|
|
|
| Registros recuperados: 47 | |
|
|
| Reecht, Yves; Gasche, Loïc; Lehuta, Sigrid; Vaz, Sandrine; Smith, Robert J; Mahevas, Stephanie; Marchal, Paul. |
| In the past decade, systematic conservation planning tools have been increasingly and successfully used to set spatial conservation plans that meet quantitative protection targets while minimizing enforcement and socioeconomic costs. However, when applied to fisheries, systematic conservation planning fails to account for (1) changes in fleet dynamics induced by new conservation constraints and their associated feedbacks on conservation costs or (2) their influence on fish population dynamics and distributions, which may in turn alter the achievement of conservation targets. Such a static approach may therefore lead to short- or medium-term misestimates in forecasted costs and target achievements. In order to circumvent such limitations of systematic... |
| Tipo: Text |
Palavras-chave: MPAs; Systematic conservation planning; Mixed fisheries dynamics; Model coupling; Eastern English Channel; Marxan with Zones; ISIS-Fish. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00293/40421/39077.pdf |
| |
|
| |
|
|
| Mahevas, Stephanie; Pelletier, Dominique. |
| Assessing the impact of management scenarii on multi-species multi-fleet fisheries requires spatially and seasonally explicit simulation tools. No such tools are currently available in fisheries science. This paper presents a software that evaluates the impact of management measures on the dynamics of a complex fishery. The simulation model is generic in order to be used for different types of fisheries. Existing knowledge about each fishery is stored in a database included in the software, and may be easily modified. This includes the parameters describing each population and each fishing activity. Furthermore, the software allows for flexibility in several model assumptions. Both management measures and behaviour of fishermen in reaction to these... |
| Tipo: Text |
Palavras-chave: Management measures; Fisheries dynamics; Complex systems; Spatial; Integration of knowledge; Simulation tool. |
| Ano: 2004 |
URL: http://archimer.ifremer.fr/doc/2004/publication-1133.pdf |
| |
|
|
| Vigneau, Joel; Mahevas, Stephanie. |
| Measuring fish on board fishing vessels or at fish markets to collect data for stock assessment purposes is one of the most straightforward actions carried out by fisheries scientists worldwide. However, such samples are not straightforward to handle and analyse because of their vector-type structure. A generic tool that allows investigation in any multinomial-like sampling scheme is provided, as long as the scheme is built on a ratio estimator, which is the case for most length sampling in the fisheries sector. The use of this tool is discussed using data obtained from two different sampling designs, one consisting of commercial market samples by category and the other on fishing activity or metier. The identification of outliers, misallocated samples, or... |
| Tipo: Text |
Palavras-chave: Stratification; Sampling design; Market sampling; Length structure. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2731.pdf |
| |
|
| |
|
|
| Lehuta, Sigrid; Petitgas, Pierre; Mahevas, Stephanie; Huret, Martin; Vermard, Youen; Uriarte, Andres; Record, Nicholas R.. |
| Assessing the validity of a model is essential for its credibility especially when the model is used as decision making tool. Complex dynamic fishery models are recommended to investigate the functioning of fisheries and to assess the impact of management strategies, particularly spatial fishing regulations. However, their use is limited due to the difficulty and computational cost of parameterizing and gaining confidence, particularly for parameter rich models. These difficulties are compounded by uncertainty regarding parameter values, many of which are often taken from literature or estimated indirectly. Here we propose a methodology to improve confidence and understanding in the model, easily transferable to any complex model. The approach combines... |
| Tipo: Text |
Palavras-chave: Bay of Biscay anchovy; Dynamic fishery model; Model selection; Uncertainty; Validation. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00148/25965/24150.pdf |
| |
|
|
| Vigneau, Joel; Mahevas, Stephanie. |
| Measuring fish on a market or on board a vessel is the most common action taken by biologists all around the world to gather data for stock assessment. The samples coming from this kind of survey are of vector type and are not straightforward to analyse and compare. This paper proposes a generic tool that enables to investigate in any multinomial like sampling scheme. The use of this tool will be discussed based on examples from two different sampling designs. One is a sampling of commercial market categories and the other is a métier based sampling. The research of outliers, misallocated samples or potential bias, the stratification and the analysis of within and between strata variance will be discussed with the objective of constructing the best... |
| Tipo: Text |
Palavras-chave: Stratification; Sampling design; Length structure; Market sampling. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/acte-2698.pdf |
| |
|
|
| Marchal, Paul; Gasche, Loic; Girardin, Raphael; Le Pape, Olivier; Huret, Martin; Mahevas, Stephanie; Travers-trolet, Morgane; Vaz, Sandrine. |
| Considerable research has been conducted in the past 15 years around the Eastern English Channel ecosystem. Data collected since the 1970s on the biotic and abiotic compartments have been collated and mapped out in the mid-2000. This spatially explicit information formed a sound basis to improve knowledge on, and model, the functioning and dynamics of key ecosystem compartments, with a focus on flatfish species and fisheries and their interactions with other sectors of activity (aggregate extractions, maritime traffic). The more recent ongoing works are dedicated to the integration of those processes into several complementary end-to-end ecosystem models. |
| Tipo: Text |
Palavras-chave: Eastern English Channel; Flatfish; Spatial analyses; Ecosystem modelling. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00293/40420/38946.pdf |
| |
|
|
| Vermard, Youen; Rivot, Etienne; Mahevas, Stephanie; Marchal, Paul; Gascuel, Didier. |
| Recent advances in technologies have lead to a vast influx of data on movements, based on discrete recorded position of animals or fishing boats, opening new horizons for future analyses. However, most of the potential interest of tracking data depends on the ability to develop suitable modelling strategies to analyze trajectories from discrete recorded positions. A serious modelling challenge is to infer the evolution of the true position and the associated spatio-temporal distribution of behavioural states using discrete, error-prone and incomplete observations. In this paper, a Bayesian Hierarchical Model (HBM) using Hidden Markov Process (HMP) is proposed as a template for analyzing fishing boats trajectories based on data available from... |
| Tipo: Text |
Palavras-chave: Bayesian Hierarchical Models; Hidden Markov Model; State-space model; VMS; Fleet behaviour; Fishing effort. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00009/11993/9342.pdf |
| |
|
|
| Lehuta, Sigrid; Mahevas, Stephanie; Le Floc'H, Pascal; Petitgas, Pierre. |
| Indicators are widely promoted as means to monitor ecosystem status or to evaluate fisheries management performance. "Which indicators are most relevant as decision-support tools in fisheries management?" still remains a topical question. Indicators should be metrics related to fish populations and fleets and should be sensitive to management strategies. However, given the complexity of the processes involved, it is often difficult to unequivocally interpret variations in metrics. A simulation approach was used to study metric properties and to identify robust and relevant fishery indicators. By applying sensitivity analysis methods, simulation designs were built that cross a variety of management scenarios and uncertainty hypotheses. Bio-economic outputs... |
| Tipo: Text |
|
| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00170/28093/26627.pdf |
| |
|
| |
|
|
| Marchal, Paul; Francis, Chris; Lallemand, Philippe; Lehuta, Sigrid; Mahevas, Stephanie; Stokes, Kevin; Vermard, Youen. |
| Managing adequately the exploitation of commercial species subject to technical interactions is a key step towards the ecosystem approach to fisheries. We evaluate here, using a bio-economic modelling approach building on the ISIS-Fish simulation platform, the relative impact of total allowable commercial catches (TACC) and of taxes applicable to over-quota landings (deemed value) on the sustainability of a selection of species exploited by the New Zealand hoki (Macruronus novaezelandiae) fishery. We investigate some aspects of the hoki mixed fisheries, consisting of four fleets and nineteen metiers, by considering the technical interactions between hoki and Southern hake (Merluccius australis). The dynamics of effort allocation were modelled using gravity... |
| Tipo: Text |
Palavras-chave: Fleet dynamics; New Zealand hoki fishery; Deemed value; Fisheries management. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00000/11168/7521.pdf |
| |
|
|
| Carrasco, Ja; Sune, V; Mahevas, Stephanie; Rubino, G. |
| The authors describe and solve a Markov model of the leaky bucket ATM generic now control mechanism. The model has a space cardinality which grows quickly with its parameters and is challenging to solve. Exploiting the cyclic nature of the model, the authors develop a methodology which allows them to efficiently solve instances of the model with 3 905 134 states and 53 869 532 transitions using 29.8Mbyte of memory and 222Mbyte of disc storage. The CPU utilisation is high (between 70% and 90%). The methodology is new and can be easily extended to any kind of finite cyclic Markov models. |
| Tipo: Text |
|
| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/00000/10303/9659.pdf |
| |
|
| |
|
|
| Mahevas, Stephanie; Vermard, Youen; Hutton, Trevor; Iriondo, Ane; Jadaud, Angelique; Maravelias, Christos D.; Punzon, Antonio; Sacchi, Jacques; Tidd, Alex; Tsitsika, Efthymia; Marchal, Paul; Goascoz, Nicolas; Mortreux, Serge; Roos, David. |
| The impact of the fishing effort exerted by a vessel on a population depends on catchability, which depends on population accessibility and fishing power. The work investigated whether the variation in fishing power could be the result of the technical characteristics of a vessel and/or its gear or whether it is a reflection of inter-vessel differences not accounted for by the technical attributes. These inter-vessel differences could be indicative of a skipper/crew experience effect. To improve understanding of the relationships, landings per unit effort (lpue) from logbooks and technical information on vessels and gears (collected during interviews) were used to identify variables that explained variations in fishing power. The analysis was undertaken by... |
| Tipo: Text |
Palavras-chave: Catchability; Fishing power; GAM; GLM; Skipper skill; Technical characteristics. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00049/16043/15172.pdf |
| |
|
|
| Marchal, Paul; Bartelings, Heleen; Bastardie, François; Batsleer, Jurgen; Delaney, Alyne; Girardin, Raphael; Gloaguen, Pierre; Hamon, Katell; Hoefnagel, Ellen; Jouanneau, Charlène; Mahevas, Stephanie; Nielsen, Rasmus; Piwowarczyk, Joanna; Poos, Jan-jaap; Schulze, Torsten; Rivot, Etienne; Simons, Sarah; Tidd, Alex; Vermard, Youen; Woillez, Mathieu. |
| The scope of this report is to present the science developed within the VECTORS project to improve the understanding of the key processes driving the behaviour of human agents utilising a variety of EU maritime domains. While particular attention has been paid to the spatial interactions between fishing activities and other human uses (e.g., maritime traffic, offshore wind parks, aggregate extractions), the behaviour of non-fishing sectors of activity has also been considered. Various quantitative and semi-qualitative approaches have been pursued to gain better insight into behavioural drivers based on past data, and also forecast how human agents would react if access was constrained by either management (e.g. Marine Protected Areas – MPA), or the... |
| Tipo: Text |
|
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00223/33377/31802.pdf |
| |
|
|
| Kraus, Gerd; Pelletier, Dominique; Dubreuil, Julien; Moellmann, Christian; Hinrichsen, Hans-harald; Bastardie, Francois; Vermard, Youen; Mahevas, Stephanie. |
| The eastern Baltic cod stock collapsed as a consequence of climate-driven adverse hydrographic conditions and over fishing and has remained at historically low levels. Spatio-temporal fishing closures [Marine Protected Areas (MPAs)] have been implemented since 1995, to protect and restore the spawning stock. However, no signs of recovery have been observed yet, either suggesting that MPAs are an inappropriate management measure or pointing towards suboptimal closure design. We used the spatially explicit fishery simulation model ISIS-Fish to evaluate proposed and implemented fishery closures, combining an age-structured population module with a multifleet exploitation module and a management module in a single model environment. The model is parameterized... |
| Tipo: Text |
Palavras-chave: Stock recovery; Model; Marine Protected Areas; Fishery management; Baltic cod. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6094.pdf |
| |
|
|
| Pardo, Sophie; Hess, Philipp; Simon, Elodie; Barille, Laurent; Geslin, Emmanuelle; Cognie, Bruno; Martin-jezequel, Véronique; Sechet, Véronique; Herrenknecht, Christine; Baron, Regis; Bourseau, Patrick; Amzil, Zouher; Masse, Anthony; Vandanjon, Laurent; Dumay, Justine; Lebeau, Thierry; Turpin, Vincent; Mondeguer, Florence; Petitgas, Pierre; Trouillet, Brice; Mercier, Denis; Guillotreau, Patrice; Guineberteau, Thierry; Mahevas, Stephanie; Schoefs, Franck; Sophie Pardo; Philipp Hess; Pauline Borgniet; Laurent Barillé; Emmanuelle Geslin; Bruno Cognie; Véronique Martin-Jezequel; Véronique Sechet; Christine Herrenknecht; Régis Baron; Patrick Bourseau; Zouher Amzil; Anthony Massé; Laurent Vandanjon; Justine Dumay; Thierry Lebeau; Vincent Turpin; Florence Mondeguer; Pierre Petitgas; Brice Trouillet. |
| COSELMAR, a 4-year project financed by the Région des Pays de la Loire at 2.1 M€, officially started on the 7th January 2013. The project is coordinated by Philipp Hess (IFREMER) and Sophie Pardo (Université de Nantes-LEMNA) and falls under the Federation for Research Institut Universitaire Mer et Littoral (IUML, FR CNRS 3473)*. COSELMAR has also been approved by the Scientific Council of the MSH Ange Guépin. COSELMAR is a research project uniting 5 research units of IFREMER and 11 laboratories of the Université de Nantes, along with academic partners, and national and international industries. The aim is to achieve a better understanding of the marine and coastal ecosystems and the associated resources. The project will also provide insights into risk... |
| Tipo: Text |
|
| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00406/51793/52550.pdf |
| |
|
|
| Mahevas, Stephanie. |
| Fisheries are defined by a set of fishermen and of marine populations impacting each other in a spatial-limited marine ecosystem. Within the over-exploitation context and according to ratified sustainable management objectives, my research has been focused on the development and a caution use of a mechanistic model describing fisheries dynamics. This model allows for integrating existing knowledge of fisheries. It aims at improving the understanding of fisheries functioning and at investigating the impact of fishing regulations on fisheries dynamics. This modelling exercise has supported many methodological developments for its parametrisation and its use in uncertainty context. Concerned with promoting a correct use of a complex model (that ambiguity link... |
| Tipo: Text |
Palavras-chave: Statistics; Spatial; Management; Optimal complexity; Sensitivity; ISIS Fish; Statistiques; Spatial; Gestion; Complexité optimale; Sensibilité; ISIS Fish. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/these-7302.pdf |
| |
|
|
| Drouineau, Hilaire; Mahevas, Stephanie; Bertignac, Michel; Fertin, A. |
| Most of the traditional assessment models are age-structured. However, many biological and exploitation processes are more length-dependent than age-dependent, and the required length-age conversion of available data is often not reliable. Consequently, length-structured or age-length structured models have undergone considerable development in recent years. The growth transition matrix used to model the mean growth and growth variability of the population, is of primary importance in a length-structured matrix model. Building this growth transition matrix is not trivial and it is necessary to assess the impact that various assumptions may have to identify robust model structures. In this study, we assess the effects of (1) time and length discretisation,... |
| Tipo: Text |
Palavras-chave: Sensitivity analysis; Discrete model; Growth; Length structured model. |
| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-4301.pdf |
| |
| Registros recuperados: 47 | |
|
|
|
