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1.
To assess the trophic relationships of consumers in a sandy lowland brook (Ladberger Mühlenbach, Northrhine-Westphalia, Germany) the fish as well as the benthic communities were sampled monthly over half a year. Analysis of stomach contents of the fishes revealed two different feeding types: detritivores (including only Cyprinidae; foremost roach, Rutilus rutilus and Prussian carp, Carassius auratus gibelio) and benthivores (mostly stone loach, Barbatula barbatula and three-spined stickleback, Gasterosteus aculeatus). The detritivores mainly foraged on detritus, but also benthic invertebrates were found in their stomachs. This latter prey (especially some Trichoptera and Coleoptera, which were selected with a high preference) is strongly associated to hard substrates, only present in the brook as coarse detritus. Benthivore fishes only foraged on benthic invertebrates, mostly Gammaridae and Chironomidae, which were the most dominant elements of the macrozoobenthos. Niche overlap between these two foraging groups was very low, while the within-group overlap was rather high. As food could not be shown to be a limiting factor, a direct competition for food between most of these species in this brook seems most unlikely.  相似文献   

2.
In the northern part of the Baltic Sea, the Gulf of Bothnia, fourhorn sculpin (Myoxocephalus quadricornis) is one of the dominant fish species. A considerable proportion of the population (up to 54% of fish in gill net catches) have been reported to have spinal deformations, with a higher frequency in polluted than in clean areas. The stomach content of sculpins with normal and with severely deformed backbone were compared, but no statistically significant differences were revealed. The diet was generally dominated by the isopod Mesidotea entomon and three-spined stickleback (Gasterosteus aculeatus).  相似文献   

3.
In a novel biomanipulation experiment salmonids were used as a tool to improve water quality. The manipulation was initiated in spring 2000 as a response to non-point sources of phosphorus in a drinking water reservoir in Saxony, Germany. Salmonids (brown trout, Salmo trutta forma lacustris) were chosen as predators as the reservoir has a large hypolimnic water body and surface temperatures rarely exceed 20 °C. The vertical distributions of prey fish and brown trout were analysed with a fleet of vertical gill nets set in the pelagic zone of the reservoir. Consumption of brown trout was estimated by means of a bioenergetic model and the diet analyses of the trout. While the dominant planktivore (roach, Rutilus rutilus) was caught almost exclusively in the epilimnion during the stratification period trout were caught mainly below a depth of 10 m. Diet analysis revealed that the trout performed vertical migrations to consume food in the epilimnic layer, as an important food component were adult terrestrial and aquatic insects. The amount of fish in the food increased strongly with the size of the brown trout. The consumption estimate suggested that the trout had consumed 2-3% of the total roach stock during the study period (May-November 2000) of the first year of biomanipulation. We conclude that in general salmonids are suitable for food-web manipulation in deep reservoirs, but the stocked fish should be as large as possible (> 300 mm) and the proportion of large trout (> 500 mm) should be as high as possible.  相似文献   

4.
Asymmetrical interspecific competition among top predators can indirectly affect the predation risk for their prey by altering the abundance, diet, and habitat use of inferior competitors. However, the indirect effects of such biological interactions are poorly known because of the difficulties in measuring predation risk in nature. We addressed this issue by assessing the effect of asymmetrical competition among brook trout (Salvelinus fontinalis) and two superior non-piscivorous competitors, creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii), on the predation risk of a brook trout prey, northern redbelly dace (Chrosomus eos). We determined the spatio-temporal patterns of relative predation risk of dace with tethering experiments in 11 lakes containing either only brook trout and dace (n = 5), or brook trout, dace, chub, and sucker (n = 6). The diel pattern of the relative predation risk and the overall relative predation risk of dace were not significantly different in lakes with or without brook trout competitors. However, we observed a significant shift in the relative predation risk from the lower pelagic to the upper pelagic and littoral zones in the presence of brook trout competitors. This study highlights the fact that the outcome of interactions can vary in space and that care should be used when extrapolating the results of small-scale experiments or coarse-scale estimates to the whole ecosystem.  相似文献   

5.
Many of the unionoid mussel species are threatened, and to be able to develop strategies for effective conservation, one of the needs is to distinguish host fish species from non-host fish species using reliable methods. Margaritifera margaritifera lives as a parasite on brown trout (Salmo trutta) and/or Atlantic salmon (Salmo salar). The aim was to compare the reliability of two methods measuring the host specificity of M. margaritifera in two rivers that flow out into Skagerrak in the Atlantic Ocean. A second aim was to compare the time- and cost-efficiency of the two methods. The methods were (1) natural encystment abundances on fish in their native streams using electrofishing, and (2) encystment abundances from controlled artificial infestation in aquaria, on fish that were sacrificed. In both rivers, young-of-the-year (YOY), but not older brown trout, were naturally infested with relatively low loads of glochidia larvae, while the Atlantic salmon was not infested at all. When using artificial infestation, both YOY and older brown had encysted glochidia larvae on their gills, while glochidia larvae were not able to develop in Atlantic salmon at all. Here, the encystment was higher on the brown trout from the Lärje River, and older brown trout from the Lärje River did not seem to have as strong immunity response compared to older brown trout from the Brattefors River. In summary, brown trout is the only host fish for M. margaritifera in these rivers. Both methods can be used to discriminate between host fish species, but the method measuring natural encystment seems most time- and cost-efficient. In addition, natural encystment can be measured using a non-destructive photo-method, and is therefore suggested to be used when discriminating between host fish species for M. margaritifera.  相似文献   

6.
The lake investigated (Lake Heiliger See near the town of Angermünde, North-East Germany) is small (10.2 ha) but deep (zmax = 12 m, ? = 6.5 m). During summer the thermocline is at a depth of 4-5 m, and the hypolimnion is filled with H2S already by mid-June, making 60-75% of the bottom area inaccessible to fish. The native fish fauna is dominated by planktivorous roach (Rutilus rutilus). A test stocking of silver carp (Hypophthalmichthys molitrix) together with an unplanned and erroneous stocking of common carp (Cyprinus carpio), coupled with an incorrectly calculated strong stocking of eel (Anguilla anguilla), which assumed that the total lake area yielded fish food organisms, brought about a strong depression of the food biomass available to native fish. Both silver carp and common carp showed a pattern of behaviour which only partly agreed with results obtained in experimental ponds prior to lake stocking. At least for 10 years there was a very low zooplankton biomass (mostly below 1 mg/l fresh weight) caused by silver carp and a strongly reduced benthos biomass (frequently below 1 g/m2 fresh weight) caused by common carp and eel on H2S-free bottom areas. Despite this extreme situation, which lasted for 20 years and is rarely found in lakes elsewhere, it was not possible to demonstrate negative effects on the native fish fauna comprising 16 species. Also the dominance pattern seems uninfluenced in the long run. A strong decline of the catchable roach stock was observed for some years, but the stock reappeared soon in comparable quantity. During the time of roach stock depression the individual growth of roach (and common carp) was particularly low. Nevertheless, roach succeeded in reproduction during this time in spite of the reduced zooplankton and detritus concentrations. Fry numbers per year ranged from 500-15 000 individuals/ha. The pike perch (Stizostedion lucioperca) was perhaps the most endangered species of all those living at small population numbers in the lake, since its fry is confined to the limnion where competition from silver carp and adult roach and perhaps predation by roach is highest. However the pike perch stock remained unchanged at the low level of 1950, the time prior of carp and eel stocking. All other rare species of Lake Heiliger See spawn in the littoral zone where fry survival conditions were less impacted. In summary, we present more evidence that the fish fauna of cyprinid lakes is more robust than in salmonid lakes. The regulation capacity of fish communities of eutrophic lakes seems to be able to offset even severe direct and indirect influences of fisheries management.  相似文献   

7.
Water quality, physical habitat, and fisheries at sixteen reaches in the Neversink River Basin were studied during 1991-95 to identify the effects of acidic precipitation on stream-water chemistry and on selected fish-species populations, and to test the hypothesis that the degree of stream acidification affected the spatial distribution of each fish-species population. Most sites on the East Branch Neversink were strongly to severely acidified, whereas most sites on the West Branch were minimally to moderately acidified. Mean density of fish populations ranged from 0 to 2.15 fish/m2; biomass ranged from 0 to 17.5 g/m2. Where brook trout were present, their population density ranged from 0.04 to 1.09 fish/m2, biomass ranged from 0.76 to 12.2 g/m2, and condition (K) ranged from 0.94 to 1.07. Regression analyses revealed strong relations (r2 - 0.41 to 0.99; p h 0.05) between characteristics of the two most common species (brook trout and slimy sculpin) populations and mean concentrations of inorganic monomeric aluminum (Alim), pH, Si, K+, NO3-, NH4+, DOC, Ca2+, and Na+; acid neutralizing capacity (ANC); and water temperature. Stream acidification may have adversely affected fish populations at most East Branch sites, but in other parts of the Neversink River Basin these effects were masked or mitigated by other physical habitat, geochemical, and biological factors.  相似文献   

8.
Modern ethohydraulics is the study of the behavioral responses of swimming fish to flow fields. However, the exact drag forces experienced by fish remain poorly studied; this information is required to obtain a better understanding of the behavioral responses of fish and their current resistance strategies. We measured near-ground frontal drag forces on preserved individuals of three benthic fish species, round goby (Neogobius melanstomus), gudgeon (Gobio gobio) and bullhead (Cottus gobio), in a flow channel. The forces were compared to acoustic Doppler velocity (ADV) measurements and fish tracking data based on video observations of live fish in the flow channel. Overall, we observed drag coefficients (CD) of ∼10−3 at Reynolds numbers ∼105. The frontal drag forces acting on preserved fish with non-spread fins ranged from -1.96 mN*g-1 (force per fish wet weight, velocity 0.55 m*s-1) to 11.01 mN*g-1 (velocity 0.85 m*s-1). Spreading the fins strongly increased the drag forces for bullhead and round goby. In contrast, the drag forces were similar for gudgeon with spread fins and all fish with non-spread fins. Video tracking revealed no clear relationship between the position of the fish in the flow field and the forces experienced by the preserved fish at these positions. Collectively, these results suggest that i) the differences in frontal drag forces between species are small in homogenous flow, ii) individuals chose their position in the flow field based on factors other than the drag forces experienced, and iii) whether fins are spread or non-spread is an essential quality that modulates species-specific differences. The methodology and results of this study will enable integration of flow measurements, fish behavior and force measurements and inform ethohydraulics research. More advanced force measurements will lead to a detailed understanding of the current resistance strategies of benthic fish and improve the design of fish passes.  相似文献   

9.
In order to determine the food preferences of young roach, gut contents of roach fry (Rutilus rutilus (L.)) were compared with the evolution of the zooplankton community in a littoral area of Lake Geneva during June and July 1985. The food of roach fry up the age of 30 d (10–15 mm standard length) was mainly small Rotifers with some Chronomid larvae. Thereafter, Chironomid larvae constitute the major part of the diet until the fry leave the littoral zone at the age of about 45 d (15–23 mm). The relevance of classical food preference analysis is critically discussed in view of the heterogeneous spatial distribution of invertebrates observed.   相似文献   

10.
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11.
Rivers are worldwide highly fragmented due to human impacts. This fragmentation has a negative effect on fish movement and dispersal. Many artificial barriers such as river bed sills and small weirs are nowadays replaced by block ramps in order to reestablish longitudinal connectivity for fish in rivers and streams. We studied the upstream passage of several fish species on different types of block ramps with slopes between 3.6 and 13.4 %. We conducted translocation experiments in the field based on mark-recapture and on the use of PIT-tags. Temporal movement patterns were observed by an instream antenna. Hydraulic and morphological characteristics of block ramps were measured and compared with fish passage efficiency. Our results clearly showed that upstream passage efficiency differs between fish species, size classes and block ramps. We observed that brown trout (Salmo trutta fario) performed better than bullhead (Cottus gobio) and several cyprinid species on the same block ramps. Passage efficiency of brown trout and chub (Leuciscus cephalus) was size-selective, with small-sized individuals being less successful. For brown trout, size-selectivity became more relevant with increasing slope of ramp. We conclude that block ramps with slopes of >5 % are ineffective for the small-sized cyprinid species and that vertical drops within step-pool ramps can hinder successful upstream passage of bullhead.  相似文献   

12.
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13.
We investigated lethal and sublethal predation effects of the benthivorous gudgeon (Gobio gobio) on the grazing mayfly Rhithrogena semicolorata and the shredding amphipod Gammarus pulex over 21 months in a largely detritus-based small stream. We hypothesised that shredders are generally less vulnerable to fish predation and therefore less likely to be predation-controlled than grazers, because the latter are visible to the predators during their feeding on stone surfaces, while shredders may hide between leaves during foraging.The hypothesis was tested in two 400 m experimental reaches of a natural stream, which were manipulated in order to contain and to lack fish, respectively. Biomass of G. pulex was significantly reduced in the fish section while that of R. semicolorata was not. Since approximately 91% of the annual production of G. pulex but only 12% of R. semicolorata production was consumed by gudgeon, the observed biomass difference of G. pulex is likely due to a lethal predation effect. However, no sublethal predation effects such as reduced concentration of storage components (triglycerides, glycogen) or reduced reproductive success were observed for both species. Lower mean body length of the R. semicolorata larvae in the fish section did not result in a lower number of eggs in the abdomen of the last instar larvae. Hence, in contrast to our initial hypothesis, in the studied stream the shredder was top-down-controlled, while the grazer was not. It is concluded that top-down control depends on the ecological characteristics of a specific predator-prey pair rather than on trophic guild of the prey.  相似文献   

14.
In eutrophic Lake Biel, Switzerland, the qualitative and quantitative food composition of roach (Rutilus rutilus L.) was examined monthly from August 1978 to August 1979. The fish caught in the littoral zone fed on phytoplankton, periphyton, makrophytes, zooplankton and molluscs. The food composition was different from month to month as well as between the different size classes of the fishes. The fish caught in the pelagic zone fed almost exclusively on crustaceans.  相似文献   

15.
The fish fauna in the northern part of the upper river Rhine close to the city of Karlsruhe (Germany) was analyzed by collecting fish from the cooling-water intake of a power plant (impingement method) between 1989 and 2001. With this method a total of 36 fish species were recorded. The results were compared between the years as well as with other studies on the fish fauna in this area. Particularly with regard to the physical structure of the river bed and banks, the pre-technical situation of the river Rhine has not been restored. However, the number of fish species has been augmented since the 1970s mainly due to improvements in the water quality and almost all autochthonous fish species are present again. Altogether only three introduced fish species (Sander lucioperca L., Lepomis gibbosus L., and Carassius auratus gibelio were found in this study. Among the long-distance migrating species three freshwater spawners (Lampetra fluviatilis, Petromyzon marinus and Salmo trutta trutta) were detected in addition to the catadromous eel. The eudominant fish species varied between years, i.e. the European eel, Anguilla anguilla, was the eudominant species 1989, whereas this species occurred in much lower numbers during the subsequent sampling campaigns. This clearly indicates that the high dominance of eels is mainly caused by stocking activities in the upper Rhine. In the following years roach, Rutilus rutilus was the eudominant fish species. Overall a positive development of the fish fauna in the upper Rhine over the last 15 years could be observed in terms of fish populations as well as in terms of species richness.  相似文献   

16.
We used carbon and nitrogen stable isotope analyses to assess the relative contributions from pelagic and littoral energy sources to higher trophic levels in a lake ecosystem before and after a major food web perturbation. The food web structure of the lake was altered when the population sizes of the most abundant fish species (small perch, roach and bream) were reduced during an attempt to improve water quality by biomanipulation. Fish removal was followed by dense year classes of young fish, which subsequently increased the utilisation of pelagic resources. This was reflected as a decrease in relative energy contribution from littoral sources and also led to more distinct pelagic and littoral food chains after fish removal. Community metrics calculated from stable isotope data indicated increased trophic diversity and occupied niche area, and reduced trophic redundancy in the food web. However, only minor changes were observed in fish trophic positions, although roach and pike occupied slightly lower trophic positions after fish removal. Despite the Jyväsjärvi ecosystem becoming more dependent on pelagic energy after fish removals, the littoral energy contribution was still substantial, particularly to certain fish species. Hence, our results support recent arguments for the importance of benthic production in lake ecosystems. More generally, our results illustrate how large-scale perturbations of food web structure can alter energy flow patterns through an entire ecosystem.  相似文献   

17.
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18.
Unionoid mussels are obligate parasites on one or more fish species. The objective was to compare growth and survival of encysted mussel larvae of the freshwater pearl mussel (Margaritifera margaritifera) on young-of-the-year (YOY) versus one-year old brown trout (Salmo trutta). YOY and one-year old trout from the Brattefors and Lärje Rivers, Sweden, were infested with mussel larvae from their home river. The mass-normalized encystment abundance was higher on YOY trout than on one-year old trout. The proportional decrease in mass-normalized encystment abundance was larger on YOY brown trout from the Brattefors River than on YOY brown trout from the Lärje River. Encystment per individual fish was higher on YOY trout than on one-year old trout from the Brattefors River, whereas this relationship was reversed for trout from the Lärje River. Larval growth was higher on YOY trout than on one-year old trout. There was a larger difference in larval growth between YOY trout and one-year old trout from the Brattefors River than on the brown trout from the Lärje River. The ability to use both YOY and older fish, such as in the Lärje River, may increase the reproduction potential of mussel populations, compared to a reduced ability to use more than one year class, such as in the Brattefors River. This may also affect the dispersal of mussels, as older brown trout often move and migrate to a higher degree within and between rivers. The dispersal potential of mussels may therefore be relatively high in the Lärje River, but low in the Brattefors River. In rivers where the mussels have to rely on YOY brown trout, it could be worth facilitating passage through migration obstacles for YOY brown trout. Infested YOY brown trout could be artificially re-distributed within rivers, to places with former mussel distributions. It could also be worth testing the suitability of brown trout of different age classes when starting breeding programs.  相似文献   

19.
The abundance of different size classes of perch and roach in the littoral zone of Lake Geneva was compared between submerged aquatic vegetation and unvegetated zones. Samples were taken with gillnets during four periods between June and October 1993. During the vegetation period (June to September), perch 9 cm and roach 10 cm were more abundant in vegetation whereas roach > 20 cm were more abundant in open water. Perch larger than 18 cm and medium roach were equally distributed in both habitats whatever the period, whereas medium perch distribution fluctuated according to the period. In October, after the decline of the vegetation, no more differences in fish distribution were observed except for small roach, which were always more abundant in the vegetated sites.  相似文献   

20.
As with many rivers of the Pyrenees Mountains, reservoirs on the River Ariège (SW Francc) are used for hydroelectricity generation, irrigation and to maintain summer flows in the River Garonne. Two river reservoirs on the River Ariège were simultaneously emptied in April 1991 to remove accumulated sediment. Fish and ten environmental variables were sampled using Point Abundance Sampling by electrofishing before (February 1991) and one year later (February 1992) at three study sites downstream of the dams. We examined the short-term impact of reservoir cleaning on the relative abundance, habitat availability and habitat use of three species of small fish: minnow Phoxinus phoxinus (L.), gudgeon Gobio gobio (L.) and stone loach Barbatula barbatula (L.).¶After the reservoir cleaning, areas covered by gravel, sand and mud increased significantly as the result of the sediment release. The three species did not react in the same manner to these environmental changes. Stone loach appeared to be the most sensitive species, with its relative abundance decreasing at all sites. Conversely, minnow seemed to be the most resistant species and as such is a leading pioneer species for colonizing new or impacted stretches of rivers channels. Finally, the number of gudgeon decreased particularly at the most downstream site where large deposits of mud were recorded.  相似文献   

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