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Auteur Bourjea, J.; Clermont, S.; Delgado, A.; Murua, H.; Ruiz, J.; Ciccione, S.; Chavance, P.
Titre Marine turtle interaction with purse-seine fishery in the Atlantic and Indian oceans: Lessons for management Type Article scientifique
Année 2014 Publication Revue Abrégée Biological Conservation
Volume 178 Numéro Pages 74-87
Mots-Clés Atlantic Ocean; Bycatch; Fishery impacts; fishery management; Indian Ocean; Marine turtle
Résumé Bycatch of endangered marine turtles is a growing issue for the management of all fisheries, including the oceanic purse-seine fishery. The aim of this study was to assess the spatial and temporal variation in bycatch rates of these species in the entire European purse-seine fishery operating in the Atlantic and Indian oceans. The study was based on data collected through observer programs from 1995 to 2011. During that period, a total of 15 913 fishing sets were observed, including 6 515 on Drifting Fish Aggregating Devices (DFADs) and 9 398 on free swimming schools, representing a global coverage of 10.3% and 5.1% of the total fishing activity in the Atlantic and Indian Ocean, respectively. Moreover, from 2003 to 2011, 14 124 specific observations were carried out on DFADs to check turtle entanglement in the net covering DFADs. We found that the purse-seine fishery has a very low impact on marine turtles. We estimated that the annual number of individuals incidentally captured was 218 (SD = 150) and 250 (SD = 157) in the Atlantic and Indian Ocean, respectively, with more than 75% being released alive. The present study also investigated the impact of DFADs; which is considered a key conservation issue for this fishery. Drifting objects may play a key role in aggregating juveniles of marine turtles, implying the need for improving their construction to avoid entanglement (e.g. avoiding nets in the structure); however, based on our study it is not the main source of incidental captures of marine turtles in this fishery.
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ISSN 0006-3207 ISBN Médium
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Numéro d'Appel LL @ pixluser @ collection 349
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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
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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
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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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