Changes in the catch composition of artisanal fisheries attributable to dolphin depredation in a Mediterranean marine reserve Auteur(s) : Rocklin, Delphine Santoni, Marie-catherine Culioli, Jean-michel Tomasini, Jean-antoine Pelletier, Dominique Mouillot, David Éditeur(s) : Oxford university press Résumé : There is increasing evidence from previous studies, and from fishers' observations, that coastal dolphins use fishing nets as an easily accessible feeding source, damaging or depredating fish caught in the nets. This study investigates the impact of dolphin depredation on artisanal trammelnets by analysing the catch composition of 614 artisanal fishing operations in the Bonifacio Strait Natural Reserve (France). Common bottlenose dolphins (Tursiops truncatus) attacked, on average, 12.4% of the nets and damaged 8.3% of the catch. However, attacked nets were characterized by statistically significantly higher catch per unit effort than unattacked ones. Catch composition also differed significantly after dolphin attacks; bentho-pelagic fish were more represented and reef-associated fish less represented. Our results suggest that (i) dolphins are attracted by high fish densities in the fishing area and/or nets, and (ii) their attacks induce specific fish-avoidance behaviour, according to the fish position in the water column. Although dolphins depredate a small part of the catch, damage to nets, not yet assessed in this area, could weaken the benefits that reserves can provide to artisanal fisheries. ICES Journal of Marine Science (1054-3139) (Oxford university press), 2009-05 , Vol. 66 , N. 4 , P. 699-707 Droits : 2009 ICES/CIEM. Oxford Journals http://archimer.ifremer.fr/doc/2009/publication-6808.pdf DOI:10.1093/icesjms/fsp036 http://archimer.ifremer.fr/doc/00000/6808/ | Partager |
Application of Leslie's model on a population of common dolphins (Delphinus delphis): Sensitivity study Auteur(s) : Fifas, Spyros Goujon, Michel Antoine, Loic Éditeur(s) : Elsevier Résumé : The rapid development of the albacore tuna (Thunnus alalunga) driftnet fishery in the Pay of Biscay (Atlantic ocean, France) has incited European management authorities to ask for a study of its ecological impact on populations of common dolphins and striped dolphins. A programme with onboard observers has been led during 1992 and 1993, and a sighting survey has allowed the evaluation of the abundances of fractions of populations in the studied area. For the population of common dolphins, the biological parameter estimation has allowed the building of a discrete age-structured model based on a Leslie matrix. Sensitivity studies have been conducted using four model parameters (age of first reproduction, interval between births, juvenile and adult survival rates). Results show that the increase rate of the population presents the highest sensitivity versus adult survival rate and, in second place versus the interval between births. Le développement rapide de la pêche au thon germon (Thunnus alalunga) au filet maillant dérivant dans le golfe de Gascogne a incité les instances de gestion européenne à demander une étude de son impact écologique sur les populations de dauphin commun et de dauphin bleu et blanc. Des observateurs embarqués à bord ont mené au cours des années 1992 et 1993 une campagne d'échantillonnage sur un parcours linéaire, ce qui a permis d'estimer l'abondance des fractions de populations présentes sur la zone étudiée. Pour la population de dauphins communs, l'estimation des paramètres biologiques a permis de construire un modèle à pas discret structuré en âge faisant appel à une matrice de Leslie. Des études de sensibilité ont été réalisées selon quatre paramètres du modèle; âge de première mise bas, intervalle entre mises bas, taux de survie des juvéniles, taux de survie des adultes sur les deux sexes confondus. Les résultats montrent que le taux d'accroissement de la population présente la plus forte sensibilité, en fonction du taux de survie des adultes avec, en deuxième ordre, l'intervalle entre mises bas. Aquatic Living Resources (0990-7440) (Elsevier), 1998-11 , Vol. 11 , N. 6 , P. 359-369 Droits : 1998 Published by Elsevier SAS http://archimer.ifremer.fr/doc/1998/publication-865.pdf DOI:10.1016/S0990-7440(99)80001-1 http://archimer.ifremer.fr/doc/00000/865/ | Partager |