摘要:

Non-native smallmouth bass became established in 1951 in Little Moose Lake, an oligotrophic Adirondack lake. Salmonids dominated the littoral zone at the time. Snorkel surveys, from late June through early August 1997, were used to determine the distribution and abundance of fish in the littoral zone. Transects were established on four habitat types: sand, wood (submerged trees), rock covered by silt (particles < 2 mm), and clean cobble (particles >64 mm). Non-native smallmouth bass were the most common fish species observed over the transects. Counts of adult smallmouth bass (Micropterus dolomieu) were greater than pumpkinseed (Lepomis gibbosus) and salmonids. Average lengths of bass were different between habitat types indicating size class segregation among the habitats in the littoral zone. Adult bass (>50 mm) were only observed on wood and cobble habitats. Nearly all bass >300 mm were observed on wood habitats. Young-of-year bass (<50 mm) were only observed on sand and silted rock. Only two brook trout (Salvelinus fontinalis) and three rainbow trout (Oncorhynchus mykiss) were observed; however, water temperature (range 21 °C to 24 °C) may have limited their presence. We conclude that non-native smallmouth bass dominate the littoral zone of this Adirondack lake during the summer.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663731

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Our study provides new information on walleye spawning behavior in impoundment tailwaters. Completion of Harry S Truman Dam (HST) in west-central Missouri, USA, in 1977 blocked a major walleye (Stizostedion vitreum vitreum) spawning migration and flooded the historic upstream spawning area. Creel survey data from 1981–1985, a tagging study, and population monitoring suggested problems with walleye recruitment. Our objective was to determine if walleye spawning movements were affected by fluctuating daily flows from peaking power operations. We used ultrasonic transmitters to monitor walleye movements intensively for eight weeks during spring 1991. We concluded that behavior of walleye in HST tailwaters during spawning season was influenced by water releases, possibly affecting spawning success.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663732

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We studied the effectiveness of sonication and filter-size-fractionation to efficiently remove and separate bacterial leaf-surface colonizers from other members of the microbial community. Leaf discs from red oak and paper birch leaves were colonizedin situfor 8 and 22 days in Little Rock Lake, WI, and sonicated at 90 W power output for 60 seconds, followed by filter-fractionation (3.0 μm) to remove and isolate bacteria. This technique consistently yielded the highest bacterial activity (relative Electron Transport System activity) and resulted in bacterial recovery efficiencies from leaf surfaces ranging from 96.5% to 98.8%. In addition, comparisons among various methods currently used to estimate bacterial densities (e.g., malachite green-INT, acridine orange direct counts, scanning electron microscopy approaches) were completed to assess the utility of the MINT method for counting bacteria removed by sonication. Bacterial counts derived from MINT and AODC methods were never significantly different, but always were significantly higher and less variable than counts from SEM. Finally, an attempt was made to address sources of variability in counting precision using the MINT method for bacteria removed from leaf surfaces. For two leaf species, on two sampling dates, most of the variability in MINT cell counts was due to variability among microscopic fields counted, while little was due to either subsample or filter used in cell counts. Thus, the combination of sonication and filter-size-fractionation to remove bacterial leaf surface colonizers appears to be an effective approach, allowing reproducible and precise measurements of bacterial densities and activities.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663733

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The scientific basis to measure impacts of non-point source pollution on streams is often lacking because insufficient information exists on upstream-downstream differences in nutrient concentrations. The primary purpose of this study was to establish patterns of concentrations of nitrate (NO3-) and soluble reactive P (SRP) in Peacheater Creek, Oklahoma, to provide a basis for selecting a station on the stream where monitoring might take place to evaluate impacts of Best Management Practices (BMP) to be installed on the watershed. In addition, chloride was used as a conservative tracer to assess the relative importance of factors that might reduce NO3concentrations. Samples were taken at base flow at five stations on six dates between September 1995 and May 1996. Downstream declines in NO3were attributed to dilution and biological activity, the former being more important downstream. SRP concentrations also declined downstream but occasionally were lowest upstream. The site farthest downstream would be the most important site to sample to assess the effects of BMP in this watershed.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663734

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Linthkanal, a medium sized artificial river canal (mean discharge 55 m3s−1), does not fit the usual concept of a s awning water for brown trout. Nevertheless, during the spawning seasons of 1995/1996 and 1996/1997 100–150 redds were observed. Microhabitat parameters such as depth, current velocity, bottom substrate composition, and proportion of fine sediment at both spawning and random sites had been measured. At the spawning sites mean values for current velocity were 56 cm s−1and for depth 159 cm. These values are notably higher than those recorded in other studies. Microhabitat references for spawning sites were analyzed using multivariate logistic regression. The result was significant, indicating that the microhabitat parameters at chosen spawning sites were different from other areas in the canal. To elucidate these differences further, suitability and electivity indices were calculated.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663735

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The fish assemblage of the Canadian River in Texas historically was dominated byHybognathus placitusandNotropis girardi. These species represented > 90% of fishes collected from the Canadian River in 1954–1955. Construction of two reservoirs on the Canadian River in the 1960s (Ute Reservoir, New Mexico, 1962; Lake Meredith, Texas, 1965) altered hydrologic conditions in the river and affected the fish assemblage. Downstream from Ute Reservoir, mean annual discharge decreased by about 38% after impoundment, butH. placitus, N. girardi, and other mainstem species still dominate the assemblage. Downstream from Lake Meredith, mean annual discharge decreased by 76% and the historic mainstem fish assemblage has been almost completely replaced by species that formerly were restricted to tributary streams. The magnitude of post-impoundment changes in the fish assemblage of the Canadian River appears to be related to the degree that discharge has declined, especially during the spawning season.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663736

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Self-sustaining trout populations in mountain streams depend on the presence of suitable spawning habitat. However, current watershed-scale habitat inventory techniques do not assess trout spawning habitat. A spawning substrate evaluation technique is a logical component of such inventories because it would provide data on spatial patterns of suitable substrate across watersheds. We evaluated a visual technique designed to assess substrate suitability for trout spawning. Comparisons of visual assessments of potential spawning sites to those using a single-probe freeze-core were made. The visual method of evaluating spawning substrate was nearly as good as the freeze-core method. Considering the time, labor, and cost efficiency of visual substrate assessment, this visual technique is a reasonable alternative when evaluating trout spawning substrate at the watershed scale.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663737

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

There is a limited understanding of the lotic macroinvertebrate fauna of West Africa, although many watercourses are heavily impacted. Macroinvertebrates were sampled from a stream running through Accra, the capital of Ghana, to provide information on the nature of these communities and their response to pollution. The physicochemical pollution gradient in the stream was reflected in the macroinvertebrate community, which showed a similar response to that observed in well studied temperate areas. Heavily polluted sites within the city supported a poor fauna and were dominated by tolerant taxa, such as the Chironomidae. The success of the macroinvertebrate fauna in revealing the pollution gradient and discriminating between sites suggest that there is potential for biological monitoring in such situations.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663738

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Physical habitat features of low-gradient (channel slope < 2 %) stream reaches during fall and winter varied with elevation and drainage area as well as between years in the Medicine Bow Mountains, southern Wyoming. The extent of snow cover increased and surface ice decreased during winter with increasing elevation and declining drainage area. At high-elevation (> 3,200 m above mean sea level), the streams were small and entirely bridged by snow and had no surface ice, and flows were a small proportion of the average annual flow (QAA). Moderate-sized, middle-elevation (2,444 −3,149 m) streams were not bridged by snow and had patches of surface ice and snow as well as open water on pools and riffles, and flows were an intermediate proportion of QAA. Larger streams at the foot of the mountains (2,242–2,374 m) had no snow cover, pools were entirely covered by surface ice, and flows were a relatively high proportion of QAA. Variation in discharge and physical habitat features occurred between the two years, especially at middle and low elevations.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663739

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Biotelemetry was used to track daily and monthly distributions of white bass (Morone chrysops) in Lake Poinsett, a South Dakota glacial lake. Ultrasonic transmitters were implanted into 30 adult white bass (332–450 mm, total length) during May 1997. White bass distribution was monitored from June to October 1997, January and February 1998, and April and May 1998. Distributions were quantified using depth and distance from shore at fish location. Fish distance from shore was significantly different among dates and diel periods (P<0.05), and the interaction term was also significant. White bass in Lake Poinsett were offshore during the summer and winter. During the spring and fall, white bass were near shore in shallow waters, which may be related to spawning and feeding activities. White bass tended to be nearer the shore during the evening crepuscular period across seasons. Significant (P≤0.05) but weak (r≤0.50) correlations were found between white bass distance from shore and environmental parameters. Temperature, cloud cover, precipitation, and moon phase were significant contributors to multiple regression models, but no model explained more than 26% of the white bass distribution.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663740

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor