1,720,956 research outputs found
Influence of corrugated boundary hydrodynamics on the swimming performance and behaviour of juvenile common carp (Cyprinus carpio)
Full text linkTo facilitate the upstream passage of small fish, corrugated culverts are often preferred over smooth pipes, due to the lower edge and mean cross sectional water velocities created. This benefit could be lost if greater intensities of turbulence induced by wall roughness cause instability and increase the energetic expense of fish locomotion. Common carp (Cyprinus carpio) swimming performance and behaviour were evaluated in a flume using four wall roughness treatments: smooth (control), small (SC), medium (MC), and large (LC) corrugations, dependent on corrugation wavelength and amplitude. Individual fish (n = 128, mean ± S.D. total length [TL] = 86 ± 8 mm) swam at a mid-channel velocity of 0.5 m s?1 for 30 min or until fatigue. Swimming performance was quantified by: (a) success (completion of 30 min trial) or failure; and (b) the time to fatigue (endurance) of those that failed. To evaluate behaviour, fish head positions were tracked manually every second. Occupancy of the area within the MC and LC troughs (concave area where velocity was lowest) was recorded and the relationships between trough occupation and (i) TL and (ii) success tested. Differences were tested for between successful and failed individuals, and among treatments, for the following dependent variables: the total distance moved, the mean distance from the flume wall occupied (FishD), and mean velocity (FishU) and turbulent kinetic energy (FishTKE) experienced. Treatment did not influence frequency of success (38–58% per treatment) or time to fatigue. During the MC and LC treatments, troughs were occupied for part of the trial by 56 and 55% of individuals, respectively. Trough occupation was independent of TL in both treatments, and more common for successful fish than failures in the LC treatment. For successful fish, the total distance moved did not differ among treatments. Successful FishD varied among treatments and was higher for the LC (mean ± S.E. = 93.2 ± 22.3 mm) than the SC (33.5 ± 2.8 mm) treatment. Despite the availability of lower velocity areas, median successful FishU was higher in the LC treatment (0.51 m s?1) than in any other (median = 0.47 m s?1, 0.44 m s?1 and 0.47 m s?1 in the MC, SC, and control treatments, respectively). Treatment did not influence successful FishTKE which was consistently low (median = 5.3–7.7 J m?3 per treatment). Although occupation of the MC and LC troughs occurred, many individuals spent little time here, and areas with lower TKE were often occupied. Under the experimental conditions created, this study does not support the assumption that low velocity areas created by wall corrugations will improve culvert passage
Corner and sloped culvert baffles improve the upstream passage of adult European eels (Anguilla anguilla)
Full text linkInstallation of baffles intended to improve fish passage through culverts can reduce discharge capacity and trap debris, increasing flood risk. A sloping upstream face may reduce this risk, but new designs must be tested for fish passage efficiency. The European eel (Anguilla anguilla) is a critically endangered species, yet the suitability of even common baffle types to aid upstream movement has not been tested. This study compared the water depth, velocity, turbulent kinetic energy (TKE), and upstream passage performance of adult yellow-phase eels, between three 6 m long culvert models: smooth and unmodified (control); containing corner baffles (treatment 1); and with prototype sloped baffles installed (treatment 2). Passage of individual fish was assessed during 25 one-hour trials per model. Performance was quantified as entrance efficiency, number of entries per fish, passage efficiency, and overall efficiency. Total and passage delay, and successful passage time were also evaluated. Despite some individuals being able to swim against unexpectedly high water velocities (>1.5 m s?1 for 4 m), passage performance in the control was poor, with an overall efficiency of 28%. Compared to the control, both treatments increased the mean centreline water depth by approximately 0.11 m, created heterogeneous flow conditions with low velocity resting areas, and reduced maximum velocities. As a result, entrance rate and all efficiency parameters were higher for the treatments than for the control (overall efficiency = 84%), despite longer passage delay. The TKE was slightly higher in treatment 2 than 1, but there was no difference in water depth or overall efficiency. The findings show that both corner and sloped baffles can mitigate for impeded upstream adult eel movement. The extent to which the sloping upstream face will improve debris transport should be explored further
A toolkit for optimizing fish passage barrier mitigation actions
Full text linkThe presence of dams, stream–road crossings and other infrastructure often compromises the connectivity of rivers, leading to reduced fish abundance and diversity. The assessment and mitigation of river barriers is critical to the success of restoration efforts aimed at restoring river integrity.In this study, we present a combined modelling approach involving statistical regression methods and mixed integer linear programming to maximize resident fish species richness within a catchment through targeted barrier mitigation. Compared to existing approaches, our proposed method provides enhanced biological realism while avoiding the use of complex and computationally intensive population/ecosystem models.To estimate barrier passability quickly and at low cost, we further outline a rapid barrier assessment methodology. The methodology is used to characterize potential passage barriers for various fish species common to the UK but can be readily adapted to different planning areas and other species of interest.We demonstrate the applicability of our barrier assessment and prioritization approach based on a case study of the River Wey, located in south‐east England. We find that significant increases in species richness can be achieved for modest investment in barrier mitigation. In particular, dams and weirs with low passability located on mid‐ to high‐order streams are identified as top priorities for mitigation.Synthesis and applications. Our study shows the benefits of combining a coarse resolution barrier assessment methodology with state‐of‐the‐art optimization modelling to cost‐effectively plan fish passage barrier mitigation actions. The modelling approach can help inform on‐the‐ground river restoration decision‐making by providing a recommended course of action that best allocates limited resources in order to restore longitudinal connectivity and maximize ecological gains
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Relationship between European eel Anguilla anguilla infection with non-native parasites and swimming behaviour on encountering accelerating flow
Full text linkThe effect of Anguillicola crassus, Pseudodactylogyrus bini and Pseudodactylogyrus anguillae infection on the behaviour of downstream migrating adult European eels Anguilla anguilla as they encountered accelerating water velocity, common at engineered structures where flow is constricted (e.g. weirs and bypass systems), was evaluated in an experimental flume. The probability of reacting to, and rejecting, the velocity gradient was positively related to A. crassus larval, adult and total abundance. High abundance of Pseudodactylogyrus spp. reduced this effect, but A. crassus was the strongest parasitic factor associated with fish behaviour, and abundance was positively related to delay in downstream passage. Delayed downstream migration at hydraulic gradients associated with riverine anthropogenic structures could result in additional energetic expenditure for migrating A. anguilla already challenged by A. crassus infection
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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