1,721,056 research outputs found
Management Strategy Evaluation of alternative approaches for the anchovy and sardine stocks in the Adriatic Sea (STECF-21-04)
No full textCommission Decision of 25 February 2016 setting up a Scientific, Technical and Economic Committee for Fisheries, C(2016) 1084, OJ C 74, 26.2.2016, p. 4–10. The Commission may consult the group on any matter relating to marine and fisheries biology, fishing gear technology, fisheries economics, fisheries governance, ecosystem effects of fisheries, aquaculture or similar disciplines. Within a management strategy evaluation harvest control rules were tuned and robustness tested for the anchovy and sardine stocks in the Adriatic Sea. This investigation was done in support of GFCM and a continuation of the preliminary report (EWG 21-adhoc-02). For the sardine stock no meaningful MSE could be conducted. For the anchovy stock two HCRs were identified to be achieving the management targets and being robust.PublishedNon Referee
An evaluation of sampling and statistical methods for long-term monitoring of subtidal reef fishes : a case study of Tsitsikamma National Park marine protected area
Full text linkTsitsikamma National Park (TNP) possesses the oldest (established 1954), and one of the largest
(350 km2) ‘no-take’ marine protected areas (MPA) in South Africa. A long-term monitoring (LTM)
programme to observe the subtidal reef fishes in the TNP MPA was established in 2007. To date, 243
angling replicates have been completed, and a total of 2,751 fish belonging to 41 different species have
been caught and released. In an era of unprecedented global biodiversity loss, data that can be used to
monitor ecosystems and gauge changes in biodiversity through time are essential. This thesis aims to
improve the methodological and statistical processes currently available for LTM of subtidal reef fish
by providing an evaluation of the TNP MPA LTM programme.
Angling data revealed definitive spatial structuring, in the form of spatial autocorrelation, and a shift in
viewing spatial dependency as a statistical obstacle to a source of ecological information created a new
avenue of data inference. Species-specific distribution maps identified localized habitat as the main
predictor variable for species abundance, emphasizing the need for accurate a priori bathymetric
information for subtidal monitoring. ‘Random forest’ analyses confirmed spatial variables are more
important than temporal variables in predicting species abundance. The effectiveness of Generalized
Linear Mixed Models (GAMMs) to account for spatial autocorrelation was highlighted, and evidence
that disregarding spatial dependencies in temporal analyses can produce erroneous results was
illustrated in the case of dageraad (Chrysoblephus cristiceps). Correlograms indicated that the current
sampling strategy produced spatially redundant data and the sampling unit size (150 m2) could be
doubled to optimize sampling.
Temporal analyses demonstrated that after 50 years of ‘no take’ protection the TNP MPA ichthyofauna
exhibits a high level of stability. Species-specific size structure was also found to be highly stable.
Dageraad was the only species to exhibit a definitive temporal trend in their size structure, which was
attributed to recruitment variation and the possibility that large individuals may migrate out of the study
area. The inadequacy of angling as a method for monitoring a broad spectrum of the fish species was
highlighted, particularly due to its selectivity towards large predators. As a result, a new sampling
technique known as Stereo Baited Remote Underwater Videos (stereo-BRUVs) was introduced to the
LTM programme in 2013. Stereo-BRUVs enabled sampling of 2640 fish belonging to 52 different
species, from 57 samples collected in less than two years. A comparison of the sampling methods
concluded that, compared to angling, stereo-BRUVs provide a superior technique that can survey a
significantly larger proportion of the ichthyofauna with minimal length-selectivity biases. In addition,
stereo-BRUVs possess a higher statistical power to detect changes in population abundance. However, a
potential bias in the form of ‘hyperstability’ in sites with unusually high fish densities was identified as
a possible flaw when using stereo-BRUVs.
In an attempt to provide a more rigorous method evaluation, simulation testing was employed to assess
the ability of angling and stereo-BRUVs to accurately describe a decreasing population. The advantage
of this approach is that the simulated population abundances are known, so that each sampling method
can be tested in terms of how well it tracks known abundance trends. The study established that stereo-
BRUVs provided more accurate data when describing a distinct population decline of roman
(Chrysoblephus laticeps) over 10- and 20-year periods. In addition, spawner-biomass was found to be a
more accurate population estimate than relative abundance estimates (CPUE and MaxN) due to the
inclusion of population size structure information, highlighting the importance of length-frequency data.
The study illustrated that an evaluation framework that utilizes simulation testing has the potential to
optimize LTM sampling procedures by addressing a number of methodological questions. This includes
developing a procedure that aligns data collected from different sampling methods by applying
correction factors, thus ensuring LTM programmes are able to adapt sampling strategies without losing
data continuity
Geographic variation in the phenotype of an African horseshoe bat species, Rhinolophus damarensis, (Chiroptera: Rhinolophidae)
Full text linkStudies involving geographic variation in the phenotypes of bats help scientists to explain why these mammals are the most species rich mammalian order second only to rodents, with well more than 1 300 species occurring worldwide. Such species richness or high diversity is the manifestation of the generation of biodiversity through the splitting of lineages within bat species. A lineage of bat species can diversify into several lineages which then differentiate from each other in allopatry. Thus, the spatial separation of a lineage into several lineages could be attributed to geographical, ecological and environmental factors across the distributional range of the species. Similarly, vicariant events may also play a role in separating lineages within species. The Damara horseshoe bat species, Rhinolophus damarensis, is widely distributed but restricted to the western half of southern Africa, where it occurs across several major biomes. Formerly regarded as the subspecies, R. darlingi damarensis, it was elevated to full species status on the basis of genetic and phenotypic differences between it and R. darlingi darlingi. Rhinolophus damarensis is itself made up of two ecologically separated genetic lineages. A total of 106 individuals of R. damarensis were sampled from seven localities across its distributional range, with a view to determining and documenting the extent of geographic variation in body size, echolocation parameters, wing parameters, cranial shape and postcranial morphology of individuals from populations of R. damarensis across the distributional range of the species. Firstly, an investigation into geographic variation in resting echolocation frequency (RF) of the horseshoe bat species, R. damarensis was carried out in the western half of southern Africa (Chapter 2). Three hypotheses were tested. The first one, James’Rule (JR), states that individuals occurring in hot humid environments generally have smaller body sizes than conspecifics that occur in cooler, dryer environments, and the largest are expected to occur in cool, dry areas. On this basis and because of the known relationship between body size and RF, it was predicted that there should be a correlation between body size and climatic factors and between body size and RF. The second hypothesis was Isolation by Environment (IbE) mediated through sensory drive, which proposes that diversification of lineage may be driven by environmentally-mediated differences in sensory systems. Under this hypothesis, it was predicted that call frequency variation should be correlated with climatic variables. The third hypothesis was that Isolation by Distance (IbD) can influence phenotypic trait variation by restricting gene flow between populations. Under the Isolation by Distance (IbD) Hypothesis, it was predicted that call frequency variation should be partitioned in accordance with geographic distance between populations. To investigate the probability of the JR, IbE and IbD, the Akaike’s information criterion AICc candidate models were evaluated with different combinations of environmental (annual mean temperature and relative humidity), spatial (latitude and region) and biological (forearm as a proxy for body size) predictor variables to determine their influence on resting frequency (RF) across the distributional range of R. damarensis. Linear mixed effects models (LMEs) were employed to analyse the relationship between the response variable (RF) and the environmental, spatial and biological predictor variables. The influence of prey detection range and atmospheric attenuation was also investigated. The results showed no evidence for JR or for random genetic drift. Body size was neither correlated with RF nor environmental variables, suggesting that variation in RF was not the result of concomitant variation in body size as proposed by JR. Similarly, the Mantel test showed no IbD effect and there was therefore no evidence that genetic drift was responsible for the variation in RFs. In contrast, the LMEs showed that there was support for IbE in the form of an association between RF and region (in the form of the variable “Reg”) which was based on the two geographically separated genetic lineages. Furthermore, RF variation was also associated with the climatic variable AMT. The taxonomic status of R. damarensis was investigated using ecological traits and phenotypic characters including skulls, wings and echolocation (Chapter 3) and three dimensional (3D) scanned skulls and mandibles (Chapter 4). The main objective (Chapter 3 and Chapter 4) was to test whether previously reported genetic divergence between the two R. damarensis lineages was associated with phenotypic divergence. Morphometric and echolocation measurements were taken from hand held individual bats in the field, and skull measurements were taken from field collected voucher specimens as well as museum specimens. Discriminant Function Analyses (DFA) revealed that there was geographic variation among populations and lineages of R. damarensis. Multivariate Linear Regressions (MLV) and Linear models (LM) on the basal parts of bacula revealed significant differences between the southern and northern lineages of R. damarenis. The bacula of the two lineages of R. damarensis appear to have different shapes. Diversification through shape analyses (Chapter 4) was investigated using three dimensional (3D) geometric morphometric analyses based on X-ray microcomputed tomography (µCT) scanning of dried skulls and mandibles of R. damarensis. Procrustes Anova results of both mandibles and skulls indicated that there were no significant differences between sexes but that the shape of skulls and mandibles varied across different localities (Chapter 4). Canonical Variate Analysis (CVA) suggested that geographic variation in R. damarensis mandibles was based on the shape and thickness of the alveolar bone. Geographic variation in the skulls was based on changes in the rostrum, anterior medial swelling and brain case. Some populations had slightly deeper rostra, slightly larger anterior medial swellings and smaller braincases, whilst others had slightly shallower rostra, slightly smaller anterior medial swellings and larger braincases. The northern lineage was found to be separated from the southern lineage based on the changes in skull and mandible shape. Therefore, separation of lineages within R. damarensis (Chapter 4) could be associated with the foraging and feeding behaviour of the species under different ecological conditions due to ecological opportunity. Overall, differences in the RF were found to be associated with Isolation by Environment mediated through sensory drive and this has led to the formation of two regional (northern and southern) groupings in RF (Chapter 2). The two lineages were supported by both the phenotypic divergence (Chapter 3) and shape variation within R. damarensis skulls and mandibles (Chapter 4). Thus, phenotypic differences corresponded to genetic differences between the two lineages and provide support for IbE
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
Geographic variation in the phenotypes of two sibling horseshoe bats Rhinolophus simulator and R.swinnyi
No full textThe study of geographic variation and its causes in the phenotypes of animals elucidates how evolutionary processes generate biodiversity. This thesis attempts to uncouple the relative contributions of adaptive and neutral mechanisms to population divergence in African horseshoe bats (genus Rhinolophus). The two species were sampled from their distributional ranges within southern Africa and several morphometric and echolocation parameters were taken. The relative contributions of adaptation and drift were first tested (Chapter 2) using the Lande's model. It was hypothesised that adaptation would predominate in the diversification of the two horseshoe bats owing to the flight-echolocation and diet-echolocation adaptive complexes that intricately tie these two species to environmental conditions. Selection was also hypothesised to be stronger in Rhinolophus swinnyi because it uses higher frequency sound which is more sensitive to atmospheric conditions. The hypotheses were tested using a combination of soft tissue parameters (Chapter 2) and hard tissue parameters (Chapter 3), i.e., 3D scanned skulls analysed using 3D geometric morphometrics. To reconstruct the selective forces, linear mixed-effects models were used to regress climatic variables against echolocation call signals (Chapter 4) based on two hypotheses, the Sensory Drive and the James' Rule as a guide. The Lande's model (Chapter 2 and 3) showed that drift had a minimal effect to the variation of body parameters and echolocation and that selection was stronger on echolocation than on morphometric parameters. Additionally selection was differentially exerted across different localities and between the two species, making the relative roles of selection and drift context specific. Climatic variables (mean annual temperature and relative humidity) were inversely related to the variation in echolocation signals (Chapter 4) within each species. Body size was unrelated to the observed variation, which provided evidence that echolocation signals did not vary as a result of the body size/climate relationship proposed by James' Rule. Bats rely on both flight and echolocation to survive and reproduce, systems that have to track local habitats closely to perform optimally. Hence selection plays a pivotal role in their diversification
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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