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Auteur |
Walker, E.; Bez, N. |
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Titre |
A pioneer validation of a state-space model of vessel trajectories (VMS) with observers' data |
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Article scientifique |
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Année |
2010 |
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Revue Abrégée |
Ecological Modelling |
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Volume |
221 |
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Pages |
2008-2017 |
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Mots-Clés  |
Bayes; data; Markov; model; Monitoring; Observers'; purse-seiners; state-space; Systems; Trajectory; Tropical; tuna; Validation; Vessel; (Vms) |
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Résumé |
In the context of the expansion of animal tracking and bio-logging, state-space models have been developed with the objective to characterise animals' trajectories and to understand the factors controlling their behaviour. In the fisheries community, the electronic tagging of vessels commonly designated by Vessel Monitoring Systems (VMS) is developing and provides a new insight for the understanding, the analysis and the modelling of the trajectories of vessels and their prospecting behaviour. VMS data are thus a clue for the proper definition of fishing effort which remains a fundamental parameter of tuna stock assessments. In this context, we used the VMS (recording of hourly positions) of the French tropical tuna purse-seiners operating in the Indian Ocean to characterise three types of movement (states) on the VMS trajectories (stillness, tracking, and cruising). Based on empirical evidences, and on the regular frequency of VMS acquisition, this was achieved by the development of a Bayesian Hidden Markov model for the speeds and turning angles derived from the hourly steps of the trajectories. In a second phase, states were related to activities disentangling stillness into fishing or stop at sea. Finally the quality of the model performances was rigorously quantified thanks to observers' data. Confronting model prediction and true activities allowed estimating that 10% of the hourly steps were misclassified. The assumptions and model' choices are discussed, highlighting the fact that VMS data and observers' data having different time resolutions, the effective use of validating data was troublesome. However, without validation, these analyses remain speculative. The validation part of this work represents an important step for the operational use of state-space models in ecology in the broad sense (predators' tracking data, e.g. birds or mammals trajectories). |
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0304-3800 |
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LL @ pixluser @ |
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112 |
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Auteur |
Lopez, J.; Moreno, G.; Lennert-Cody, C.; Maunder, M.; Sancristobal, I.; Caballero, A.; Dagorn, L. |
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Titre |
Environmental preferences of tuna and non-tuna species associated with drifting fish aggregating devices (DFADs) in the Atlantic Ocean, ascertained through fishers' echo-sounder buoys |
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Article scientifique |
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Année |
2017 |
Publication |
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Revue Abrégée |
Deep-Sea Res. Part II-Top. Stud. Oceanogr. |
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Volume |
140 |
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127-138 |
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Mots-Clés |
behavior; catch rates; Echo-sounder buoy; Environmental preferences; equatorial atlantic; fad; floating objects; french-polynesia; gamm; habitat; pacific-ocean; Pelagic fish; Purse seine; thunnus-albacares; Tropical tuna; Tuna; western indian-ocean |
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Understanding the relationship between environmental variables and pelagic species concentrations and dynamics is helpful to improve fishery management, especially in a changing environment. Drifting fish aggregating device (DFAD)-associated tuna and non-tuna biomass data from the fishers' echo-sounder buoys operating in the Atlantic Ocean have been modelled as functions of oceanographic (Sea Surface Temperature, Chlorophyll-a, Salinity, Sea Level Anomaly, Thermocline depth and gradient, Geostrophic current, Total Current, Depth) and DFAD variables (DFAD speed, bearing and soak time) using Generalized Additive Mixed Models (GAMMs). Biological interaction (presence of non-tuna species at DFADs) was also included in the tuna model, and found to be significant at this time scale. All variables were included in the analyses but only some of them were highly significant, and variable significance differed among fish groups. In general, most of the fish biomass distribution was explained by the ocean productivity and DFAD-variables. Indeed, this study revealed different environmental preferences for tunas and non-tuna species and suggested the existence of active habitat selection. This improved assessment of environmental and DFAD effects on tuna and non-tuna catchability in the purse seine tuna fishery will contribute to transfer of better scientific advice to regional tuna commissions for the management and conservation of exploited resources. |
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English |
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0967-0645 |
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MARBEC @ alain.herve @ |
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2177 |
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Auteur |
Sempo, G.; Dagorn, L.; Robert, M.; Deneubourg, J.-L. |
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Titre |
Impact of increasing deployment of artificial floating objects on the spatial distribution of social fish species |
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Article scientifique |
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Année |
2013 |
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Revue Abrégée |
Journal of Applied Ecology |
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50 |
Numéro |
5 |
Pages |
1081-1092 |
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Mots-Clés |
behaviour-based modelling; Bycatch; Fad; Fob; sustainable fishery; tuna |
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Résumé |
* Approximately 300 pelagic fish species naturally aggregate around floating objects (FOBs) at the surface of the oceans. Currently, more than 50% of the world catch of tropical tuna comes from the industrial tuna fisheries around drifting FOBs. Greater understanding of the complex decision-making processes leading to this aggregation pattern and the impact of the massive release of artificial FOBs by fishermen on the spatial distribution and management of tuna is needed. * We analyse how the interplay between social (relationships between individuals) and non-social (responses to the environment) behaviours may affect the spatial distribution of a population in a multi-FOB environment. Taking the example of tropical tunas associating with FOBs and using differential equations and stochastic simulations, we examine how, when increasing the number of FOBs, fish aggregation dynamics and the distribution of the population among patches are affected by the population size, level of sociality and the natural retentive and/or attractive forces of FOBs on individual tuna. * Our model predicts that, depending on the species' level of sociality, fish will be scattered among FOBs or aggregated around a single FOB based on the number of FOBs deployed in a homogeneous oceanic region. * For social species, we demonstrated that the total fish catch is reduced with increasing FOBs number. Indeed, for each size of population, there are a number of FOBs minimizing the total population of fish associated with FOBs and another number of FOBs maximizing the total population of associated fish. * Synthesis and applications. In terms of fisheries management, the total catch volume is directly linked to the total number of floating objects (FOBs) for non-social species, and any limit on the number of sets would then result in a limit on the total catch. For social species (e.g. tuna), however, increasing the number of FOBs does not necessarily lead to an increase in the total catch, which is a non-intuitive result. Indeed, our model shows that, for specific values of the parameters, deploying a greater number of FOBs in the water (all other parameters being constant) does not necessarily help fishermen to catch more tuna, but does increase the level of fishing effort and bycatch. |
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1365-2664 |
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LL @ pixluser @ |
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265 |
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Auteur |
Govinden, R.; Jauhary, R.; Filmalter, J.; Forget, F.; Soria, M.; Adam, S.; Dagorn, L. |
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Titre |
Movement Behaviour of Skipjack (Katsuwonus Pelamis) and Yellowfin (Thunnus Albacares) Tuna at Anchored Fish Aggregating Devices (FADs) in the Maldives, Investigated by Acoustic Telemetry |
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Article scientifique |
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Année |
2012 |
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Revue Abrégée |
Aquatic Living Resources |
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FirstView |
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Behaviour; Fish Aggregating Devices; Indian Ocean; Passive acoustic telemetry; skipjack tuna; Yellowfin tuna |
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LL @ pixluser @ |
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193 |
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Auteur |
Dueri, S.; Guillotreau, P.; Jiménez-Toribio, R.; Oliveros-Ramos, R.; Bopp, L.; Maury, O. |
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Food security or economic profitability? Projecting the effects of climate and socioeconomic changes on global skipjack tuna fisheries under three management strategies |
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Article scientifique |
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2016 |
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Revue Abrégée |
Global Environmental Change |
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41 |
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1-12 |
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Bioeconomic model; climate change; fishery management; Mey; Msy; Skipjack tuna |
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We investigate the interactions between anthropogenic climate change, socioeconomic developments and tuna fishery management strategies. For this purpose, we use the APECOSM-E model to map the effects of climate change and commercial fishing on the distribution of skipjack tuna biomass in the three oceans, combined with a new bioeconomic module representing the rent or profit of skipjack fisheries. For forcing, we use Representative Concentration Pathway (RCP) 8.5, the highest emission scenario for greenhouse gas concentrations presented in the IPCC’s Fifth Assessment Report (AR5), and the IPCC Socioeconomic Shared Pathway (SSP) 3, which is characterized by low economic development and a strong increase in the world population. We first investigate the impact of climate change on regional skipjack abundance, catches and profits in three oceans (Atlantic, Indian and Pacific) in 2010, 2050 and 2095. We then study the effects of three management strategies (maximum sustainable yield or MSY, maximum economic yield or MEY, and zero rent or ZR) on the future distribution of fishing fleets between oceans and on global economic rent. Our model projections for 2050 and 2095 show an increase in global skipjack biomass compared to 2010 and major changes in its distribution, impacting local and regional fishing efforts. The Pacific Ocean will continue to dominate the skipjack market. In our modeling of management strategies, the currently predominant MSY strategy would have been unprofitable in 2010, due to a decreased catch per unit effort (CPUE). In the future, however, technological developments should increase fishing efficiency and make MSY profitable. In all the scenarios, a MEY strategy is more profitable than MSY but leads to the lowest catches and the highest prices. This raises ethical questions in a world where food security may become a top priority. In the scenarios where MSY generates an economic loss (e.g. 2010), a ZR strategy allows global stocks to be exploited at high but still profitable levels. Conversely, in the scenarios where MSY is profitable, (e.g. 2095) ZR leads to overfishing and smaller global catches. We conclude that the most appropriate management strategy at any time is likely to change as environmental and socioeconomic conditions evolve. The decision to follow one or other strategy is a complex one that must be regularly reviewed and updated. |
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0959-3780 |
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MARBEC @ isabelle.vidal-ayouba @ |
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1601 |
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