1,720,961 research outputs found
A review of factors influencing the availability of dissolved oxygen to incubating salmonid embryos
No full textPrevious investigations into factors influencing incubation success of salmonid progeny have largely been limited to the
development of empirical relationships between characteristics of the incubation environment and survival to emergence. It is
suggested that adopting a process-based approach to assessing incubation success aids identification of the precise causes of
embryonic mortalities, and provides a robust framework for developing and implementing managerial responses.
Identifying oxygen availability within the incubation environment as a limiting factor, a comprehensive review of trends
in embryonic respiration, and processes influencing the flux of oxygenated water through gravel riverbeds is provided. The
availability of oxygen to incubating salmonid embryos is dependent on the exchange of oxygenated water with the riverbed, and
the ability of the riverbed gravel medium to transport this water at a rate and concentration appropriate to support embryonic
respiratory requirements. Embryonic respiratory trends indicate that oxygen consumption varies with stage of development,
ambient water temperature and oxygen availability. The flux of oxygenated water through the incubation environment is
controlled by a complex interaction of intragravel and extragravel processes and factors. The processes driving the exchange
of channel water with gravel riverbeds include bed topography, bed permeability, and surface roughness effects. The flux
of oxygenated water through riverbed gravels is controlled by gravel permeability, coupling of surface–subsurface flow and
oxygen demands imposed by materials infiltrating riverbed gravels. Temporally and spatially variable inputs of groundwater
can also influence the oxygen concentration of interstitial water
Refinement and re-calibration of a conductiometric standpipe method of assessing interstitial flow velocities
No full textA refinement to the conductiometric standpipe method for determining interstitial flow velocities is described. Three modifications to the original calibration are presented: (i) development of calibration curves for gravels of varying permeability; (ii) statistical validation of a practicable field run time; and (iii) integration of zero velocity flow data to the calibration procedure. These modifications are shown to improve the conductiometric probe’s ability to delineate interstitial flow velocities considered critical to salmonid incubation success. Field deployment of the probe highlighted its practical application for determining interstitial flow velocities in salmonid spawning gravels
The impact of fine sediment accumulation on the survival of incubating salmon progeny: Implications for sediment management
No full textThis paper draws on results from a recent research programme on the impact of fine sediment transport through catchments to present a case for the development of new approaches to improving the quality of salmonid spawning and incubation habitats. To aid the development of these programmes, this paper summarises the mechanisms by which fine sediment accumulation influences the availability of oxygen (O2) to incubating salmon embryos. The results of the investigation indicate that incubation success is inhibited by: (i) the impact of fine sediment accumulation on gravel permeability and, subsequently, the rate of passage of oxygenated water through the incubation environment; (ii) reduced intragravel O2 concentrations that occur when O2 consuming material infiltrates spawning and incubation gravels; and (iii) the impact of fine particles (clay) on the exchange of O2 across the egg membrane. It is concluded that current granular measures of spawning and incubation habitat quality do not satisfactorily describe the complexity of factors influencing incubation success. Furthermore, an assessment of the trends in fine sediment infiltration indicates that only a small proportion of the total suspended sediment load infiltrates spawning and incubation gravels. This casts doubt over the ability of current catchment-based land use management strategies to adequately reduce fine sediment inputs. <br/
A field-based assessment of oxygen supply to incubating Atlantic salmon(salmon salar) embryos
No full textOxygen fluxes through artificially created salmon redds within four UK rivers were quantified and assessed against survival to hatching of Atlantic salmon embryos. All sites recorded high spatial variability in survival. Minimum survival to hatching was zero at all sites. Maximum survival to hatching ranged from 35% to 91%. Mean survival to hatching ranged from 8·7% to 71%.
Intra- and inter-site variations in rates of oxygen supply were observed. Generally, interstitial dissolved oxygen concentrations declined over the incubation period from a maximum recorded directly after redd creation, although localized fluctuations were recorded. Similarly, interstitial flow velocities declined over the incubation period from a maximum directly after redd creation to a minimum at hatching. With respect to the causes of embryo mortalities, oxygen supply was shown to be a stronger determinant of survival than interstitial oxygen concentration or interstitial flow velocity.
To improve delineation of potential causes of embryo mortalities in the field, the statistical analysis was integrated within mass transfer theory of the processes controlling respiration to determine the likely mechanisms inhibiting respiration. Based on this analysis, mortalities were assessed to have resulted from periods of lethal oxygen concentrations, from periods of interstitial flow velocities that were insufficient to remove metabolic waste, or from combinations of oxygen concentration and interstitial flow that did not support respiratory requirements. A set of oxygen-supply-related thresholds for assessing incubation habitat quality are proposed
Impact of clay particles on the cutaneous exchange of oxygen across the chorion of Atlantic salmon eggs
No full textRates of oxygen consumption for Atlantic salmon Salmo salar embryos approaching hatching were determined. Values were recorded using a 'closed system' experimental set-tip. A magnetic stirrer was used to ensure that zones of oxygen depletion did not develop in the microenvironment surrounding the respiring eggs. Recorded values of oxygen consumption ranged from 0.0024 to 0.0038 mg O-2 egg(-1) h(-1), with a mean consumption rate of 0.0032 mg 0, egg(-1) h-1. The values of oxygen consumption were similar to those reported in other studies using a closed system experimental set-up, however, they were lower than those reported in a study adopting a flow-through system. The introduction of clay-sized sediment to the incubation chamber created a thin film (<1 mm) of sediment on the egg surface, and resulted in reduced rates of oxygen consumption. The additional 0.3 g of clay sediment reduced oxygen consumption by an average of 41 % and the addition of a further 0.2 g of clay sediment reduced consumption by an average of 98%. Two explanations for the recorded reduction in consumption were proposed: (i) the creation of a low permeability seal around the eggs restricted the availability of oxygen to the incubating embryos and (ii) the clay-sized fine sediment physically blocked the micro-pore canals in the egg membrane, thereby restricting oxygen uptake
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
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
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