Daniel Guerault
IFREMER
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Featured researches published by Daniel Guerault.
Journal of Sea Research | 2003
Olivier Le Pape; Florence Chauvet; Stéphanie Mahévas; Pascal Lazure; Daniel Guerault; Yves Desaunay
Abstract This study describes the spatial distribution of young-of-the-year sole based on autumnal beam trawl surveys conducted in the Bay of Biscay (France) during a 15-y period. Previous studies showed that habitat suitability for juvenile sole varies according to physical factors such as bathymetry, sediment structure and river plume influence. These factors, which are known exhaustively for the entire Bay of Biscay from static maps (bathymetry and granulometry) or temporal maps based on a hydrodynamic model (the river plume), were used as descriptors in a generalised linear model of habitat suitability in order to characterise the distribution of juvenile 0-group sole according to delta distribution. This model was used to identify the habitats in which juvenile 0-group sole are concentrated. The respective areas of these habitats were determined from a Geographic Information System (GIS), and their respective contribution to the sole population in the Bay of Biscay was calculated in terms of the estimated number of young fish (GIS area×density derived from the model). Despite the great variability of survey data, this quantitative approach emphasises the highly important role of restricted shallow, muddy estuarine areas as nursery grounds of sole in the Bay of Biscay and demonstrates the relation between interannual variations of nursery habitat capacity (with respect to estuarine extent) and sole recruitment.
Journal of Sea Research | 2003
O. Le Pape; F. Chauvet; Yves Desaunay; Daniel Guerault
Abstract This study describes the spatial distribution of juvenile sole on the basis of a 10-year beam trawl survey of Vilaine Bay, an estuarine nursery ground within the Bay of Biscay (France). A significant relationship between fluvial discharges in winter-spring and the area covered by high densities of 0-group juveniles was indicative of the favourable effects of freshwater supply on nursery size. The extent of the river plume influences both the larval supply and the size and biotic capacity of habitats in estuarine nursery grounds and determines the number of juveniles produced. The correlation between river flow and sole recruitment for Vilaine Bay was confirmed for the Bay of Biscay stock. As the recruitment of the Bay of Biscay sole stock depends partly on the influence of river plumes on nursery grounds, it appears to be less variable than for other sole stocks affected essentially by larval supply. The balance between the different factors influencing recruitment differs according to the area concerned, and recruitment variability depends on the respective roles of these factors.
Estuarine Coastal and Shelf Science | 2003
O. Le Pape; J. Holley; Daniel Guerault; Yves Desaunay
Abstract Survival and growth of early fish stages are maximal in coastal and estuarine habitats where natural shallow areas serve as nurseries for a variety of widely distributed species on the continental shelf. Processes occurring in these nursery grounds during the juvenile stage affect growth and may be important in regulating the year-class strength of fishes and population size. The need, therefore, exists to protect these essential fish habitats hence to develop indicators to estimate their quality. The purpose of the present study was to use the growth of juvenile sole as a means of comparing the quality of coastal and estuarine nursery habitats in the Bay of Biscay (France). These sole nurseries were clearly identified from studies based on trawl surveys carried out during the last two decades. The size of 1-group juveniles at the end of their second summer, as estimated from these surveys, is an indicator of growth in these habitats during the juvenile phase and can be used to compare habitat quality. A model taking into account the role of seawater temperature in spatial and interannual variations of juvenile size was developed to compare growth performance in the different nursery sectors. This study shows that the size of juvenile sole after two summers of life is not density-dependent, probably because the size of the population adapts to habitat capacity after high mortality during early-juvenile stages. Size is on one hand positively related to temperature and on the other hand higher in estuarine than in non-estuarine habitats. This high growth potential of juvenile fish in estuarine areas confirms the very important role played by estuaries as nursery grounds and the essential ecological interest of these limited areas in spite of their low water quality. If a general conclusion on habitat quality is to be reached about studies based on the growth of juvenile fish, it is necessary to use not only an integrative indicator of growth, like size, representative of the intrinsic habitat quality, but also more sensitive and less integrative means, such as otolith increments or caging experiments, which better respond to anthropogenic disturbance. Moreover, it is necessary to take juvenile densities into account.
Archives of Polish Fisheries | 2012
Yves Desaunay; Raymonde Lecomte-Finiger; Daniel Guerault
Abstract Glass eels were sampled, according to the 1991 EIFAC Working Party recommendation (Anon., 1991), in three estuaries, about 800 km apart along the French coast. Only preliminary data are presented here for the peak of immigration in February - March 1992. Biometrics, otolith structure and estimates of larval duration lead to several assumptions on the early life dynamics. Results show that: i) the body size, the otolith development and the mean age are not correlated with the latitude; ii) the migration over the continental shelf is not reflected in the otolith proportionally to the shorter distance from the shelf edge to the estuary; iii) marginal structures of the otolith could be related to the delay before entering freshwater.
Estuarine Coastal and Shelf Science | 2006
C. Gilliers; O. Le Pape; Yves Desaunay; Jocelyne Morin; Daniel Guerault; Rachid Amara
Aquatic Living Resources | 2004
Guy Claireaux; Yves Desaunay; Farida Akcha; B. Auperin; Gilles Bocquene; Hélène Budzinski; Jean-Pierre Cravedi; Fariba Davoodi; Robert Galois; Camille Gilliers; Christelle Goanvec; Daniel Guerault; Nathalie Imbert; Olivier Mazéas; Guy Nonnotte; Liliane Nonnotte; Patrick Prunet; Philippe Sébert; Aurélie Vettier
Scientia Marina | 2006
Yves Desaunay; Daniel Guerault; Olivier Le Pape; Jean-Charles Poulard
Marine Ecology Progress Series | 2004
O. Le Pape; Daniel Guerault; Yves Desaunay
Scientia Marina | 2006
Camille Gilliers; Olivier Le Pape; Yves Desaunay; Jean-Pierre Bergeron; Nathalie Schreiber; Daniel Guerault; Rachid Amara
Archive | 1996
Daniel Guerault; Didier Dorel; Yves Desaunay