The physical and electrochemical characteristics such as density, viscosity, electrical conductivity and cyclic voltammetry of three different non-aqueous palladium electrolytes were analysed. The ...cyclic voltammetry behaviour showed typical reduction and oxidation peaks corresponding to the deposition and stripping of palladium in the electrolytes employed. The electrodeposition of palladium films from choline chloride/ethylene glycol (ChCl-EG), choline chloride/urea (ChCl-urea) and 1-butyl-3-methylimidazolium chloride-tetrafluoroborate (BMIM-Cl-BF
4
) solutions was demonstrated. Compact deposits were obtained with galvanostatic electrolysis. The scanning electron micrographs of the deposits revealed predominantly nodular Pd particles.
Morphological differentiation and microhabitat segregation of two ecologically similar populations of pelagic planktivorous fishes, Coregonus albula and the smaller Coregonus fontanae, were studied ...in Lake Stechlin (northern Germany). Both populations performed diel vertical migrations, although C. fontanae was always situated in deeper pelagic water than C. albula both during day and night. Landmark‐based geometric morphometrics revealed that sympatric C. albula and C. fontanae differ in external morphology, with main differences found in head length and eye position, as well as in length and width of the caudal peduncle. Moreover, while C. albula has a similar morphology over all sizes, the shape of C. fontanae changes with size. Accordingly, the morphology of the two is most different at smaller size. Although the morphological differences may reflect adaptations to the slightly differing microhabitats of the two populations, there is no conclusive evidence that this correspondence between ecology and morphology is the main mechanism behind the coexistence of the closely related coregonids in Lake Stechlin.
The negative impact of stress on the mental health of perinatal women is well-established. Prior research using data from the Pregnancy Risk Assessment Monitoring System (PRAMS) confirms three ...distinct stress domains: financial, relationship, and trauma. In 2013, an item assessing perceived racial discrimination was added to the Iowa PRAMS. Using the first phase of available data, we examine whether perceived racial discrimination represents an independent stress domain and assess its association with postpartum depressed mood.
A principal component analysis of the Iowa PRAMS data (2013–2015: N = 2,805) evaluated stress and perceived racial discrimination. Logistic regression examined the effect of racial discrimination on postpartum depressed mood.
In Iowa, 4.4% of respondents perceived racial discrimination, with higher rates among non-Hispanic Black women and Hispanic women. The principal component analysis identified five stress domains: financial, relational, traumatic, emotional, and displacement. Perceived racial discrimination did not load onto any of these domains, suggesting that it represents an independent stress component. Logistic regression indicated that those who experienced perceived racial discrimination were twice as likely to have experienced depressed mood.
Racism, in the form of perceived racial discrimination among pregnant women, is a unique domain of stress that is significantly associated with an increased risk for depressed postpartum mood. Decreasing discrimination's effects on perinatal mental health could begin with ensuring respectful and compassionate health care during pregnancy and the postpartum period.
Recent studies have indicated that in fish populations performing diel vertical migrations (DVM), some individuals do not migrate but reflect a resident phenotype, a pattern named as partial DVM. I ...present data on fish densities and the proportion of residents in Lake Stechlin (Germany) as obtained by annual midwater trawling over four discrete depths during nighttime over 8 years. The lake is inhabited by the sympatric vendace (Coregonus albula) and Fontane cisco (Coregonus fontanae). The proportion of vendace residents increased with the density of vendace, whereas the proportion of Fontane cisco residents declined with increasing density, indicating that density plays a role in the migration patterns for both species, but in opposite directions. There were almost no differences in mean size, size-frequency distributions, or Fulton condition factor between resident or migrant parts of the populations in both species. However, the proportion of dry mass in wet mass, which indicates individual nutritional status, had a tendency to be lower in migrants than in residents in both species in the years 2011, 2012, and 2013. These data suggest that density dependence may be an important factor that modifies the proportion of residents in vertically migrating fish populations. In contrast, length-dependent predation vulnerability or systematic individual differences in nutritional status were not strongly supported as potential predictors of the proportion of residents. It needs to be discussed whether partial DVM is conceptually similar to partial seasonal migrations of fish, or whether DVM reflects variants of the ideal free distribution, which are inherently density-dependent.
Cold‐water fish populations in lakes are predicted to be most vulnerable to global warming due to their geographical isolation and their requirement for habitats with low temperatures. In contrast, ...higher fisheries catches of cold‐water species often correlate with warmer winter and spring temperatures. Mechanistic understanding of the relationships between annual temperatures and population densities can only be achieved by integrating physiology and behavioral ecology of the focal species, an approach that has so far not been applied to freshwater fish populations. We took advantage from a unique biological system, the coexistence of two cold‐water Coregonus species in a deep lake. These fish species show discrete thermal windows (4–5°C vs. 7–9°C) and life histories (spring‐ vs. autumn‐spawning). We analyzed short (6–11 years) time series of pelagic fish densities obtained by hydroacoustics and trawl catches, their zooplankton prey densities, and water temperature in Lake Stechlin (Germany). Young‐of‐year fish densities increased after warm winters. In contrast, densities of juveniles and adults were correlated with metalimnetic June temperatures, but an opposite response direction of the sympatric species was caused by their discrete thermal windows. Densities of the species with a 4–5°C thermal optimum increased in years with warm June, whereas densities of the other species with a 7–9°C optimum declined in these warm years. The occupied depths of both populations at night shifted towards less suitable water temperatures if densities of the competing species increased, suggesting interactive niche segregation. Therefore, growth of fishes may be reduced and hence mortality increased by additional metabolic costs induced by occurrence in layers outside of the metabolic optima. Temperature‐driven inter‐ and intra‐specific competition in the metalimnetic layer may cause a complex response of cold‐water fish assemblages in lakes to warming. More approaches testing the relative performance of interacting species are needed to improve predictions on the consequences of global change on lake ecosystems.
Monthly (April to November) hydroacoustic surveys and parallel gillnet catches were used to determine vendace Coregonus albula abundance, biomass and population dynamics in a deep oligotrophic lake. ...By hydroacoustic surveys, recruitment of 0+ year vendace could clearly be detected. In contrast, gillnet catches resulted in low numbers of 0+ year fish, and similarly under‐represented proportions of the oldest vendace. Consequently, the correlation between hydroacoustics and gillnets with respect to fish numbers and geometric mean fish total length was high only for the age groups 1 + to 4+ years. Annual variability in hydroacoustic estimates offish abundance and biomass was high (CV=26–29%) which reflects the seasonal population dynamics of vendace.
– The size structure of a predator population can cause differences in the relative survival of different prey length classes whereby the biggest prey may reach a safe size because of the ...size‐dependent character of predation. In the present study, the diet of European catfish was investigated to examine if catfish feeding can prevent cyprinids from reaching such a size refuge. In the lake studied, catfish was stocked for biomanipulation purposes to reduce unwanted roach and bream populations. Crayfish and roach were the most important prey items of catfish. If only species composition in the diet was considered, no clear changes were recorded in relation to catfish size. However, the length of roach as prey significantly increased with catfish length. Catfish were significantly larger than the other piscivorous fish in the lake, but took relatively smaller roach in comparison with similar‐sized pike or pikeperch. Nevertheless, because of the high mean length of catfish, roach cannot reach a size refuge. For unknown reasons, the expected and intended predation on bream was not observed. Catfish took smaller prey than could be expected from mouth gape data. By extending the relationship between catfish as predator and roach as prey beyond the predator length range currently found in the lake, it could be shown that even catfish of 150 cm length will probably feed upon only 65% of all available bream length classes. Therefore, stocking with catfish cannot prevent a size refuge for the bream.
Resumen
1. Como la intensidad de las interacciones entre peces piscívoros y sus peces presa está relacionada con restricciones morfológicas de los procesos alimenticios debido al tamaño limitado de la boca o a medidas del esófago, la estructura en tamaños de la población predadora puede causar diferencias en la supervivencia relativa de diferentes clases de tamaños de las presas y con ello, capacitar a las presas mas grandes a alcanzar un tamaño refugio.
2. En este estudio, investigamos la dieta de Silurus glanis, el piscívoro con el mayor potencial de crecimiento que habita los lagos europeos, con el fin de examinar si su alimentación puede prevenir que los ciprínidos alcancen un tamaño refugio. Los objetivos concretos fueron los siguientes: a) Si ciertamente S. glanis alcanza mayores longitudes medias que otros piscívoros; b) Si la composición de la dieta de S. glanis cambia como respuesta a incrementos en longitud; c) Si la proporción longitud predador/longitud presa es comparable a las de otras especies piscívoras, y d) Si S. glanis contribuye desproporcionadamente a la reducción de la población no deseada de Abramos brama del lago.
3. El ciprínido Rutilus rutilus y el cangrejo Orconectes limosus fueron las presas más importantes de S. glanis. Cuando solo consideramos la composición de especies en la dieta, no observamos cambios claros en relación al tamaño de S. glanis. Sin embargo, la longitud de R. rutilus como presa incrementó significativamente al aumentar la longitud de S. glanis. La longitud media de S. glanis fue significativamente mayor que la de otros piscívoros en el lago pero se alimentaron de R. rutilus relativamente menores que otros piscívoros de tamaños de tamaños similares tales como Esox lucius o Sander lucioperca. Sin embargo, debido a la mayor longitud media de S. glanis, Rutilus rutilus no puede alcanzar el tamaño refugio.
4. S. glanis se alimentó de peces presa menores que los esperados de los datos de tamaño de la boca. Al extender la relación entre S. glanis como predador y R. rutilus como presa, más allá del rango de longitudes del predador observado en el lago, y simultáneamente considerar la mayor anchura del cuerpo de A. brama respecto a R. rutilus, se puede mostrar que incluso S. glanis de 150 cm de longitud probablemente se alimentarían de solamente el 65% de las clases de longitud de A. brama. Por ello, repoblaciones con S. glanis no pueden prevenir un tamaño refugio para A. brama.
The process of cold flat rolling is a widespread industrial technique to manufacture semi-finished products, e.g., for the automotive or homewares industry. Basic knowledge of the process regarding ...dimensioning and adjustment of defined characteristics is already state of the art. However, a detailed consideration and analysis with respect to local inhomogeneous residual stresses in several process steps mostly remains disregarded. A broad understanding of the process due to the distribution of residual stresses in the workpiece and the direction of the stress tensors allows for a definition of the characteristics of the workpiece even before the actual manufacturing process. For that purpose, it is necessary to perform numerical investigations by means of the finite element analysis (FEA) of cold flat rolling processes. Within this contribution, several approaches for the calibration of the FEA with the real flat rolling process will be addressed and discussed. To ensure that the numerical consideration provides realistic results, this calibration is indispensable. General parameters such as geometry, height reduction, rolling temperature, process time, and the rolling speed are considered as well as a photogrammetric survey, and calculated residual stresses with results of X-ray diffraction (XRD) will be compared. In the course of the experiments, a good agreement between the stress results of the FEA and the XRD was found in the center of the specimen. In combination with the allocation of the stress orientations, the agreement close to the edges is also fine. Some issues that cause differences between the FEA and the experiment are dis-cussed.
Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect ...of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways.
1. The influence of water temperature on occurrence and duration of a midsummer decline (MSD) of Daphnia galeata was studied in the biomanipulated Bautzen Reservoir in Germany. The proportion of ...piscivores in the fish community of the reservoir has been enhanced experimentally since 1981. As a consequence, Daphnia galeata has dominated the zooplankton. Over 18 years of study (1981–1998), a long‐lasting MSD (longer than 30 days) occurred in 7 years, whereas a short MSD (shorter than 30 days) was observed in 6 years. During the remaining 5 years, an MSD was not observed. 2. Two hypotheses were examined to explain the observed patterns. First, we postulated that high water temperature during winter and early spring (January–April) leads to an MSD after an early and high spring peak of daphnids. On the other hand, low temperature during winter and early spring should not cause an MSD owing to a slower increase of the population, resulting in a later peak of daphnids. Second, we hypothesized that the mean water temperature during early summer (May and June) influences the occurrence of an MSD (by controlling young‐of‐the‐year (YOY) fish predation on daphnids). 3. The water temperature during winter and early spring explains 83%, and the early summer water temperature 55%, of interannual variation in the occurrence of an MSD. 4. The interannual variation in duration of an MSD was neither explained by temperature during winter and early spring nor by early summer temperature alone, but in 14 of the 18 years (78%) by a combination of both. 5. We conclude that water temperature during winter and early spring had a strong impact on Daphnia mortality by influencing height and timing of the spring peak which, in turn, influenced the extent of overexploitation of their food resources. By contrast, the water temperature during early summer probably influenced the mortality of daphnids caused by predation of YOY fish. The relative timing of both sources of mortality, which depends on the temperature regime during the first 6 months of the year, is the key process in controlling the occurrence and duration of an MSD. A long‐lasting MSD, therefore, is likely in Bautzen Reservoir only if temperatures are high during winter and early spring, as well as during early summer. 6. As a consequence of climate warming, recent climate records reveal warming during winter, spring and early summer in middle Europe, rather than an increase in mean annual temperatures. If our findings and conclusions are related to this regional and temporal pattern of climate warming, an increasing frequency of years with a long‐lasting MSD and, consequently, a decreasing efficiency of biomanipulation can be predicted.
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