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Auteur Lett, C.; Semeria, M.; Thiebault, A.; Tremblay, Y.
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 (up)
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Numéro d'Appel LL @ pixluser @ collection 350
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Auteur van den Hout, P.J.; van Gils, J.A.; Robin, F.; van der Geest, M.; Dekinga, A.; Piersma, T.
Titre Interference from adults forces young red knots to forage for longer and in dangerous places Type Article scientifique
Année 2014 Publication Revue Abrégée Animal Behaviour
Volume 88 Numéro Pages 137-146
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Numéro d'Appel MARBEC @ alain.herve @ 1072 collection 1374
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Auteur Benazzouz, A.; Mordane, S.; Orbi, A.; Chagdali, M.; Hilmi, K.; Atillah, A.; Pelegri, J.L.; Demarcq, H.
Titre An improved coastal upwelling index from sea surface temperature using satellite-based approach : the case of the Canary Current upwelling system Type Article scientifique
Année 2014 Publication Revue Abrégée Continental Shelf Research
Volume 81 Numéro Pages 38-54
Mots-Clés Canary upwelling system; Coastal upwelling; Coastal upwelling index; Remote sensing; Sea surface temperature; West Africa
Résumé A new methodology to derive an SST-based upwelling index was based on a rigorous spatial analysis of satellite SST fields and their variability, by referring to previous works, from Wooster et al. (1976) to Santos et al. (2011). The data was precautiously processed by considering data quality aspects (including cloud cover) and the best way to derive accurate coastal SST and its offshore reference. The relevance of the developed index was evaluated by comparing its spatial and seasonal consistency against two wind-based indices as well as with the previous SST-based indices, largely superseding these later ones in term of overall quality and spatio-temporal dynamic. Our index adequately describes the spatio-temporal variability of the coastal upwelling intensity in the Canary Current upwelling system and has the advantage of describing complementary aspects of the coastal dynamics of the region that were not covered by Ekman-based indices. The proposed methodology is generic and can be easily applicable to various coastal upwelling systems, especially the four major eastern boundary upwelling ecosystems.
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ISSN 0278-4343 ISBN Médium (up)
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Numéro d'Appel LL @ pixluser @ collection 351
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Auteur Bez, N.; Braham, C.B.
Titre Indicator variables for a robust estimation of an acoustic index of abundance Type Article scientifique
Année 2014 Publication Revue Abrégée Canadian Journal of Fisheries and Aquatic Sciences
Volume 71 Numéro 5 Pages 709-718
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Résumé In North West Africa, pelagic fisheries are an essential economic sector. However, the scientific community fails to perform satisfactory assessments of key pelagic species like sardinella, owing to a lack of relevant indices of abundance to tune the model. This paper provides an alternative acoustic index based on a semiquantitative modelisation of acoustic densities. Acoustic energy is split into binomial variables coding for null, low, medium, large, and very large densities. A multivariate geostatistical approach allows (i) mapping the spatial distribution of classes of densities and (ii) computing a new acoustic index of abundance for Sardinella aurita and Sardinella maderensis. We used the surveys of RV Fridtjof Nansen (1995-2006) and RV Al-Awam (2007-2010). Our results indicated that empirical spatial structures were highly stable over time for both between areas and surveys. Co-kriging maps also showed that sardinella had stable hot spots of distribution. The indices of abundance developed in the present study were tested in an assessment procedure and outperformed all the indices used routinely by the FAO-CECAF (Fishery Committee for the Eastern Central Atlantic) assessment working group.
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Numéro d'Appel LL @ pixluser @ collection 352
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Auteur Bodin, N.; Lucas, V.; Dewals, P.; Adeline, M.; Esparon, J.; Chassot, E.
Titre Effect of brine immersion freezing on the determination of ecological tracers in fish Type Article scientifique
Année 2014 Publication Revue Abrégée European Food Research and Technology
Volume 238 Numéro 6 Pages 1057-1062
Mots-Clés Brine immersion; Fatty acids; Frozen storage; Large pelagic fish; Persistent organic pollutants; Stable isotopes
Résumé The use of a multi-ecological tracer approach provides valuable and complementary insights to investigate the complex biology and ecology of large pelagic fish. Brine immersion freezing is the most common preservation technique used onboard for large fish to be frozen whole until they are delivered for sale and processing. We evaluated the effect of brine freezing on lipid and fatty acid composition, C and N stable isotope ratios, and organochlorine contaminant levels of yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis). Fresh tunas were stored in a saturated sodium chlorine brine immersion tank maintained at -20 A degrees C for 6 weeks, and ecological tracers were analysed on dorsal muscle samples collected before and after brine freezing. No significant effect of the fish preservation technique was found except for delta N-15 whose signatures slightly increased after a 6-week period of brine immersion. Because N isotopic shift was close to the analytical precision and probably related to a higher risk of salt penetration in small tunas with abraded skin, we consider our results as conservative and conclude that ecological tracers can indeed be analysed on brine-freezing-preserved tunas.
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ISSN 1438-2377 ISBN Médium (up)
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Numéro d'Appel LL @ pixluser @ collection 353
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