ISSN:0886-9375    

DOI:10.1002/rrr.3450080102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450080103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450080104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of intermittent power generation on the fish fauna and benthic invertebrates of several Austrian rivers have been investigated quantitatively. In contrast to the more or less local adverse effects of impoundments or stream channelization, artificial flow fluctuations generally disturb a long section of a given river. Within all the river sections investigated, a breakdown of the benthic invertebrate biomass of between 75 and 95% was observed within the first few kilometres of river length. A reduction of between 40 and 60% of biomass compared with undisturbed areas could be detected within the following 20–40 km. The reduction of the fish fauna is within the same order of magnitude and correlates well with the amplitude of the flow fluctuations. Several reasons for the breakdown are summarized and proposals for the minimization of these detrimental effects of artificial short‐term fluctuations are gi

ISSN:0886-9375    

DOI:10.1002/rrr.3450080105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA conceptual model has been developed to test river regulation concepts by linking physical habitat and water temperature with salmonid population and production in cold water streams. Work is in progress to examine numerous questions as part of flow evaluation and habitat restoration programmes in the Trinity River of California and elsewhere. For instance, how much change in pre‐smolt chinook salmon (Oncorhynchus tshawytscha) production in the Trinity River would result from a different annual instream allocation (i.e. up or down from 271 × 106m3released in the late 1980s) and how much change in pre‐smolt production would result from a different release pattern (i.e. different from the 8.5 m3s−1year‐round release). The conceptual model is being used to: design, integrate and improve young‐of‐year population data collection efforts; test hypotheses that physical habitat significantly influences movement, growth and mortality of salmonid fishes; and analyse the relative severity of limiting factors during each life stage. The conceptual model, in conjunction with previously developed tools in the Instream Flow Incremental Methodology, should provide the means to more effectively manage a fishery resource below a regulated reservoir and to provide positive feedback to planning of annual reservoi

ISSN:0886-9375    

DOI:10.1002/rrr.3450080106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTemporal alterations in the structure of hydropsychid guilds were studied along a regulated stream (Río Duratón, northern Spain) to examine the role of interspecific competitive interactions and environmental perturbations in determining species persistence. Discharge fluctuations of hypolimnial waters with a significant oxygen deficit were produced daily by Burgomillodo Dam. Under unregulated conditions (upstream sampling site), it is assumed that the coexistence of competing hydropsychid species is a function of species dominance (d') and resource limitation (R), as major causes of interaction strength among competitors, and the niche overlap (O) as a major cause of connectance among competitors,d' tends to increase with the number of subordinate species. Thus, and according to May's model of stability, a hydropsychid guild will tend to be unstable (by competitive displacement) ifd'R(SO)0.5>1, whereSis the number of competing species in the guild. The productd'R(SO)0.5is used as a competition coefficient (β′). To facilitate the calculation of β′, the values ofRand0are assumed to be 1 and 0.5, respectively. Riffle macrobenthic surveys were undertaken in June and December 1987, and in June 1988. Upstream from the dam, values of β′ were 0.599, 1080 and 0.656, and values ofSwere 7, 7 and 6. Downstream from the dam, β′ was less than unity during all sampling surveys, butSdecreased at all downstream sampling sites (mainly just below the dam). Total density and total biomass were significantly higher downstream than upstream (except just below the dam).Hydropsyche pellucidulawas dominant upstream, whereasH. siltalaibecame dominant downstream. Temporal variations in individual weights ofH. bulbiferaandH. exocellatadownstream were different from those upstream. This fact is interpreted as a phenomenon of character displacement. It is concluded that interspecific competitive interactions upstream and environmental perturbations downstream determined species persistence in hydrop

ISSN:0886-9375    

DOI:10.1002/rrr.3450080107

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractResource utilization and growth of brown trout were studied in four deep (mean depths 16.2–37.5 m) Norwegian hydroelectric reservoirs by benthic and pelagic gillnet sampling. In all the reservoirs supplementary stockings are carried out. The brown trout were spatially segregated according to size as the habitat use of small individuals (<180–220 mm) was completely restricted to benthic habitats, whereas larger individuals mainly utilized the upper strata of pelagic waters. It is argued that the pelagic habitat is the more rewarding, and that small‐sized brown trout are forced into the less favourable benthic habitat through social interactions with larger specimens. This is supported by an increase in growth of brown trout from their third to fifth year of life, which seems to be related to the shift from benthic to pelagic behaviour. It is also argued that the conditions for small‐sized brown trout may be a bottleneck in the capacity to produce brown trout in hydroelectric reservoirs with limited benthic feeding conditions, despite ample access to food in pelagic habitats.When evaluating the possibility of increasing the yield of brown trout through supplementary stockings, it is therefore important to consider food and growth conditions for all age and size groups of brown trout. In reservoirs with poor benthic feeding conditions it may be necessary to stock with brown trout of sizes that are large enough to utilize pelagic habitat, to avoid the limiting benthic livin

ISSN:0886-9375    

DOI:10.1002/rrr.3450080108

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe benthic invertebrate fauna of the lowland part of the Aurland River was investigated in 1966–7 over a full year cycle. The watershed was built out for hydropower production during 1979–83. In this study the life cycle and production ofBaetis rhodanifrom pre‐regulated conditions (1966–7) was compared with two types of post‐regulation streams (1988–9). Before regulation the water flow was high during May‐June and in autumn, combined with heavy rainfall. The lowest flow was in winter and early spring. The pre‐regulated temperature was low in winter, increasing from April to a maximum in August (10–14°). After regulation one part of the river received reduced flow and increased summer temperatures (upper part) and one received hypolimnion release and reduced summer temperatures (lower part). In the upper part the density ofB. rhodaniincreased between 10 and 20 times. The reason for this seems to be increased temperature, reduced accidental drift of larvae and increased amount of stored organic material on the bottom. In the lower part the density increase was two to five times and the production two times higher after regulation. The lower increase in production than density was due to a much higher proportion of small larvae.B. rhodanihad mainly an univoltine life cycle before regulation, but a small part of the population was bivoltine. After regulation the species was univoltine in the lower part. In the upper part the life cycle was about one month faster, but no clear indication of bivoltinism was seen. The absence of the second generation is due to low temperatures and probably a lack of signals connecte

ISSN:0886-9375    

DOI:10.1002/rrr.3450080109

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring the past century freshwater mussel populations have declined precipitously throughout North America. Much of this loss has resulted from the construction of dams. In the Cumberland River system, 23% (22 species) of the historic mussel fauna is extinct or listed as endangered. Several additional species have either been extirpated from the Cumberland River or exist only in small, non‐reproducing populations. Mussels of headwater streams have been severely affected by coal mining and poor land use practices. An intensive survey was conducted in the Caney Fork River, a major tributary to the Cumberland River, to determine the historic and extant mussel fauna. The results indicate that at least 37 species of mussels have been extirpated from the Caney Fork River, mainly as a result of the construction and operation of the Center Hill Dam. Among the species extirpated, two are now extinct, five are endangered and five are candidates for listing as threatened or endangered. Effects associated with this dam include the inundation of 102 km of riverine habitat, the discharge of hypolimnetic water (which limits mussel reproduction) and an alternating pattern of stream bed scouring and dewatering. The recognition of mussel life history requirements during preconstruction could have reduced many of these effect

ISSN:0886-9375    

DOI:10.1002/rrr.3450080110

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe abundance/biomass comparison (ABC) method, proposed by Warwick (1986) for detecting pollution effects on marine macrobenthic communities, was tested on distribution patterns of numbers and biomass among fish species in regulated and non‐regulated lowland rivers in Belgium. The biomass and abundance of the fish populations were determined by electrofishing. The sample sites represent a range of physically disturbed watercourses, from natural meandering to heavily channelized reaches. Sites upstream and downstream from a polluting discharge were also evaluated. The physical habitat and water quality were measured on each site. Our data show a significant correlation between the qualitatively measured physical habitat and an ABC index, calculated from the ABC graph data. A significant correlation was also found between the pollution level and the ABC index. It is concluded that the ABC method is applicable to the assessment of disturbance in fish communities in rivers, and that the method gives information about both pollution and physical disturbance. The ABC method is a useful instrument to assess the status of a fish community before and after river channel works or natural and human induced river restoration

ISSN:0886-9375    

DOI:10.1002/rrr.3450080111

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY