| 1. |
- Eriksson, Marie, et al.
(author)
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Avloppsvatten : Rening av avloppsvatten i Sverige
- 2016
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Reports (other academic/artistic)abstract
- Utvecklingen de senaste 200 åren har gått från nedgrävda latriner via underjordiska kloaker som släpptes ut i närmaste sjö eller kustvatten till avancerade avloppsreningsverk. Avloppsfrågan har förändrats från att vara lösningen på ett lokalt sanitärt problem till att bli en global miljöfråga.Rening av avloppsvatten i Sverige ges ut av Naturvårdsverket och beskriver hur reningen av avloppsvatten från tätorter utvecklats i Sverige under 1900- och 2000-talen. Skriften ges ut vartannat år och har uppdaterats med senaste statistiken från 2014 angående utsläpp och slam från reningsverk.Informationen presenteras enligt artikel 16 i avloppsdirektivet (91/271/EEG). Direktivet omfattar allt avloppsvatten som samlas upp i ledningsnät, men kvantitativa krav ställs bara för de reningsverk som betjänar mer är 2 000 personer. I Sverige motsvarar det drygt 400 anläggningar. De gamla medlemsländerna i EU (EU15) skulle ha uppfyllt alla åtgärder inom ramen för direktivet vid utgången av 2005. De 12 nya EU-länderna har olika övergångsregler.
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| 2. |
- Höjesjö, Johan, 1967, et al.
(author)
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Size-related habitat use in juvenile Atlantic salmon: the importance of intercohort competition
- 2016
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In: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 73:8, s. 1182-1189
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Journal article (peer-reviewed)abstract
- In stream-living salmonids, an underlying mechanism for the critical period after emergence has generally been assumed to be size-dependent swimming capacity constraining fry (age-0) to low-velocity habitats with reduced food availability and intense competition. A further plausible mechanism is that intercohort habitat exclusion confines fry to marginal habitats. This possibility was tested using a seminatural stream with 16 test arenas, each comprising one high-velocity, deep habitat and one low-velocity, shallow habitat. We observed groups of newly emerged Atlantic salmon (Salmo salar) fry, either alone or in sympatry with one or two age-1 salmon. Salmon fry used high-velocity areas (42.2 +/- 0.4 cm.s(-1)) most extensively in the absence of intercohort competition, where they obtained more food than in low-velocity areas (3.3 +/- 0.3 cm.s(-1)), even though foraging efficiency was lower (though not significantly so). In sympatry with older cohorts, fry increased their use of the low-velocity habitat, with a reduced foraging activity, suggesting that strong older cohorts in natural populations may have the potential to influence the strength of the recruiting cohort by negative density dependence due to interference competition for habitat.
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| 3. |
- Kaspersson, Rasmus, 1978
(author)
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Age-class interactions in Atlantic salmon and brown trout: Effects on habitat use and performance
- 2010
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Doctoral thesis (other academic/artistic)abstract
- This thesis investigates the underlying mechanisms and the density-regulatory effects of age-class interactions, using juvenile Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) as study species. Field experiments were performed in streams along the western coast of Sweden, in which densities of older age-classes were reduced and the response on young-of-the-year habitat use and performance (growth, movement and survival) was observed (Papers I and II). Observational data from 159 trout populations was extracted from the Swedish Electro-fishing Register to test the generality of age-class competition (Paper III) and observations in controlled artificial stream environments were used to establish the underlying mechanisms with regard to habitat use and behavioural interactions (Papers IV and V). The combined findings of these studies show that age-classes of stream-living salmonids compete for limited resources in the stream habitat. This competition favours old individuals, although the behavioural observations of Paper V suggest that their competitive benefit may decrease at increasing densities of young-of-the-year fish. Density-reductions of older cohorts in field increased the growth of young-of-the-year trout, an effect that was observed at the later part of the growth season (Papers I and II). The observational data-set (Paper III), provided further evidence of the prevalence of inter-cohort competition, reflected as a negative association between density of older cohorts and young-of-the-year body-size, in the same magnitude as on an intra-cohort level. In accordance with previous studies, juvenile salmon and trout were segregated in the stream habitat, with young-of-the-year individuals using shallow, low-velocity, habitats close to the spawning area while older cohorts were positioned in deep, high-velocity, areas (Papers II and IV). However, when experimentally reducing the density of older cohorts in field and lab (Papers II and IV), this spatial pattern was shown to be an effect of habitat exclusion rather than size-dependent habitat preference, as suggested in previous studies, with subsequent negative effects on young-of-the-year foraging activity (Paper IV). Thus, this finding provides a potential underlying mechanism to the negative effect on young-of-the-year performance presented in Papers I, II and III. From an applied point of view, the findings of this thesis highlight the importance of taking age-class interactions into account when investigating density-dependence and habitat use among stream-living salmonids. The findings also suggest that marginal stream habitats may be essential during the first months after emergence by acting as refuges from inter-cohort competition, thus emphasizing the importance of maintaining and restoring these habitats in the wild.
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| 6. |
- Kaspersson, Rasmus, 1978, et al.
(author)
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Density-dependent growth rate in an age-structured population: a field study on stream-dwelling brown trout Salmo trutta
- 2009
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In: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 74:10, s. 2196-2215
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Journal article (peer-reviewed)abstract
- A field experiment during autumn, winter and spring was performed in a small stream on the west coast of Sweden, aiming to examine the direct and indirect consequences of density-dependent intercohort competition in brown trout Salmo trutta. Individual growth rate, recapture rate and site fidelity were used as response variables in the young-of-the-year (YOY) age class, experiencing two different treatments: presence or absence of yearlings and over-yearlings (age ≥ 1+ year individuals). YOY individuals in stream sections with reduced density of age ≥ 1+ year individuals grew significantly faster than individuals experiencing natural cohort structure. In the latter, growth rate was negatively correlated with density and biomass of age ≥ 1+ year individuals, which may induce indirect effects on year-class strength through, for example, reduced fecundity and survival. Movement of YOY individuals and turnover rate (i.e. proportion of untagged individuals) were used to demonstrate potential effects of intercohort competition on site fidelity. While YOY movement was remarkably restricted (83% recaptured within 50 m from the release points), turnover rate was higher in sections with reduced density of age ≥1+ year individuals, suggesting that reduced density of age ≥1+ year individuals may have released favourable microhabitats.
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| 7. |
- Kaspersson, Rasmus, 1978, et al.
(author)
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Effects of density on foraging success and aggression in age-structured groups of brown trout
- 2010
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In: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 79:3, s. 709-715
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Journal article (peer-reviewed)abstract
- The benefit of monopolizing a limited resource is influenced by competitor density and by the relative competitive ability of defenders and intruders. Nevertheless, few studies have investigated the effect of density on resource defence in groups with large asymmetries in competitive ability, as a consequence of, for example, age and/or body size. We used two age classes (i.e. size groups) of stream-living brown trout, Salmo trutta, to investigate this issue. While old (and large) trout are assumed to be superior during interference competition, younger individuals may be both numerically dominant and constitute more than half of the total population biomass. In this experiment, the ability of one yearling to monopolize a concentrated food source was observed at four densities of under-yearlings (zero, two, six and 12) in an indoor seminatural stream. We predicted that the success of defence would decrease with increasing under-yearling density and that the frequency of defence (i.e. aggression) would peak at an intermediate density. As predicted, yearlings made significantly more unsuccessful foraging attempts and adopted darker body coloration at high density of under-yearlings, suggesting increased stress levels. However, in contrast to our second prediction, the number of aggressive interactions increased progressively with density. These novel findings suggest that the cost of defence increases with under-yearling density, probably as a consequence of stress from interference with under-yearlings employing alternative competitive strategies. However, the difference in size seems to enable yearlings to defend the food resource at higher density of competitors than predicted from the resource defence theory.
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| 8. |
- Kaspersson, Rasmus, 1978, et al.
(author)
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Habitat exclusion and reduced growth: a field experiment on the effects of inter-cohort competition in young-of-the-year brown trout
- 2012
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In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 169:3, s. 733-742
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Journal article (peer-reviewed)abstract
- Competition during the juvenile phase is a key process for regulating density in organisms with high fecundity. Juvenile density-dependent bottlenecks may become even more pronounced if several cohorts compete, but this has received relatively limited attention in previous literature. We performed a manipulation experiment in seven coastal streams to investigate the presence of inter-cohort competition, using habitat selection, body-size and density of newly emerged (age-0) brown trout (Salmo trutta) as response variables. The trout population (age ≥1 fish) was estimated using electro-fishing prior to the emergence of fry (April–May) and was either removed (manipulated sections) or maintained (control sections). Age-0 habitat selection was examined in June while density and body-size was evaluated in October (end of the growth season). We found that age-0 trout selected habitats that were located further from riffles (nursery habitats) in the absence of age ≥1 trout, suggesting a niche overlap between cohorts in the habitat dimension and, hence, that both inter-cohort competitive interactions and ontogenetic preference may influence habitat utilisation in the wild. Furthermore, we also found age-0 body-size to be significantly larger in manipulated sections and negatively related to its own density. We argue that competition from older cohorts influence the availability of age-0 feeding territories at the critical phase of emergence with secondary negative effects on age-0 growth. These results not only have implications for understanding the mechanisms of density dependence but can also provide valuable knowledge to the management of salmonid populations and their habitats in the wild.
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| 9. |
- Kaspersson, Rasmus, 1978, et al.
(author)
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Modes of Competition: Adding and Removing Brown Trout in the Wild to Understand the Mechanisms of Density-Dependence
- 2013
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In: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 8:5
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Journal article (peer-reviewed)abstract
- While the prevalence of density-dependence is well-established in population ecology, few field studies have investigated its underlying mechanisms and their relative population-level importance. Here, we address these issues, and more specifically, how differences in body-size influence population regulation. For this purpose, two experiments were performed in a small coastal stream on the Swedish west coast, using juvenile brown trout (Salmo trutta) as a study species. We manipulated densities of large and small individuals, and observed effects on survival, migration, condition and individual growth rate in a target group of intermediate-sized individuals. The generality of the response was investigated by reducing population densities below and increasing above the natural levels (removing and adding large and small individuals). Reducing the density (relaxing the intensity of competition) had no influence on the response variables, suggesting that stream productivity was not a limiting factor at natural population density. Addition of large individuals resulted in a negative density-dependent response, while no effect was detected when adding small individuals or when maintaining the natural population structure. We found that the density-dependent response was revealed as reduced growth rate rather than increased mortality and movement, an effect that may arise from exclusion to suboptimal habitats or increased stress levels among inferior individuals. Our findings confirm the notion of interference competition as the primary mode of competition in juvenile salmonids, and also show that the feedback-mechanisms of density-dependence are primarily acting when increasing densities above their natural levels. BOTT JC, 1989, BEHAVIOUR, V108, P104
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| 10. |
- Sundström, L. Fredrik, 1972, et al.
(author)
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Density-Dependent Compensatory Growth in Brown Trout (Salmo trutta) in Nature
- 2013
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In: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 8:5
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Journal article (peer-reviewed)abstract
- Density-dependence is a major ecological mechanism that is known to limit individual growth. To examine if compensatory growth (unusually rapid growth following a period of imposed slow growth) in nature is density-dependent, one-year-old brown trout (Salmo trutta L.) were first starved in the laboratory, and then released back into their natural stream, either at natural or at experimentally increased population density. The experimental trout were captured three times over a one-year period. We found no differences in growth, within the first month after release (May-June), between the starved fish and the control group (i.e. no evidence of compensation). During the summer however (July-September), the starved fish grew more than the control group (i.e. compensation), and the starved fish released into the stream at a higher density, grew less than those released at a natural density, both in terms of weight and length (i.e. density-dependent compensation). Over the winter (October-April), there were no effects of either starvation or density on weight and length growth. After the winter, starved fish released at either density had caught up with control fish in body size, but recapture rates (proxy for survival) did not indicate any costs of compensation. Our results suggest that compensatory growth in nature can be density-dependent. Thus, this is the first study to demonstrate the presence of ecological restrictions on the compensatory growth response in free-ranging animals.
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