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Auteur Dueri, S.; Maury, O. doi  openurl
  Titre Modelling the effect of marine protected areas on the population of skipjack tuna in the Indian Ocean Type Article scientifique
  Année 2013 Publication Revue Abrégée (up) Aquatic Living Resources  
  Volume 26 Numéro Pages 171-178  
  Mots-Clés Chagos MPA; fishery management; Fishery scenarios; marine reserves; null; Tropical tuna  
  Résumé The benefits of implementing no-take Marine Protected Areas (MPAs) for the conservation of highly migratory species are not easy to assess. They depend on several factors, such as the fish mobility, fisher behaviour and the area covered by the MPA with respect to the distribution area of the species to protect. In this study, we explore the simultaneous effects of MPAs and fishing scenarios on skipjack tuna population dynamics, using the spatially-explicit APECOSM-E model. The model represents the size-structured population dynamics of skipjack tuna in the Indian Ocean and their dependence on climatic variability and exploitation by fisheries. Numerical experiments were run from the beginning of industrial fisheries in the early 1980s to the year 2030, considering different scenarios for the future development of fisheries. These scenarios combined different trends in fishing effort and technological development, either assuming a continuous increase following historical trends or a stabilization of these factors at present values. The simulations were designed to explore the effects of two MPAs of different size and location: the recently established Chagos MPA, and a hypothetical MPA covering a large part of the Western Indian Ocean, where most of the skipjack catches are presently made. We modelled the redistribution of fishing effort around the MPAs assuming that the fishers had partial knowledge of the spatial distribution of the skipjack population. The effects of the two MPAs on the population dynamics, catch and fishing mortality are shown. Our results revealed a very minor effect of the Chagos MPA on the skipjack tuna population, while the Western Indian Ocean MPA had an important impact on the fishing mortality and succeeded in stabilizing the spawning population. The simulations also showed that the effect of an MPA depends on the evolution of fisheries and it is therefore important to explore different fishery scenarios to assess the future benefits of an MPA.  
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  Numéro d'Appel LL @ pixluser @ collection 257  
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Auteur Amandé, M.; Ariz, J.; Chassot, E.; Molina, A.D. de; Gaertner, D.; Murua, H.; Pianet, R.; Ruiz, J.; Chavance, P. url  doi
openurl 
  Titre Bycatch of the European purse seine tuna fishery in the Atlantic Ocean for the 2003-2007 period Type Article scientifique
  Année 2010 Publication Revue Abrégée (up) Aquatic Living Resources  
  Volume 23 Numéro 4 Pages 353-362  
  Mots-Clés atlantic Ocean; Bycatch; discards; Purse seining; Tuna fisheries  
  Résumé Bycatch of several groups of species and their characteristics are presented for the period 2003 to 2007 for the European purse seine tuna fishery operating in the Atlantic Ocean. Data were collected through French and Spanish observer programmes and represented a total of 27 trips corresponding to 2.9% coverage. Bycatch is defined as non-targeted species and small or damaged target species. Bycatch species composition, main species length, sex ratio and the fate of the most common species are presented first. Stratified ratios relative to landings of major commercial tunas were then used to estimate the total bycatch; these ratios were considered the most appropriate variable for extrapolation. Stratification was based on the fishing mode (free school vs. floating object), season (quarters) and spatial areas. The annual average bycatch was estimated at about 6400 t, corresponding to a mean annual value of 80.8 t per 1000 t of tuna landed or 7.5% of the total catch. Tunas represent 83% (67.2 t/1000 t) of the total bycatch, followed by other bony fishes (10%, 7.8 t/1000 t), billfishes (5%, 4.0 t/1000 t), sharks (1%, 0.9 t/1000 t) and rays (1%, 0.9 t/1000 t). Based on estimates of the annual bycatch, 16% was kept on board and sold in local markets.  
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  Numéro d'Appel LL @ pixluser @ collection 56  
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Auteur Gaertner, D. url  doi
openurl 
  Titre Estimates of historic changes in total mortality and selectivity for Eastern Atlantic skipjack (Katsuwonus pelamis) from length composition data Type Article scientifique
  Année 2010 Publication Revue Abrégée (up) Aquatic Living Resources  
  Volume 23 Numéro Pages 3-11  
  Mots-Clés analysis; Bayesian; change-point; Fad; Fishing; Mortality; rate; Skipjack; strategies; tuna  
  Résumé Catch-at-size data of the eastern Atlantic skipjack were used to estimate changes in total mortality from 1969 to 2007. We used a transitional model of mean length that generalized the Beverton-Holt mortality estimator to allow change in mortality rate under nonequilibrium conditions. Then, from homogeneous periods of time, length-converted catch curves were used to access qualitative changes in selectivity patterns for two surface fisheries (the baitboat fishery operating from Dakar, Senegal, and the European and associated purse seine fisheries). To explore the impact of catch on the mortality rate, a Bayesian change-point analysis was conducted on the catch time series to detect concomitant variation between mortality rates and catch. Finally, potential causes of these changes are discussed in relation to the implementation of new fishing technology, such fish aggregating devices (FAD). The general pattern depicted by total mortality is in agreement with previous knowledge on this fishery: a state of complete or practically complete exploitation during the nineties followed by the decrease in nominal purse seine fishing effort in the last decade, combined with the effect of a seasonal moratorium on FAD fishing operations. There was no evidence of a change in selectivity between the two contrasted periods of time considered: 1969-1979 and 1986-1999; the second period being characterized by the introduction of new technology onboard vessels. In contrast, the covariation over time between total catch and mortality rate three years later highlights the effect of the fishing pressure on the stock of eastern Atlantic skipjack.  
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  Numéro d'Appel LL @ pixluser @ collection 74  
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Auteur Torres-Irineo, E.; Gaertner, D.; Molina, A.D. de; Ariz, J. url  doi
openurl 
  Titre Effects of time-area closure on tropical tuna purse-seine fleet dynamics through some fishery indicators Type Article scientifique
  Année 2011 Publication Revue Abrégée (up) Aquatic Living Resources  
  Volume 24 Numéro 4 Pages 337-350  
  Mots-Clés Fishery indicators; Fleet dynamics; Time-area closure; Tropical tuna  
  Résumé Time-area closures have become a frequently used tool to control fishing effort and protect feeding and spawning areas. However, because time-area closure strata are mainly based on biological and ecological considerations, and do not accounts for fishermen's behavior-at-sea, this type of regulation tool may not entirely achieve its objectives. With the aim of comparing the impact of two different time-area regulations: (1) a moratorium on Fish Aggregating Devices (FAD) sets (1997-2005) and (2) a no-take area for surface fleets (2005-2010) on the dynamics of the European (EU) tuna purse seine fleet operating in the eastern tropical Atlantic, several fishery indicators were evaluated through a Before-After, Control-Impact (BACI) approach. The results showed that prior to any regulation, the fleet used to be concentrated within the Gulf of Guinea area. During the first years of the moratorium on FAD (from November to January within a large region in the eastern Atlantic) there was a movement towards outside the protected area, increasing the total sets on FAD (restricted fishing activity). In general, this moratorium fulfilled its objectives; however, it was not respected during the last years of this regulation. The no-take time-area closure restricted all tuna catches for the surface fisheries but only in November and within a small area (i.e., the Picolo zone). As a result, there was an increase in activities on free schools outside the no-take area. Our findings suggest the use of some simple fishery indicators to understand fleet dynamics as a complement of ecological information before implementing new time area closures. Furthermore, since tunas are highly mobile species, anticipating the possible re-allocation of effort of purse seiners to adjacent areas in response to the spatial regulation is required to design different candidate time-area closures and to evaluate their effectiveness to protect juvenile tunas.  
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  Numéro d'Appel LL @ pixluser @ collection 163  
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Auteur Fonteneau, A.; Pereira, J.G. url  doi
openurl 
  Titre Analysis of the Daily Catch and Effort Data of the Bluefin (Thunnus Thynnus) Algarve Trap Fishery During the Years 1898–1900 Type Article scientifique
  Année 2012 Publication Revue Abrégée (up) Aquatic Living Resources  
  Volume FirstView Numéro Pages  
  Mots-Clés Bluefin tuna; Daily catches; East Atlantic; Fish behaviour; Fish trap; Historical survey; Portugal; Spawning migration pattern  
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  Numéro d'Appel LL @ pixluser @ collection 187  
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