of vertical migrations.

  • 25.
    Nordahl, Oscar
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Koch-Schmidt, Per
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Tibblin, Petter
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Linnaeus University, Linnaeus Knowledge Environments, Water.
    Forsman, Anders
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Linnaeus University, Linnaeus Knowledge Environments, Water.
    Larsson, Per
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Vertical movements of coastal pike (Esox lucius): on the role of sun basking2020In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 29, no 1, p. 18-30Article in journal (Refereed)
    Abstract [en]

    Knowledge of patterns and drivers of the spatiotemporal distribution of top predatory fish is key to understand ecological dynamics and to successful management. Here, we integrated field and laboratory approaches to study vertical movements of pike (Esox lucius) in relation to season, light regimes and body temperature. We tagged pike from the Baltic Sea with data storage tags during spawning migration and retrieved them during migration the following years to obtain high‐resolution data from full year of movements. The results showed seasonal and diel patterns of activity and body temperature that conformed to distinct patterns of crepuscular activity and diel vertical migrations. The latter manifested as two different patterns, either a stationary phase in the surface water during day followed by night‐time in deeper water or vice versa. The occurrence of these two behaviours varied among individuals and within individuals among seasons. Diel vertical migration has previously not been described for this shallow‐dwelling species, but was a common and consistent behaviour among individuals in this study. We suggest that the function of the daytime surface behaviour in pike is to increase body temperature through sun basking. This thermoregulatory role of surfacing was supported by the laboratory study where individuals sought the surface layer, exposed themselves to infrared light and thereby attained body temperatures in excess of ambient water. These results support sun basking as a mechanism for heat gain and further suggest that access to sunlight in the surface layer could be an important driver of vertical migrations.

  • 26.
    Nyqvist, Daniel
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Greenberg, Larry
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Calles, Olle
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Goerig, Elsa
    nst Natl Rech Sci, Ctr Eau Terre & Environm, Quebec City, PQ, Canada.
    Bergman, Eva
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Ardren, William
    S Fish & Wildlife Serv, Western New England Complex, Essex Jct, VT USA.
    Castro-Santos, Theodore
    USGS Leetown Sci Ctr, SO Conte Anadromous Fish Res Ctr, Turners Falls, MA USA.
    Migratory delay leads to reduced passage success of Atlantic salmon smolts at a hydroelectric dam2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, no 4, p. 707-718Article in journal (Refereed)
    Abstract [en]

    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 migrating fish will use. Passage solutions must address not only the number or percentage of fish that successfully pass a barrier, but also the time it takes to pass. Here, we used radiotelemetry to study the functionality of a fish bypass for downstream-migrating wild-caught and hatchery-released Atlantic salmon smolts. We used time-to-event analysis to model the influence of fish characteristics and environmental variables on the rates of a series of events associated with dam passage. Among the modelled events were approach rate to the bypass entry zone, retention rates in both the forebay and the entry zone and passage rates. Despite repeated attempts, only 65% of the tagged fish present in the forebay passed the dam. Fish passed via the bypass (33%), via spill (18%) and via turbines (15%). Discharge was positively related to approach, passage and retention rates. We did not detect any differences between wild and hatchery fish. Even though individual fish visited the forebay and the entry zone on multiple occasions, most fish passed during the first exposures to these zones. This study underscores the importance of timeliness to passage success and the usefulness of time-to-event analysis for understanding factors governing passage performance.

  • 27.
    Piccolo, John
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    The Land Ethic and conservation of native salmonids2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, p. 160-164Article in journal (Refereed)
  • 28.
    Piccolo, John J.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Challenges in the conservation, rehabilitation and recovery of native stream salmonid populations: beyond the 2010 Luarca symposium2010In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 20, no 3, p. 346-351Article in journal (Refereed)
    Abstract [en]

    In May, 2010, some 100 salmonid ecologists gathered in Luarca, Spain for the international symposium Advances in the population ecology of stream salmonids Topics included individual behaviour, life history, genetics and population dynamics, covering multiple scales from microhabitats to ecosystems. There were also sessions on conservation and restoration of native salmonids, human impacts, and salmonids as invasives. On the last day of the symposium I chaired a session on the challenges to salmonid conservation. I suggested that in addition to scientific challenges, a major challenge, in my opinion, will be improving the links between ecologists, conservationists, and policy makers. The Luarca symposium focused on mainly on ecological research, and little time was explicitly devoted to conservation. In this paper I begin with a brief overview of research highlights from the symposium. My objective, however, is to further the discussion on the role of ecological research in informing salmonid conservation. I use selected examples to show that ecological research already contributed much towards informing salmonid conservation, but that ecologists will always have limitations in their predictive ability. I suggest that conservation will need to move forward regardless of these limitations, and I call attention to some recent efforts wherein ecological research has played a crucial role. I conclude that ecologists should take urgent action to insure that their results are available to inform resource managers, conservation organizations, and policy makers regarding past losses and present threats to, native, locally-adapted salmonid stocks

  • 29.
    Rejas, Danny
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Universidad Mayor de San Simón, Bolivia.
    Oberdorff, Thierry
    Declerck, Steven A. J.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The introduced Arapaima gigas in the Bolivian Amazon: Trophic position and isotopic niche overlap with native species2023In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 32, no 4, p. 926-937Article in journal (Refereed)
    Abstract [en]

    Non-native fish species may generate major ecological impacts on native assemblages. This study aims to assess the potential impact of the introduced Arapaima gigas on native fish assemblages in two oxbow lakes of the Bolivian Amazon. Stable isotope data were used to determine trophic position (TP) and isotopic niche overlap, to evaluate potential predation and competition interactions, respectively. Results suggest that A. gigas is more an omnivore than a top predator, as often claimed. Arapaima gigas occupied an intermediate TP between detritivore/herbivore and piscivore fish species and showed broader isotopic niche compared to most native species analysed. The isotopic niche of A. gigas significantly overlapped with most native fish species in one lake (i.e. Lake Mentiroso), while there was low niche overlap in the second (i.e. Lake Miraflores). Given its omnivorous tendencies, the predation impact of A. gigas on other fish species is likely less than currently claimed and likely varies with the food web structure of the ecosystem. More precise data on resource availability and use are necessary to infer whether niche overlap will have negative impacts on native fish species through potential competitive interactions. Increasing our understanding on the processes generating impact of these introductions on resident communities through food web ecology will pave the way for better resource management and conservation efforts. 

  • 30.
    Sjöberg, Niklas B.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Wickström, Håkan
    Asp, Anders
    Petersson, Erik
    Migration of eels tagged in the Baltic Sea and Lake Malarenin the context of the stocking question2017In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 26, no 4, p. 517-532Article in journal (Refereed)
    Abstract [en]

    Eels (Anguilla spp.) are in decline worldwide, and the signs of reduced recruitment have been observed in continental Europe since the early 1970s. To aid recovery of the European eel, stocking is used by many European countries as a management option. In this study, tagging experiments were conducted to follow eel migration from Lake Malaren and four sites along the Swedish east coast in the Baltic Sea. The recaptured tagged eels were retrieved from fishermen, allowing for the opportunity to investigate their origin (brackish water, stocked in freshwater or a mix in between) by otolith microchemistry and to assess for morphological differences after tagging. Several changes took place; for example, eye index increased while weight and condition decreased with migrated distance and time until recapture. In Lake Malaren, the majority of tagged eels did not migrate out of the outlets, irrespective of their origin. Most of them were caught in the opposite direction and continued to be caught in the lake 1-3years after tagging, with significant weight losses. Overall, overwintering is suggested to be an inferior option, but it is uncertain whether this is a natural behaviour or a result of translocation and restocking. For coastal eels, origin had no effect on migratory behaviour; a majority of the tagged eels migrated towards the outlet of the Baltic Sea. Interestingly, a minority of the recaptured eels originated from stocked fish. Instead, recaptures were dominated by natural immigrants that had spent most of their lives in brackish waters.

  • 31.
    Skov, Christian
    et al.
    DTU-AQUA, Denmark.
    Brodersen, Jakob
    Lund University.
    Nilsson, P. Anders
    Lund University.
    Hansson, L. Anders
    Lund University.
    Brönmark, Christer
    Lund University.
    Inter- and size-specific patterns of fish seasonal migration between a shallow lake and its streams2008In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 17, no 3, p. 406-415Article in journal (Refereed)
    Abstract [en]

    This study used passive telemetry (passive integrated transponders) to evaluate winter migration in three species of cyprinids (roach (Rutilus rutilus (L.)), white bream (Blicca bjoerkna (L.)) and rudd (Scardinius erythrophthalmus (L.))) and their potential predators (pike (Esox lucius (L.)) and perch (Perca fluviatilis (L.))) between a shallow lake and its streams. Migration patterns were investigated from October to June, and a substantial part of the roach (40%) and white bream (55%) populations tagged in the lake during autumn migrated during winter into the streams, whereas only very few piscivores (<2%) migrated. In contrast to roach and white bream, only few rudd (<6%) migrated, which is likely a consequence of different overwintering strategies, e.g., rudd overwintering in shallow highly structured habitats. Small rudd migrated more than larger rudd, whereas there were no size-differentiated migration patterns for roach or white bream. Migration of the cyprinid fishes was generally initiated in late October and ended in May, and specific synchronised bursts of migration were observed in December, January and April, suggesting that migration is triggered by one or more proximate environmental cues. The cyprinid fishes generally entered the streams in late afternoon or in the morning, depending on season, but overall migration patterns varied between the three streams. We suggest and discuss that our results have great implications for lake management as well as for the interpretation of seasonal trophic dynamics in shallow lakes.

  • 32.
    Tibblin, Petter
    et al.
    Linnéuniversitetet, Institutionen för naturvetenskap, NV.
    Koch-Schmidt, Per
    Linnéuniversitetet, Institutionen för naturvetenskap, NV.
    Larsson, Per
    Linnéuniversitetet, Institutionen för naturvetenskap, NV.
    Stenroth, Patrik
    Linnéuniversitetet, Institutionen för naturvetenskap, NV.
    Effects of salinity on growth and mortality of migratory and resident forms of Eurasian perch in the Baltic Sea2012In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 21, no 2, p. 200-206Article in journal (Refereed)
    Abstract [en]

    In the coastal areas of the Baltic Sea, there are two forms of perch (Perca fluviatilis). One of the forms is migratory and spawns instreams entering the Baltic Sea. The other form is resident and spawns in brackish water. Both forms utilise the coastal habitat for foraging. We examined the spawning success of the two forms in fresh and brackish water (7 parts per thousand, equal to salinity in thesouth Baltic Sea). The experiments showed that hatching success was equally high in freshwater and in brackish water despite female origin. The survival of yellow-sac and free swimming fry was significantly reduced in brackish water, which was independent if the fish wasof migratory or brackish resident origin. Further, growth rate of perch fry was severely reduced in brackish water. The results indicate thatperch has not developed any tolerance to brackish water in the young life stages. The migratory life strategy of perch can thus be explained by higher survival of fry in freshwater.

  • 33.
    Tibblin, Petter
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Koch-Schmidt, Per
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Larsson, Per
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Stenroth, Patrik
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Effects of salinity on growth and mortality of migratory and resident forms of Eurasian perch in the Baltic Sea2012In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 21, no 2, p. 200-206Article in journal (Refereed)
    Abstract [en]

    In the coastal areas of the Baltic Sea, there are two forms of perch (Perca fluviatilis). One of the forms is migratory and spawns instreams entering the Baltic Sea. The other form is resident and spawns in brackish water. Both forms utilise the coastal habitat for foraging. We examined the spawning success of the two forms in fresh and brackish water (7 parts per thousand, equal to salinity in thesouth Baltic Sea). The experiments showed that hatching success was equally high in freshwater and in brackish water despite female origin. The survival of yellow-sac and free swimming fry was significantly reduced in brackish water, which was independent if the fish wasof migratory or brackish resident origin. Further, growth rate of perch fry was severely reduced in brackish water. The results indicate thatperch has not developed any tolerance to brackish water in the young life stages. The migratory life strategy of perch can thus be explained by higher survival of fry in freshwater.

  • 34.
    Turesson, H.
    et al.
    Lund university, Sweden.
    Brönmark, Christer
    Lund university, Sweden.
    Wolf, Annett
    Lund university, Sweden.
    Satiation effects in piscivore prey size selection2006In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 15, no 1, p. 78-85Article in journal (Refereed)
    Abstract [en]

    We present a functional response model that primarily evaluates effects of satiation in piscivore prey-size selection. The model also includes other passive processes, such as prey-size-dependent encounter rate and prey-size-dependent capture success, where capture success decreases and encounter rate increases with prey size. The model generates a wide variety of outcomes, where small, intermediate or large prey is positively selected for. These very different selectivity patterns are generated without any active prey choice included in the model. The results stress the importance of controlling for satiation and other passive processes in empirical studies on prey-size selection, especially if the aim is to test active prey choice in piscivores. © 2005 The Authors Journal compilation 2005 Blackwell Munksgaard.

  • 35.
    van Dorst, Renee M.
    et al.
    Swedish Univ Agr Sci, Inst Coastal Res, Dept Aquat Resources, Oregrund, Sweden..
    Gardmark, Anna
    Swedish Univ Agr Sci, Dept Aquat Resources, Oregrund, Sweden..
    Svanbäck, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Huss, Magnus
    Swedish Univ Agr Sci, Dept Aquat Resources, Oregrund, Sweden..
    Zooplanktivore fish body growth responses to browning-induced light limitation vary over ontogeny, but not with fish density2022In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 31, no 1, p. 17-28Article in journal (Refereed)
    Abstract [en]

    Ongoing climate change is leading to browning of many lakes and coastal areas, which can impair fish body growth and biomass production. However, whether and how effects of light limitation caused by browning on fish body growth vary over early ontogeny is unknown. In this study, we set up a mesocosm experiment to test whether roach (Rutilus rutilus) body growth responses to browning depend on body size, and if findings are robust over roach densities. We also studied a potential mechanism for size-specific responses by conducting an aquaria experiment to test if size-specific prey selectivity in roach changes with browning. We found that roach body growth responses to browning-induced light limitation vary over ontogeny (independent of roach density), negatively affecting body growth of young-of-the-year (YOY) but not of 1-year-old individuals. We also show that this difference in growth response is likely a consequence of browning-induced alterations in zooplankton community composition and variation in prey selectivity between YOY and 1-year-old fish. This suggests that we should account for the diverse effects of browning over fish ontogeny, mediated via altered prey composition and ontogenetic changes in prey preference, when assessing overall impacts of browning on aquatic ecosystems.

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  • 36.
    Watz, Johan
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Piccolo, John J
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    The role of temperature in the prey capture probability of drift-feeding juvenile brown trout (Salmo trutta)2011In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 20, no 3, p. 393-399Article in journal (Refereed)
    Abstract [en]

    Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift-feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 °C and 14 °C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 °C to 53% at 5.7 °C. At 8 °C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics-based drift-foraging models, which to date have not incorporated a temperature-dependent prey capture function.

  • 37. Westerberg, Håkan
    et al.
    Sjöberg, Niklas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Institute of Freshwater Research, Swedish University of Agricultural Sciences, Sweden.
    Overwintering dormancy behaviour of the European eel (Anguilla anguilla L.) in a large lake2015In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 24, no 4, p. 532-543Article in journal (Refereed)
    Abstract [en]

    Overwintering dormancy behaviour was studied in female silver eels in Lake Mälaren in Sweden between 2008 and 2010. Depth choices and movements in relation to temperature were analysed from pressure andtemperature records for 13 eels with implanted data storage tags, covering 17 overwintering periods and threeintervening summer periods. Dormancy commenced in October–November as temperatures fell below 4–12 °C.Eels tended to remain motionless throughout the winter, with some short periods of activity signalled by smallchanges in depth distributions. During dormancy, the eel shows a clear avoidance of shallow areas <5 m in favourof the 10–25-m-depth interval. Activity tended to resume 4–6 months later in April–May as temperatures roseabove 3–7 °C and ice cover broke, and eels spent more time at shallower depths of <5–10 m. The majority of theeels were assessed as being in the silver eel stage at the time of tagging. During the autumn months, the divingbehaviour, with frequent and large vertical excursions and periods at the surface, was similar to that seen inmigrating eels in the Baltic and Atlantic Ocean. In spring and summer, the behaviour differed, being dominated bymore gradual depth variations, implying that the eels reverted from silver eel migration behaviour to yellow eelforaging behaviour. Body weight declined during dormancy, but other studies of starvation over comparable timeperiods showed significantly higher average specific weight losses, implying that the Mälaren silver eels must havefed between the end of dormancy and recapture.

  • 38. Wickström, Håkan
    et al.
    Sjöberg, Niklas B.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Institute of Freshwater Research, Swedish University of Agricultural Sciences, Sweden.
    Traceability of stocked eels - the Swedish approach2014In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 23, no 1, p. 33-39Article in journal (Refereed)
    Abstract [en]

    Stocking of eels is one of the management measures in the eel regulation (EC No 1100/2007) to recover the stock. The Swedish Eel Management Plan doubles the numbers stocked to 2.5 million eels per year. Whether stocked eels contribute to the spawning stock or not has been questioned: stocked eels might not migrate as successful as wild recruited eels. The EIFAAC/ICES Working Group on Eel (2011) recommended that all stocked eel should be marked and thereby separable from wild eel in subsequent sampling'. Since 2009, eels stocked in Sweden have been bathed in a strontium (Sr) solution, which gives a detectable mark in their otoliths. So far, 5.5 million eels have been marked in Sweden; Finland imports eels for stocking via Sweden, and these 0.6 million eels were marked by two Sr rings. We present results on marking success and recapture rates and also from marking with alizarin complexone and PIT tags in combination with Sr. If all eels stocked in the Baltic are marked, their contribution to the spawning run can be estimated. Using different combinations of marks in different regions, the relative contribution from separate stocking programmes can be evaluated. To increase the set of suitable marks, barium was tested as an additional tracer.

  • 39.
    Wysujack, Klaus
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Bergman, Eva
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Olsson, Ivan
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    The role of the environment in partial migration: food availability affects the adoption of a migratory tactic in brown trout Salmo trutta2009In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 18, no 1, p. 52-59Article in journal (Refereed)
    Abstract [en]

    Alternative reproductive tactics are commonly reported for salmonids (Pisces) and typically involve large migratory and small resident individuals. Variation in migratory tendency should reflect the different benefits and costs that the two different phenotypes face with regard to fitness. Therefore, the effect of food availability on the adoption of a migratory tactic in brown trout was investigated. Fifty trout were placed in each of 12 tanks and fed at three different levels. Growth-related variables were measured regularly, and at the end of the experiment, the proportion of migrants and residents was recorded. Low food availability led to increased numbers of migratory fish. The expected sex-bias was also present, with a lower percentage of resident females than resident males. As all fish originated from the same gene pool, the changing proportions of the migratory tactics can be classified as phenotypic plasticity. The study provides evidence that the different phenotypes reflect alternative tactics within a conditional strategy. Some differences in growth-related variables were present between the sexes, and a very pronounced difference in condition factor was found between resident and migratory males, but not in females. Thus, the results provide evidence that different selective forces may be acting on the sexes.

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