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1.
The occurrence and density of ≥ 1+ brown trout, Salmo trutta L., and their relationship with prevailing instream and catchment characteristics were studied in 50 small forest streams, partially dredged for forest ditching. The occurrence of trout at a stream site was largely determined by the abundance of pools, size of upper catchment and water pH. Moreover, at sites where trout occurred, the abundance of pools was lower at dredged locations than at those in a natural state. In riffles in a natural state, there was a positive relationship between trout density and three instream variables: the abundance of stream pools, cascades and instream vegetation, while an inverse relationship was found with the abundance of substratum of 2–10 cm in diameter. Of the catchment variables, correspondingly, the proportion of forest in the upper catchment was positively related and the proportion of peatland negatively related to trout density. No significant regression model could be fitted for dredged riffles. The possibility of enhancing trout populations in dredged riffles is discussed.  相似文献   

2.
Abstract– Habitat is important in determining stream carrying capacity and population density in young Atlantic salmon and brown trout. We review stream habitat selection studies and relate results to variable and interacting abiotic and biotic factors. The importance of spatial and temporal scales are often overlooked. Different physical variables may influence fish position choice at different spatial scales. Temporally variable water flows and temperatures are pervasive environmental factors in streams that affect behavior and habitat selection. The more frequently measured abiotic variables are water depth, water velocity (or stream gradient), substrate particle size, and cover. Summer daytime, feeding habitats of Atlantic salmon are size structured. Larger parr (>7 cm) have a wider spatial niche than small parr. Selected snout water velocities are consistently low (3–25 cm. s?1). Mean (or surface) water velocities are in the preferred range of 30–50 cm. s?1, and usually in combination with coarse substratum (16–256 mm). However, salmon parr demonstrate flexibility with respect to preferred water velocity, depending on fish size, intra- and interspecific competition, and predation risk. Water depth is less important, except in small streams. In large rivers and lakes a variety of water depths are used by salmon parr. Summer daytime, feeding habitat of brown trout is also characterized by a narrow selection of low snout water velocities. Habitat use is size-structured, which appears to be mainly a result of intraspecific competition. The small trout parr (<7 cm) are abundant in the shallow swift stream areas (<20–30 cm depths, 10–50 cm. s?1 water velocities) with cobble substrates. The larger trout have increasingly strong preferences for deep-slow stream areas, in particular pools. Water depth is considered the most important habitat variable for brown trout. Spatial niche overlap is considerable where the two species are sympatric, although young Atlantic salmon tend to be distributed more in the faster flowing and shallow habitats compared with trout. Habitat use by salmon is restricted through interspecific competition with the more aggressive brown trout (interactive segregation). However, subtle innate differences in behavior at an early stage also indicate selective segregation. Seasonal changes in habitat use related to water temperatures occur in both species. In winter, they have a stronger preference for cover and shelter, and may seek shelter in the streambed and/or deeper water. At low temperatures (higher latitudes), there are also marked shifts in habitat use during day and night as the fish become nocturnal. Passive sheltering in the substrate or aggregating in deep-slow stream areas is the typical daytime behavior. While active at night, the fish move to more exposed holding positions primarily on but also above the substrate. Diurnal changes in habitat use take place also in summer; brown trout may utilize a wider spatial niche at night with more fish occupying the shallow-slow stream areas. Brown trout and young Atlantic salmon also exhibit a flexible response to variability in streamflows, wherein habitat selection may change considerably. Important topics in need of further research include: influence of spatial measurement scale, effects of temporal and spatial variability in habitat conditions on habitat selection, effects of interactive competition and trophic interactions (predation risk) on habitat selection, influence of extreme natural events on habitat selection use or suitability (floods, ice formation and jams, droughts), and individual variation in habitat use or behavior.  相似文献   

3.
Parr of the Atlantic salmon in subarctic River Teno, northern Finland (70°N, 28°E), are found to migrate to small tributaries that are not spawning areas for the adult salmon. The age distribution of the salmon differs significantly between these brooks and the natal rivers, the parr in the brooks being typically 2–4 years old, whereas those in the main rivers were mostly of age 0–2 years. The older fish were found in the uppermost regions of the brooks. The ratio of salmon to brown trout decreases towards the upper reaches of the brooks. At least some of the young salmon overwinter in the brooks. However, the number of fish and the area inhabited diminished towards the autumn in some occasions. It is suggested that this migratory behavior may be an adaptational phenomenon that could cause variation in survival among young salmon in the River Teno.  相似文献   

4.
Abstract  Breakpoints in both length and weight that represent the onset of first maturation, revealed that growth and maturation were correlated with density-related parameters in stream-dwelling resident brown trout, Salmo trutta L., from nine different rivers in Serbia. The determination of density dependence of growth is not simple, as both river width and depth, as single variables of habitat and relative biomass, and density were not significantly correlated with breakpoints. The significant relationship between breakpoints and the mean weight of brown trout ( x p) suggests that differences in breakpoints were inversely related to brown trout density. The implications of density dependence for management of streams holding resident brown trout are discussed.  相似文献   

5.
Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., fry were point and scatter stocked in the early part of June at densities of 63–263 fry 100 m−2 per species in the River Viantienjoki, a small river in northern Finland, and their population densities were assessed in late summer. Both species were always stocked together in similar quantities. Point stocking was used in the first 2 years and scatter stocking in the following 2 years. In point stocking, there was no correlation between the distance from the stocking sites (maximum = 250 m) and parr density in census sites ( r = −0.013 and 0.019 for brown trout and Atlantic salmon, respectively). The stocking density of fry did not influence parr density in August by either method or by species. Stocking density explained only from 11% to 23% of the parr survival depending on the species or stocking method. The mean densities of Atlantic salmon and brown trout parr did not differ significantly from each other at any fishing site ( P > 0.05). Both point and scatter stocking appear to be suitable methods for use in small rivers. The parr densities depend more on the other factors (e.g. habitat quality) than the stocking method, and the choice between methods could be based on the time and labour available.  相似文献   

6.
Abstract –  Along a stream, we investigated whether the abundance of stone loach ( Barbatula barbatula , L.) was related to the presence of brown trout ( Salmo trutta , L.) and instream habitat variables. First, a field survey was carried out where different habitat variables and the densities of both species were quantified and subjected to principal components analysis. Then the abundance of stone loach was related to the scores of the retained axes (eigenvalues >1). The abundance of stone loach was positively correlated to substrate particle size, amount of shade, temperature, discharge and current velocity, but negatively correlated to brown trout abundance. Secondly, a month-long field enclosure experiment in a stream was performed to test for any negative effects of brown trout on stone loach growth. Four treatments were used: intraspecific competition (stone loach at double density), interspecific competition (stone loach + small trout), predation (stone loach + large trout) and a control (stone loach alone). The results showed that large trout tended to have negative effects on final stone loach biomass. The absence of a negative effect of large trout on resource density suggests that nonlethal effects rather than resource competition caused this trend.  相似文献   

7.
Abstract – In-stream habitat was measured and trout density was estimated in Merrick Brook (105 habitat units) and the Tankerhoosen River (135 habitat units), Connecticut to determine relationships between habitat use of brook trout Salvelinus fontinalis and brown trout Salmo trutta and woody debris. In each habitat unit, woody debris was inventoried, and length, width, depth, area, width : depth ratio and undercut bank area were estimated. Trout abundance was estimated by snorkeling. Multiple regression was used to test relationships between trout density and principal components describing habitat unit variables. In Merrick Brook, habitat unit size and shape explained most of the variability in density of brook trout (<130 and ≥130 mm) and brown trout (<150 mm) among habitat units, although principle components describing large woody debris or fine woody debris contributed significantly to variations in density of brook trout (≥130 mm) and brown trout (<150 and ≥150 mm). In the Tankerhoosen River, fine woody debris explained most of the variability in density of brook trout (<130 and ≥130 mm), followed by habitat unit size and shape. Both large woody debris and fine woody debris contributed significantly to variations in density of brown trout (≥150 mm). These results suggest that woody debris is an important component of wild trout habitat above that provided by habitat unit shape and size alone.  相似文献   

8.
Abstract –  Lipid density appears to influence life-history decisions in salmonid fishes. This study shows that parr and smolts of anadromous Atlantic salmon from a south Norwegian river have on average between 30 and 40% higher energy level than corresponding brown trout in spring and summer, which may explain differences in life-history traits between the two species. The higher energy density of young salmon was chiefly due to a 1.8 times higher lipid density in parr and 2.4 times higher lipid density in smolts. The difference was smaller among immature parr in the autumn, with only 1.4 times higher lipid density in salmon than trout. The reason for the decreased difference was probably that the more energy rich salmon parr had attained maturity at the time. Among mature male parr, the somatic energy density was approximately 10% higher in trout than salmon. However, the gonadal energy content was more than twice as high in salmon than in trout. The higher somatic energy allocation in parr of Atlantic salmon probably influences protein growth of the two species in fresh water, and increases the ability of salmon relative to trout to undertake long distance feeding migrations and make large investments in reproduction.  相似文献   

9.
Interactive segregation has been suggested as the ruling competition mechanism determining niche and niche segregation between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Results from allopatry–sympatry observations of habitat use in both nature and in experiments were contrary to predictions derived from the interactive segregation hypothesis. Habitat use parameters under natural conditions such as distance to shore for Atlantic salmon parr were nearly identical in allopatric (mean ± SD; 3.2 ± 1.4 m) and sympatric (3.3 ± 1.4 m) situations. Occupied water depths largely reflected available water, but water depths <15 cm were avoided by salmon parr. Under experimental conditions, habitat use of allopatric salmon was density independent and salmon size had only minor effects, with smaller fish being more likely to occur in the shallow. Habitat use of salmon in sympatry with trout did not differ from allopatric salmon habitat use, and only salmon size had minor effects on depth choice – occurrence of trout or fish density had no effect. Allopatric trout was in general more frequent in the shallow habitat than salmon. Habitat use of sympatric trout was affected by the occurrence of salmon and trout size, resulting in a higher use of the shallow habitats for small trout. To conclude, selective segregation has a dominant role in salmon habitat use (not affected by trout occurrence), whereas a mixed situation occurs in trout habitat use with elements of interactive segregation when competing with Atlantic salmon (affected by salmon occurrence).  相似文献   

10.
Many investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s?1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m2 over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.  相似文献   

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