bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects on growth and survival of retention of rod‐caught cyprinids in large keepnets
Authors: RAAT A.J.P. , KLEIN BRETELER J.G.P. , JANSEN S.A.W. 
Published: November 2003

The long‐term (about 2 months) mortality and the growth of five species of cyprinids retained and not retained in large keepnets (490 L, 2.5 mm mesh, knotless netting) were determined in drainable ponds. All experiments were carried out at least in duplicate. No statistically significant difference was found in mortality and growth between fish that were kept in the keepnets and fish that did not undergo this treatment. Differences in growth and mortality were related to fish species and season. No effect of retention time in the keepnet on mortality and growth was observed. No statistically significant difference in mortality and growth was found between bream, Abramis brama (L.), captured by anglers and the controls. Also, no differences were found in mortality and growth of rod‐caught bream retained in keepnets and rod‐caught bream that did not undergo this treatment. No statistically significant effect of lifting of the keepnets could be determined.Based on the available evidence, it was concluded that the holding of rod‐captured cyprinids in a small keepnet may cause temporary adaptations to the behaviour and physiology of the fish. Depending on the type and size of the keepnet, the material and the mesh of the netting, loss of scales and secretion of mucus may take place. The data from experiments with large keepnets do not show irreversible changes, leading to decreased fitness and ultimately to death of the cyprinids.
Variability in the spawning habitat of Pacific sardine (Sardinops sagax) off southern and central California
Authors: Lynn Ronald J. 
Published: November 2003

AbstractThe spatial pattern of sardine spawning as revealed by the presence of sardine eggs is examined in relation to sea surface temperature (SST) and mean volume backscatter strength (MVBS) measured by a 150 kHz acoustic Doppler current profiler (ADCP) during four spring surveys off central and southern California in 1996–99. Studies in other regions have shown that MVBS provides an excellent measure of zooplankton distribution and density. Zooplankton biomass as measured by survey net tows correlates well with concurrently measured MVBS. The high along‐track resolution of egg counts provided by the Continuous Underway Fish Egg Sampler (CUFES) is a good match to the ADCP‐based data. Large interannual differences in the pattern and density of sardine eggs are clearly related to the concurrently observed patterns of surface temperature and MVBS. The strong spatial relationship between sardine eggs and MVBS is particularly evident because of the large contrast in zooplankton biomass between the 1998 El Niño and 1999 La Niña. The inshore distribution of sardine spawning appears to be limited by the low temperatures of freshly upwelled waters, although the value of the limiting temperature varies between years. Often there is an abrupt offshore decrease in MVBS that is coincident with the offshore boundary of sardine eggs. Possible reasons for this association of sardine eggs and high zooplankton biomass include an evolved strategy that promotes improved opportunity of an adequate food supply for subsequent larval development, and/or adult nutrient requirements for serial spawning. Hence, the distribution of these parameters can be used as an aid for delineating the boundaries of sardine spawning habitat.
Absence or masking of metabolic fractionations of 13C in a freshwater benthic food web
Authors: FRANCE R. L. 
Published: November 2003

1. Although marine research has indicated that metabolic fractionations of 13C due to differences in organismal trophic position and proximal composition can complicate the isotopic interpretation of energy flow pathways, such potentially confounding problems have never been examined in freshwater benthic food webs.2. The δ13C values of animals comprising a littoral benthic food web composited from four Canadian Shield lakes showed no relationship with either individual trophic position (δ15N) or lipid content (C/N ratios).3. Differences in the relative incorporation of autochthonous and allochthonous energy sources by freshwater benthic organisms will alter their δ13C and δ15N values, thereby masking any possibility of observing 13C trophic enrichment.4. Removal of the possibly confounding influences of lipids through either empirical correction or by analytical extraction may be unnecessary in studies of freshwater benthic food webs. Likewise, a priori adjustments in δ13C for freshwater benthic organisms in order to accommodate trophic fractionations which are presumed to occur, based on data from marine offshore food webs, may also be inappropriate.
Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs
Authors: TOWNSEND SIMON , LUONG‐VAN JIM , BOLAND KEVIN 
Published: November 2003

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8‐year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir’s euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.4. Although the colour of catchment run‐off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log10 transformed data for both reservoirs.5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.
Monitoring acid waters in the U.K.: an overview of the U.K. Acid Waters Monitoring Network and summary of the first interpretative exercise
Authors: PATRICK S. , BATTARBEE R.W. , JENKINS A. 
Published: November 2003

1. The U.K. Acid Waters Monitoring Network (AWMN) was established in 1988. It comprises eleven lake and eleven stream sites located throughout the U.K. in areas sensitive to acidification. The principal objective of the AWMN is to provide a long‐term, high‐quality chemical, biological and palaeolimnological record which, in conjunction with the U.K. precipitation monitoring networks, will facilitate the assessment of trends within U.K. surface waters.2. The first interpretation of results generated by the AWMN (April 1988–March 1993) has recently been completed and is summarized. During this period there have been no sustained changes in atmospheric deposition in the U.K. Trends are recognized in certain chemical and/or biological parameters at individual AWMN sites, but despite some (regional) patterns no regional trends toward increasing or decreasing acidification are apparent. The data comprise an excellent baseline with which future changes may be compared.3. The methodology of the AWMN is reviewed and some amendments are suggested in the light of the first 5 years experience. These include: additional determinations for nitrogen species and total phosphorus; changes to the frequency of macrophyte and palaeolimnological sampling; new emphasis on data generated by sediment traps at lake sites; and the addition of extra sites to address better the full extent of acid‐sensitive surface waters revealed by the national critical loads mapping programme, and to pay particular attention to the acidifying role of nitrogen.4. The contribution of AWMN data to other national and international environmental monitoring programmes is highlighted. In addition, AWMN sites provide data to develop and validate critical loads models and dynamic models of acidification, and could also be used to monitor the impact of other air pollutants such as trace metals and persistent organic compounds on the freshwater environment.
The determination of total nitrogen and total phosphorus concentrations in freshwaters from land use, stock headage and population data: testing of a model for use in conservation and water quality management
Authors: JOHNES PENNY , MOSS BRIAN , PHILLIPS GEOFFREY 
Published: November 2003

1. Nutrient concentrations (particularly N and P) determine the extent to which water bodies are or may become eutrophic. Direct determination of nutrient content on a wide scale is labour intensive but the main sources of N and P are well known. This paper describes and tests an export coefficient model for prediction of total N and total P from: (i) land use, stock headage and human population; (ii) the export rates of N and P from these sources; and (iii) the river discharge. Such a model might be used to forecast the effects of changes in land use in the future and to hindcast past water quality to establish comparative or baseline states for the monitoring of change.2. The model has been calibrated against observed data for 1988 and validated against sets of observed data for a sequence of earlier years in ten British catchments varying from uplands through rolling, fertile lowlands to the flat topography of East Anglia.3. The model predicted total N and total P concentrations with high precision (> 95% of the variance in observed data explained). It has been used in two forms: the first on a specific catchment basis; the second for a larger natural region which contains the catchment with the assumption that all catchments within that region will be similar. Both models gave similar results with little loss of precision in the latter case. This implies that it will be possible to describe the overall pattern of nutrient export in the UK with only a fraction of the effort needed to carry out the calculations for each individual water body.4. Comparison between land use, stock headage, population numbers and nutrient export for the ten catchments in the pre‐war year of 1931, and for 1970 and 1988 show that there has been a substantial loss of rough grazing to fertilized temporary and permanent grasslands, an increase in the hectarage devoted to arable, consistent increases in the stocking of cattle and sheep and a marked movement of humans to these rural catchments.5. All of these trends have increased the flows of nutrients with more than a doubling of both total N and total P loads during the period. On average in these rural catchments, stock wastes have been the greatest contributors to both N and P exports, with cultivation the next most important source of N and people of P. Ratios of N to P were high in 1931 and remain little changed so that, in these catchments, phosphorus continues to be the nutrient most likely to control algal crops in standing waters supplied by the rivers studied.
Diatoms as indicators of river quality in the Nepalese Middle Hills with consideration of the effects of habitat‐specific sampling
Authors: JÜTTNER INGRID , ROTHFRITZ HEIKE , ORMEROD S.J. 
Published: November 2003

1. Using a replicated survey design at the catchment scale, we compared the composition and diversity of diatom communities in three stream groups in the Middle Hills of Nepal: semi‐natural reference (Arun Valley), enriched by agricultural runoff (Likhu Khola) and grossly polluted by sewage (Kathmandu Valley). We sampled riffles at all sites; in the Kathmandu Valley and Likhu Khola we also sampled diatoms in pools and on vegetation.2. Species richness and diversity H′ were significantly higher in agricultural streams than in either organically polluted streams or references. Community composition, as shown by principal components analysis, varied significantly between all three stream types due to differences in the abundances of species characteristic of organic enrichment (Kathmandu Valley), moderate enrichment (Likhu Khola) or undisturbed hillstreams (Arun Valley).3. Few species varied in relative abundance between pools, riffles and vegetation so that variations in community composition and diversity were stronger between stream groups than between habitats. Samples from any one habitat produced only 75.7% (± 8.6 SD) of the species from three habitats, so that surveys aimed at recording biodiversity may need more comprehensive habitat coverage than surveys for biomonitoring.4. We conclude that diatom communities can indicate different sources of pollution in Nepalese streams, and advocate further studies to develop this indicator potential over a wider area of the Himalaya. Comparisons between replicate groups of streams selected a priori helped to clarify effects which were sometimes obscured by other survey designs.
A functional model for maximum growth of immature stone loach, Barbatula barbatula, from three populations in north‐west England
Authors: ELLIOT J.M. , HURLEY M.A. , ALLONBY J.D. 
Published: November 2003

1. The chief objective was to develop a functional model for growth of stone loach, Barbatula barbatula, using immature fish from three populations. The growth model had been developed previously for brown trout, Salmo trutta, but new estimates of the five parameters for the stone loach had to be obtained from laboratory experiments.2. Fish from four size groups (initial arithmetic mean live weights 0.053 g, 0.231 g, 0.840 g, 1.612 g, with five fish per group) from Great Oaks Wood Beck were acclimatized to constant temperatures of either 3, 5, 10, 15, 20 or 25 °C. Each fish was kept in a separate tank and fed to satiation on freshwater shrimps. Weights and lengths of each fish were recorded at the start and finish of a growth period of 35 days. For each of the other populations (Black and Ford Wood Becks), there were only three temperatures(5, 10, 20 °C) with ten fish per temperature.3. The growth model was an excellent fit (P < 0.001, R2 > 0.99) for the 120 fish from Great Oaks Wood Beck. Growth rates were negative at 3 °C, close to zero at 5 and 25 °C, and positive at 10, 15 and 20 °C, with an optimum value of 19 °C. When growth rates were positive, they decreased markedly with increasing fish weight for small fish but decreased more slowly for larger fish. At the start of the experiments, weight–length relationships were similar for fish from all three populations and were well described by a power function. There was excellent agreement between growth rates estimated from the fitted growth model for fish from Great Oaks Wood Beck and values obtained for fish from Black and Ford Wood Becks. Data from all three populations were therefore pooled (n = 180) to obtain new estimates of the five parameters in the model.4. Comparisons between parameter estimates for trout and stone loach showed that the latter grew better in warmer waters (e.g. optimum value for growth was 19.0 °C for stone loach and 13.1 °C for trout, with ranges for growth of 5.0–25.0 °C and 3.6–19.5 °C, respectively).
Functional differences in epiphytic microbial communities in nutrient‐rich freshwater ecosystems: an assay of denitrifying capacity
Authors: ERIKSSON PEDER , WEISNER STEFAN 
Published: November 2003

1. The denitrifying capacity of epiphyton was used to evaluate differences in the function of epiphytic microbial communities on submersed macrophytes in nutrient‐rich freshwater ecosystems. The denitrifying capacity of epiphyton on Potamogeton perfoliatus shoots of different age and with different epiphytic abundances from a eutrophic lake was investigated in laboratory microcosms in the light and dark. Additionally, differences between epiphyton on shoots of Potamogeton pectinatus grown under different in situ nutrient and hydraulic conditions were investigated by examining their denitrifying capacity.2. Denitrification was registered in well‐developed epiphytic layers on both mature and senescent shoots in the dark, with activities 3‐ to 10‐fold higher in the epiphytic communities of senescent shoots. No activity was detected on young shoots with sparse epiphyton or on shoots from which loosely attached epiphyton had been removed. Denitrification never occurred during illumination.3. Even though the epiphytic abundance was similar in magnitude, the denitrifying capacity of epiphyton adapted to high nutrient loadings was about a hundred times higher than that of epiphyton adapted to lower nutrient levels. Additionally, epiphytic abundance and denitrifying capacity were higher at sites less exposed to wave turbulence or water currents, than at sites with more water turbulence.4. The results illustrate how the hydraulic and nutrient conditions of the surrounding water affect both the quantity and function of epiphytic microbial communities in nutrient‐rich freshwater ecosystems.
Oral deformities in tadpoles (Ranacatesbeiana) associated with coal ash deposition: effects on grazing ability and growth
Authors: CHRISTOPHER ROWE , KINNEY OWEN , FIORI ALISON , CONGDON JUSTIN 
Published: November 2003

1. Tadpoles of the bullfrog (Ranacatesbeiana) collected in a coal ash deposition basin (contaminated with As, Cd, Cr, Cu, Se and other elements) and a downstream drainage swamp had a reduced number of labial teeth and deformations of labial papillae when compared with tadpoles from reference areas. Tadpoles from the coal ash‐affected areas had 90% fewer teeth in anterior tooth row number 2 and 40% fewer teeth in posterior row number 1 than reference animals. In the deposition basins, drainage swamp and reference ponds, respectively, 96.2, 85.1 and 2.9% of tadpoles had oral deformities.2. Tadpoles with deformities were less able to graze periphyton than were normal tadpoles, when tested in the laboratory. When presented with periphyton as a sole food source, tadpoles with deformed teeth had lower (negative) growth rates than those with normal teeth, which had slightly positive growth rates. When particulate food was also available, tadpoles grew well regardless of deformities.3. It appears that the morphological deformities associated with this coal ash‐polluted environment can have ecological ramifications for the affected organisms by limiting the type of food that can be consumed and the ability to grow when multiple food types are unavailable.
Multi‐scale approach to species–habitat relationships: juvenile fish in a large river section
Authors: POIZAT GILLES , PONT DIDIER 
Published: November 2003

1. Juvenile fish were sampled by electrofishing using the point abundance sampling method from August to November 1991 in the Lower Rhône River. Variations in fish abundance between point samples were partitioned according to three spatial scales of habitat heterogeneity.2. The compartment scale, differentiating channel and ‘dike fields’ (an area marginal to the main channel partially enclosed by an artificial embankment), was associated with variation in water current, temperature and biological productivity. Every juvenile fish species studied was more abundant in the dike fields, using them as a nursery.3. Within both compartments (i.e. main channel and dike fields), the same five bank types were represented, defining the intermediate scale of habitat heterogeneity. In the dike fields, beaches were selected by most of the species, whereas steep silt banks were more often selected in the main channel.4. After having removed the variation explained at the two larger habitat scales, only depth and shelter were found to have a significant effect on fish abundance at the microhabitat scale.5. When compared with a classical single‐scale approach, the multi‐scale approach was found to explain a greater amount of fish abundance variations and to facilitate the interpretation of observed patterns by scaling the species’ responses to habitat heterogeneity. The difference between the amounts of variation explained was proposed as a measure of how much habitat selection is hierarchical.
Effects of aggregative behaviour on the bioenergetics of the freshwater predatory leech Nephelopsis obscura (Erpobdellidae)
Authors: SMITH D.E.C. , DAVIES RONALD 
Published: November 2003

1. Supplied with ad libitum prey, the effects of different group sizes (one, five, ten, twenty‐five, fifty or 100) on the acquisition and allocation of energy were examined over the entire life cycle of the freshwater predatory leech Nephelopsis obscura, to evaluate the bioenergetic costs and/or benefits of aggregation.2. In terms of growth, asymptotic biomass and ingestion, group sizes larger than one and less than ten are optimal. As group size increases from ten to 100, N. obscura has slower growth and lower weekly food ingestion, suggesting interference competition. Single leeches had lower food consumption than group sizes of less than 100 animals. With a lower asymptotic biomass, single leeches have lower fecundity and presumed lower fitness. Lipid deposition was unaffected by group size.3. Size‐ and time‐specific respiration rates declined with increasing group size. For group sizes between five and fifty, the same relative proportion of ingested energy was allocated to respiration. Above this threshold group size, leeches allocated a higher proportion of ingested energy to growth, i.e. had higher growth efficiency, as did leeches cultured individually.4. In the largest group size, total time spent in activity was highest (reflecting the high degree of interference between conspecifics), but as a result of the lower hourly costs of respiration they allocated a lower proportion of ingested energy to total respiration.5. Optimum group size of N. obscura in the laboratory is within the typical range of group sizes found on stony shores in the field.
Differential behavioural responses of mayflies from streams with and without fish to trout odour
Authors: McINTOSH ANGUS , PECKARSKY BARBARA 
Published: November 2003

1. In streams, mayflies (Order Ephemeroptera) are at risk from fish feeding visually in the water column. The effect of fish odour on the behaviour of Baetis bicaudatus from a fishless stream and a trout stream was investigated in four large oval tanks supplied with water from the fishless stream.2. For each mayfly population, mayfly positioning on the substratum and movement in the water column (drift) were measured during the day and night, over 3 days. Brook trout (Salvelinus fontinalis) odour was added to two tanks to test the effect of a threat from fish.3. Throughout the experiment more mayflies from the trout stream were observed on the substratum surface and in the water column during the night than the day, but the magnitude of night drift was less in tanks with fish odour.4. Baetis from the fishless stream also displayed a nocturnal periodicity in drift and positioning, but their night‐time drift was not affected by the presence of fish odour. On the first day of the experiment, however, more mayflies were observed on the substratum surface and drifting in tanks without fish odour during the day.5. Sensitivity to fish odour may enable mayflies to alter their behaviour according to the risk of predation from fish.