1,721,237 research outputs found
Location of whitefish (Coregonus lavaretus) spawning grounds using Eurasian otter (Lutra lutra) spraints and prey remains
No full textThe assessment of spawning grounds is frequently an objective of conservation
management, but their locations remain scantily described for many lacustrine fish
species. This study explored the use of whitefish (Coregonus lavaretus) scales in
Eurasian otter (Lutra lutra) spraints and the remains of otter-predated fish to locate
whitefish spawning grounds at two lakes (Ullswater and Haweswater) in the English
Lake District, U.K. At Ullswater, regular spraint collections were made at a known
whitefish spawning ground from the spawning season in February 2010 through to the
end of the subsequent spawning season in March 2011. The frequency of spraints
was several times higher during the spawning seasons and whitefish scales were
almost entirely restricted to spraints collected during these periods. At the same time,
motion-triggered infra-red cameras recorded otters bringing fish ashore to eat. More
extensive searches around the shore of Ullswater during the spawning seasons of 2010
and 2011 found whitefish remains and high numbers of spraints in numerous other
places. At nearby Haweswater, a survey of the lake’s shore during the spawning
season of 2010 found remains of otter-predated whitefish only at sites on the east
shore, including an area adjacent to the only known whitefish spawning ground
Assessment and conservation of gwyniad (Coregonus lavaretus) in Llyn Tegid, U.K.: persistence in the face of eutrophication, water level fluctuations and ruffe (Gymnocephalus cernuus) introduction
No full textThe whitefish (Coregonus lavaretus (L.)) exists as only one native population in Wales, U.K., where it occurs in Llyn Tegid and is known as the gwyniad. This population is of national conservation importance but faces a number of environmental threats. Although eutrophication has not directly impacted on gwyniad habitat availability, associated low oxygen levels in the hypolimnion periodically approach its tolerance limit of 2 mg L-1. Anthropogenic water level fluctuations and a 1980 introduction of ruffe (Gymnocephalus cernuus (L.)), a predator of gwyniad eggs, also pose potential threats. Despite these concerns, gill-netting surveys in the 1960s, 1991, 2003 and 2008 have shown no marked changes in gwyniad population biology in terms of length, weight and condition factor. Furthermore, hydroacoustic surveys from 2003 to 2009 have shown an increasing trend in total fish abundance. On the basis of gill-netting data, this increase is shared by gwyniad which in July 2009 reached a population density of 2,302.2 fish ha-1 (lower and upper 95% confidence limits of 1,795.8 and 2,951.4 fish ha-1, respectively). Nevertheless, a precautionary approach has been adopted to the conservation of this unique population and from 2005 to 2007 a translocation programme transferred 81,300 eggs from 366 male and 50 female gwyniad to the nearby water body of Llyn Arenig Fawr. Monitored hatching rates were generally high and in 2009 a hydroacoustic and gill-netting survey revealed that although the fish community of this site was sparse (1.7 fish ha-1, with lower and upper 95% confidence limits of 0.8 and 3.8 fish ha-1), it now included adult gwyniad. Although it does not yet confirm successful translocation, this observation does demonstrate that the gwyniad is able to reach sexual maturity in the recipient site
Assessment and conservation of whitefish (Coregonus lavaretus) in the U.K.
No full textThe whitefish (Coregonus lavaretus (L.)) is of high biodiversity value in the U.K., where it exists as a total of only seven native populations in England (Brotherswater, Haweswater, Red Tarn and Ullswater), Scotland (Loch Eck and Loch Lomond) and Wales (Llyn Tegid also known as Bala Lake), and is protected by national conservation legislation. However, an absence of fisheries means that information on its populations is scarce and must be obtained by dedicated surveys and associated activities. A standardised national assessment protocol using hydroacoustics and survey gill netting is described and results are presented from its use on the three whitefish populations of Scotland and Wales. For the remaining four English populations where the assessment protocol has not yet been specifically applied, comparable data are available from similar surveys, augmented by long-term fish entrapment records at one lake. These surveys revealed that the whitefish populations of Loch Eck, Red Tarn and Ullswater were in favourable condition. However, the condition of whitefish in Brotherswater, Haweswater, Llyn Tegid and Loch Lomond was considered to be unfavourable. Conservation measures specific to the whitefish populations of greatest concern in Haweswater, Llyn Tegid and Loch Lomond are described, including the management of water levels, local control of nesting cormorants (Phalacrocorax carbo (L.)) and establishment of refuge populations
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
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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