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Since the 1980s, the Common Fisheries Policy (CFP) has shaped European fisheries. It has often been criticised for being too prescriptive and, above all, for failing to protect either fishermen or ecosystems. The last reform dates back to the early 2010 s and has led to a slight but slow improvement in the state of ecosystems. Given that the CFP is in the process of evaluation, a group of French fishery scientists set up an initiative to add to the debate on what should be retained, reinforced or added to a possible new reform. This initiative came 10 years after a previous manifesto that presented their vision for fisheries in Europe. Four major issues emerged from the current initiative: (1) a need for transparency and simplification in fisheries management, (2) a need for more consultation and dialogue between stakeholders, (3) the urgency of the situation in the Mediterranean Sea, and (4) the necessity of putting into practice all research developments for an ecosystem approach to fisheries. Compared to 10 years ago, the response of scientists shows that the focus is no longer on achieving the maximum sustainable yield, but rather on the following steps to protect ecosystems and fisheries. An ecosystem approach to fisheries remains indispensable for both ecosystems and fishing activities. To this end, scientists put forward numerous proposals to improve the CFP, acknowledging that the final solutions should emerge from consultation with stakeholders. Climate change, an issue raised much more than in the manifest, reinforces the need to act.

Small-scale fisheries are often seen as a solution for ensuring sustainability in marine exploitation. They are viewed as a suitable alternative to industrial fisheries, particularly when considering their social and economic importance in developing countries. Here, we show that the booming small-scale fishery sector in Senegal, in the context of increasing foreign demand, has induced the collapse of one of the most emblematic West African marine fish species, a large grouper Epinephelus aeneus, historically called ‘false cod’ by European fishers. The overexploitation of this species appears to be on account of the increasing effort sustained by a growing international demand and important subsidies, which resulted in a relative stability of the average economic yield per fishing trip and an incentive for continuing targeting this species to almost extinction. It is a critical time for addressing and mitigating the pressure of the small-scale fisheries to prevent declines of fish species that are highly ...

In most coastal countries the fisheries sector satisfies multiple socioeconomic needs. This is especially the case in many coastal developing countries where fisheries represent a substantial source of food, jobs, and income. However, fisheries exert strong pressures on marine resources with threats to their sustainability. The context of overexploitation of marine resources is combined with a great diversity of stakeholders intervening in the governance of the fisheries. Thus, a better understanding of the challenges fisheries face is essential to enact management policies to ensure sustainability. Through a case study of the Senegalese fisheries, this article develops quantitative indicators of social, economic, and ecological states of the fisheries. Standardized principal components analysis combined with the Hodrick-Prescott filter is used to assess trends in the indicators. These indicators can contribute to an adaptive management framework in a context of multiple management objectives wit...

Abiotic and biotic variables of coastal lagoons are highly heterogeneous in both space and time, and this heterogeneity complicates the assessment of their ecological status. These variables are essential to the monitoring and preservation of these fragile ecotones and the resources and services they sustain. 2 An integrative approach for evaluating the ecological status of coastal lagoons, based on field investigations of the key parameters driving their functioning and a set of selected ecological indicators matching lagoon management information needs for societal benefits, is investigated. Consistency in lagoon status evaluation from multiple and different variables was estimated, through a case study comparing three adjacent yet contrasting French Mediterranean shallow water lagoons. 3 French Mediterranean shallow water lagoons are used to demonstrate the potential of such an approach and to underline the need for a multi-faceted framework, for correctly evaluating lagoon status, and underlining the need for high-frequency lagoon monitoring to avoid errors in status assessment and resulting management plans. 4 Based on the results, a continuous monitoring system is proposed that would record high frequency biotic and abiotic data in the lagoons. The use of such an ad hoc observatory system, based on appropriate diagnostic indicators and risk estimators would simplify interactions between scientists and managers and would improve the efficiency of their analyses. 5 A lagoon management plan based on a holistic approach is proposed to help scientists and local managers to reach a consensus about the set of ecological indicators to monitor in the lagoons needed to assess their 'global health' status in accordance with both conservation and/or societal needs.

Guest Edited by Emmanuel Torquebiau and Russell D. Taylor".; International audience; Isolated trees have distinctive economic, social and cultural value for the Betsileo people living on the edge of the protected forest corridor between Ranomafana and Andringitra national parks, in South-East Madagascar. Many of these trees are Ficus spp., traditionally protected and respected. At the landscape level, they are isolated features in a heterogeneous mosaic, providing fruit, shade and aesthetic services in open cultivated areas. Within the current management system, isolated trees may also contribute significantly to the provision of ecological services by enhancing bird diversity in open areas outside the forest. We identified practices and values linked to isolated tree uses and management through ethnographic data collection. Bird presence and abundance were sampled by 338 point counts in isolated trees and open areas of the agricultural mosaic. Isolated trees were occupied by 18 out of 32 (56%) bird species in the agricultural mosaic, including 8 (25%) endemic forest species. Endemic forest birds were significantly more numerous in isolated trees than in open habitats, both in species richness and abundance (mean P value < 0.001). Overall bird species richness was significantly higher in open areas containing isolated trees, than in areas without isolated trees. Bird species richness in Ficus spp. was significantly higher than in other isolated tree species, although no differences were detected in abundance or within guilds. Community-based management of isolated trees may thus represent an opportunity for convergence between bird conservation goals outside protected areas and local management values and practices.

English Models are used as tools for studying sustainable development. They are a priori neutral, but this neutrality can be upset if the analysis of observations done to answer questions in reference to a given a priori definition of sustainability leads to the identification of sustainability contexts that do not correspond to the initial definition. The practice of actors may for example involve substitution between elements of a natural capital, which may not be in agreement with a strong definition of sustainability. Therefore we may have to consider the need for transition from a prescriptive to a descriptive approach. The context of modelling depends on the object we want to be preserved (what we observe). If this object is a resource-exploitation system, the perception of sustainability comes from observation of the system. The observation process may have been initiated by a mono-disciplinary question, but, sustainability being dependent on an object which must be described, no unique definition can be proposed. The definition and perception of sustainability are themselves processes to which modelling sciences may have to contribute. French Des modèles sont utilisés comme outils dans le contexte des études sur le développement durable. Ils sont a priori neutres, mais cette neutralité peut être mise à mal si des analyses d'observations réalisées pour répondre à des questions posées en référence à une définition donnée de durabilité conduisent à identifier des contextes de durabilité qui ne correspondent pas nécessairement à la définition initialement adoptée. La pratique d'acteurs peut ainsi par exemple reposer sur des substitutions entre éléments d'un capital naturel, ce qui peut ne pas correspondre à une définition très forte de la durabilité. Dans ces conditions on peut discuter du passage d'une approche prescriptive à une approche descriptive. La question du choix d'un contexte de modélisation dépend de l'objet que l'on veut préserver (ce que l'on observe). S'il s'agit d'un système d'exploitation d'une ressource, la perception de la durabilité découle de l'observation du système. Le processus d'observation a pu être initié selon une définition a priori associée à un questionnement souvent "mono-disciplinaire", mais la durabilité étant inféodée à un objet qu'il faut représenter, on ne peut en proposer une définition unique. La définition et la perception de la durabilité sont des processus auxquels les sciences de modélisation peuvent être amenées à contribuer

International audience

A parameter of a model becomes a decision support indicator if it is used as an argument of a decision function. This implies consideration of a wider model than the initial one and to acknowledge its complexity. It is also necessary to include the estimation of parameters in indication theory and to consider a data driven approach. Data analysis leads us to provide sets of indicators. With reference to the statistical concept of sufficiency (Fisher 1925), such a set may also be considered as a set for indication, equivalent to the original data for any subsequent purpose of indication. From the same data set, several models may be built providing different sets for indication. None of them can be considered as the best; this depends both on the context (e.g. fishing practices) and on the addressed questions. No model must be chosen to the exclusion of alternatives: an illustration is given with models in relation to a catch-effort data set, with a case study on Senegalese small scale fisheries. dans une approche guidee par les donnees. Un parametre d'un modele devient un indicateur d'aide a la decision lorsqu'il est utilise comme argument d'une fonction de decision. Cela implique de le considerer au sein d'un modele plus large que le precedent et de reconnaitre la complexite du systeme etudie. Il est egalement necessaire d'inclure l'estimation dans la theorie de l'indication et de considerer une approche fondee sur les donnees. L'analyse des donnees conduit a produire des jeux d'indicateurs. En reference au concept statistique d'exhaustivite (Fisher 1925), un tel jeu peut egalement etre vu comme « jeu indicateur » equivalent aux donnees initiales pour toute production ulterieure d'indication. A partir d'un meme jeu de donnees, plusieurs modeles peuvent etre construits conduisant a des jeux indicateurs differents. Il n'est pas possible de dire quel serait le meilleur ; cela depend a la fois du contexte (nature des pratiques de peche en particulier) et des questions auxquelles on cherche a repondre. Le danger est de privilegier un modele a l'exlusion des autres. Avec un cas d'etude relatif a la peche artisanale au Senegal, cette discussion est illustree par des modeles associes a des donnees de capture et d'effort.

Ce texte decrit une experience singuliere de partenariat avec mon collegue Alassane Samba de l’Institut senegalais de recherches agricoles (Isra), sans donc pretendre, a priori, lui donner une valeur generale. Mais bien sur, cette experience n’a pu se derouler que grâce au contexte « favorable » plus large de partenariat avec l’affectation de chercheurs au sein d’un centre de recherches senegalais – le centre de recherches oceanographiques de Dakar Thiaroye (CRODT) – ou collaboraient des chercheurs senegalais de l’Isra et des chercheurs d’autres pays, pour la plupart francais affectes par l’Orstom. Cette diversite s’accompagnait d’une pluralite disciplinaire impliquant une diversite des points de vue a partir desquels un objet completement a-disciplinaire, la peche artisanale senegalaise, pouvait etre defini et observe. Il etait ainsi possible de parler de la peche artisanale avec des biologistes, des sociologues, des economistes, des geographes et des ecologues... Et nous ne parlions pas de la meme chose1.

Scientific programmes whose objectives are to provide pertinent knowledge and information for sustainable use of a natural resource always include data collection operations. Functions of the data collected are obtained from surveys. These functions (estimators) are formulae constructed according to the survey’s model defined by the design of the survey and the sample selection procedures. In complex designs, a ‘superpopulation model’ is always present. This model, accounting for available knowledge on the observed system, is defined by assumptions on the distribution of the collected data. Users consider not only the quality of the estimates (outputs of the survey) but also, and possibly primarily, the quality of these estimates as input (information) to their own decision frameworks, which also constitute a superpopulation model. Hence, a survey combines at least two models; a survey model and a user’s model. These different models are discussed in this paper with the help of three examples that differ in the types of system under study, in the objectives of the surveys, and in the nature of the collected information. Specific functions of the collected survey data may be considered as estimators when considered as output of the survey model and as indicators when considered as input to the user’s model. A user may build indicators from many sources of information and, as several different users may use the estimates, a survey is an element of an information system. Analysis of data leads to improved knowledge of the system under study and to the better identification of the various associated models. Therefore, surveys are elements of dynamic systems in which theory and practice are complementary. Although classical sampling theory often appears not to be sufficient in this global context, it remains necessary. The use of information from different sources to be used from different points of view implies an increased level of rigour with many models, all of which must be explicitly defined.

Fisheries exploitation systems are characterized by reciprocal interactions between fisheries activity and the harvested resource. Variability and changes affecting ‘natural’ and ‘socio-economic’ environments generate non stationarity of the variables used to describe the fishing activity, the resource and the yields. This characteristic needs to be taken into account in describing the evolution of the relationships between those variables, and in describing fisheries adaptability and sustainability. We present a dynamical system model with an application to data from surveys on activity and results of the Senegalese artisanal fishery from 1974 to 1992. A fitting procedure is proposed, giving estimates of the parameters of the model. A simulation is then made with the fitted model in order to apraise possible impacts of various events of different kind.

Even when fishing effort data are not available in a developing fishery, it is often still possible to develop a simple fishery indicator to obtain information about the status of the stock. Using catch data only, Grainger and Garcia , (FAO Fish. Tech. Pap. 359, 1996) showed that the changes over time in the relative rate of catch increase (RRCI) can be used to detect when a stock reaches its over-fishing level, i.e., the year when RRCI falls to zero. The method presupposes that fishing effort increased steadily over the period concerned. We propose a generalization of this method that consists in obtaining a crude estimate of the maximum sustainable yield (MSY) by plotting the trend in catches against the smoothed RRCI. The yellowfin tuna (Thunnus albacares) fishery in the Eastern Atlantic was used to show the strong relationship between MSY estimates obtained from standard equilibrium production models and from this method. Given that it is very difficult to estimate effective fishing effort for skipjack tuna (Katsuwonus pelamis), we show how this simple fishery indicator can be used to obtain proxies of MSY for skipjack fisheries located in the Eastern Atlantic Ocean and in the Indian Ocean.

Les programmes interdisciplinaires font systématiquement référence à une problématique thématique et à une confrontation avec la réalité. Un objet commun est construit en confrontant et articulant des points de vue disciplinaires. L'importance de la modélisation est généralement reconnue, apportant des outils nécessaires à la construction de cet objet commun. A la lumière du concept statistique d'exhaustivité, nous discutons de la nature synthétique des réponses aux questions posées. La mise en oeuvre de l'outil peut conduire, de façon légitime dans un contexte interdisciplinaire, à montrer le besoin de reformuler le questionnement général et à participer à la reformulation de l'objet commun. A partir d'un exemple, la description d'une exploitation halieutique, il s'avère que certaines questions sont "orphelines", parce que non reconnaissables à partir de chacun des points de vue disciplinaires initiaux. Ces questions peuvent s'imposer lorsqu'elles sont liées à la problématique thématique du programme. Leur adoption marque alors l'une des étapes de la problématique progressive générale du programme. L'objet commun n'a de sens que s'il coexiste avec les objets disciplinaires explicites. Donner à la présentation de ces objets l'importance qui leur revient, peut être de nature à permettre une meilleure identification du statut de la modélisation dans une démarche interdisciplinaire. (Résumé d'auteur)

In multifleet–multispecies fisheries exploitation, fishing units of some fleets may choose between different fishing tactics targeting different species combinations. Such fishing units may be very important for different reasons, and must be accounted for in global frameworks. Such a framework was built in order to qualitatively represent the main features of the Senegalese artisanal fishery. Simulations may be carried out with output comparable to available data, so that the parameters of the model may be estimated using a least squares criterion. One of the sources of uncertainty comes from a lack of knowledge of both the real dynamics of the fishing strategies and the dynamics of the harvested populations. We show, with a simple simulated fishery, that very different models may fit classical catch effort data, and that the assumptions made on the `biological' and on the `socio-economical' aspects of the fishery are very closely linked. We also show some of the consequences of the choice of a model in terms of prediction of results for economical and biological aspects.

Principal Component Analysis with respect to Instrumental Variables (PCAIV) is a statistical tool for exploratory analysis combining both principal component analysis and multivariate regression analysis. This tool is used to analyse mean fortnightly catches obtained by Senegalese fishermen in two ports from 1975 to 1991. The aim of the study is to identify significant sources of variation and to present separately the impact of each of them. These descriptions are used to characterize the initial data.

A l’issue d’etudes universitaires hybrides, combinant statistique mathematique et genetique, je me suis retrouve « mathematicien – informaticien en oceanographie » a l’Orstom (actuel IRD, Institut de recherche pour le developpement). Il m’a alors fallu du temps pour me forger une identite disciplinaire, et Jean-Marie Legay a eu une influence determinante dans cette construction1. En effet, le travail au sein d’un centre de recherche oceanographique auSenegalm’a conduit aparticiper aux etudes sur la peche artisanale senegalaise, objet qu’aucune discipline scientifique ne peut s’approprier sans faire d’hypotheses – en general implicites, et souvent meme inconscientes – dans le champd’autres disciplines. Le statisticien se voit demander de traiter des donnees pour en produire des syntheses (des statistiques) en reference a des questions posees par d’autres, et au service desquelles il accepte de se mettre. Une meme synthese peut alors contribuer aux reponses a plusieurs questions possibles, et il peut y avoir des contradictions entre les points de vue a partir desquels ces questions sont posees. Ainsi, une evolution de rendements de peche peut s’interpreter d’au moins deux points de vue differents, comme une evolution de l’abondance de la ressource exploitee ou bien comme une evolution des choix d’especes cibles faits par les pecheurs. Le statisticien se trouve au centre de ces contradictions, dans une situation qui va bien au-dela de celle qu’impliquerait la simple acceptation de faire de la statistique appliquee. Lorsque plusieurs interpretations sont possibles, le choix d’une d’entre elles revient a adopter un point de vue particulier et implique une part d’arbitraire. L’existence de ce choix est liee a la complexite de l’objet observe. Et c’est la que l’apport de Jean-Marie Legay est precieux. Il qualifie de complexe « un systeme que la

In Madagascar, despite acute land use pressure on forests coupled with unprecedented loss of endemic species and natural habitats, data on species distributions outside natural habitats are strikingly scarce. In this study, this gap is addressed by measuring bird diversity both within a protected forest corridor, and in the agricultural mosaic surrounding it. Results show that the diversity of all birds, and also of several functional guilds was higher in the mosaic than in the corridor. Moreover, 69% of all species found in the forest (61% of those classified as forest species) also occupied the agricultural mosaic. The diversity of frugivores, canopy insectivores and forest species in the mosaic was highly dependent upon the variety of scattered trees, small forest patches, plantations and secondary habitats distributed throughout the landscape. Generalist frugivores were particularly abundant in the mosaic, implying high potential for the maintenance of seed dispersal and fallow regeneration ecosystem services. Forest species in the mosaic were more generalist and less abundant, however, than those in the forest, suggesting the presence of both source–sink dynamics and potential biotic homogenization of the community in this landscape. Although under current conditions of heterogeneity and composition, the agricultural mosaic harbors a significant proportion of the endemic bird community, this study confirms the need for both sustained protection of large forest areas, and for adequate management of the agricultural landscape, particularly through the maintenance and enhancement of old-growth and isolated tree structures and fragments.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASAREViewpoint article; We, members of the Association Francaise d'Halieumetrie, share the conviction that European fisheries have a future. It is time to get off the wrong track. Radical change is required to embark on the path of sustainable development and truly implement the ecosystem approach to fisheries. Today, high fishing pressure is deployed to catch a rare resource, which in return is responsible for the rarity. We must reverse the situation: an abundant resource that affords high catches applying moderate fishing pressure. All management tools and especially all actors must be mobilized. The transition is not simple, and European solidarity must accompany the changes. It is well worth the effort. By reducing fishing pressure, it will be possible in the medium term to restore fish stocks, to make ecosystems return to good ecological status, to stabilize and even increase catches and to considerably improve economic efficiency. This is obviously in the interest of fishers but it is also in the interest of future generations and all users of this common heritage that is the sea. (C) 2011 Elsevier B.V. All rights reserved.

Detection patterns of coral reef fish were assessed from the meta-analysis of distance sampling surveys performed by visual census in New Caledonia and French Polynesia, from 1986 to 1999. From approximately 100,000 observations relating to 593 species, the frequency distributions of fish detection distances perpendicular to the transect line were compared according to species characteristics and sampling conditions. The shape and extension of these detection profiles varied markedly with fish size, shyness, and crypticity, indicating strong differences of detectability across species. Detection of very small and cryptic fish decreased strongly 1 m away from the line. Conversely, sightings of shy and large species were excessively low in the first meters due to diver avoidance prior to detection. The larger the fish, the greater the fleeing distance. Distance data underscore how inconsistent detectability biases across species and sites can affect the accuracy of visual censuses when assessing coral reef fish populations.

The article evaluates the impact of EU fishing activities for the sustainable development of Senegal's maritime fishery. An evaluation of Senegalese fisheries’ policy discourse introduces the idea that Senegalese fisheries’ policies have not been fully compatible with the sustainable development of the country's fishery sector. A comparative analysis of the sustainable development impacts associated with the activities of different fishery user groups shows that managed activities of heterogeneous user groups can benefit the sustainable development of the sector. Conclusions suggest that the heterogeneity of the user groups frequenting Senegal's marine fishery system can be capitalised upon through allocating fishery access in accord with each group's ability to generate sustainable development benefits. On the basis of these findings the article suggests that the presence of an EU fleet in Senegalese waters could play a meaningful role in ensuring the sustainable development of Senegal's marine fishery.

International audience; Les tactiques et stratégies de pêche déployées par les chalutiers côtiers au Sénégal sont étudiées à partir des compositions spécifiques des captures obtenues lors de marées réalisées entre 1990 et 2001. Les types des marées (tactiques de pêche) sont définis à partir de la composition des captures selon quatorze stocks et les types d'unités de pêche (stratégies) sont définis à partir des listes de tactiques qu'elles peuvent mettre en oeuvre. Les deux typologies sont construites à partir de la méthode des K MEANS, méthode de classification non hiérarchique. Douze tactiques et six stratégies de pêche sont d'abord identifiées. À partir de connaissances d'experts, des regroupements ont été faits et huit tactiques et cinq stratégies de pêche sont retenues et présentées avec les articulations entre stocks, tactiques et stratégies

Around Niamey, in Niger, the shrub Guiera senegalensisdominates all of the fallows in almost totally monospecific stands. The species has a strong resprouting ability enabling it to survive cutting when clearing land for crops, whereas all other species succumb to cutting. However, in this dry environment (560 mm of annual rainfall from June through September), this remnant-increaser species has to cope with variations of available water in space and time. The daily course of its water status is an indicator of the variation of the intensity of water flux between the soil, vegetation and atmosphere, and it is often estimated with Soil Vegetation Atmosphere Transfer (SVAT) models. We assessed the water status of G. senegalensis through its daily cycle leaf water potential ( Ψ ), using six populations representative of the local diversity by measuring three shrubs per population on two excised leaves per shrub for each measurement. We made our measurements over two vegetative cycles (from July 1994 to December 1995), fortnightly during the rainy season, and once a month during the dry season, until the sample shrubs lost their leaves in their deciduous cycle. We used linear models to characterize the daily Ψ cycle of the shrubs, and of the populations during each season. For each population, three sources of variation were considered: the shrub number, the date and the hour in day. Date and hour in day effects are presented as trend surface models defined by the degrees of polynomials and the status of shrub effects. The status of shrub effects characterizes the variability in accounting for environmental conditions. The group of plant populations that explain the least variability in every model as well as the least total variance among the shrubs and between seasons were in locations with the best water supply. Two other groups were defined according to the median and the highest explained variability of Ψ , respectively. For all stations, the most temporal variability is explained by models accounting for the interaction between shrubs and the temporal variation, with the least variability for models that do not account for the shrub effect at all. Models accounting only for the additive effect of shrubs explain intermediate values. The models used herein indicate the large range of variability in G. senegalensis water status, both for inter- and intra-populations. This high physiological plasticity must contribute to the strong species-dominance stability in its current distribution area. © 2003 Elsevier B.V. All rights reserved.

La coviabilité est présentée comme un modèle conceptuel des systèmes halieutiques visant à la définition d'une gestion pertinente des pêcheries marines. Après un aperçu du contexte de crise dans lequel évoluent l'exploitation des ressources marines et les recherches scientifiques dans ce domaine, l'histoire récente de la pêcherie d'anchois du Pérou est présentée comme une illustration de l'imbrication complexe dans le temps des systèmes politique, écologique et économique. Nous présentons alors différents résultats de modélisation sur les interfaces environnement-ressources, ressources-exploitations et leurs dynamiques. Un exemple illustre les problèmes d'échelle (globale et locale) liés à cette thématique. Les modèles de gestion actuels et les principales alternatives sont enfin présentés. Au délà d'un concept commun, l'approche en terme de coviabilité cherche à établir quelles articulations permettraient un enrichissement mutuel de différentes connaissances et perceptions. Elle pourrait par exemple contribuer à concilier les visions conservatrice et productiviste qui s'affrontent actuellement dans le domaine marin. (Résumé d'auteur)

La reflexion sur la modelisation comme outil d’accompagnement proposee par le collectif ComMod, dans la revue Natures Sciences Societes (2005, 13, 2, 165-168) est relative a un sujet passionnant pour des raisons a la fois pratiques et theoriques. Les questions deontologiques soulevees par le recours a la modelisation dans les recherches interdisciplinaires finalisees sont essentielles et la reflexion proposee est de ce point de vue tres utile. Comme statisticien implique dans des programmes de recherche presentant nombre des caracteristiques de ceux qui sont a la base de cette reflexion – et donc comme acteur de « modelisation d’accompagnement » –, je me suis evidemment senti tres concerne par cette demarche. Et ce, d’autant plus que je partage tres largement le souci d’accorder une place centrale aux « questions de terrain », qui est au cœur de la demarche proposee a la reflexion. Cependant, l’ensemble du texte m’a laisse perplexe, car certains des choix sur lesquels il repose me posent question. C’est tout d’abord celui de sa forme : pourquoi se doter d’une « doctrine », aussi « refutable » soit-elle, et pourquoi la presenter dans le cadre d’une « charte » ? C’est ensuite le statut central – et apparemment exclusif – donne a la modelisation pour caracteriser la posture d’un groupe multidisciplinaire. C’est egalement la selection, au sein de la modelisation, de demarches et d’outils particuliers. C’est enfin la definition a priori de limites aux questions auxquelles il est envisage de pouvoir repondre. La posture decrite en introduction s’appuie sur l’idee que les recherches « impliquees » associent des questions theoriques et des questions « de terrain » bien distinctes les unes des autres. Cela conduit a afficher un certain nombre d’objectifs avec lesquels on ne peut guere, en premiere analyse, etre en desaccord. Il est en effet souhaitable de considerer que « toutes les idees a la base de la modelisation ont comme vocation d’etre remises en cause

Nous discutons, à l'aide d'exemples, certains aspects des modèles globaux de dynamique des populations marines exploitées. La précision de certaines estimations de paramètres apparaît bonne, mais une très forte asymétrie des intervalles de confiance et un impact important du choix d'une formulation de données sur les estimateurs peuvent rendre illusoire cette impression. Les modèles sont souvent formés à partir de considérations biologiques, mais il peut être dangereux de donner une valeur biologique aux (estimations des) paramètres. La standardisation des efforts de pêche ne conduit pas nécessairement à des estimations utiles dans le domaine de l'aménagement, et la pêche peut d'elle-même rendre inacessible tout état d'équilibre. Dans le domaine de l'analyse des pêcheries, selon des cadres généraux de représentation dont l'évaluation de la ressource ne constitue pas le seul objectif, les modèles globaux peuvent cependant s'avérer être des outils très souples et peu exigeants en nombres de paramètres. (Résumé d'auteur)

It is generally assumed, when using a surplus production model, that production of biomass is described as a function of exploited biomass. If a constant quantity of biomass is unaccessible, this assumption may be false. We propose here two formulations of production models assuming the existence of a quantity of unaccessible biomass. When this quantity change during the history of a fishery, such models may be useful. Using environmental data in Ivory Coast, this approach describes the fishery of Sardinella aurita in Ivory Coast and Ghana from 1966 to 1980. nie suggested adjustements are effective but they do not allow us to choose between the two formulations, each of them leading to different conclusions for stock management.

With special reference to tunas and using recent results obtained on the skipjack tuna #Katsuwonus pelamis$, the author point out that Gonad Index (GI, defined as the ratio between the weight of the gonads and the size of the fish to the cube) is an inaccurate indicator of each of the different sexual maturity stages commonly used to describe the sexual maturation process of marine fishes. They also show that it would be of interest to determine a GI critical value in order to distinguish females in an advanced stage of maturation from the others. Using diameter measurements of skipjack tuna oocytes they adjust a non linear model between GI and the diameter of the most advanced group of oocytes. This permits the estimation of a GI critical value. This critical value is discussed. (Résumé d'auteur)

L'ouvrage résulte de sessions de l'AME, Atelier modélisation environnement tenues entre 2003 et 2005 dont la liste et les intitulés sont présentés en appendice; National audience

L'ouvrage résulte de sessions de l'AME, Atelier modélisation environnement tenues entre 2003 et 2005 dont la liste et les intitulés sont présentés en appendice; National audience

L'ouvrage résulte de sessions de l'AME, Atelier modélisation environnement tenues entre 2003 et 2005 dont la liste et les intitulés sont présentés en appendice; National audience

Prologue de Marcel Jollivet ; L'ouvrage résulte de sessions de l'AME, Atelier modélisation environnement tenues entre 2003 et 2005 dont la liste et les intitulés sont présentés en appendice.; National audience

Colloque international: "Modélisations à l'interface entre Natures et Sociétés" de l'association Natures, Sciences, Sociétés, organisé par Dominique Hervé, IRD, Université de Montpellier, 7-9 décembre 2005.A paraître dans NSS ou dans la collection "Indisciplines" (EDP Sciences); Comment les modèles, la modélisation et la simulation ont modifié les rapports entre sciences et philosophies, et comment ils engagent un nouvel usage des distinctions épistémologiques construites au XXème siècle.

Prologue, Marcel Jollivet ; L'ouvrage résulte de sessions de l'AME, Atelier modélisation environnement tenues entre 2003 et 2005 dont la liste et les intitulés sont présentés en appendice de l'ouvrage; National audience

The biology of European hake has been largely studied, however some specific processes of its biology, especially growth and migration, are still poorly known. Those uncertainties have consequences on the quality of the stock assessments and on the stock management by limiting the possibility to assess the effect of spatial management measures. Therefore, we develop an integrated length-structured and spatialised model of population dynamics aiming at improving the estimation of unknown parameters of the population dynamic. The model relies on a state model describing the dynamics of the population and the fishing activity, and on an observation model describing the observation processes and providing a likelihood function. A review of the literature shows that modelling growth is a key point in length-structured model. Consequently, we develop a method to assess the impact of several assumptions of time and length discretisation and growth increments distribution in a length-structured population growth model. The method relies (i) on the construction of a design of experiments and (ii) on its analysis using linear models and multivariate regression trees. This generic approach is useful to assess the impact of any discretisation processes in a discret model. In our case, it shows that a quartertly time step, 1cm wide length classes and a gamma distribution of growth increments are appropriate for the Northern stock of hake. A specific attention to the likelihood function has been necessary during the development of the model to provide a robust function and to be consistent with the observation processes. A quasi-Newton algorithm has been selected among several optimisation algorithms to maximize the likelihood function. Estimations of migration and growth rates are obtained by fitting the model to available data. Migration rates are consistent with previous analysis while estimated growth rates are slightly lower than estimates obtained from tagging data. The diagnostic on the spawning stock biomass provided by the model is quite close to current diagnostics obtained from other assessments conducted by ICES. Some parameters of the model are still not identifiable. This, however, does not concerned parameters of interest., Bien que le merlu de l'Atlantique Nord-Est ait été largement étudié, certaines caractéristiques de sa biologie sont encore assez mal connues. C'est en particulier le cas de ses migrations saisonnières et de sa croissance, dont une campagne récente de marquage montre qu'elle était probablement largement sous-estimée. Ces incertitudes ont plusieurs conséquences tant sur la qualité des diagnostics établis à l'aide des modèles de dynamique des populations usuels, que sur la gestion en limitant notamment les possibilités d'évaluation de mesures de gestions spatialisées. Pour améliorer l'estimation des paramètres de ces processus, nous avons développé un modèle de dynamique de population intégré spatialisé et structuré en longueur reposant sur un modèle d'états décrivant la dynamique de la population et de l'activité de pêche, et sur un modèle décrivant les processus d'observation, permettant l'écriture d'une fonction de vraisemblance. Une revue bibliographique des modèles structurés en longueur existants a mis en évidence le rôle clé de la modélisation du processus de croissance dans ce type de modèles. Pour s'assurer de la robustesse des hypothèses du modèle liées à la discrétisation de ce processus continu et à la variabilité individuelle de croissance, nous avons réalisé une analyse de sensibilité du modèle de croissance. Cette méthode d'exploration numérique du modèle repose sur (i) le développement de plans d'expériences et (ii) l'ajustement de modèles statistiques aux sorties du modèle pour quantifier l'impact de ces hypothèses. Cette démarche générique est transposable à toute analyse de sensibilité d'un modèle discret décrivant un processus continu. Dans notre cas, elle a permis de mettre en évidence que pour le merlu de l'Atlantique Nord-Est il était préférable de choisir un pas de temps trimestriel, des classes de 1 cm, une distribution gamma des incréments de croissance et une distribution uniforme des individus au sein des classes. Au cours du développement du modèle, une attention particulière a été portée à l'écriture de la fonction de vraisemblance afin qu'elle soit robuste et cohérente avec les processus d'observation. Différents algorithmes ont également été testés pour réaliser l'optimisation numérique de cette fonction, le choix se portant finalement vers un algorithme de type quasi-Newton. L'ajustement du modèle de dynamique de population aux observations disponibles a permis l'estimation des taux de migration et du taux de croissance, plus faible que celui estimé à partir des données de marquage. Il a permis également d'établir un diagnostic en terme d'évolution de la biomasse féconde cohérent avec les diagnostics préalablement établis à l'aide du modèle actuel d'évaluation. Cependant, du fait de sa complexité et très certainement de la mauvaise qualité de certaines observations, l'ajustement du modèle est difficile. Le modèle souffre de certains problèmes d'identifiabilité même si les paramètres de migration et de croissance ne semblent pas concernés.