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W. D. RILEY M. G. PAWSON V. QUAYLE & M. J. IVES 《Fisheries Management and Ecology》2009,16(2):100-111
Abstract The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels. 相似文献
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Abstract – Juvenile salmon density was related to invertebrate density in 13 streams within the River Tana, northern Norway. There were only small, nonsignificant, differences in benthic density between streams with and without juvenile salmon. All streams with a high density of juvenile salmon had low benthic densities at the stream mouth. Juvenile salmon were not found, or were in very low densities, in streams where the benthic density at the stream mouth was as high or higher than that in the stream. A multiple regression model showed that parr density was related negatively to benthic density at the stream mouth, water velocity and pH, and positively to benthic density within the stream and the proportion of the substratum covered by moss. The amount of overhanging cover in the different streams explained 93% of the variation in the drift density of terrestrial invertebrates in August. The highest densities of juvenile salmon were found in streams with riparian vegetation, and were thus associated with an abundant supply of drift food, especially terrestrial invertebrates. 相似文献
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1. Ten south Swedish streams were selected to represent two distinct types—natural woodland streams and channelized streams. Measurements were made on leaching, decomposition and microbial respiration of the dominant riparian vegetation (European Black Alder), structure of the benthic macroinvertebrate community, macroinvertebrates inhabiting leaf material, channel morphometry, macrophyte composition, water chemistry and total accumulated degree days. 2. Leaf decomposition rates were not significantly different when channelized streams were compared with natural woodland streams. In channelized streams the average decomposition rate was −0.0556±0.0337 (±S.D.) day−1 compared with −0.0457±0.0115 day−1 in natural woodland streams. 3. There was significantly higher variation in leaf decomposition among the five channelized streams compared with the five natural streams (F–test, p<0.05). This was mainly due to extremely high decomposition rates in channelized streams colonized by emergent macrophytes. 4. Alder decomposition rates were low in channelized streams without macrophytes (−0.0053 °day−1), intermediate in natural streams (−0.0087 °day−1), and high in channelized streams with macrophytes (−0.0136 °day−1). 5. The shredder functional group ranged from 13 to 70% of the benthic community in the natural streams. Channelized streams had a more variable shredder population ranging from 0.5 to 80%. The highest values were found in channelized streams that had become colonized by macrophytes. 6. There was a significant difference in total accumulated degree days between the channelized (256 °day) and natural woodland streams (209 °day). This is most likely an effect of drainage tiles contributing warmer groundwater to the channelized streams during fall. 7. It is concluded that, contrary to the prevailing conceptual model of stream systems, decomposition rates and macroinvertebrate functions are not necessarily reduced in streams without riparian vegetation. The loss of the riparian canopy can stimulate emergent macrophytes which will provide autochthonous detritus for benthic communities. This will change benthic community structure and the life cycle strategies present. © 1998 John Wiley & Sons, Ltd. 相似文献
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1. Patterns in the community structure and feeding guild composition among macroinvertebrates in the margins and riffles of 66 streams in upland Wales and Scotland were appraised and related to site chemistry, physiography and riparian management. We aimed to assess the effectiveness of riparian strips of broadleaves and moorland/grassland in protecting stream communities and their trophic function during commercial forestry. 2. The composition of macroinvertebrate communities in margins and riffles most strongly reflected stream pH and aluminium concentrations; acidic riffles contained fewest species of all major macroinvertebrate groups. However, the character of marginal habitats had some influence on communities in stream margins through the presence of broadleaf trees or moorland/grassland vegetation in the riparian zone. Even at low pH, streams with moorland riparian zones had different macroinvertebrates from those with pure conifer. 3. Stream chemistry was important in explaining patterns among feeding guilds. Species richness and abundances of grazers and filterers were reduced at acidic sites with high aluminium concentrations. The number of shredder species was significantly lower in riffles at low pH than at high pH. 4. In contrast, marginal habitat structure was of overriding importance in explaining patterns among collectors and predators. These functional groups were most abundant at sites with riparian zones of moorland and grassland, but scarce in streams where the bankside vegetation consisted of coniferous or broadleaved trees. Total grazer abundances were lowest at sites with riparian zones of pure conifer. 5. We conclude that riparian management can modify effects of forestry on the trophic dynamics and structure of the macroinvertebrate communities of upland streams, but the effect operates within a strong gradient due to acidity. Thus, the array of macroinvertebrates which may benefit from riparian management in forest streams is liable to be restricted by low pH. 6. We discuss the wider ramifications of riparian management for the conservation of streams during commercial forestry. In particular we assess if management proposals set out by the forestry industry are supported. We also discuss the problem of scale when considering measures implemented for stream conservation, emphasizing that the control of problems such as acidification may only be possible at a regional level. 相似文献
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Abstract Dense riparian tree canopy is generally found to have a negative effect on salmonid populations. Canopy can affect fish both directly via trophic impacts and its effects as cover, and indirectly via its effects on the distribution of instream vegetation. This study examined the impact of riparian canopy on the ecology of juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in south‐west Ireland. Riparian canopy reduced the density, length and gut contents of juvenile salmon, but not brown trout. The negative relationship between canopy cover and fish size and feeding was strongly influenced by the abundance of instream macrophytes, which in turn varied as a function of catchment water chemistry. As a management strategy, the reduction of dense riparian canopy is unlikely to have the same effect on juvenile salmonids on all streams within an ecoregion because of differences in catchment‐wide factors. 相似文献
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Feeding strategy of the non‐native rainbow trout,Oncorhynchus mykiss,in low‐order Patagonian streams
The dietary composition and feeding strategy of rainbow trout, Oncorhynchus mykiss (Walbaum), in two low‐order Patagonian streams were studied. Benthic macroinvertebrate availability was estimated in both riffles and pools. Fish stomach contents were examined to determine prey richness and diversity, prey electivity, food‐niche width, and the feeding strategy employed by trout throughout the year. Availability of benthos varied seasonally with Ephemeroptera, Trichoptera, Plecoptera and Diptera species dominating. Rainbow trout diet was composed mainly of benthic macroinvertebrates, followed by terrestrial insects, fish, algae and plants. Different trout size classes segregated the use of food resources to reduce predation pressure. Elected prey included organisms displaying no to high mobility. A high feeding plasticity allows trout to buffer changes in food availability by switching from a specialised to a generalised feeding behaviour. Consequently, trout may exploit abundant but temporary food resources opportunistically, which would explain their marked expansion in Patagonian environments. 相似文献
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In‐stream wood can increase shelter availability and prey abundance for stream‐living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in‐stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small‐sized trout. In a laboratory stream experiment, we tested the behavioural response of young‐of‐the‐year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four‐fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others. 相似文献
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Abstract – The objective was to compare juvenile salmon density in 20 streams throughout the very large River Tana, northern Norway, and to relate variation in density to a suite of environmental factors. Four sampling sites were electrofished in each stream (one at the mouth of the stream and three within the stream) in August and October 2000, 2001, 2002. 0+ salmon parr were absent from seven streams, present at the mouth of 11 streams, and present within only two streams, both of which were probably spawning streams. Older parr migrated upstream into most streams and their highest densities were usually found in streams flowing directly into the spawning habitat in the three largest tributaries of the Tana or the river itself. Juvenile salmon were sparse or absent in streams flowing into smaller tributaries. Most streams with high parr densities were those of dense riparian vegetation that provided terrestrial invertebrates as drift food for the salmon parr, cover for fish, cooler stream temperatures in summer, and food for benthic stream invertebrates that were also a source of food for the parr. 相似文献
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Abstract. Following the rapid recession of a neoglacial ice sheet within the last 250 years, colonization of recently deglaciated streams by salmonid fishes was investigated in Glacier Bay National Park, south-eastern Alaska. The primary factors governing the establishment, species diversity composition and abundance of salmonids in Glacier Bay streams were water temperature, sediment loading and stream discharge. No salmonids were found in the turbid meltwater streams emerging from retreating ice. Coho, Oncorhynchus kisutch (Walbaum), and sockeye, Oncorhynchus nerka (Walbaum). salmon and Dolly Vardcn, Salvelinus malma (Walbaum), charr were the first salmonids to colonize the youngest clearwater stream. Juvenile Dolly Varden were more abundant than juvenile coho salmon in the most recently formed clearwater stream because of the characteristic absence of pool habital. Densities of juvenile coho salmon were six times greater in a stream with a series of lakes compared with a stream of similar age without lakes. Future advancement of salmonid stocks will probably depend upon the rate and extent of the development of riparian vegetation and inputs of large woody debris from the developing forest to provide further instream cover, habitat variation and channel stabilization. 相似文献
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Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams 
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下载免费PDF全文 Invasive species in riparian forests are unique as their effects can transcend ecosystem boundaries via stream‐riparian linkages. The green alder sawfly (Monsoma pulveratum) is an invasive wasp whose larvae are defoliating riparian thin‐leaf alder (Alnus tenuifolia) stands across southcentral Alaska. To test the hypothesis that riparian defoliation by this invasive sawfly negatively affects the flow of terrestrial prey resources to stream fishes, we sampled terrestrial invertebrates on riparian alder foliage, their subsidies to streams and their consumption by juvenile coho salmon (Oncorhynchus kisutch). Invasive sawflies altered the composition of terrestrial invertebrates on riparian alder foliage and as terrestrial prey subsidies to streams. Community analyses supported these findings revealing that invasive sawflies shifted the community structure of terrestrial invertebrates between seasons and levels of energy flow (riparian foliage, streams and fish). Invasive sawfly biomass peaked mid‐summer, altering the timing and magnitude of terrestrial prey subsidies to streams. Contrary to our hypothesis, invasive sawflies had no effect on the biomass of native taxa on riparian alder foliage, as terrestrial prey subsidies, or in juvenile coho salmon diets. Juvenile coho salmon consumed invasive sawflies when most abundant, but relied more on other prey types selecting against sawflies relative to their availability. Although we did not find effects of invasive sawflies extending to juvenile coho salmon in this study, these results could change as the distribution of invasive sawflies expands or as defoliation intensifies. Nevertheless, riparian defoliation by these invasive sawflies is likely having other ecological effects that merits further investigation. 相似文献
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The independent effects of in‐stream structure (ISS) and fish foraging on stream properties have been well documented, but few studies have explored the interactive effects of ISS and fishes on streams. Herein, we tested the independent and interactive effects of ISS and a generalist fish (Blacktail shiner, Cyprinella venusta) on suspended organic matter (SOM), benthic algae, invertebrate density and fish growth using experimental mesocosms. We found that Blacktail shiner foraging affected all of the ecosystem properties; however, in some cases, the fish effects differed between mesocosms with and without ISS. Specifically, mesocosms with ISS provided greater surface area for invertebrate colonisation and enhanced food resources for Blacktail shiner. As a result, benthic foraging by Blacktail shiner was reduced in these mesocosms. The reduced benthic foraging in turn enhanced benthic algae and benthic invertebrates via a bottom‐up, nutrient excretion pathway. The ISS‐dependent effects of fish on these stream properties, however, were only evident at low and intermediate fish densities (1 and 2 fish·m?2 respectively). This was likely because at the highest fish density (4 fish·m?2) intense fish foraging overrode any mediating effects of ISS. Furthermore, fish growth decreased with fish density because of intraspecific competition, but this negative effect on growth was reduced in mesocosms with ISS because of the increased forage base. However, the positive effect on fish growth was weak and only marginally significant. Our data suggest that fish‐mediated effects on streams are context dependent, changing with microhabitat availability (e.g. ISS) and density of the fish population. 相似文献
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Abstract – Decreases in body growth with increasing population density may be caused by reduced prey delivery rate. However, changes in food quality because of an increasing inclusion of suboptimal prey in the diet may also contribute to such effects. Here, we test for density‐dependent diet composition by creating spatial variation in Atlantic salmon young‐of‐the‐year (YOY) density in three replicate streams and obtain detailed information on individual positions (±1 m) and diet. Diet breadth with respect to prey size increased with increasing local density for the two most common prey types (Chironomidae and Ephemeroptera). For the largest prey type (Ephemeroptera), there was also an increase in mean prey size with increasing density, suggesting that YOY salmon preferentially utilise the smaller prey among those available. According to optimal foraging theory, changes in diet with increasing local density are likely to come at an energetic cost and hence may contribute to the commonly observed density‐dependent growth of juvenile salmonids. 相似文献
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Kari-Matti Vuori Ilona Joensuu Jyrki Latvala Eero Jutila Anssi Ahvonen 《水产资源保护:海洋与淡水生态系统》1998,8(6):745-759
1. Forest drainage, including mainly ditching of waterlogged peatlands in order to increase wood growth, has caused substantial changes in the hydrology and water quality of Finnish streams. However, knowledge on the ecological impact of these changes is poor. This paper studies the potential impact of forest drainage, catchment characteristics and habitat factors on the water quality and benthic macroinvertebrates in headwater streams of the River Isojoki, western Finland. An intensive programme of water sampling was carried out at nine study sites, while zoobenthic samples covered a total of 18 streams. 2. According to multivariate regression models concentrations of aluminium and suspended solids in stream water at nine study sites increased significantly with increasing forest drainage of the catchment area. Further, drainage intensity contributed significantly to the decrease in minimum values of alkalinity. 3. In a Canonical Correspondence Analysis, the variation in macroinvertebrate species distribution and abundance was largely explained by drainage intensity, moss coverage and the concentrations of aluminium and iron in stream water. A significant positive correlation was established between the species richness of benthic macroinvertebrates and the proportional cover of vegetation on the stream bed, whereas a significant negative correlation was found between species richness and sand cover. 4. The results suggest that drainage has significantly contributed to the deterioration of water quality and habitat structure, and impoverishment of benthic communities in the headwater streams of the River Isojoki. In order to protect the ecological integrity of such boreal headwater streams, more effective protection schemes in forestry practices and rehabilitation of the adversely affected streams and their catchment areas are needed. © 1998 John Wiley & Sons, Ltd. 相似文献
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Trophic pathways supporting Arctic grayling in a small stream on the Arctic Coastal Plain,Alaska 下载免费PDF全文
下载免费PDF全文 Beaded streams are prominent across the Arctic Coastal Plain (ACP) of Alaska, yet prey flow and food web dynamics supporting fish inhabiting these streams are poorly understood. Arctic grayling (Thymallus arcticus) are a widely distributed upper‐level consumer on the ACP and migrate into beaded streams to forage during the short 3‐month open‐water season. We investigated energy pathways and key prey resources that support grayling in a representative beaded stream, Crea Creek. We measured terrestrial invertebrates entering the stream from predominant riparian vegetation types, prey types supporting a range of fish size classes, and how riparian plants and fish size influenced foraging habits. We found that riparian plants influenced the quantity of terrestrial invertebrates entering Crea Creek; however, these differences were not reflected in fish diets. Prey type and size ingested varied with grayling size and season. Small grayling (<15 cm fork length (FL)) consumed mostly aquatic invertebrates early in the summer, and terrestrial invertebrates later in summer, while larger fish (>15 cm FL) foraged most heavily on ninespine stickleback (Pungitius pungitius) throughout the summer, indicating that grayling can be insectivorous and piscivorous, depending on size. These findings underscore the potential importance of small streams in Arctic ecosystems as key summer foraging habitats for fish. Understanding trophic pathways supporting stream fishes in these systems will help interpret whether and how petroleum development and climate change may affect energy flow and stream productivity, terrestrial–aquatic linkages and fishes in Arctic ecosystems. 相似文献
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Abstract – We examined prey utilisation patterns of brown trout ( Salmo trutta Linnaeus) as related to available benthos in a cold tailwater (Little Red River, Arkansas) having low biodiversity of benthic macroinvertebrates and low availability of fish as prey. Benthic macroinvertebrates were sampled monthly in upstream and downstream sites over a 1-year period. Stomach content analysis was also performed on 30 brown trout (10 each of three size classes) collected monthly from each site. Benthic and diet diversities were low at both sites, as isopods ( Lirceus ) accounted for 67% and 51% of the numerical abundance upstream and downstream, respectively, and 80% and 70% of all prey consumed by upstream and downstream brown trout. Physid snails (upstream) and chironomid larvae (downstream) accounted for most of the remaining prey taxa consumed. Piscivory and consumption of terrestrial invertebrates were rare. There was no clear relation between diet diversity and trout size. Densities of benthic macroinvertebrates and prey consumption were significantly greater upstream than downstream. Benthic macroinvertebrate assemblages and prey consumption were seasonally constant at both sites. Generally, prey consumption was consistent with availability of each prey in the benthos; the lack of benthic diversity and overwhelming abundance of one taxon ( Lirceus) most likely contributed to food selection patterns. Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna because of the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major limitation to brown trout growth. 相似文献
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- 1. Freshwater crayfish that burrow into river banks are likely to be affected by riparian land uses that affect soil conditions and vegetation cover. The aim of this research was to determine whether burrow densities of two crayfish species (Engaeus sericatus Clark and Geocharax gracilis Clark) were associated with riparian land use and vegetation type in three streams in south‐west Victoria, Australia.
- 2. Four riparian land‐use categories were studied on each stream: native forest blocks; thin strips of mature native vegetation, fenced, with pasture adjacent; riparian pasture areas, fenced, with no cattle access to the stream; pasture and cattle access to the water's edge. Crayfish burrows were counted and a range of water quality and riparian condition variables were measured.
- 3. Native forest areas were found to have more than twice the densities of freshwater crayfish burrows than other land uses, which did not differ. Native forest areas also had higher mean burrow mound heights but lower burrow activity levels. Riparian characteristics also differed between land uses. In particular, soil compaction was the lowest in native forest areas, which also had better riparian condition scores and water quality than pasture areas.
- 4. This study suggests that cattle grazing may have reduced populations of burrowing crayfish in these streams, and that subsequent fencing and the presence of remnant native vegetation may be insufficient to ameliorate these effects. Blocks of native forest that remain on these streams may act as an important refuge for these species in agricultural areas.
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Terrestrial invertebrates falling from the riparian canopy are a major energy source for fishes in headwater streams. Because quantity and quality of such allochthonous resources can vary depending on riparian conditions, conversion of riparian forests to conifer plantations may affect stream productivity. We compared falling and drifting invertebrate abundances and the diet of masu salmon (Oncorhynchus masou) among stream reaches bordered by deciduous broadleaved forests, conifer plantations (Cryptomeria japonica), and clear‐cut sites in southwestern Japan. We also examined whether among‐reach variation in salmon abundance was related to the riparian vegetation types. The results indicated that, on an annual basis, falling inputs of terrestrial invertebrates at the broadleaved reaches were 2–4 times higher than those at the plantation and clear‐cut reaches. In nonwinter seasons, terrestrial invertebrates made up 40–60% and 30–90% of drift and masu salmon diets, respectively, and drifting invertebrate abundance was higher in the broadleaved reaches than in the plantation reaches. Furthermore, a multivariate analysis of salmon abundance showed that variation in salmon biomass was explained primarily by riparian vegetation type, with broadleaved and clear‐cut reaches having higher biomass than the plantation reaches. These results indicate that terrestrial invertebrates are an important resource for masu salmon, and suggest that streams bordered by conifer plantations receive lower terrestrial prey inputs, which results in lower salmon abundance. In regions where natural forests have been extensively converted to conifer plantations, forest management that allows and facilitates recovery of natural riparian stands is important. 相似文献