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| Registros recuperados: 99 | |
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| Foster, Scott D.; Vanhatalo, Jarno; Trenkel, Verena; Schulz, Torsti; Lawrence, Emma; Przeslawski, Rachel; Hosack, Geoffrey R.. |
| Data are currently being used, and reused, in ecological research at an unprecedented rate. To ensure appropriate reuse however, we need to ask the question: “Are aggregated databases currently providing the right information to enable effective and unbiased reuse?” We investigate this question, with a focus on designs that purposefully favour the selection of sampling locations (upweighting the probability of selection of some locations). These designs are common and examples are those designs that have uneven inclusion probabilities or are stratified. We perform a simulation experiment by creating datasets with progressively more uneven inclusion probabilities, and examine the resulting estimates of the average number of individuals per unit area... |
| Tipo: Text |
Palavras-chave: Bias; Survey Design; Database; Population Density Estimate; Model; Horvitz‐Thompson; FAIR; Reuse; Data; Inclusion Probability. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00691/80339/83422.pdf |
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| Mahe, Kelig; Oudard, Clemence; Mille, Tiphaine; Keating, James P; Gonçalves, Patricia; Clausen, Lotte Worsøe; Petursdottir, G; Rasmussen, H; Meland, E; Mullins, E; Pinnegar, Jk; Hoines, A; Trenkel, Verena. |
| Information on stock identification and spatial stock structure provide a basis for understanding fish population dynamics and improving fisheries management. In this study otolith shape analysis was used to study the stock structure of blue whiting (Micromesistius poutassou) in the northeast Atlantic using 1693 samples from mature fish collected between 37°N and 75°N and 20°W and 25°E. The results indicated two stocks located north and south of ICES Divisions VIa and VIb (54°5 to 60°5 N, 4° to 11°W). The central area corresponds to the spawning area west of Scotland. Sampling year effects and misclassification in the linear discriminant analysis suggested exchanges between the northern and southern stocks. The results corroborate previous studies... |
| Tipo: Text |
Palavras-chave: Micromesistius poutassou; Forme de l’otolithe; Descripteurs de Fourier; Discrimination de stock; Nord-est de l’Océan atlantique.; Micromesistius poutassou; Otolith shape; Fourier descriptors; Stock discrimination; Northeast atlantic. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00334/44508/44202.pdf |
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| Elvarsson, B. P.; Taylor, L.; Trenkel, Verena; Kupca, V.; Stefansson, G.. |
| Statistical models of marine ecosystems use a variety of data sources to estimate parameters using composite or weighted likelihood functions with associated weighting issues and questions on how to obtain variance estimates. Regardless of the method used to obtain point estimates, a method is required for variance estimation. A bootstrap technique is introduced for the evaluation of uncertainty in such models, taking into account inherent spatial and temporal correlations in the datasets, which are commonly transferred as assumptions from a likelihood estimation procedure into Hessian-based variance estimation procedures. The technique is demonstrated on a real dataset and the effects of the number of bootstrap samples on estimation bias and variance... |
| Tipo: Text |
Palavras-chave: Bootstrapping; Correlated data; Fish population dynamics; Non-linear models. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00193/30459/29913.pdf |
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| Hammond, T; Trenkel, Verena. |
| Landings statistics can be lower than true catches because many fish are discarded or landed illegally. Since many discards do not survive, treating landings as true catches can lead to biased stock assessments. This paper proposes treating catch as censored by bounding it below by the landings, L, and above by cL (for scalar c > 1), We demonstrate the approach with a simulation study, using a Schaefer surplus production model. Parameters were estimated in a Bayesian framework with BUGS software using two sets of priors. Both the traditional true-catch method and a survey-and-effort method (which was landings free) performed worse on average than the censored approach, as measured by the Bayes risk associated with estimates of maximum sustainable yield... |
| Tipo: Text |
Palavras-chave: Stock assessment; Misreporting; Discarding; Censored data. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-641.pdf |
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| Trenkel, Verena; Hintzen, Niels T.; Farnsworth, Keith D.; Olesen, Christian; Reid, David; Rindorf, Anna; Shephard, Samuel; Dickey-collas, Mark. |
| International policy frameworks such as the Common Fisheries Policy and the European Marine Strategy Framework Directive define high-level strategic goals for marine ecosystems. Strategic goals are addressed via general and operational management objectives. To add credibility and legitimacy to the development of objectives, for this study stakeholders explored intermediate level ecological, economic and social management objectives for Northeast Atlantic pelagic ecosystems. Stakeholder workshops were undertaken with participants being free to identify objectives based on their own insights and needs. Overall 26 objectives were proposed, with 58% agreement in proposed objectives between two workshops. Based on published evidence for pressure-state links,... |
| Tipo: Text |
Palavras-chave: Ecosystem-based management; Marine pelagic community; Management objective; MSFD; CFP. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00251/36214/34774.pdf |
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| Poulard, Jean-charles; Trenkel, Verena. |
| Survey indices play an important role in stock assessments as they provide information on stock trends. In certain cases large interannual variations have been observed which are unlikely to reflect true underlying stock changes but are rather outliers. When survey indices for several species appear to be outliers for the same year, the suspicion is raised that something happened during the survey of that year. This is called a year-effect in survey catches. To study the potential year-effect in survey catches for the French autumn groundfish survey taking place in the Bay of Biscay, several indicators for survey design and wind conditions were derived as explanatory variables and Principal Component Analysis was used to study the relationship between... |
| Tipo: Text |
Palavras-chave: Bay of Biscay; Survey conditions; Time trends; Catchability; Survey index. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2690.pdf |
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| Cotter, John; Petitgas, Pierre; Abella, Alvaro; Apostolaki, Panayiota; Mesnil, Benoit; Politou, Chrissi-yianna; Rivoirard, Jacques; Rochet, Marie-joelle; Spedicato, Maria Teresa; Trenkel, Verena; Woillez, Mathieu. |
| Ideas and considerations are put forward for managing fisheries and marine populations using primarily trawl surveys to supply biological and spatial indicators of the state of stocks, and to permit catch per unit effort (CPUE)-based assessments. Trawl surveys seldom allow absolute estimates of fish population sizes but, if appropriately located, timed, and designed, can provide a broad range of information about catchable fish species and the ecosystem that supports them. This information may be more conducive to sustainable management of fisheries than the traditional focus on the abundances of selected stocks. The paper first briefly proposes how survey-based methods might supplement existing fishery-dependent stock assessments, as would be necessary... |
| Tipo: Text |
Palavras-chave: Fishing effort indicator; Fisheries independent assessment; Survey based stock assessment; Spatial indicator; State indicator; Trawl survey; Fisheries management. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6691.pdf |
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| Trenkel, Verena; Pinnegar, John; Rochet, Marie-joelle; Rackham, Brian. |
| Choice of sampling method and survey period can have an important impact on the perception of the structure and dynamics of an ecological community. For the Celtic Sea fish assemblage we compared data obtained by three different trawl surveys: an autumn groundfish survey with a GOV trawl, and a spring and an autumn groundfish survey, both carried out with a Portuguese high-headline trawl. Time-series of abundance estimates were not consistent among surveys for all species and were generally very noisy. An analysis of variance components showed that the sampling method contributed more to the variance in abundance estimates compared to survey period, interannual variability, or even sampling variance. Overall community assessments based on indicators such... |
| Tipo: Text |
Palavras-chave: Trawl; Survey; Species diversity; Size spectrum; Celtic Sea; Abundance. |
| Ano: 2004 |
URL: https://archimer.ifremer.fr/doc/2004/publication-899.pdf |
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| Rochet, Marie-joelle; Trenkel, Verena; Rice, Jake. |
| Currently many multi-year management plans are being developed either for rebuilding depleted stocks or for avoiding difficult negotiations when management decisions must be revisited on a regular basis. Management plans are commonly evaluated by intensive model simulations that describe the ecological and economic dynamics, and the management loop. Under the results-based management paradigm, the fishing industry or particular fishing sectors will develop their own management plans, potentially leading to a huge number of plans to be evaluated. Guidelines for evaluating the plans on a qualitative level before launching quantitative evaluations will be essential. Here we propose a framework for evaluating management strategies in a qualitative way. A... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00029/13988/11166.pdf |
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| Cauvy-fraunié, Sophie; Trenkel, Verena; Daufresne, Martin; Maire, Anthony; Capra, Hervé; Olivier, Jean-michel; Lobry, Jérémy; Cazelles, Bernard; Lamouroux, Nicolas. |
| Long-term ecological surveys (LTES) often exhibit strong variability among sampling dates. The use and interpretation of such interannual variability is challenging due to the combination of multiple processes involved and sampling uncertainty. Here, we analysed the interannual variability in ~30 years of 150 species-density (fish and invertebrate) and environmental-observation time series in four aquatic-systems (stream, river, estuary, and marine continental shelf) with different sampling efforts to identify the information provided by this variability. We tested, using two empirical methods, whether we could observe simultaneous fluctuation between detrended time series corresponding to widely acknowledged assumptions about aquatic population dynamics:... |
| Tipo: Text |
Palavras-chave: Long-term ecological surveys (LTES); Aquatic species (stream -river-estuary- marine); Interannual variability; Symbolic analyses; Sampling efficiency. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00606/71805/70293.pdf |
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| Morin, Jocelyne; Bertrand, Jacques; Cochard, Marie-laure; Coppin, Franck; Leaute, Jean-pierre; Lobry, Jeremy; Mahe, Jean-claude; Poulard, Jean-charles; Rochet, Marie-joelle; Schlaich, Ivan; Souplet, Arnauld; Trenkel, Verena; Vaz, Sandrine; Verin, Yves. |
| Since about twenty years, Ifremer have carried out fishery surveys along the French coasts. A dynamic indicator-based approach to the assessment of multi-stock fisheries has been applied to these data series. Reference points for non-commercial populations and community indicators are seldom available, but reference directions are well established: it is known whether fishing will increase or decrease the indicator, hence the direction that should be avoided. A set of simple indicators of fishing impacts on fish populations and communities were estimated from time-series data provided by scientific surveys (population abundance and average length, community total biomass and number, average length and weight, and size spectrum). Trends in these indicators... |
| Tipo: Text |
Palavras-chave: Communauté; Population; Indicateurs; Campagnes scientifiques; Pêcheries multi spécifiques; Approche écosystémique pour la gestion des pêches. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/rapport-7293.pdf |
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| Ravard, David; Brind'Amour, Anik; Trenkel, Verena. |
| Fishing affects fish populations through direct and indirect effects. It can change size structures and/or modify population mean weights. Reference values are thus needed to assess the status of populations in exploited ecosystems. These reference values can either be set by a historical approach, i.e. using information from before the onset of exploitation or overexploitation, or by a simulation approach. Using a model based on life-history parameters, we predicted population mean weights and length structures at equilibrium (in the absence of fishing and for fishing equal to different fishing mortalities) which we compared with contemporary data collected during scientific surveys in the Bay of Biscay. Contemporary mean weights were 88% to 30% smaller... |
| Tipo: Text |
Palavras-chave: Indicators; Fishing impacts; Ecosystem based management; Fish community; Reference points; Northeast Atlantic. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00188/29968/28485.pdf |
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| Reecht, Yves; Rochet, Marie-joelle; Trenkel, Verena; Jennings, S.; Pinnegar, J. K.. |
| An ecomorphological method was developed, with a focus on predation functions, to define functional groups in the Celtic Sea fish community. Eleven functional traits, measured for 930 individuals from 33 species, led to 11 functional groups. Membership of functional groups was linked to body size and taxonomy. For seven species, there were ontogenetic changes in group membership. When diet composition, expressed as the proportions of different prey types recorded in stomachs, was compared among functional groups, morphology-based predictions accounted for 28-56% of the interindividual variance in prey type. This was larger than the 12-24% of variance that could be explained solely on the basis of body size. (C) 2013 The Fisheries Society of the British Isles |
| Tipo: Text |
Palavras-chave: Ecomorphology; Functional traits; Predation strategy; Trophic functions. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00152/26294/24831.pdf |
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| Trenkel, Verena; Berger, Laurent; Bourguignon, Sebastien; Doray, Mathieu; Fablet, Ronan; Masse, Jacques; Mazauric, Valerie; Poncelet, Cyrille; Quemener, Gael; Scalabrin, Carla; Villalobos, Hector. |
| This paper provides an overview of the progress Ifremer has made recently in fisheries acoustics and the study of small pelagic fish by: i) pushing observation frontiers using a range of platforms including an autonomous underwater vehicle, AUV, ii) developing measuring instruments and methods and iii) studying fish distributions. Presently, information from several frequencies of single-beam echosounders is routinely collected together with data from the ME70 multibeam echosounder. For onboard data acquisition control the HERMES software was developed. The new MOVIES 3D software includes modules for simultaneous realistic 3D visualisation and post-processing such as bottom detection, school extraction and calculation of descriptors and integration of all... |
| Tipo: Text |
Palavras-chave: Multibeam echosounder; Oceanographic AUV; Pelagic fish; Fisheries acoustics. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00000/11165/7517.pdf |
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| Pinnegar, J. K.; Goni, N.; Trenkel, Verena; Arrizabalaga, H.; Melle, W.; Keating, J.; Oskarsson, G.. |
| There is increasing demand for information on predator-prey interactions in the ocean as a result of legislative commitments aimed at achieving sustainable exploitation. However, comprehensive datasets are lacking for many fish species and this has hampered development of multispecies fisheries models and the formulation of effective food-web indicators. This work describes a new compilation of stomach content data for five pelagic fish species (herring, blue whiting, mackerel, albacore and bluefin tuna) sampled across the northeast Atlantic and submitted to the PANGAEA open-access data portal (www.pangaea.de). We provide detailed descriptions of sample origin and of the corresponding database structures. We describe the main results in terms of diet... |
| Tipo: Text |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00195/30641/29096.pdf |
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| Trenkel, Verena; Rochet, Marie-joelle. |
| P>1. Metrics have become a standard way for summarizing environmental monitoring results. Different metrics react differently to natural variations and human-induced stressors. We suggest that combined analysis of time trends in selected biological metrics allows identification of biological processes (e.g. individual growth, mortality or recruitment) that have changed (increased or decreased) persistently. Alternatively, time trends in the abundance of sensitive species could indicate changes in environmental stressors. 2. We calculate the joint likelihood of time trends in three metrics and use it to evaluate the evidence in the data for different combinations of metric time trends. A simulation study provides guidelines for interpreting... |
| Tipo: Text |
Palavras-chave: Generalized additive model; Indicators; Likelihood principle; Quadratic programming; Survey data. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00008/11926/8988.pdf |
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| Registros recuperados: 99 | |
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