摘要:

We collected data for five years from the lower Missouri River including discharge (819–10032 m3s−1), mean depth (2.7–9.3 m), underwater irradiance (0.1–3.7 Ein m−2d−1), suspended solids (19–2340 mg L−1), total phosphorus (131–1810 μg L−1), total nitrogen (0.9–4.2 mg L−1), nitrate-N (380–3050 μg L−1), silica (8.2–16.8 mg L−1) and chlorophyll (4.5–107 μg L−1). Suspended solids, phosphorus and light attenuation varied directly with discharge. Nitrate, ammonium-N, silica and chlorophyll were strongly seasonal. Chlorophyll was temperature dependent exhibiting winter minima (<8 μg L−1) and spring and fall maxima (>40 μg L−1). In the growing season, chlorophyll co-varied with light and varied inversely with silica and dissolved P. Poor light conditions (mixed depth:photic depth > 10) and rapid flow rates (≈ 150 km d−1) suggest thatin situproduction of algae is less important than flux of biomass from upstream. Chlorophyll flux and pheophytin increased with discharge indicating contributions of benthic or terrestrial inputs. About a fourth of the particulate organic nitrogen transported by the river may be autochthonous. Algal uptake may reduce silica flux by >22%.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663747

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A survey of the helminth fauna of largemouth bass (Micropterus salmoides) was conducted to examine helminth biodiversity and community structure in a northwestern Missouri reservoir. Twenty bass were collected from Smithville Reservoir in May and again in September of 1996 and necropsied in search of helminth parasites. Seven species of helminths were recovered:Proteocephalus ambloplitis, Spinitectus sp., Contracaecum sp., Camallanus sp., Posthodiplostomum minimum, Crepidostomum sp., and Neoechinorhynchus cylindratus. The acanthocephalan,N. cylindratus, was the most prevalent parasite in fish sampled in May with 95% of the fish infected with this species. The plerocercoid ofP. ambloplitiswas the most prevalent parasite in fish sampled in September, again with 95% of the fish infected. For both of these species, the high prevalence in one month was significantly different from its prevalence in the other month. When any of the seven parasite species was significantly more prevalent in a given month, it also comprised a significantly larger portion of the helminth community and exhibited a significantly greater mean abundance. The frequency distribution of the number of parasite species per host was similar between months, but the parasite species diversity was significantly different with the component community of May being more diverse than that of September.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663748

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We evaluated the behavioral effects of the fluctuating temperature regime on spawning phase smallmouth bass in a thermal discharge canal on Lake Erie. Fiftythree adult fish were angled from the discharge canal at the beginning of the 1994 spawning season and implanted with temperature sensing radio transmitters. The distribution of tagged fish in the discharge canal was continuously monitored and recorded from late June to early October using three fixed monitoring stations. Seventeen of the tagged fish left the discharge canal immediately following tagging and did not return. The remaining fish, particularly males guarding nests, resided in the heated discharge during the spawning period despite daily temperature fluctuations of up to 16°C. Some females and non-nesting and post-nesting males moved in and out of the discharge canal throughout the study period. Fish numbers within the canal declined throughout the summer and, by early October, all tagged bass had left the discharge. Water temperatures experienced by discharge residents closely matched station outflow values, as there was little difference in temperature throughout the 550 m long discharge canal. On several occasions temperatures were near the published upper avoidance and tolerances, but the nesting males did not leave the canal, until after the broods dispersed.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663749

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Effects of bridge and culvert construction or replacement were studied on 41 streams in Tennessee. One 100-m stream reach above and two 100-m reaches below were sampled at each bridge or culvert with a 50-m buffer zone separating each reach. Fish communities were sampled bi-annually for two years following single pass depletion techniques using a backpack electrofishing unit. Sediment depth and silt-clay percentages were measured during the spring at the upper end of each 100-m sampling reach.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663750

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The morphology of a population ofD. middendorffianacollected during spring and autumn in a fishless pond of the Southern Andes was examined to identify seasonal variations in growth patterns. Body size, tail spine length, width, thickness and biomass were analyzed, and growth was characterized by correlating various morphological dimensions with biomass. A pattern of three growth stages was identified: a juvenile stage characterized by body growth without variation of the tail spine length, a transition stage during which the tail spine experienced a sudden length reduction, and an adult stage with growth patterns similar to the first stage. Specific cyclomorphic growth patterns were found. The dimensions displaying most apparent seasonal differences were tail spine length and body flatness.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663751

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In headwater coastal streams of southwestern British Columbia, previous research suggested that light limited periphyton growth and abundance of grazing invertebrates. Logging along a reach of stream allowed us to further examine the importance of light, as well as other abiotic factors, in regulating stream periphyton and grazers. We placed unglazed ceramic tiles in three watershed, two of which served as controls. In the third watershed, we placed tiles in one reach that was newly harvested, as well as in an upstream, forested reach. Tiles were placed in streams in late June and removed weekly over a six-week period for determination of periphyton chlorophyll α and ash-free dry mass. We also measured discharge, dissolved nitrate and phosphate, and counted the number of invertebrate grazers on each removed tile weekly. Peak biomass, as chlorophyll α, was reached on day 29 with alga biomass at the logged site (19 μg m−2) seven to fourteen times higher than at the control sites. Stepwise, multiple linear regression suggested that light was the single best predictor explaining 64% of the variation in peak biomass of chlorophyll a Although periphyton biomass on tiles was much higher in the clearcut reach, so was fine sediment. Inorganic mass entrapped in the periphyton mat was two to four times higher in the clearcut stream than at other sites. Grazer abundance was not related to periphyton biomass, but was negatively related to sediment levels. Our results are consistent with the hypothesis that grazer abundance was determined by sediment levels rather than alga biomass.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663752

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Gill nets were used to determine the spatial and seasonal distributions of fishes in Lake Kampeska (simple morphometry) and at Lake Enemy Swim (complex morphometry), South Dakota. Each season (spring, summer, and autumn) gill nets were randomly placed at littoral and limnetic sites and fished for approximately 24 h. Gill nets were allowed to fish for approximately 24 h. At Lake Kampeska, 811 fishes were collected representing 16 species; statistical analyses were completed for five species. A total of 2,881 fishes was collected at Lake Enemy Swim with analyses completed for seven species. Significant (P<0.05) differences between littoral and limnetic gill net catch rates were identified during the spring at Lake Kampeska for walleye (Stizostedion vitreum), yellow perch (Perca flavescens), and white sucker (Catostomus commersoni). At Lake Enemy Swim, significant differences between littoral and limnetic sites occurred for yellow perch (spring and autumn) and rock bass (Ambloplites rupestris) (summer). Differences between median lengths of littoral and limnetic caught fishes were identified for white sucker at Lake Kampeska and yellow perch and smallmouth bass (Micropterus dolomieu) at Lake Enemy Swim. Significant seasonal differences in gill net catch rates and median lengths were identified at both lakes.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663753

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Laboratory experiments were used to determine what factors might affect predation on larvae ofGlyptotendipesspp. (Diptera: Chironomidae) byGambusia holbrooki(Baird and Girard). Tube presence, tube construction material, prey size, and habitat heterogeneity were examined as factors influencing predation. Tube presence significantly reduced predation byG. holbrooki, and large larvae were preyed on significantly more often than were small larvae. Predation was not significantly affected by differing levels of habitat heterogeneity.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663754

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The ebony shell (Fusconaia ebena) is extirpated from much of the upper Mississippi River drainage. Nonetheless, in the past 25 years 94 live individuals were collected at 23 sites in the upper Mississippi River between Lock and Dam 6 and 26, three sites in the lower St. Croix River, and one site in the lower Wisconsin River. Most of the recent records were from the lower St. Croix River and the lower reaches of the upper Mississippi River. These data support the hypothesis that Lock and Dam 19 inhibitsF. ebenafrom recolonizing the Mississippi River above the dam by preventing its migratory host fish, skipjack herring (Alosa chrysochloris), from moving upstream. Populations above Lock and Dam 19 are probably pre-lock and dam remnants that have persisted for over a half century and are at risk of extirpation. Conservation efforts should focus on artificial propagation and dam modifications that allow the passage of migratory fishes.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663755

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Population parameters ofDaphnia roseawere studied at various concentrations ofChlorellasp. (0.25, 0.75 and 3.0 mg C 1−1) at several temperatures (20, 25, 28, and 30 °C) in the laboratory. Although there were some differences in the degrees of the effects of the various temperature-food combinations, both food and temperature exerted influences on almost all of the main population parameters ofD. rosea. At a water temperature of 28 °C, growth and reproduction were reduced, and at the lowest food level (0.25 mgC 1−1), reproduction failed.D. roseadid not survive at 30 °C in spite of abundant food supply, indicating that 30 °C is a physiological limit.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663756

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor