1,720,964 research outputs found
Krill distribution in relation to environmental parameters in mesoscale structures in the Ross Sea
No full textKrill, a key pelagic resource of the Antarctic food web, provides an important link between primary and secondary plankton production and top predators. Since krill abundance is a crucial factor in Antarctic ecosystem functioning, its monitoring supplies vital data. Acoustic surveys are an effective approach to estimating krill abundance. An acoustic survey was conducted in the western Ross Sea in January 2014â10 years after a similar survey by our team - to estimate krill abundance and biomass and monitor oceanographic conditions. Antarctic krill (Euphausia superba) was detected in the northern part of the western Ross Sea and dense swarms of ice krill (Euphausia crystallorophias) were found in its central coastal area. Data analysis revealed an inverse correlation between E. superba density and salinity in the water column, whereas a positive correlation was found between E. crystallorophias abundance and fluorescence; the latter relationship was confirmed in thematic maps of E. crystallorophias spatial distribution and fluorescence. Comparison of 2004 and 2014 biomass data showed a much greater abundance of both species in the more recent survey
First target strength measurement of Trachurus mediterraneus and Scomber colias in the Mediterranean Sea
Full text linkKnowing the species-specific target strength (TS) allows converting volume backscattering strength to numerical
abundance. Since the acoustic surveys conducted for biomass assessment in the Mediterranean Sea currently
focus on the echoes of two or three target pelagic species, the TS of non-target species has seldom been investigated
in this basin. This is the first study of the TS of two pelagic species – Mediterranean horse mackerel
(Trachurus mediterraneus) and Atlantic chub mackerel (Scomber colias) – in the Mediterranean Sea. A pilot
approach using tethered live fish but not involving hooks and anaesthetic was tested in experiments using a split-beam
scientific echosounder operating at 38, 120, and 200 kHz. The mean TS was estimated for 29 live fish. The
relationship between TS and fish length was determined with a standard linear regression model; the b20 conversion
parameter was obtained with the slope forced to 20. b20 was computed at all frequencies for both species.
The key values at 38 kHz were 71.4 dB for T. mediterraneus and 71.6 dB for S. colias. Although these results
differ from those obtained with in situ and ex situ experiments using Pacific chub mackerel and other species of
the genus Trachurus, they have the potential to provide new reference values for T. mediterraneus and S. colias
biomass assessment in the Mediterranean Sea. The proposed method removes some potential biases due to the
unnatural behaviour of anaesthetized fish. Moreover, it provides an alternative to hooks, although the use of a piece
of rope instead of the hook seems to increase the acoustic reflectivity of the tethering apparatus
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
Estimating selectivity of experimental diamond (T0) and turned mesh (T90) codends in multi-species Mediterranean bottom trawl
Full text linkThis paper evaluates the effect of changing from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery. In sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting and differing only in mesh configuration were alternately mounted on the same trawl. Overall, the T90 mesh significantly improved codend size selection for all the species analysed. The difference in the predicted average L50 values between the T90 and T0 codend was particularly marked in European hake (Merluccius merluccius, 21.26 vs 11.26 cm total length), common squid (Loligo vulgaris, 12.06 vs 7.88 cm mantle length) and mantis shrimp (Squilla mantis, 20.78 vs 13.35 mm carapace length). Both codends showed an excessive size selectivity, which involves a commercial loss, especially for red mullet (Mullus barbatus), Mediterranean horse mackerel (Trachurus mediterraneus) and whiting (Merlangius merlangus). These findings demonstrate the efficiency of the T90 configuration in excluding undersized specimens, especially of hake, whose average L50 was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution can contribute to improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery
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
Preliminary target strength measurement of Sprattus sprattus and its influence on biomass estimates in the Adriatic Sea (Mediterranean Sea)
No full textPost-processing data analysis has the ability to affect target strength (TS) measurement, which in turn influence the biomass estimates of acoustic surveys. In situ experiments are considered as the best method to measure species-specific acoustic reflectivity since fish are measured in their natural environment without constrains. Nevertheless, this approach poses some problems concerning the methods to be applied to analyze acoustic data, especially when only a small number of monospecific hauls are available. In this study we tested several alternative ways to compute the b20 of sprat (Sprattus sprattus) in a poor data state in the Mediterranean Sea where the TS of the species is seldom studied. The method proposed by MacLennan and Menz (1996) and a pilot approach were used in parallel with the implementation of three single target detection algorithms to analyze two monospecific sprat hauls performed in the Adriatic Sea in 2014 and 2020. Next, we applied a Monte Carlo simulation to investigate the influence of TS variability on biomass estimates. We obtained six b20 values (range, -68.8 dB to -65.5 dB), all higher than the current known value of - 71.7 dB. The resulting coefficient of variation in the overall uncertainty on absolute biomass estimates overcame the 17%. The different models provided different total biomass estimates, however, the method proposed herein applied on high-density filter single target detection data suggest a value of b20 between - 67.5 dB and - 68.8 dB for sprat in the Mediterranean Sea, which significantly reduces absolute sprat biomass values between 2014 and 2021
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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