1,720,997 research outputs found
Measures of hydraulic dredge efficiency and razor clam production, two aspects governing sustainability within the Scottish commercial fishery
No full textA study was made of the efficiency of a commercially available hydraulic dredge design in use on the west coast of Scotland and of the annual biomass production of two different razor clam (Ensis spp.) beds within the Clyde Sea area. These two parameters, viz fishing efficiency and population annual production, are fundamentally important to any proper attempt to assess the long term sustainability of a fishery. The hydraulic dredge used in this study was found to have an absolute efficiency of 90.1% when expressed in terms of the collected wet weight biomass, representing the first time that the efficiency of a hydraulic dredge of this nature has been measured rather than simply inferred from track width. This indicates that this dredge design has the potential to remove the majority of a clam population, including undersized immature individuals, within a 45 cm swath in a single tow. Annual production estimates were also made for two separate razor clam beds. One population of Ensis siliqua was located in Irvine Bay and the other two populations (one E. siliqua and one E. arcuatus) occurred in a mixed bed on Hunterston Sands. Each location was sampled quantitatively on a regular basis using the same hydraulic dredge. Dredged areas were measured by SCUBA divers so that the population densities could be calculated for each sampling event. Size-classes within each population were identified from siphonal shell breadth measurements and production estimates were calculated using a size-cohort analysis procedure designed for stocks exhibiting recruitment but that do not have separable age-classes. Production of all three populations was low during the study (1.82–18.08 g AFDW 10 m-2) as were the production/biomass estimates (0.01–0.11). These data indicate that populations of Ensis spp. on the west coast of Scotland are slow-growing and typical of K-selected species. These data highlight the conflicting pressures facing any razor clam fishery: the design of extremely efficient hydraulic gear and the slow-growth of the target species. It is clear that the future commercial exploitation of these species will need very careful management to ensure sustainability and avoid fishery over-depletion
The impact of hydraulic blade dredging on a benthic megafaunal community in the Clyde Sea area, Scotland.
No full textA study was made of the impacts on a benthic megafaunal community of a hydraulic blade dredge fishing for razor clams Ensis spp. within the Clyde Sea area. Damage caused to the target species and the discard collected by the dredge as well as the fauna dislodged by the dredge but left exposed at the surface of the sea bed was quantified. The dredge contents and the dislodged fauna were dominated by the burrowing heart urchin Echinocardium cordatum, approximately 60 – 70% of which survived the fishing process intact. The next most dominant species, the target razor clam species Ensis siliqua and E. arcuatus as well as the common otter shell Lutraria lutraria, did not survive the fishing process as well as E. cordatum, with between 20 – 100% of individuals suffering severe damage in any one dredge haul. Additional experiments were conducted to quantify the reburial capacity of dredged fauna that was returned to the sea bed as discard. Approximately 85% of razor clams retained the ability to rapidly rebury into both undredged and dredged sand, as did the majority of those heart urchins Echinocardium cordatum which did not suffer aerial exposure. Individual E. cordatum which were brought to surface in the dredge collecting cage were unable to successfully rebury within three hours of being returned to the sea bed. These data were combined to produce a model of the fate of the burrowing megafauna dredged and dislodged in order to collect 10 kg of marketable razor clams
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
The ecological and evolutionary importance of maternal effects in the sea
No full textMaternal effects are non-genetic effects of the maternal phenotype or environment on the phenotype of offspring. Whilst maternal effects are now recognised as fundamentally important in terrestrial systems, they have received less recognition in the marine environment despite being remarkably common. The authors review the maternal effect literature and provide a simple framework for understanding maternal effects that increase offspring fitness (termed anticipatory maternal effects) and maternal effects that increase maternal fitness at the expense of offspring fitness (termed selfish maternal effects). The review then addresses various well-studied (offspring size effects, maternal care, oviposition effects) and poorly studied (manipulating offspring dispersal potential, toxicant resistance, sibling competition, mate choice) examples of maternal effects in the marine environment with a focus on marine invertebrates and fish. Offspring size effects are strong and pervasive in the marine environment but the sources and underlying causes of offspring size variation remain poorly understood. More generally, the authors suspect that changes in offspring phenotype are often adaptive maternal effects in response to environmental change. Maternal effects are of particular importance to marine systems because they not only form a link between the phenotypes of different generations, but the biphasic life cycle of most marine organisms suggests that maternal effects also link the phenotypes of populations
Estimating connectivity in marine fish populations: what works best?
Get PDFMeasuring connectivity in marine populations is a key, yet poorly understood issue. The degree of connectivity determines the spatial scales over which population dynamics operate, the spatial scales over which fisheries should be managed and how marine protected areas should be designed and implemented. Thus, much research is directed towards a better understanding of connectivity. The tools currently used to measure connectivity broadly include larval distribution, numerical models (physical or biophysical), genetic techniques and otolith chemistry. However, few studies use more than one of these approaches, and users of connectivity estimates are frequently unclear about what any approach actually measures or whet her it is the best approach for their purposes. That is, does the tool provide information on evolutionary connectivity or ecological connectivity, can it forecast connectivity, what do the results of such studies mean in that context, and what are the limitations of the tool? This review provides an overview of these four approaches to estimating connectivity and how they work, examines what each actually measures, outlines the spatial and temporal scales over which each is appropriate and details the pros and cons of each. A historical approach is used to describe the development of these four approaches, focusing on examples using reef fishes. However, the key points are broadly applicable to marine and estuarine fishes and some invertebrates. Finally, we discuss the advantages of using multiple methods to elucidate a more complete understanding of marine connectivity
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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