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| 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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| 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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| 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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