摘要:

Trichopterans were collected from both coarse woody debris (CWD) and benthic habitats from three streams in northwest Arkansas from February 1992 through February 1993. Overall density of caddisflies was significantly greater in benthic habitats than on CWD. Trichopteran larvae had significantly greater densities during summer and fall than during winter and spring.Lype diversawas the only species that showed a preference for decay stage and was collected in greatest densities on wood with loose bark or on decayed wood with many interstitial spaces. No species tested showed a preference for volume of biofilm. However, on wood with bark remaining, wood with bark of rough texture produced greater densities of caddisflies than did wood with smooth bark.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664435

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

High water turbidity developed in the 1970s in shallow windswept Rice Lake, Wisconsin, and created a depauperate macrophyte community that has persisted more than a decade later. In 1989, this flora was characterized by species with early spring growth, summer leaf canopies, and winter tubers or rhizomes. The community was dominated inshore by water lilies (Nymphaea tuberosaandNuphar variegatum) and offshore by pondweeds (Potamogeton pectinatusandP. natans). Together with coontail (Ceratophyllum demersum), water crowfoot (Ranunculus longirostris), and elodea (Elodea canadensis), the submersed flora reached a summer dry-weight standing crop of only 28–31 g/m2.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664436

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Weight-length data from 51 brown troutSalmo truttapopulations (N= 10,673) in 14 states and one Canadian province were used to develop a standard weight (Ws) equation for stream-dwelling brown trout. The regression-line-percentile technique was used to develop theWsequation from weight-length regressions for individual brown trout populations. The proposed Ws. equation is log10Ws(g) = −4.867 + 2.960 log10TL (mm), and the English equivalent is log10Ws(lb) = −3.366 + 2.960 log10TL (in). This equation is valid for fish 140 mm (approximately 6 in) and longer. Benchmark length categories were established using percentages applied to the largest individual of the data set. Proposed length category standards are 150 mm (6 in), 230 mm (9 in), 300 mm (12 in), 380 mm (15 in), and 460 mm (18 in) for stock, quality, preferred, memorable, and trophy lengths, respectively.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664437

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We collected various substrate and water samples during the late summer and autumn of 1991 from acid sensitive Faylor Lake in Union County, Pennsylvania. The substrate samples included sediment, bark shavings from submerged wood, and aquatic macrophyte leaves. These samples, taken from September through November, were fixed in a 0.5% osmium tetroxide solution and observed with a scanning electron microscope. The water samples, collected from January to November, were preserved with Lugol's iodine and observed under light microscopy. Our purpose was to examine the life cycles of the dinoflagellate speciesPeridinium inconspicuum.Peridinium wisconsinense. andPeridinium gatunense. The water samples showed that dinoflagellate populations peaked in late summer and then quickly disappeared from the water column. The substrate data showed that the differentPeridiniumspecies showed a preference for specific substrates prior to zygote formation. This suggests a selective function for the planozygote stage during the life cycle.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664438

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The relationship between 18 species of native unionid bivalves and the exotic zebra mussel,Dreissena polymorpha, was explored at a monitoring site in Pool 26 of the Mississippi River. From 1992 to 1993, colonization rates increased from 27% to 99.7% of unionids, and the mean number ofD. polymorphaper unionid increased from 2.2 to 37.4. The number ofD. polymorphaper unionid shell was related to shell length and varied among species. Four types of colonization patterns were found, each differing from the others in the relative number of colonizingD. polymorpha.Shell and ornamentation types were differentially colonized. Thick-shelled, ornamented species were more heavily colonized than were thin-shelled, unornamented species. Habitat alteration of the gravel bar site was profound, with the zebra mussels forming a pavement over the gravel bar. This resulted in adverse effects on the unionids. Once mussels exited the substrate, they were unable to penetrate the entangled mass of zebra mussels and pebbles. Consequently, unionids were exposed when water levels fell, and considerable mortality occurred.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664439

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Tidal freshwater fish assemblages were sampled quantitatively from beds ofHydrilla verticillatain the Potomac River, Maryland, to assess local impacts of mechanical plant harvesting. Seasonal and diel estimates of fish density, biomass and species richness were compared at an undisturbed site and an adjacent mechanically harvested site. Harvesting had a “pruning” effect onHydrilla: plant biomass levels at the harvested site exceeded those at the undisturbed site after periods > 23 d. Fish species composition at the two sites was very similar and species richness differences were minor. Significantly lower (P<0.05) mean fish density and biomass values were found at the harvested versus the undisturbed site < 23 d after plant removal. However, 43 d after plant removal, fish density was significantly higher (P<0.05) at the harvested site, while biomass differences were minor. Species-specific differences suggested that harvesting improved habitat for pelagic species (e.g.,Menidia beryllina) but negatively affected cover-oriented species (e.g.,Fundulus diaphanus). Results suggest impacts of mechanical harvesting on the fish assemblages investigated were short-term and minor at the local, community level. However, ten species were killed in the mechanical harvesting process. We estimated that this immediate loss represented 11–22% of fish numbers and 4–23% of biomass. Mechanical harvesting, when macrophyte beds are in short supply, may not be prudent.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664440

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This study evaluated several habitat features relative to the natural distribution of Eurasian watermilfoil (Myriophyllum spicatumL.) in Lake Wingra, Wisconsin, using data collected in 1970, when the biomass of this macrophyte was near its historic peak in the lake. Water depth, biomass of other species, and the extinction coefficient of light, in that order, were significant factors for predicting milfoil biomass. Because of multiple correlations between factors, these parameters were probably also acting as surrogate representatives for other factors. A linear regression model for predicting milfoil biomass was weak, but optimal ranges of water depth, substrate organic matter, and substrate texture for milfoil growth were identified.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664441

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Anglers harvested approximately 122 black crappies (Pomoxis nigromaculatus)/ha at 18-ha Murdo Lake, South Dakota, in 1992. Based on a mean length of 26.2 cm for harvested black crappies, anglers likely harvested 36.1 kg/ha. The following spring (1993), proportional stock density (PSD) for black crappies collected with trap nets was 10—far lower than for any of the previous four years. Thus, we conclude that angling can have a substantial effect on the black crappie population in a small impoundment.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664442

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The mechanistic basis of differences in adult body size between two closely related freshwater amphipod species (Hyalellaspp.) are investigated. The study populations, Duck Lake and George Pond, are representative of two sibling species found in southeast Michigan, U.S.A that differ in adult body size and life history. An analysis of relative growth rates across size classes indicated that growth rates were similar in small size classes, but divergent at larger size classes, with higher growth rates inHyalellafrom George Pond. Because the timing of the divergence coincides with the onset of reproduction in the Duck Lake population, which reaches sexual maturity at a smaller body size than individuals in the George Pond population, tradeoffs in allocation of resources between growth and reproduction probably contribute substantially to population differences in adult body size. Resource consumption rates were similar between populations in small and intermediate size classes, but large Duck Lake adults had lower consumption rates than George Pond individuals of similar size. Thus, differences in resource consumption rate may also contribute to differences in adult growth rate and body size.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664443

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Tolerance ofHesperophylaxsp. to a low pH mine tailings seep which contained high concentrations of heavy metals was documented in Lake County, Colorado.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664444

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor