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  • 1.
    Bowes, Rachel E.
    et al.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Lafferty, M. Holliday
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Thorp, James H.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Less means more: nutrient stress leads to higher delta N-15 ratios in fish2014In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 9, p. 1926-1931Article in journal (Refereed)
    Abstract [en]

    1. Isotopic ratios of nitrogen are often used in food-web studies to determine trophic position (including food chain length) and food sources, with greater ratios of 15N/14N (d15N) usually considered indicative of higher trophic position. However, fasting and starving animals may also show a progressive increase in d15N over time as they catabolise their own tissues.

    2. To determine the importance of starvation, we conducted a 4-month laboratory experiment testing effects of starvation on body condition and isotope ratios in the muscle tissue of freshwater guppies (Poecilia reticulata). We also compared laboratory results and conclusions with analyses of body condition and isotope ratios in various small species of fish collected in four seasons from the Kansas River in north-eastern Kansas, U.S.A.

    3. Fish starved in our laboratory experiment had significantly higher 15N values and poorer body condition than those fed more regularly. The diverse group of fish species collected in summer (July) from the Kansas River had higher weight-to-length ratios and lower 15N values than those retrieved in other seasons. Overall body condition resulting from reduced food consumption explained 44 and 53% of the variability in 15N for field and laboratory fish, respectively.

    4. These results are applicable to a wide variety of food-web research but are especially pertinent to studies of organisms that undergo large changes in life history, dormancy, extended fasts or periods of significant nutritional allocation to young.

  • 2.
    Calles, Olle
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Karlsson, Simon
    Vezza, Paolo
    Politecnico di Torino.
    Comoglio, Claudio
    Politecnico di Torino.
    Tielman, Johan
    E.ON Vattenkraft.
    Success of a low-sloping rack for improving downstream passage of silver eels at a hydroelectric plant2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, p. 2168-2179Article in journal (Refereed)
    Abstract [en]

    1. The European eel (Anguilla anguilla) is a critically endangered species, and one major threat is thesurvival of silver eels migrating downstream towards the sea from lake and river rearing areas. Duringthis migration, many eels are impinged and die on intake racks, or are injured or killed whenpassing through turbines.2. Intake racks at a hydroelectric plant were modified to avoid impingement and to collect eels withoutinjury; high mortality on both racks and in turbines was previously documented. Modificationsconsisted of reducing the rack gap width from 20 to 18 mm, decreasing the rack slope from 63 to 35degrees, increasing the rack surface area by 58% and installing six openings in the rack leading totraps.3. Downstream passage conditions for silver eels at the hydroelectric plant were significantlyimproved, reducing mortality from >70% at the old steep 20 mm racks to <10% at the modified18 mm rack collection facility. No tagged eels were impinged and killed on the racks, and 80%entered the collection facility.4. Survival can probably be improved even more, as the individuals that passed the facility mostlikely escaped through holes in the traps. Moreover, injured untagged eels were still encountered atthe modified racks, illustrating the need for rehabilitative measures to be implemented at all obstaclesbetween the main eel rearing areas and the sea.

  • 3.
    Calles, Olle
    et al.
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Schmitz, Monika
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Greenberg, Larry
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Olsson, Ivan
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Comoglio, C
    Kemp, P.S
    Blunden, L
    Size-dependent mortality of migratory silver eels at a hydropower plant, and implications for escapement to the sea2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 10, p. 2167-2180Article in journal (Refereed)
  • 4.
    Enefalk, Åsa
    et al.
    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).
    Greenberg, Larry
    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).
    Winter sheltering by juvenile brown trout (Salmo trutta): Effects of stream wood and an instream ecothermic predator2017In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 62, no 1, p. 111-118Article in journal (Refereed)
    Abstract [en]

    In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators.We tested the effects of burbot (Lota lota) on the winter sheltering behaviour of PIT-tagged 0+ brown trout (Salmo trutta) in daylight and darkness. Sheltering in the streambed by trout was studied in the presence and absence of fine wood bundles.We found that the use of streambed and fine wood was lower in darkness than in daylight. Availability of fine wood significantly decreased sheltering in the streambed, and this effect was more pronounced in daylight than in darkness. The presence of a burbot significantly decreased sheltering in the streambed, had no effect on use of fine wood and resulted in a higher number of exposed trout.Our results indicate that juvenile brown trout decrease streambed sheltering in response to a burrowing, ectothermic predator.

  • 5.
    Filipsson, Karl
    et al.
    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).
    Österling, Martin
    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).
    Watz, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Effects of temperature and a piscivorous fish on diel winter behaviour of juvenile brown trout (Salmo trutta)2019In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Low winter temperatures constrain predator-detection and escape capabilities, making poikilotherms vulnerable to predation. Investigations of temperature effects on predator-prey interactions can therefore be of special importance in light of ongoing climate change, where winter temperatures are predicted to increase substantially at northern latitudes. Behavioral responses of stream fishes to terrestrial predators in winter are well recognised, whereas responses to predatory fish have received little attention. Using stream flumes, we examined the anti-predator behaviour of one-summer-old brown trout (Salmo trutta) at 3 and 8 degrees C in the presence and absence of burbot (Lota lota) under night, dawn, and daylight conditions. Burbot was placed upstream of the trout, separated by net screens. Lower temperature and the presence of burbot reduced trout activity. Light increased trout shelter use, and trout sheltered more in the presence of burbot. An interaction between the presence of burbot and light conditions affected trout position in the flumes: at night and dawn, trout positioned themselves further downstream when burbot were present than when absent, whereas during the day, trout maintained the same position in the presence or absence of the predator. Our results suggest that piscivorous fish, in addition to terrestrial predators, shape the behaviour of prey fishes in streams during winter. We show how predator avoidance results in altered diel patterns of juvenile brown trout under winter conditions, and that temperature has additional effects on trout behaviour.

  • 6.
    Giller, Paul
    et al.
    Natl Univ Ireland Univ Coll Cork, Sch Biol Earth & Environm Sci, Cork, Ireland..
    Greenberg, Larry
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    The relationship between individual habitat use and diet in brown trout2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 2, p. 256-266Article in journal (Refereed)
    Abstract [en]

    Salmonids exhibit considerable variation within and between individuals in growth, diet, foraging strategy and habitat use, but little is known about how these characteristics covary. Previous work has shown that habitat use strongly influences growth rates in brown trout (Salmo trutta). We examined individual variation in diet of PIT-tagged Salmo trutta in three stream enclosures in relation to individual habitat use, size, sex and growth. Each enclosure consisted of a fine substratum pool and a coarse substratum riffle. By placing antennae between these habitats, we continuously monitored habitat use under field conditions. Fish were recaptured four times over the 2-month study period, and diet, which was examined through stomach flushing, was related to habitat use over the previous 48h. Individual fish growth was also measured. Based on habitat use, trout were classified as either movers or stayers, with stayers being of two types, those using only pools and those using only riffles and movers using and swimming between pools and riffles. The stayers in pools took more terrestrial prey than the stayers in riffles, whereas the latter fed more on aquatic invertebrates such as the crustacean Gammarus pulex, the plecopteran Leuctra and cased caddis larvae. Movers had diets intermediate between the stayers in pools and the stayers in riffles. Results of canonical correspondence analysis showed that variation in diet amongst individual fish over the study period was significantly influenced by enclosure, growth and % time spent in the pool during the day. Graphical models of diet analysis showed that population and mean individual prey diversity tended to differ amongst enclosures and suggested that stayers in pools consumed a greater prey diversity, whereas stayers in riffles consumed more prey. Discriminant analysis of diets revealed significant discrimination by habitat and sex on two of the four sampling occasions, based on daytime habitat use, but only on one date based on night-time habitat use. Stoneflies and terrestrial prey contributed most to the separation.

  • 7.
    Gustafsson, Pär
    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.
    Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream2014In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 12, p. 2488-2501Article in journal (Refereed)
    Abstract [en]
    1. Changes to the riparian vegetation of forest streams during timber harvesting may have considerable impacts on stream biota, but few studies have attempted to separate the effects of individual factors that are altered during clear-felling operations.
    2. We studied the effects of large wood and terrestrial invertebrate supply, two factors affected by forest harvesting, on the growth and diet of two size classes of brown trout (Salmo trutta) during a two-month (June–August) field enclosure experiment. Twelve 20-m-long enclosed stream reaches were used in a 2 × 2 factorial design, with large wood either absent or added to mimic pre-modern forestry conditions, and terrestrial invertebrate inputs either reduced or maintained at ambient levels.
    3. The addition of large wood had a positive effect on the growth of large trout but no effect on small trout, whereas terrestrial invertebrate input had no effect on the growth of either size class. Growth rates were highest in the treatment with ambient terrestrial invertebrate inputs and added wood, were lowest in the treatment with reduced terrestrial invertebrate inputs and no added wood and were intermediate in the other two treatments.
    4. Dietary analyses showed no difference in treatments with and without added wood, perhaps because instream wood influences growth by producing profitable stream positions for trout, rather than by acting as a source of prey. Terrestrial invertebrate inputs affected the diet, as trout in enclosures with reduced inputs had a lower proportion of terrestrial invertebrate biomass in the diet than trout in enclosures with ambient terrestrial inputs.
    5. Our results suggest that leaving woody debris in streams when harvesting forests may enhance trout growth and that this is probably due to the physical changes in depth and current velocity caused by the wood rather than to changes in dietary prey composition.
  • 8.
    Gustafsson, Pär
    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.
    The influence of large wood on brown trout (Salmo trutta) behaviour and surface foraging2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, no 5, p. 1050-1059Article in journal (Refereed)
    Abstract [en]

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

    2. In a laboratory stream experiment, we tested how two size classes of brown trout, Salmo trutta, (mean size of 85 and 125 mm), alone and together, responded to a gradient of large wood in terms of activity, foraging on terrestrial drift and interactions between conspecifics.

    3. The results showed that the presence of large wood significantly reduced the overall activity of the fish, the number of agonistic interactions between individuals and the proportion of captured prey. However, activity decreased relatively more than the proportion of captured prey, resulting in a significant positive net effect of wood on the number of prey captures per time spent active (PTA). This indicates that trout living in habitats with high wood density may have a higher net energy gain than trout living in habitats with less wood.

    4. There were no observable size-class differences in the benefits of large wood or in the utilisation of surface-drifting terrestrial prey.

    5. These results suggest that the presence of large wood may be an important factor shaping stream communities and that a lack of structural complexity may decrease energy gain, increase agonistic interactions and, consequently, lower the production of brown trout

  • 9.
    Jonsson, Bror
    et al.
    Norway.
    Jonsson, Nina
    Norway.
    Ugedal, Ola
    Norway.
    Production of juvenile salmonids in small Norwegian streams is affected by agricultural land use2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, p. 2529-2542Article in journal (Refereed)
    Abstract [en]

    1. We estimated the biomass and production of juvenile anadromous brown trout (Salmotrutta) and Atlantic salmon (Salmo salar) (parr) in 12 streams in the Skagerrak area ofNorway to identify controlling environmental factors, such as land-use and waterchemistry.2. Production estimates correlated positively with fish density in early summer, but notwith the size of the catchment. The summer biomass of age-0 brown trout and Atlanticsalmon was smaller than that of age-1 and constituted 27.4 and 25.7%, respectively, of thetotal biomass of the two groups.3. Mean production of brown trout from July to September varied between streams, but inmost cases it was below 2 g 100 m)2 day)1. Yearly cohort production from age-0 in July toage-1 in July was 10 g m)2 or less, with mean annual production of 1.32 g 100 m)2 day)1,equivalent to 4.8 g m)2 year)1. The corresponding annual cohort production of Atlanticsalmon was 0.38 g 100 m)2 day)1 or 1.4 g m)2 year)1. Annual production to biomass ratio(P⁄B) for brown trout of the same cohort in the various streams was between 1.47 and 4.37;the overall mean (±SD) for all streams was 2.25 ± 0.94. Mean turnover rate of Atlanticsalmon was 2.73 ± 0.24.4. Production of 0+ brown trout during the summer correlated significantly with thepercentage of agricultural land and forest⁄bogs in the catchment, with maxima at 20 and75%, respectively. Age-0 brown trout production also correlated with concentration ofnitrogen and calcium in the water, with maxima at 2.4 and 14 mg L)1, respectively.5. The results support the hypothesis that brown trout parr production reflects the qualityof their habitat, as indicated by the dome-shaped relationship between percentage ofagricultural land and the concentration of nitrogen and calcium in the water.

  • 10.
    Nicola, Graciela G.
    et al.
    Department of Environmental Sciences, University of Castilla-La Mancha, Toledo, Spain.
    Almodovar, Ana
    Department of Zoology, Complutense University of Madrid, Madrid, Spain.
    Jonsson, Bror
    Norwegian Institute for Nature Research, Oslo, Norway.
    Elvira, Benigno
    Department of Zoology, Complutense University of Madrid, Madrid, Spain.
    Recruitment variability of resident brown trout in peripheral populations from southern Europe2008In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 53, p. 2364-2374Article in journal (Refereed)
    Abstract [en]

    1. Population regulation was studied for seven consecutive years (1992–98) in five rivers at

    the periphery of the distribution of Salmo trutta, where the fish were living under

    environmental constraints quite different from those of the main distribution area.

    2. Recruitment is naturally highly variable and the populations had been earlier classified

    as overexploited. Thus we expected that densities of young trout in most populations

    would be too low for density-dependent mortality to operate. We tested this by fitting the

    abundance of recruits to egg densities over seven consecutive years (stock–recruitment

    relationship), and used the results to judge whether exploitation should be restricted in the

    interests of conserving the populations.

    3. The density of 0+ trout in early September, as well as the initial density of eggs and

    parents, varied greatly among localities and years. The data for all populations fitted the

    Ricker stock–recruitment model. The proportion of variance explained by the population

    curves varied between 32% and 51%. However, in most cases the observations were in the

    density-independent part of the stock–recruitment curve, where densities of the recruits

    increased proportionally with egg densities.

    4. Our findings suggest that recruitment densities in most rivers and years were below the

    carrying capacity of the habitats. Although density-dependent mechanisms seemed to

    regulate fish abundance in some cases, environmental factors and harvesting appeared

    generally to preclude populations from reaching densities high enough for negative

    feedbacks to operate. The findings thus lend support to Haldane’s (1956) second

    hypothesis that changes in population density are primarily due to density-independent

    factors in unfavourable areas and areas with low density due to exploitation. Exploitation

    should be reduced to allow natural selection to operate more effectively.

  • 11.
    Nilsson, Christer
    et al.
    Umeå University, Umeå, Sweden.
    Polvi, Lina E
    Umeå University, Umeå, Sweden.
    Lind, Lovisa
    Umeå University, Umeå, Sweden.
    Extreme events in streams and rivers in arctic and subarctic regions in an uncertain future2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 12, p. 2535-2546Article in journal (Refereed)
    Abstract [en]

    We review the predicted changes in extreme events following climate change in flowing waters in arctic and subarctic regions. These regions are characterised by tundra or taiga ecosystems in either erosional or depositional glacial landforms or presently glacierised areas of the Northern Hemisphere. The ecological and geomorphic effects of extreme meteorological and hydrological events, such as episodes of strongly increased precipitation, temperatures and flows, can be exacerbated by altered base conditions. For example, winter temperature variations between frost and thaw will become more frequent at many places because mean temperature during the winter is closer to 0 °C, potentially leading to changes in the production of ice and intensified disturbance of riparian and aquatic habitats during extreme floods. Additionally, thawing of permafrost and glaciers can lead to increased bank erosion because of thaw slump and glacial outburst floods. We discuss the abiotic and biotic effects of these and other extreme events, including heavy precipitation, floods, drought and extreme air or water temperatures, and summarise our findings in a model that aims to stimulate further research in this field.

  • 12.
    Ranåker, Lynn
    et al.
    Lund University, Sweden.
    Jönsson, Mikael
    Lund University, Sweden.
    Nilsson, P. Anders
    Lund University, Sweden.
    Brönmark, Christer
    Lund University, Sweden.
    Effects of brown and turbid water on piscivore-prey fish interactions along a visibility gradient2012In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 57, p. 1761-1768Article in journal (Refereed)
    Abstract [en]

    1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predatorprey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predatorprey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free-swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free-swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predatorprey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher-order interactions.

  • 13.
    Setzer, Malin
    et al.
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    Norrgård, Johnny
    Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
    Jonsson, Tomas
    Systems Biology Research Centre, Skövde University, Skövde, Sweden.
    An invasive crayfish affects egg survival and the potential recovery of an endangered population of Arctic charr2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, ISSN 0046-5070, no 56, p. 2543-2553Article in journal (Refereed)
    Abstract [en]

    1. Many fish stocks have declined, because of overharvesting, habitat destruction and introduced species. Despite efforts to rehabilitate some of these stocks, not all are responding or are recovering only slowly.

    2. In freshwater systems, introduced crayfish are often problematic, and it has been suggested that their egg predation could reduce recruitment in depleted stocks of native fish.

    3. Here, we report the results of a field experiment, using experimental cages, on the extent of predation on eggs of great Arctic charr (Salvelinus umbla) in Lake Vättern, Europe’s fifth largest lake. Here, the great Arctic charr has declined dramatically and is listed as critically endangered.

    4. We were able to partition the total loss rate of eggs into background mortality, predation by introduced signal crayfish (Pacifastacus leniusculus) and predation by native fish. The mortality rate of charr eggs because of crayfish was estimated at more than five times that because of native fish. Of the total loss of eggs, 80% is believed to be caused by crayfish and 14% by fish, with 6% being natural background mortality.

    5. In a worst case scenario, our data infer that only 25% of the original number of eggs would survive, compared with 75% in the absence of crayfish. This could impair recovery of the stock of the endangered great Arctic charr in Lake Vättern.

    6. Contrary to earlier claims that crayfish predation on eggs of great Arctic charr is insignificant, our results indicate that crayfish predation may exceed fish predation and suggest that the abundance of signal crayfish on the spawning sites of great Arctic charr should be managed.

  • 14.
    Su, X.
    et al.
    School of Life Sciences, Southwest University, Chongqing, China; Umeå universitet.
    Polvi, L. E.
    Umå universitet.
    Lind, Lovisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Umeå universitet.
    Pilotto, F.
    Umår universitet.
    Nilsson, C.
    Swedish University of Agricultural Sciences, Umeå.
    Importance of landscape context for post-restoration recovery of riparian vegetation2019In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 64, no 5, p. 1015-1028Article in journal (Refereed)
    Abstract [en]

    We tested whether the recovery of riparian vegetation along rapids that have been restored after channelisation for timber floating can be predicted based on floristic and geomorphic characteristics of surrounding landscape units. Our study was located along tributary stream networks, naturally fragmented in rapids, slow-flowing reaches, and lakes (i.e. process domains), in the Vindel River catchment in northern Sweden. We tested whether landscape characteristics, specifically to what extent the geomorphology (affecting local abiotic conditions), species richness, and species composition (representing the species pool for recolonisation), as well as the proximity to various upstream process domains (determining the dispersal potential), can predict post-restoration recovery of riparian vegetation. Our results indicate that post-restoration recovery of riparian vegetation richness or composition is not strongly related to landscape-scale species pools in these streams. The restored rapids were most similar to upstream rapids, geomorphically and floristically, including plant traits. Species richness of adjacent landscape units (upstream process domains or lateral upland zone) did not correlate with that of restored rapids, and proximity of upstream rapids or other process domains was only weakly influential, thus diminishing support for the hypothesis that hydrochory or other means of propagule dispersal plays a strong role in riparian vegetation community organisation after restoration in this fragmented stream network. We conclude that, in these naturally fragmented stream systems with three discrete process domains (rapids, slow-flowing reaches and lakes), hydrochory is probably not the main predictor for short-term riparian vegetation recovery. Therefore, other factors than landscape context can serve in prioritising restoration and, in these systems, local factors are likely to outweigh landscape connectivity in the recovery of riparian vegetation.

  • 15.
    Watz, Johan
    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.
    Piccolo, John
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Greenberg, Larry
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Effects of ice cover on the diel behaviour and ventilation rate of juvenile brown trout2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, no 11, p. 2325-2332Article in journal (Refereed)
    Abstract [en]
    1. Winter ice conditions in boreal streams are highly variable, and behavioural responses by fish to river ice may affect overwinter survival rates. One type of ice, surface ice, stabilises water temperatures, reduces instream light levels and may provide overhead cover.
    2. Because surface ice is believed to afford protection against endothermic predators, we predicted that metabolic costs associated with vigilance would be lower under surface ice than in areas lacking surface ice. This potentially favourable effect of ice cover was tested by observing ventilation rates of juvenile brown trout (Salmo trutta) in a laboratory stream at dawn, during the day and at night in the presence and absence of real, light-permeable surface ice. Further, we offered trout drifting prey during daylight to test whether ice cover increased daytime foraging activity.
    3. Ice cover reduced ventilation rates during the day, but not at night or dawn. Moreover, fish made more daytime foraging attempts in the presence of ice cover than in its absence.
    4. We suggest that the most plausible explanation for these results is that fish experience a reduced perceived predation risk under surface ice.
  • 16.
    Watz, Johan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan.
    Calles, Olle
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Carlsson, Niclas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Teemu, Collin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Huusko, Ari
    Natural Resources Institute Finland (Luke), Kainuu Fisheries Research Station, Paltamo, Finland.
    Jörgen, Johnsson
    Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.
    Nilsson, Per Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Lund University.
    Norrgård, Johnny
    Gammelkroppa Lax, Filipstad.
    Nyqvist, Daniel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Institute of Marine Research in Norway, Bergen, Norway.
    Wood addition in the hatchery and river environments affectspost-releaseperformance of overwintering brown trout2018In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 64, no 1, p. 71-80Article in journal (Refereed)
    Abstract [en]

    1. Habitat structural complexity affects the behaviour and physiology of individuals,and responses to the environment can be immediate or influence performancelater in life through delayed effects.

    2. Here, we investigated how structural enrichment, both pre-release in the hatcheryrearing environment and post-release in the wild, influenced winter growthand site fidelity of brown trout stocked into side channels of a regulated river.

    3. Experiencing structural enrichment in the rearing environment during 3 months inautumn had no pre-release effect on growth, but a delayed positive effect afterrelease during the subsequent winter. Moreover, trout recaptured in wood-treatedsections of the side channels had grown more than trout recaptured in controlsections. Wood enrichment in the side channels also increased overwinter sitefidelity.

    4. These results show that adding structure during a relatively short period may altergrowth trajectories, and adding wood to side channels is a cost-effective methodto enhance winter habitat carrying capacity for juvenile salmonids in regulatedrivers.

  • 17.
    Watz, Johan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan.
    Otsuki, Y.
    Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
    Nagatsuka, K.
    Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
    Hasegawa, K.
    Hokkaido National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Sapporo, Japan.
    Koizumi, I.
    Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan.
    Temperature-dependent competition between juvenile salmonids in small streams2019In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, p. 1534-1541Article in journal (Refereed)
    Abstract [en]

    Biotic interactions affect species distributions, and environmental factors that influence these interactions can play a key role when range shifts in response to environmental change are modelled. In a field experiment using enclosures, we studied the effects of the thermal habitat on intra- versus inter-specific competition of juvenile Dolly Varden Salvelinus malma and white-spotted charr Salvelinus leucomaenis, as measured by differences in specific growth rates during summer in allopatric and sympatric treatments. Previous laboratory experiments have shown mixed results regarding the importance of temperature-dependent competitive abilities as a main driver for spatial segregation in stream fishes, and no study so far has confirmed its existence in natural streams. Under natural conditions in areas where the two species occur in sympatry, Dolly Varden dominate spring-fed tributaries (cold, stable thermal regime), whereas both species often coexist in non-spring-fed tributaries (warm, unstable thermal regime). Enclosures (charr density = 6 per m2) were placed in non-spring-fed (10–14°C) and spring-fed (7–8°C) tributaries. In enclosures placed in non-spring-fed tributaries, Dolly Varden grew 0.81% per day in allopatry and had negative growth (−0.33% per day) in sympatry, whereas growth rates were similar in allopatry and sympatry in spring-fed tributaries (0.68 and 0.58% per day). White-spotted charr grew better in sympatry than in allopatry in both thermal habitats. In non-spring-fed tributaries, they grew 0.17 and 0.79% per day and in spring-fed tributaries 0.46 and 0.75% per day in allopatry and sympatry, respectively. The negative effect of inter-specific competition from white-spotted charr on Dolly Varden thus depended on the thermal habitat. However, there was no strong evidence of a temperature-dependent effect of intra- and inter-specific competition on white-spotted charr growth. Multiple factors may shape species distribution patterns, and we show that temperature may mediate competitive outcomes and thus coexistence in stream fish. These effects of temperature will be important to incorporate into mechanistic and dynamic species distribution models.

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