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Registros recuperados: 7
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A state-space model to derive bluefin tuna movement and habitat from archival tags ArchiMer
Royer, Francois; Fromentin, Jean-marc; Gaspar, P.
Archival tagging provides a unique way to study the spatial dynamics and habitat of pelagic fish. This technique generates lagrangian data of a particular type in marine ecology: although highly informative about processes at different scales (e.g. horizontal movements versus diving behaviour), such data are impaired by location errors and the lack of combination with actual environmental variability. The present paper introduces a framework for modelling bluefin tuna movement in relation to its habitat, using records of light, depth and temperature from archival tags. Based on data assimilation concepts and methods, we show how an explicit formulation of the observation process and the statistics of external variables (e.g. ambient temperature) can...
Tipo: Text Palavras-chave: Tag; Archival; Habitat; Movement; Bluefin tuna.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-671.pdf
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Association between bluefin tuna schools and oceanic features in the western Mediterranean ArchiMer
Royer, Francois; Fromentin, Jean-marc; Gaspar, P.
We present an analysis of the distribution of bluefin tuna Thunnus thynnus schools spotted during aerial surveys in the Gulf of Lions, in relation to oceanographic features. Bio-optical and thermal properties of the sea surface derived from high-resolution sensors (AVHRR and SeaWiFS) were studied on a daily basis, and an edge-detection technique was applied to detect frontal zones. Geostatistics and point-process analyses were used to evaluate the role of the environment in structuring the spatial pattern of bluefin tuna (BFT). The distribution of schools spotted was strongly non-stationary both in space and time; this is believed to be an effect of the survey design (transect sampling) and the influence of transient oceanographic structures (surface...
Tipo: Text Palavras-chave: Thunnus thynnus; Gulf of Lions; Point process analysis; Front detection; Sea surface temperature; Ocean colour; Aggregation.
Ano: 2004 URL: http://archimer.ifremer.fr/doc/00000/10786/7585.pdf
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Contribution à l'étude de la dynamique du thon rouge Atlantique - Approches écologiques et océanographiques ArchiMer
Royer, Francois.
[1] The spatial and temporal dynamics of Atlantic bluefin tuna, Thunnus thynnus, are here investigated through data analysis and statistical modelling. The local, regional and global scales are considered successively. A phenomenological approach is favoured, as well the extended use of image processing tools and estimation theory techniques. Their potential role in partially observed or ill-defined problems in marine ecology is presented and discussed. The acute need for frequency-explicit methods is in particular stressed out. Hypothesis testing and significance testing of ecological space/time processes are further discussed. [2] The first chapter depicts how surface fronts can structure the pelagic habitat: dedicated detection and mapping tools are...
Tipo: Text Palavras-chave: Archival tags; Kalman filter; Density dependence; Oceanic fronts; Time series; Thunnus thynnus; Marques archives; Filtre de Kalman; Densite dependence; Fronts oceaniques; Series temporelles; Thunnus thynnus.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/these-636.pdf
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Determining bluefin tuna habitat through frontal features in the Mediterranean sea ArchiMer
Royer, Francois; Fromentin, Jean-marc; Farrugio, Henri; Gaspar, Philippe.
The distribution patterns of bluefin tuna schools observed during the STROMBOLI EU project (2000-2002) were analysed in relation to oceanographic conditions. High-resolution radiometers (AVHRR and SeaWiFS) were used on a daily basis to derive maps of environmental variability. An edge detection technique was especially applied to estimate the position of frontal features. Using a variety of geostatistical and point process techniques, we were able to show that the distribution of bluefin schools was partially driven by the occurrence of transient fronts in the Gulf of Lions. This is believed to be mainly a trophic association, since enhanced convergence and retention processes occur at fronts, possibly leading to higher prey densities (e.g. anchovies). The...
Tipo: Text Palavras-chave: Thunnus thynnus; Aerial survey; Gulf of Lions; Sea surface temperature; Ocean colour; Fronts.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/00194/30504/28914.pdf
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Environmental noise in spawning areas: the case of Atlantic bluefin tuna (Thunnus thynnus) ArchiMer
Royer, Francois; Fromentin, Jean-marc.
This paper provides an exploratory analysis aiming to seek whether the colour of environmental noise theory could help in understanding the intriguing reproductive strategy of Atlantic bluefin tuna (BFT). A frequency-based approach based on spectral exponents, f(beta) with beta < 0, is chosen and applied on 10 biogeographical provinces covering the North Atlantic. The major BFT spawning area, i.e. the Mediterranean Sea, was the only one to display a pink power spectrum, whereas open ocean regions displayed more reddened fluctuations, i.e. greater variance at low frequencies. Environmental noise in the Mediterranean could, thus, offer more favourable characteristics on the long-term than the open ocean. The implications of these findings are discussed in...
Tipo: Text Palavras-chave: Thunnus thynnus; Spectral analysis; Spawning; Sea surface temperature; Environmental noise.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-2437.pdf
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Open environmental databases for open-sea fisheries biologists ArchiMer
Fromentin, Jean-marc; Royer, Francois; Marsac, Francis.
The present working document aims to list the main environmental databases (including in-situ observations, remote-sensing data and ocean models outputs), that are currently available on the Net and of interest in open-sea fisheries biology and ecology.
Tipo: Text Palavras-chave: In-situ observations; Remote sensing data collections; Ocean model outputs.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/00194/30501/28911.pdf
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Recurrent and density-dependent patterns in long-term fluctuations of Atlantic bluefin tuna trap catches ArchiMer
Royer, Francois; Fromentin, Jean-marc.
We present a methodology for the non-linear analysis of long-term ecological time series. Using a time-delay embedding procedure, we investigated the complexity of 1-dimensional signals and compared their structure to their stochastic counterparts. Recurrence-based statistics and surrogate testing were used for this purpose. The method was first tested on elementary models for illustrative purposes and its potentialities and limits reviewed. We then investigated the time structure of 6 Mediterranean bluefin tuna trap catches known to display long-term fluctuations. These time series showed significantly more determinism than linear stochastic processes, displaying more recurring patterns/states than stochastic surrogates. The short term structure of these...
Tipo: Text Palavras-chave: Embedding; Surrogate testing; Density dependence; Recurrence; Thunnus thynnus.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1982.pdf
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