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Fish collective behaviour in flowing waters
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Aggregation in Riverine Fish: A Review from a Fish Passage Perspective
Full text linkAccording to the most recent Living Planet Report, freshwater fish species are among the most threatened species on Earth, with many of them showing a decline in population due to altered river connectivity caused by barriers. Fish passages are conservation measures aimed at mitigating the impact of such obstructions for migrating freshwater fish, providing corridors that should not harm, kill, stress, or excessively delay fish movement. Fish passage efficiency, however, is highly variable and often unknown, particularly for non-salmonids. Despite many species being gregarious, research aiming at assessing and improving passage efficiency has focused almost solely on the behaviour and swimming performance of individual fish. Collective behaviour can, in fact, affect the way fish approach, enter, and pass a fishway. The mechanisms for which group behaviour affects fish movement in hydrodynamically complex environments, such as those occurring within fish passages, are multiple and not limited to: reduced energy expenditure, better navigation, reduced stress levels, increased exploratory behaviour, and change of predation dynamics. In this work, we review current research to illustrate how collective behaviour can be relevant for fish passage research. Our aim is to provide an overview of how collective behaviour might affect fish passage efficiency and how future research could improve the fish passage design
Flow velocity and boundary effects on fish interaction
Full text linkAbstract How do environmental cues shape the coordination rules underlying collective motion in fish shoals? This question is crucial as freshwater migratory fish are globally declining due to river fragmentation, and collective motion is known to influence the effectiveness of fish pass solutions. However, experimental data on individual interactions and the effects of solid boundaries and hydrodynamic conditions remain limited. Adopting a reductionist approach - using fish pairs as the minimal shoal’s unit - we examined how mean flow velocity and boundary proximity affect interaction dynamics in a riverine species. Towards this end, we tracked pairs of Italian riffle dace (Telestes muticellus) across three bulk flow velocities (2, 4 and 7 BL/s) and four regions in a confined open channel flow. We found shoaling time to be flow-invariant; however, fish shifted from side-by-side to in-line formations as flow increased, especially near walls. Correlation analysis revealed stronger velocity coupling at short distances (< 6 BL) that remain largely stable across flow velocities. Response times differed by coordination direction: longitudinal responses (~ 0.5 s) were flow-invariant and symmetrical between lead and rear fish, while lateral responses primarily involved the rear fish reacting to the front one, and accelerated with increasing flow. Longitudinal coordination emerged only near side walls and in the central region, whereas lateral coupling peaked in central areas and strengthened with increasing flow. These findings reveal how physical context shapes coordination in riverine fish and provide empirical insights for fish pass design and fish movement modelling
The interplay of group size and flow velocity modulates fish exploratory behaviour
Full text linkSocial facilitation is a well-known phenomenon where the presence of organisms belonging to the same species enhances an individual organism's performance in a specific task. As far as fishes are concerned, most studies on social facilitation have been conducted in standing-water conditions. However, for riverine species, fish are most commonly located in moving waters, and the effects of hydrodynamics on social facilitation remain largely unknown. To bridge this knowledge gap, we designed and performed flume experiments where the behaviour of wild juvenile Italian riffle dace (Telestes muticellus) in varying group sizes and at different mean flow velocities, was studied. An artificial intelligence (AI) deep learning algorithm was developed and employed to track fish positions in time and subsequently assess their exploration, swimming activity, and space use. Results indicate that energy-saving strategies dictated space use in flowing waters regardless of group size. Instead, exploration and swimming activity increased by increasing group size, but the magnitude of this enhancement (which quantifies social facilitation) was modulated by flow velocity. These results have implications for how future research efforts should be designed to understand the social dynamics of riverine fish populations, which can no longer ignore the contribution of hydrodynamics
PIT-tagging Italian spined loach (Cobitis bilineata): Methodology, survival and behavioural effects
Full text linkThe Italian spined loach (Cobitis bilineata) is an elongated, small-sized (<12 cm) spined loach native to northern Italy, Slovenia and Croatia. As for loaches in general, little is known about the individual movements of this loach in nature. Passive integrated transponders (PIT-tags) are small (typically 7-32 mm), relatively cheap and allow tracking of individual fish movements and behaviour. A fundamental assumption in animal telemetry is that the performance of a tagged animal does not deviate substantially from its natural performance. Although PIT-tagged fish often display high survival and tag retention, the effect varies between species and contexts, and few studies have looked at behavioural effects of PIT-tagging. Here we demonstrate a PIT-tagging methodology for spined loaches, and compare survival, activity and provoked escape response (maximum swimming speed) between tagged and control fish. We also track tag retention in the tagged fish. Italian spined loaches tagged with 12 mm PIT-tags displayed high tag retention and no extra mortality, and no effects of tagging on activity or maximum swimming speed were observed. The tag-to-fish weight and length ratios in our study ranged from 2% to 5% and from 10% to 16%, respectively, and we conclude that PIT-tagging, within these ratios, appears suitable for Italian spined loach
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
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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