摘要:

AbstractThe decline of heavily exploited stocks of large, high quality, food fishes in central Amazonia has led to increasing fishing pressure on smaller taxa, especially the jaraqui (Semiprochilodusspp.). The Prochilodontids, now the most important species to the fisheries, are seined by commercial fishermen during three distinct peridos. At the beginning of the annual floods, schools of mature jaraquis in poor‐water tributaries migrate downstream to spawn in the nutrient rich white‐water rivers. During these rapid spawning runs, fishing effort is concentrated in the lowermost reaches of the tributaries. After spawning, they return in small groups to feed intensively in the flooded forest of the same tributaries from which they had migrated. This period, of approximately three months, may be considered as a natural closed season to the fisheries. The dispersal migration is most complex and requires distinct fishing strategies. In the middle of the floods large schools of fat jaraqui descend from the tributaries to the white‐water rivers again. From there, they move upstream to different poor‐water tributaries. As downstream movements are more diffcult to observe, fishermen remain at fixed fishing grounds. This contrasts with the dynamic strategies of the subsequent upstream fishing period which contributes 60 per cent of the annual catches.Fluctuations in catch are shown to reflect year to year variations in abundance, which are linked to the hydrological cycle. Considering that fishing over the stocks of jaraqui has already more than compensated for the deficit in catch of larger species, a combination of increased effort and environmental problems could lead, in a short period to a depletion of one of the most profitable fisheries of central Amazonia. Regulation of the fisheries could benefit from a more reasonable distribution of effort among other migratory illiophagous species which remain unexploited, if the goal of sustainable yield and conservation of these stocks is to be achieved. Reserved waters in large strategic units of at least 300 km along white‐water rivers (which is equivalent to the maximum upstream displacement of jaraqui during their dispersal migrations) could also be useful to compensate for the loss of floodplain areas due to deforestaion, river regulation, use of pesticides, and mining. River impoundments in tributaries in central Amazonia may have little effect on jaraqui stocks, as spwning movements are unlikely to be directly interrupted by dams. However, alterations of the hydrological regime may also benefit from simulation of the flood cycle to mitigate potential negativ

ISSN:0886-9375    

DOI:10.1002/rrr.3450050302

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractBenthic macroinvertebrates were quantitatively sampled from thirty sites along two river systems in southwestern Australia, and patterns in community structure related to physical and chemical parameters. Classification and ordination showed a major separation between upland and lowland sites, irrespective of river system. The change in benthic community structure reflected the rapid transition in geomorphology, stream hydraulics, and water chemistry as upland forested streams exit the Darling Escarpment to give rise to open rivers, disturbed by agriculture and urban development.One upland site was clearly influenced by a storage reservoir immediately upstream and consistently grouped with lowland sites; evidence of recovery was apparent at sites downstream. The remaining upland sites were separated on the basis of catchment; this was most likely related to stream flow permanence than any inherent catchment difference. A seasonal pattern was also detected for upland sites. Samples taken in summer or autumn were distinct from those taken in winter or spring.In constrast, lowland sites could not be separated into distinct groups on the basis of season or drainage basin. The presence of cosmopolitan and tolerant species with a high likelihood of dispersal, together with the homogeneous nature of the sites, may account for the high degree of similarity among benthic communities of sites along the lowland rivers.Much of the spatial and temporal variation in benthic community structure was explained by physical characteristics of the sites. Prediction of community type using chemical data alone was poor, however, this success could be improved by combining physical and chemical data, particularly for upland sites. The poor predictive success using chemical data was likely the result of the abrupt changes in the physical nature of the streams, and the absence of large spatial differences in water quality.The successful predictive relatioship betweenm benthic community structure and physical data will enable water management authorities to detect subsequent changes in water quality in these two river systems. The predictive power of the model could be assessed in adjacent river systems for which the patterns in benthic community structure are as yet unknown.

ISSN:0886-9375    

DOI:10.1002/rrr.3450050303

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe estimation of the area of a stream reach suitable as habitat for an aquatic species by the Instream Flow Incremental Methodology is described. An important component of the methodology is PHABSIM, which is a collection of computer programs whereby useable stream area is computed as a function of discharge. This comprises a variety of options for both hydraulic and habitat simulation. A single data set is used to calculate the useable area at one discharge for three life stages of brown trout, using various options in habitat simulation. The results are shown to vary greatly according to the particular combination of options selected, so unless calculations are founded on biologically realistic assumptions the potential within PHABSIM for the „fudging”︁ of results is conside

ISSN:0886-9375    

DOI:10.1002/rrr.3450050304

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn 1984, a broad size range of sediment (boulder to sand) was introduced into a high elevation Rocky Mountain stream in southeastern Wyoming, U.S.A. In the spring of 1986, this stream was exposed to a high discharge of 7.5 m3s−1. From 1985 to 1987 a study was conducted to assess the impact of sediment deposition and flow regime on the aquatic insect community in context of the substrate occurrences of the insect fauna. Using a modified Surber sampler, samples were collected from June through September each year at nine stations which were rated as unimpacted, slightly‐impacted, and impacted. The addition of the sediment had minimal effect on the abundance and diversity of aquatic insects. However, high water discharge severely reduced the abundance of aquatic insects and diversity was also negatively impacted. Recovery from these impacts was very rapid. The greatest insect abundance was found in samples taken in gravel and most taxa occurred predominantly on gravel or rubble substra

ISSN:0886-9375    

DOI:10.1002/rrr.3450050305

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe recruitment of 0+ fishes in the River Great Ouse, East Anglia (U.K.), was investigated using electrofishing by Point Abundance Sampling, in order to compare the distribution and extent of fish reproduction in the river and its annexes (side channels, backwaters, etc.) with similar but unregulated lowland rivers of Europe. In all, 44 sites were sampled during three weeks in August 1989. Correspondence Analysis of the Sites‐by‐Species matrix (44 × 17) in density (fishes per m2) revealed a slight but notable longitudinal zonation of fish reproduction, unusual for lowland rivers, with the limnophilsBlicca bjoerkna(L.),Scardinus erythrophthalmus(L.) andAbramis brama(L.) limited to lentic downstream sites and the rheophilBarbus barbus(L.) restricted to a few upstream sites. Thus, compared with unregulated rivers of Europe, the River Great Ouse differs by: (1) the absence of pelagic spawners, e.g.Lota lota(L.), which were historically reported as abundant; (2) the reduced range and abundance of both rheophilic and limnophilic cyprinids, e.g.B. barbus(L.),Alburnus alburnus(L.) andBlicca bjoerkna(L.),Scardinus erythrophthalmus(L.),Abramis brama(L.),Tinca tinca(L.); and (3) the predominance of generalists throughout the system,Rutilus rutilus(L.) downstream andPhoxinus phoxinus(L.) withGasterosteus aculeatus(L.) upstream, probably to the additional detriment of the localized specialists, both limnophilic and rheoph

ISSN:0886-9375    

DOI:10.1002/rrr.3450050306

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe biological consequences of instituting a summer minimum flow from the Conowingo Hydroelectric Dam were investigated by comparing invertebrate abundance in the Susquehanna River during 1980, when flow shutdowns were frequent, to that in 1982, when the minimum flow (142 m3s−1) was maintained. The minimum flow was only maintained from April 15 to September 15, and additional investigations compared invertebrate abundance before and after the minimum flow was terminated in the fall of 1982 and 1983. There was a large difference in summer invertebrate density in the between‐year comparison, with almost a 100‐fold increase in the year when the minimum flow was maintained. Most of this difference was exhibited by two taxa, chironomids and net‐spinning trichopterans. These results were consistent with findings from the fall of 1982 and 1983, when cessation of the minimum flow in September led to declines of more than three orders of magnitude in both of these taxa. The rate of decline was faster in the shoal habitat (areas dewatered at low flow, but submerged when the minimum flow is released), suggesting that dewatering was the predominant mechanism of effect. Declines were also evident in the channel habitat (always submerged), suggesting that maintenance of current velocity is also an important beneficial component of the minim

ISSN:0886-9375    

DOI:10.1002/rrr.3450050307

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis study attempted to resolve regulation problems up‐ and downstream of Flathead Lake and on the lake proper. Members of a technical working group, representing eight water and wildlife management agencies, contributed 75 regulation scenarios they deemed necessary to conserve or enhance ecological (fish and wildlife) and societal (hydropower production, flood control, and recreation) resources for which they had management authority. The hydrology model simulated the effect of each scenario on system water balance; scenarios that were within the physical and legal constraints of the system were accepted for determination of cumulative impacts on resources. A multiattribute tradeoff analysis was used to assess cumulative impacts to key resources as a consequence of each regulation scenario (simulation) accepted for evaluation. Impacts were subjectively and independently quantified by each member of the working group following a point and importance weighting system agreed toa priori.Valuation of impacts was done on the basis of 36 technical studies of the effects of regulation on system resources. Impact valuations were summed to yield a variable referred to as weighted cumulative impact (WCI), where the highest, positive WCI indicated least cumulative impact on resources. Scenarios were then ranked in terms of WCI. When ecological resources only were evaluated, the preregulation Flathead Lake scenario generated the highest WCI. However, when all resources were considered, scenarios ranked very differently but a preferred alternative was identified by virtue of its highest WCI. This interactive process of hydrology simulation and computation of cumulative impacts mediated resource conflicts and served as an important tool in deriving water management recommendations in the Flathead River Basin. The process may be useful elsewher

ISSN:0886-9375    

DOI:10.1002/rrr.3450050308

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450050301

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY