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Auteur Lett, C.; Semeria, M.; Thiebault, A.; Tremblay, Y. url  doi
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  Titre Effects of successive predator attacks on prey aggregations Type Article scientifique
  Année 2014 Publication Revue Abrégée Theor Ecol  
  Volume 7 Numéro 3 Pages 239-252  
  Mots-Clés Animal aggregation; Animal group; Attraction-repulsion model; Flock; Plant Sciences; School; Swarm; Theoretical Ecology/Statistics; Zoology  
  Résumé We study the cumulative effect of successive predator attacks on the disturbance of a prey aggregation using a modelling approach. Our model intends to represent fish schools attacked by both aerial and underwater predators. This individual-based model uses long-distance attraction and short-distance repulsion between prey, which leads to prey aggregation and swarming in the absence of predators. When intermediate-distance alignment is added to the model, the prey aggregation displays a cohesive displacement, i.e., schooling, instead of swarming. Including predators, i.e. with repulsion behaviour for prey to predators in the model, leads to flash expansion of the prey aggregation after a predator attack. When several predators attack successively, the prey aggregation dynamics is a succession of expanding-grouping-swarming/schooling phases. We quantify this dynamics by recording the changes in the simulated prey aggregation radius over time. This radius is computed as the longest distance of individual prey to the aggregation centroid, and it is assumed to increase along with prey disturbance. The prey aggregation radius generally increases during flash expansion, then decreases during grouping until reaching a constant lowest level during swarming/schooling. This general dynamics is modulated by several parameters: the frequency, direction (vertical vs. horizontal) and target (centroid of the prey aggregation vs. random prey) of predator attacks; the distance at which prey detect predators; the number of prey and predators. Our results suggest that both aerial and underwater predators are more efficient at disturbing fish schools by increasing their attack frequency at such level that the fish cannot return to swarming/schooling. We find that a mix between aerial and underwater predators is more efficient at disturbing a fish school than a single type of attack, suggesting that aerial and underwater foragers may gain mutual benefits in forming foraging groups.  
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  ISSN 1874-1738, 1874-1746 ISBN Médium  
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  Numéro d'Appel LL @ pixluser @ collection 350  
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Auteur Filmalter, J.D.; Cowley, P.D.; Potier, M.; Menard, F.; Smale, M.J.; Cherel, Y.; Dagorn, L. doi  openurl
  Titre Feeding ecology of silky sharks Carcharhinus falciformis associated with floating objects in the western Indian Ocean Type Article scientifique
  Année 2017 Publication Revue Abrégée J. Fish Biol.  
  Volume 90 Numéro 4 Pages 1321-1337  
  Mots-Clés atlantic; By-catch; diet; ecosystem; fad; fish aggregating devices; fish aggregation device; food-consumption; isurus-oxyrinchus; pacific-ocean; pelagic fishes; Pelagic shark; Purse-seine fishery; shortfin mako; Yellowfin tuna  
  Résumé The silky shark Carcharhinus falciformis is commonly associated with floating objects, including fish aggregating devices (FADs), in the Indian Ocean. While the motives for this associative behaviour are unclear, it does make them vulnerable to capture in the tuna purse seine fishery that makes extensive use of FADs. Here, the diet of 323 C. falciformis, caught at FADs in the Indian Ocean, was investigated to test the hypothesis that trophic benefits explain the associative behaviour. A high proportion of stomachs with fresh contents (57%) suggested that extensive feeding activity occurred while associated with FADs. Multiple dietary indices showed that typical non-associative prey types dominated, but were supplemented with fishes typically found at FADs. While the trophic benefits of FAD association may be substantial, our results suggest that associative behaviour is not driven solely by feeding. (C) 2016 The Fisheries Society of the British Isles  
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  ISSN 0022-1112 ISBN Médium  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 2142  
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Auteur Thiebault, A.; Pistorius, P.; Mullers, R.; Tremblay, Y. doi  openurl
  Titre Seabird acoustic communication at sea: a new perspective using bio-logging devices Type Article scientifique
  Année 2016 Publication Revue Abrégée Sci Rep  
  Volume 6 Numéro Pages 30972  
  Mots-Clés aggregations; birds; colony; flocks; gannets; identify; information; penguins; recognition; successive predator attacks  
  Résumé Most seabirds are very noisy at their breeding colonies, when aggregated in high densities. Calls are used for individual recognition and also emitted during agonistic interactions. When at sea, many seabirds aggregate over patchily distributed resources and may benefit from foraging in groups. Because these aggregations are so common, it raises the question of whether seabirds use acoustic communication when foraging at sea? We deployed video-cameras with built in microphones on 36 Cape gannets (Morus capensis) during the breeding season of 2010-2011 at Bird Island (Algoa Bay, South Africa) to study their foraging behaviour and vocal activity at sea. Group formation was derived from the camera footage. During similar to 42 h, calls were recorded on 72 occasions from 16 birds. Vocalization exclusively took place in the presence of conspecifics, and mostly in feeding aggregations (81% of the vocalizations). From the observation of the behaviours of birds associated with the emission of calls, we suggest that the calls were emitted to avoid collisions between birds. Our observations show that at least some seabirds use acoustic communication when foraging at sea. These findings open up new perspectives for research on seabirds foraging ecology and their interactions at sea.  
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  ISSN 2045-2322 ISBN Médium  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 1636  
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Auteur Robert, M.; Dagorn, L.; Lopez, J.; Moreno, G.; Deneubourg, J.L. url  doi
openurl 
  Titre Does social behavior influence the dynamics of aggregations formed by tropical tunas around floating objects ? An experimental approach Type Article scientifique
  Année 2013 Publication Revue Abrégée Journal of Experimental Marine Biology and Ecology  
  Volume 440 Numéro Pages 238-243  
  Mots-Clés Aggregation; Binary choice; FADs; Social behavior; tuna  
  Résumé Tropical tunas associate with objects floating at the surface of the ocean, a behavior widely exploited by fishers. However, the respective roles played by environmental variables and behavioral processes (e.g., social behavior) in the formation of these aggregations remain elusive. To investigate the role of social behavior in the dynamics of such aggregations, we used the binary choice approach. The experimental design comprised two close and identical anchored fish aggregating devices (FADS) equipped with an echo sounder buoy to monitor the aggregated biomass of tuna under each device. Analysis of the results entailed characterizing whether the aggregated biomass is distributed asymmetrically (indicative of social behavior playing a role in the dynamics) or symmetrically between the two close and identical FADs, and comparing the results with theoretical distributions based on different definitions of basic units (individual fish or small schools). The results suggest that social interactions underlie aggregation processes, which represents a major advance in our understanding of these aggregations, a priority for science-based fishery management. While recognizing the logistical and technical constraints, we encourage the development of experimental studies (e.g., in which animals are presented with controlled situations) to enhance our understanding of the behavior of large pelagic fish.  
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  ISSN 0022-0981 ISBN Médium  
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  Numéro d'Appel LL @ pixluser @ collection 249  
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Auteur Rufino, M.M.; Bez, N.; Brind'Amour, A. doi  openurl
  Titre Ability of spatial indicators to detect geographic changes (shift, shrink and split) across biomass levels and sample sizes Type Article scientifique
  Année 2020 Publication Revue Abrégée Ecol. Indic.  
  Volume 115 Numéro Pages 106393  
  Mots-Clés aggregation; bay; coast; communities; distributions; fish; Fisheries management; Marine conservation; Monitoring; patterns; Spatial metrics; time  
  Résumé Spatial indicators are widely used to monitor species and are essential to management and conservation. In the present study, we tested the ability of 11 spatial indicators to quantify changes in species' geographic patterns: (1) spatial displacement of a patch of biomass ('shift'), (2) a spatial decrease in a patch, accompanied either by a loss of biomass ('shrink0') or (3) a relocation of the same biomass ('shrink1'), and (4) splitting of a patch into smaller patches ('split'). The geographic changes were simulated by manipulating the spatial distributions of the demersal species (observed during bottom trawl surveys). Hence, the spatial distributions of the latter being used as input data on which the manipulations were done. Additionally, other aspects of the indicators affecting the responses to the geographic changes were also tested, (1) homogeneous increase in biomass throughout the patch and (2) different sample sizes. The center of gravity (defined by latitude and longitude) was the only indicator that accurately detected the 'shift' in biomass. The index of aggregation identified a decrease in the area and biomass of the main biomass patch ('shrink0'), while the Gini index, equality area and spreading area were accurately identified a decrease in the area of the main biomass patch when total biomass did not decreased ('Shrink1'). Inertia and isotropy responded to all geographic changes, except for those in biomass or distribution area. None of the indicators successfully identified 'split' process. Likewise, one of the indicators were sensitive to a homogeneous increase in biomass or the type of spatial distribution. Overall, all indicators behaved similarly well when sample sizes exceeded 40 stations randomly located in the area. The framework developed provides an accessible and simple approach that can be used to evaluate the ability of spatial indicators to identify geographic processes using empirical data and can be extended to other indicators or geographic processes. We discuss perspectives of the development of spatial indicators especially within the application of EU's Marine Strategy Framework Directive.  
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  ISSN 1470-160x ISBN Médium  
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  Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2871  
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