A model-based evaluation of Marine Protected Areas: the example of eastern Baltic cod (Gadus morhua callarias L.) Auteur(s) : Kraus, Gerd Pelletier, Dominique Dubreuil, Julien Moellmann, Christian Hinrichsen, Hans-harald Bastardie, Francois Vermard, Youen Mahevas, Stephanie Éditeur(s) : Oxford university press Résumé : 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 based on (i) the large amount of biological knowledge available for cod and (ii) an analysis of existing spatially disaggregated fishery data. As the population dynamics of eastern Baltic cod depend strongly on the climate-driven hydrographic regime, we considered two production regimes of the stock. MPAs were only effective for stock recovery when they reduced overall fishing effort. The performance of MPAs needs to be evaluated relative to environmental regimes, especially for stocks facing strong environmental variability. ICES Journal of Marine Science (1054-3139) (Oxford university press), 2009 , Vol. 66 , N. 1 , P. 109-121 Droits : 2008 ICES/CIEM http://archimer.ifremer.fr/doc/2009/publication-6094.pdf DOI:10.1093/icesjms/fsn166 http://archimer.ifremer.fr/doc/00000/6094/ | Partager |
The influence of the environment on the variability of monthly tuna biomass around a moored, fish-aggregating device Auteur(s) : Doray, Mathieu Petitgas, Pierre Nelson, Laetitia Mahevas, Stephanie Josse, E Reynal, Lionel Éditeur(s) : Oxford university press Résumé : Fish-aggregating devices (FADs) are increasingly used worldwide to enhance tuna catches. Meanwhile, ecosystem-based management of this fishery is constrained by a paucity of information regarding the interaction of FAD-associated tuna aggregations with their local environment. This paper reports the results of a nine-month study around a FAD moored near Martinique Island, aimed at assessing the effects of the local environment on the variability of monthly estimates of proximate tuna biomass. Dual-frequency, active acoustics provided highresolution quantitative data on the pelagic community around the FAD, from fish to micronekton forage. Geostatistics were used to compute biomass estimates of the tuna aggregation comprising most of the FADassociated fish biomass, with a sampling error of 27%. Environmental variability was summarized by a small set of principal components (PCs) derived from profiles of temperature, salinity and dissolved oxygen vs. depth; and maps of chlorophyll a derived from remotely sensed, sea-surface colour. A generalized linear model was used to relate tuna biomass to environmental PCs and revealed a positive correlation between tuna abundance and: i) a micronekton layer sensed at 38 kHz and potentially consisting of preferred prey at about 180 m depth; and ii) low subsurface salinity (6080 m). These favourable environmental conditions may be related to thepresence of North Brazilian Current eddies that migrating tuna follow when not temporally associated with the FADs. ICES Journal of Marine Science (1054-3139) (Oxford university press), 2009-07 , Vol. 66 , N. 6 , P. 1410-1416 Droits : 2009 Oxford university press http://archimer.ifremer.fr/doc/2008/publication-6162.pdf DOI:10.1093/icesjms/fsp039 http://archimer.ifremer.fr/doc/00000/6162/ | Partager Voir aussi Lesser Antilles tuna environment geostatistics biomass estimation fish aggregating device Télécharger |
Identifying fishing trip behaviour and estimating fishing effort from VMS data using Bayesian Hidden Markov Models Auteur(s) : Vermard, Youen Rivot, Etienne Mahevas, Stephanie Marchal, Paul Gascuel, Didier Éditeur(s) : Elsevier Science Bv Résumé : 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 satellite-based vessel monitoring systems (VMS). The analysis seeks to enhance the definition of the fishing pressure exerted on fish stocks, by discriminating between the different behavioural states of a fishing trip, and also by quantifying the relative importance of each of these states during a fishing trip. The HBM approach is tested to analyse the behaviour of pelagic trawlers in the Bay of Biscay. A hidden Markov chain with a regular discrete time step is used to model transitions between successive behavioural states (e.g., fishing, steaming, stopping (at Port or at sea)) of each vessel. The parameters of the movement process (speed and turning angles) are defined conditionally upon the behavioural states. Bayesian methods are used to integrate the available data (typically VMS position recorded at discrete time) and to draw inferences on any unknown parameters of the model. The model is first tested on simulated data with different parameters structures. Results provide insights on the potential of HBM with HMP to analyze VMS data. They show that if VMS positions are recorded synchronously with the instants at which the process switch from one behavioural state to another, the estimation method provides unbiased and precise inferences on behavioural states and on associated movement parameters. However, if the observations are not gathered with a sufficiently high frequency, the performance of the estimation method could be drastically impacted when the discrete observations are not synchronous with the switching instants. The model is then applied to real pathways to estimate variables of interest such as the number of operations per trip, time and distance spent fishing or travelling. (C) 2010 Elsevier B.V. All rights reserved. Ecological Modelling (0304-3800) (Elsevier Science Bv), 2010-07 , Vol. 221 , N. 15 , P. 1757-1769 Droits : 2010 Elsevier B.V. All rights reserved. http://archimer.ifremer.fr/doc/00009/11993/9342.pdf DOI:10.1016/j.ecolmodel.2010.04.005 http://archimer.ifremer.fr/doc/00009/11993/ | Partager Voir aussi Bayesian Hierarchical Models Hidden Markov Model State-space model VMS Fleet behaviour Fishing effort Télécharger |
Spatially explicit fisheries simulation models for policy evaluation Auteur(s) : Pelletier, Dominique Mahevas, Stephanie Éditeur(s) : Blackwell science Résumé : This paper deals with the design of modelling tools suitable for investigating the consequences of alternative policies on the dynamics of resources and fisheries, such as the evaluation of marine protected areas (MPA). We first review the numerous models that have been developed for this purpose, and compare them from several standpoints: population modelling, exploitation modelling and management measure modelling. We then present a generic fisheries simulation model, Integration of Spatial Information for FISHeries simulation (ISIS-Fish). This spatially explicit model allows quantitative policy screening for fisheries with mixed-species harvests. It may be used to investigate the effects of combined management scenarios including a variety of policies: total allowable catch (TAC), licenses, gear restrictions, MPA, etc. Fisher's response to management may be accounted for by means of decision rules conditioned on population and exploitation parameters. An application to a simple example illustrates the relevance of this kind of tool for policy screening, particularly in the case of mixed fisheries. Finally, the reviewed models and ISIS-Fish are discussed and confronted in the light of the underlying assumptions and model objectives. In the light of this discussion, we identify desirable features for fisheries simulation models aimed at policy evaluation, and particularly MPA evaluation. Fish and Fisheries (1467-2960) (Blackwell science), 2005-12 , Vol. 6 , N. 4 , P. 307-349 Droits : 2005 Blackwell Publishing, Inc http://archimer.ifremer.fr/doc/2005/publication-1031.pdf DOI:10.1111/j.1467-2979.2005.00199.x http://archimer.ifremer.fr/doc/00000/1031/ | Partager |
Evaluation of the bioeconomic sustainability of multi-species multi-fleet fisheries under a wide range of policy options using ISIS-Fish Auteur(s) : Pelletier, Dominique Mahevas, Stephanie Drouineau, Hilaire Vermard, Youen Thebaud, Olivier Guyader, Olivier Poussind, Benjamin Éditeur(s) : Elsevier Résumé : In order to provide reliable scientific advice and support for fisheries management, it is necessary to evaluate the biological and economic sustainability of complex fisheries, such as multi-species multi-fleet fisheries. Existing policy-screening modelling tools are not fully suitable in this purpose due to either an over-simplified description of population dynamics, or due to the lack of consideration of economic aspects. In this paper, we present a package that enables quantitative bioeconomic assessment of management scenarios. Population dynamics is described through spatially- and seasonally-explicit models. Exploitation dynamics is characterized by several fishing activities with specific spatial and seasonal features, and practiced by several kinds of vessels with specific technical characteristics. Exploitation costs and revenues are considered at several levels: the fishing trip, the fishing unit (vessel and crew), and the vessel owner. The model is generic and can be used for different types of fisheries. A database is attached to the software for the storage and updating of information for each fishery. This includes the specification of model dimensions and of the parameters describing populations and exploitation. Several model assumptions regarding either population or exploitation may be adapted to suit a specific fishery. Both policies and corresponding fishers' response may be interactively specified through JAVA (TM) scripts. This version of ISIS-Fish allows for the calculation of biological and economic consequences of a range of policies, including conventional ones like catch and effort controls, and alternative policies such as marine protected areas. To facilitate policy-screening in a high-dimension parameter space, the software includes features, like interfaces for sensitivity analysis and simulation queues. (C) 2009 Elsevier B.V. All rights reserved. Ecological Modelling (0304-3800) (Elsevier), 2009-04 , Vol. 220 , N. 7 , P. 1013-1033 Droits : 2009 Elsevier B.V. All rights reserved. http://archimer.ifremer.fr/doc/2009/publication-6782.pdf DOI:10.1016/j.ecolmodel.2009.01.007 http://archimer.ifremer.fr/doc/00000/6782/ | Partager |
Combining sensitivity and uncertainty analysis to evaluate the impact of management measures with ISIS-Fish: marine protected areas for the Bay of Biscay anchovy (Engraulis encrasicolus) fishery Auteur(s) : Lehuta, Sigrid Mahevas, Stephanie Petitgas, Pierre Pelletier, Dominique Éditeur(s) : Oxford Univ Press Résumé : Spatio-seasonal explicit simulation models can predict the impact of spatial management measures on marine fish populations and fishing activities. As fisheries are complex systems, fisheries simulation models are often complex, with many uncertain parameters. Here, the methodology is provided to deliver fishery diagnostics within an uncertainty context using a complex simulation tool. A sensitivity analysis of the model is performed on model outputs using partial least-squares to identify the most sensitive parameters. The impact of several management measures is then simulated using a statistical simulation design taking into account the uncertainty of the selected sensitive parameters. This approach was applied to the Bay of Biscay anchovy stock using the ISIS-Fish (Integration of Spatial Information for Simulation of Fisheries) model to assess the impact of imposing marine protected areas (MPAs) conditionally on parameter uncertainty. The diagnostic appeared to be highly sensitive to the mortality of larvae and juveniles, growth, and reproduction. The uncertainty of the values of these parameters did not permit any of the simulated MPA designs to be proposed. However, according to anchovy catch and biomass, the simulations allowed the low impact of closure duration to be shown and underscored the utility of protecting such key processes as spawning. Ices Journal Of Marine Science (1054-3139) (Oxford Univ Press), 2010-07 , Vol. 67 , N. 5 , P. 1063-1075 Droits : 2010 ICES/CIEM. Oxford journals http://archimer.ifremer.fr/doc/00011/12234/9281.pdf DOI:10.1093/icesjms/fsq002 http://archimer.ifremer.fr/doc/00011/12234/ | Partager Voir aussi Bay of Biscay anchovy marine protected area sensitivity analysis simulation uncertainty analysis Télécharger |
An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets Auteur(s) : Mahevas, Stephanie Vermard, Youen Hutton, Trevor Iriondo, Ane Jadaud, Angelique Maravelias, Christos D. Punzon, Antonio Sacchi, Jacques Éditeur(s) : Oxford Univ Press Résumé : 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 applying a combination of generalized additive models and generalized linear models to data from several European fleets. The study highlights the fact that taking into account information that is not routinely collected, e. g. length of headline, weight of otter boards, or type of groundrope, will significantly improve the modelled relationships between lpue and the variables that measure relative fishing power. The magnitude of the skipper/crew experience effect was weaker than the technical effect of the vessel and/or its gear. Ices Journal Of Marine Science (1054-3139) (Oxford Univ Press), 2011-11 , Vol. 68 , N. 10 , P. 2252-2263 Droits : 2011 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved. http://archimer.ifremer.fr/doc/00049/16043/15172.pdf DOI:10.1093/icesjms/fsr150 http://archimer.ifremer.fr/doc/00049/16043/ | Partager |