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International audience; The Nile tilapia (Oreochromis niloticus) was introduced in Southeast Asia, such as in Thailand, in the mid-1960s for aquaculture purposes (Pullin et al., 1997; De Silva et al., 2004). The species was later promoted for aquaculture development in the early 1990s in Lao PDR (Garaway et al., 2000). In Lao People’s Democratic Republic (PDR), like in other countries, this exotic species is well established due to its self-reproduction (De Silva et al., 2004; CABI, 2018) facilitated by its particular life history traits and plasticity (Ishikawa et al., 2013). The species was then suspected to be introduced in the seventies in Laos and subsequently in the Nam Theun watershed where the NT2 Reservoir was impounded in 2008. Population parameters of this alien fish were investigated using the FiSAT II software with the most popular methods of bioparameters assessment to check their interchangeability within a same stock and the same year 2016. The length-at-age data analysis (using otoliths analysis, N = 258) gave slightly different results with the length frequency distribution analysis of fish landings (11 820 individuals). Furthermore, experimental fishing data provided irrelevant parameters due to insufficient representativeness of the sample size. The growth parameter K was estimated to be 0.23 year−1, with asymptotic length L∞ = 52.5 cm based on the length frequency distribution analysis with the fish landing data. According to these landing data, the total, natural and fishing mortality were Z = 1.41 year−1, M = 0.30 year−1 and F = 1.11 year−1. The exploitation rate E = 0.79 is over the Emax = 0.594 obtained by relative yield and biomass per recruit. This estimated stock of 165 tons (more than 700 000 tilapias) was characterized by high mortality (no population growth). These results showed that the population is overfished with too many juveniles caught (L50 = 210.4 mm; 50% mature stages at 295 mm). To maximize the yield per recruit, increase the biomass and sustain this fishery, enlarging the gillnet mesh size of the gill-net is recommended. This example highlights the variability of the parameters calculated from different methods and thus weaken worldwide and even inter-site comparisons. Despite this issue, the Growth Performances Indices (φ′) gathered into the literature can serve as baseline and confirmed the wide phenotypic plasticity of the species due to environmental factors. Analyses revealed difference between fast growing domesticated fish rose for aquaculture with φ′ higher to the tilapia growing in natural and challenging environments.; Le Tilapia du Nil (Oreochromis niloticus) a été introduit en Asie du sud-ouest, notamment en Thaïlande, dans le milieu des années 1960, à des fins d’aquaculture. Ce n’est que dans les années 1990 que cette espèce a été introduite au Laos pour ce même objectif. Cette espèce exotique, de par sa capacité de reproduction naturelle induite par ses traits d’histoire de vie et sa plasticité phénotypique, est bien établie au Laos, ainsi que dans d’autres pays asiatiques. Cette espèce présente dans le bassin versant de Nam Theun aurait ainsi colonisé le réservoir de Nam Theun 2 (NT2) lors de sa mise en eau en 2008, avec également des actions sporadiques d’empoissonnements. Les paramètres de la population du réservoir de NT2 ont été étudiés en recourant à FiSAT II avec les méthodes d’évaluation des bio-paramètres les plus populaires pour vérifier leur interchangeabilité dans un même stock et pour une même année (2016). L’analyse de la relation taille-âge, via l’analyse de 258 otolithes, a donné des résultats légèrement différents de l’analyse des fréquences de tailles issues des débarquements réalisées sur 11 820 individus. Les données issues des pêches expérimentales ont quant-à-elles fournis des résultats non pertinents de par le faible effectif des échantillons. La croissance (k) a été estimée à 0,23 cm an−1 avec une longueur asymptotique (L∞) de 52,5 cm. Selon les données de débarquements la mortalité totale, naturelle et par pêche étaient respectivement de 1,41, 0,30 et 1,11 an−1. Le taux d’exploitation (0,79) était supérieur au taux d’exploitation maximal (0,594) obtenu par le rendement relatif et la biomasse par recrue. Le stock estimé de 165 tonnes (plus de 700 000 individus) était caractérisé par une mortalité élevée. Ces résultats ont montré que la population était surexploitée et que de nombreux juvéniles étaient capturés (L50 = 210,4 mm; 50% mature à 295 mm). Pour maximiser le rendement par recrue, augmenter la biomasse, et soutenir la pêche, il est recommandé d’augmenter la taille des mailles des filets de pêche. Cet exemple met en évidence la variabilité des paramètres calculés à partir de différentes méthodes ce qui sous-entend que les comparaisons avec les autres populations dans le monde, mais également inter-sites sont difficiles. Toutefois les indices de performance de croissance (φ′) relevés dans la littérature peuvent servir de référentiel et confirmer la grande plasticité phénotypique de cette espèce selon les facteurs environnementaux. Les analyses ont révélé que les populations aquacoles présentaient une croissance plus rapide que celle des populations vivant dans les environnements naturels contraignants.

The common sole (Solea solea) is a nursery-dependent flatfish that has been overexploited in the Eastern English Channel stock (division VIId). An explanation of such decline could be the misalignment between the management unit (stock) and the biological unit (population). This thesis aimed at assessing the spatial structure of the Eastern English Channel stock of common sole by focusing on sub-adults and adults and determining the potential mismatch between the stock unit and the underlying population. To do so, a multitracer holistic approach was developed by combining population and individual-based approachesFirst, analyses of population growth and synchrony of abundances-at-age series revealed the existence of a long-lasting signal of spatial stock structure made of three subunits with potential isolation ofone of these subunits. Then, genetics, otolith shape and otolith microchemistry analyses highighted three subunits within the stock. Finally, a semiquantitative Stock Differentiation Index suggested a strong spatial structure in three subunits. Therefore, this thesis evidenced a metapopulation structure of the common sole of the Eastern English Channel that should be integrated in the assessment – management process to provide a sustainable exploitation of the stock.; La sole commune (Solea solea) est un poisson plat nourricerie-dépendant ayant été surexploité en Manche Est (division VIId). L’une des causes de ce déclin pourrait être le décalage entre l’unité de gestion (stock) et l’unité fonctionnelle (population). L’objectif de cette thèse était de déterminer la structure spatiale du stock de sole commune de Manche Est en se focalisant sur les stades de vie préadultes et adultes et de statuer sur le potentiel décalage entre l’unité de stock et la population sous-jacente. Pour cela, une approche holistique multitraceur a été développée en combinant des approches populationnelles et individuelles.D’abord, une étude de la croissance populationnelle et de la synchronie des abondances aux âges a mis en évidence l’existence d’un signal à long terme de structure spatiale du stock en trois sous-unités avec l’isolement probable de l’une d’entre elles. Ensuite, des analyses génétiques, de forme des otolithes et de microchimie des otolithes ont mis en évidence une structure spatiale en trois sousunités. Enfin, un Indice semi-quantitatif de Différentiation du Stock a suggéré une forte structure spatiale en trois sous-unités. Ainsi, cette thèse a démontré une structure de type métapopulation de la sole commune en Manche Est qui devrait être prise en compte dans le processus d’évaluation et de gestion du stock afin d’atteindre une gestion durable.

International audience; The Nile tilapia (Oreochromis niloticus) was introduced in Southeast Asia, such as in Thailand, in the mid-1960s for aquaculture purposes (Pullin et al., 1997; De Silva et al., 2004). The species was later promoted for aquaculture development in the early 1990s in Lao PDR (Garaway et al., 2000). In Lao People’s Democratic Republic (PDR), like in other countries, this exotic species is well established due to its self-reproduction (De Silva et al., 2004; CABI, 2018) facilitated by its particular life history traits and plasticity (Ishikawa et al., 2013). The species was then suspected to be introduced in the seventies in Laos and subsequently in the Nam Theun watershed where the NT2 Reservoir was impounded in 2008. Population parameters of this alien fish were investigated using the FiSAT II software with the most popular methods of bioparameters assessment to check their interchangeability within a same stock and the same year 2016. The length-at-age data analysis (using otoliths analysis, N = 258) gave slightly different results with the length frequency distribution analysis of fish landings (11 820 individuals). Furthermore, experimental fishing data provided irrelevant parameters due to insufficient representativeness of the sample size. The growth parameter K was estimated to be 0.23 year−1, with asymptotic length L∞ = 52.5 cm based on the length frequency distribution analysis with the fish landing data. According to these landing data, the total, natural and fishing mortality were Z = 1.41 year−1, M = 0.30 year−1 and F = 1.11 year−1. The exploitation rate E = 0.79 is over the Emax = 0.594 obtained by relative yield and biomass per recruit. This estimated stock of 165 tons (more than 700 000 tilapias) was characterized by high mortality (no population growth). These results showed that the population is overfished with too many juveniles caught (L50 = 210.4 mm; 50% mature stages at 295 mm). To maximize the yield per recruit, increase the biomass and sustain this fishery, enlarging the gillnet mesh size of the gill-net is recommended. This example highlights the variability of the parameters calculated from different methods and thus weaken worldwide and even inter-site comparisons. Despite this issue, the Growth Performances Indices (φ′) gathered into the literature can serve as baseline and confirmed the wide phenotypic plasticity of the species due to environmental factors. Analyses revealed difference between fast growing domesticated fish rose for aquaculture with φ′ higher to the tilapia growing in natural and challenging environments.; Le Tilapia du Nil (Oreochromis niloticus) a été introduit en Asie du sud-ouest, notamment en Thaïlande, dans le milieu des années 1960, à des fins d’aquaculture. Ce n’est que dans les années 1990 que cette espèce a été introduite au Laos pour ce même objectif. Cette espèce exotique, de par sa capacité de reproduction naturelle induite par ses traits d’histoire de vie et sa plasticité phénotypique, est bien établie au Laos, ainsi que dans d’autres pays asiatiques. Cette espèce présente dans le bassin versant de Nam Theun aurait ainsi colonisé le réservoir de Nam Theun 2 (NT2) lors de sa mise en eau en 2008, avec également des actions sporadiques d’empoissonnements. Les paramètres de la population du réservoir de NT2 ont été étudiés en recourant à FiSAT II avec les méthodes d’évaluation des bio-paramètres les plus populaires pour vérifier leur interchangeabilité dans un même stock et pour une même année (2016). L’analyse de la relation taille-âge, via l’analyse de 258 otolithes, a donné des résultats légèrement différents de l’analyse des fréquences de tailles issues des débarquements réalisées sur 11 820 individus. Les données issues des pêches expérimentales ont quant-à-elles fournis des résultats non pertinents de par le faible effectif des échantillons. La croissance (k) a été estimée à 0,23 cm an−1 avec une longueur asymptotique (L∞) de 52,5 cm. Selon les données de débarquements la mortalité totale, naturelle et par pêche étaient respectivement de 1,41, 0,30 et 1,11 an−1. Le taux d’exploitation (0,79) était supérieur au taux d’exploitation maximal (0,594) obtenu par le rendement relatif et la biomasse par recrue. Le stock estimé de 165 tonnes (plus de 700 000 individus) était caractérisé par une mortalité élevée. Ces résultats ont montré que la population était surexploitée et que de nombreux juvéniles étaient capturés (L50 = 210,4 mm; 50% mature à 295 mm). Pour maximiser le rendement par recrue, augmenter la biomasse, et soutenir la pêche, il est recommandé d’augmenter la taille des mailles des filets de pêche. Cet exemple met en évidence la variabilité des paramètres calculés à partir de différentes méthodes ce qui sous-entend que les comparaisons avec les autres populations dans le monde, mais également inter-sites sont difficiles. Toutefois les indices de performance de croissance (φ′) relevés dans la littérature peuvent servir de référentiel et confirmer la grande plasticité phénotypique de cette espèce selon les facteurs environnementaux. Les analyses ont révélé que les populations aquacoles présentaient une croissance plus rapide que celle des populations vivant dans les environnements naturels contraignants.

The common sole (Solea solea) is a nursery-dependent flatfish that has been overexploited in the Eastern English Channel stock (division VIId). An explanation of such decline could be the misalignment between the management unit (stock) and the biological unit (population). This thesis aimed at assessing the spatial structure of the Eastern English Channel stock of common sole by focusing on sub-adults and adults and determining the potential mismatch between the stock unit and the underlying population. To do so, a multitracer holistic approach was developed by combining population and individual-based approachesFirst, analyses of population growth and synchrony of abundances-at-age series revealed the existence of a long-lasting signal of spatial stock structure made of three subunits with potential isolation ofone of these subunits. Then, genetics, otolith shape and otolith microchemistry analyses highighted three subunits within the stock. Finally, a semiquantitative Stock Differentiation Index suggested a strong spatial structure in three subunits. Therefore, this thesis evidenced a metapopulation structure of the common sole of the Eastern English Channel that should be integrated in the assessment – management process to provide a sustainable exploitation of the stock., La sole commune (Solea solea) est un poisson plat nourricerie-dépendant ayant été surexploité en Manche Est (division VIId). L’une des causes de ce déclin pourrait être le décalage entre l’unité de gestion (stock) et l’unité fonctionnelle (population). L’objectif de cette thèse était de déterminer la structure spatiale du stock de sole commune de Manche Est en se focalisant sur les stades de vie préadultes et adultes et de statuer sur le potentiel décalage entre l’unité de stock et la population sous-jacente. Pour cela, une approche holistique multitraceur a été développée en combinant des approches populationnelles et individuelles.D’abord, une étude de la croissance populationnelle et de la synchronie des abondances aux âges a mis en évidence l’existence d’un signal à long terme de structure spatiale du stock en trois sous-unités avec l’isolement probable de l’une d’entre elles. Ensuite, des analyses génétiques, de forme des otolithes et de microchimie des otolithes ont mis en évidence une structure spatiale en trois sousunités. Enfin, un Indice semi-quantitatif de Différentiation du Stock a suggéré une forte structure spatiale en trois sous-unités. Ainsi, cette thèse a démontré une structure de type métapopulation de la sole commune en Manche Est qui devrait être prise en compte dans le processus d’évaluation et de gestion du stock afin d’atteindre une gestion durable.

Many diadromous fishes such as salmon and eels that move between freshwater and the ocean have evolved semelparous reproductive strategies, but both groups display considerable plasticity in characteristics. Factors such as population density and growth, predation risk or reproduction cost have been found to influence timing of maturation. We investigated the relationship between female size at maturity and individual growth trajectories of the long-lived semelparous European eel, Anguilla anguilla . A Bayesian model was applied to 338 individual growth trajectories of maturing migration-stage female silver eels from France, Ireland, the Netherlands and Hungary. The results clearly showed that when growth rates declined, the onset of maturation was triggered, and the eels left their growth habitats and migrated to the spawning area. Therefore, female eels tended to attain larger body size when the growth conditions were good enough to risk spending extra time in their growth habitats. This flexible maturation strategy is likely related to the ability to use diverse habitats with widely ranging growth and survival potentials in the catadromous life-history across its wide species range.

International audience; Long-term plasticity of otolith shape has become a unifying principle to use morphological differences as indicator of environmental conditions. Contrary to the longstanding paradigmatic view that otolith shape can only reflect residency in particular environmental conditions over long time periods, data emphasize that otolith ontogenetic trajectory may be reoriented in case of short-term episodes of environmental disturbance during early lifetime. Using geometric morphometrics, discrimination was posible in absence of growth-related differences between control and brown trout (Salmo trutta Linnaeus, 1758) that have experienced brief thermal stress prior to their emergence but have grown in similar conditions (i.e., cohabiting within the same aquarium) during 6 months. Data emphasize that brief stress during key developmental periods can durably influence ontogenetic trajectories, subsequent otolith development, and can consequently change otolith morphology in juveniles. Therefore, differences in shape between groups of fish may not be exclusively indicative of long-time residency in contrasted and (or) separated habitats as it is generally assumed. Moving beyond long-term assumptions is fundamental if otolith shape is to be used as an effective tool for management of fisheries resources in the future.; La plasticité à long terme de la forme des otolites est devenue un principe unificateur pour l’utilisation de différencesmorphologiques comme indicateurs des conditions ambiantes. Contrairement à la vision paradigmatique bien établie voulant que la forme des otolites ne puisse refléter qu’une résidence dans des conditions ambiantes précises pendant une longue période, des données font ressortir le fait que la trajectoire ontogénétique des otolites peut être réorientée en cas d’épisodes de perturbation environnementale de courte durée au début de la vie. En utilisant des paramètres morphométriques géométriques, la discrimination est possible en l’absence de différences associées à la croissance entre des témoins et des truites de mer (Salmo trutta Linnaeus, 1758) assujetties à un bref stress thermique préalablement à leur émergence, qui ont cru dans des conditions semblables (c.-à-d. cohabitation dans le même aquarium) pendant six mois. Les données indiquent qu’un stress bref durant des périodes clés du développement peut influencer de manière durable les trajectoires ontogénétiques et le développement subséquent des otolites et ainsi modifier la morphologie des otolites chez les juvéniles. Des différences de forme entre groupes de poissons pourraient ne pas simplement indiquer des résidences de longue durée dans des habitats différents ou séparés, comme cela est généralement présumé. L’utilisation de la forme des otolites comme outil efficace pour la gestion des ressources halieutiques nécessitera donc une approche qui va au-delà des hypothèses axées sur le long terme.

International audience; The common dentex, Dentex dentex, is an iconic marine coastal fish of the Mediterranean Sea. Despite its economic and ecological importance, data on the population structure of this species are still very limited. The aim of this study was to identify the stock structure of the common dentex at relatively fine spatial scale around Corsica Island, using a combination of markers that have different spatial and temporal scales of integration: microsatellite DNA markers, otolith shape analysis and parasites communities. Microsatellite analysis indicated that there was no significant genetic differentiation in D. dentex between the four sampling sites around Corsica. Otolith shape analysis suggests one potential distinct population unit of D. dentex centered in one site (Cap Corse) varying in their degree of differentiation from those in the other zones. Multivariate analysis on parasite abundance data highlights to a lower extent two sites (Bonifacio and Galeria) with some connectivity between adjacent zones. The combination of these three markers together highlights the resulting three sites while giving complementary insights and an opportunity to compare their utility and potential to understand population interactions. A complex population structure around Corsican coasts is then proposed, providing a new perspective on common dentex fishery stock conservation and management strategies.

International audience; The selection of an otolith optimal zone where to obtain interpretable chronological data (e.g. chemical transect, increment width) and valid age estimation is fundamental if otoliths are to be used as an effective tool for investigating life history traits or environments experienced by fish. In the remote sub-Antarctic Kerguelen Islands (49° S, 70° E), introduced brown trout populations are invading the archipelago since the 50's and life histories information is of great interest to understand the invasion dynamics. Unfortunately, few studies have used otolith as a tool to estimate brown trout age at these extreme latitudes and little is known about otolith growth and annulus formation in these sub-polar conditions. Furthermore, no formal procedure exists at the population level to select an otolith optimal zone where to concomitantly extract chronological data aiming at investigating life history traits and growth chronologies. In this context, the aims of this study were (1) to validate the otolith age estimation method by the determination of the position of the first annulus and the annual formation of subsequent annuli; (2) to define an optimal zone where chronological data could be coupled to age estimates. A brown trout population located near the Port-au-Français station was studied and sampled repeatedly using mark-recapture method and Alizarin Red S marking. After to 2 years of recaptures 53 sagittae were analysed. A composite index was created to select an optimal zone where chronological data transects have the maximum probabilities to cross readable annuli. Results showed that brown trout forms annuli at the end of September, starting with the first winter after the December hatching. Annulus formation up to 2 years after marking was validated. The area between 80° and 120° perpendicular to the rostrum/core axis was optimal for the positioning of data transect. The proposed formal approach allows distinguishing the zone that identifies the best compromise between spatial resolution and precise annulus positioning along otolith chronological series

International audience; Otolith shape analysis provides a practical basis for stock separation, useful in fisheries management. A wide range of factors affect otolith morphology and a fundamental challenge in morphometric stock identification is to develop a consensus on the biological interpretation of otolith shape variation. To date, there are few comprehensive reports that have examined various factors simultaneously at multiple scales in natural conditions. In this study, I identified sources of otolith shape variation across spatial and taxonomic scales using a new hierarchical partitioning method embedded in a geometric morphometric framework. Various environmental, taxonomic and endogenic factors which affect otolith shape were quantitatively investigated in 2077 coral reef fishes. Using the new partitioning method, allometry accounted for a considerable degree of otolith shape variation at all scales and contributed more variation to regional differences than did habitats or islands. While large-scale variations are expected to be associated with significant shape variation, the study provides quantitative evidence that both local environmental variables and large-scale patterns contribute equally to total otolith shape variation. Models that aim at discriminating stocks and forecasting stock boundaries implicitly assume that the within-stock morphological variation is negligible in regard to the variation that exists among stocks. The importance of local environmental variables may therefore act as an important confounding effect into those predictive models. More generally, the degree of contribution of some variables differed substantially among the taxonomic scales, as did their relationship among spatial scales. A scale dependent understanding of factors affecting otolith morphology is critical in understanding theintegrity of fish populations and is an effective tool in management of fisheries resources

International audience; During the last decades, ecologists have paid a great deal of attention to the proper techniques to track fish movement in the wild. In this context, otoliths have proved useful and were increasingly used in a wide range of species worldwide. Otolith material incorporates elements from the surrounding water in a layered manner that preserves the timing of deposition. Elemental composition along otolith centre-edge transects thus represent a permanent record of the growing habitats experienced by the fish throughout its entire lifetime. While the analysis of these elements is of primary importance in fishery management and population ecology, the traditional approaches mostly fail to capture the multivariate nature of structural change in time series data. In this paper, I propose a simple approach aiming at coping with the multi-elemental compositional otolith transect in a multi-scale quantitative manner. More specifically, the proposed recursive partitioning method tries to bias the chronological clustering process by accommodating some form of user-specified constraints based on both intra- and inter-groups characteristics. This allows researchers to focus on biologically relevant information (i.e. the one researcher look for and can interpret). The finding of this study may be considered from the more general perspective of the utility of chronological clustering study of multivariate time series. Chronological clustering based on recursive partition is easily interpretable and directly applicable to detection of hidden discontinuities in any multivariate time series. In a multi-proxy context, it also provides a powerful exploratory tool for assessing the relative importance of cross-correlated variables in structuring the environmental histories, as well as the congruency between variables. Ultimately, this approach demonstrates the actual interest in using advanced processing techniques to fully exploit the rich potential of individual biological archives, such as fish otoliths, to characterize individual life history. This appears as a promising new tool for ecologists wishing to extract environmental histories from dendro- and sclerochronological structures and would be a great help for practitioners working with chemical fingerprints. New functions for recursive partitioning using the R software environment are provided in a package and in the online Supplementary material together with a complete tutorial using full worked examples

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Otolith morphometrics have been shown to provide a practical basis for stock discrimi- nation and subsequent fisheries management. However, the determinants of otolith shape are not fully understood and analysis does not distinguish between genotype and environmentally induced differences. In this context, understanding how those 2 components act synergetically on the otolith shape is fundamental. The use of non-indigenous fish of multiple origins provides an interesting tool for evaluating the relative importance of genetic and environmental components in determining otolith shape. This paper investigates to what extent a dual regulation (i.e. genetic and environmen- tal) of the otolith shape from an introduced coral reef snapper (Lutjanus kasmira) exists, in order to determine how each component specifically acts on otolith morphology. Using geometric morpho- metrics, we discriminated between native and introduced range as well as between individuals belonging to different lineages (i.e. origins) but growing under the same environmental conditions (individuals cohabiting within the same shoals in the wild). Here we show that both genetic and envi- ronmental influences play a substantial role in determining the shape of the otolith. More specifically, while environment induces an overall change in otolith shape, genetically induced changes locally affect otolith shape. In addition, data suggest that both nuclear and mitochondrial components act synergetically. This information is fundamental if otolith shape is to be used as an effective tool for management of fisheries resources in the future.

International audience; The adaptive mechanisms on the early life stages of fishes to hypersaline stress are still poorly understood and probably determine the resistance of a population to disruption, compared with other less plastic species. The Casamance River in Senegal is an ideal location to test the adaptation to salinity as a dam was built in 1998 to exclude saline water intrusion. This lowered the salinity from 70 to 5 upstream and 60 downstream. The salinity influence on the growth in the early life of three West African fish species (Ethmalosa fimbriata, Sarotherodon melanotheron, and Tilapia guineensis) was studied using the width of microstructures in the otoliths and the individual migratory behaviour analysed from strontium (Sr) to calcium (Ca) ratios in the otoliths. The Sr:Ca ratio was quantified along individual transects measured from the posterior edge of the otolith to the core. The fishes were sampled on both sides of the dam that separated water with low salinity upstream from metahaline and hyperhaline water downstream. The results showed that salinity has different influence on the growth of each species. Ethmalosa fimbriata has the highest growth during the first 180 days in the freshwaters, indicating growth inhibition in the hyperhaline areas. For the two other species no growth difference were found. The Sr/Ca ratio varied widely, in Tilapia and Sarotherodon from below the dam. Individual life histories were more heterogeneous than upstream and showed a crossing of the dam for some individuals which could reach half of the fishes analysed. On the contrary in E. fimbriata, despite the large range of salinity, identical Sr/Ca profiles were found both upstream and downstream. This indicated that Sr/Ca ratio was not appropriate to evaluate life history patterns linked to salinity for this specie.

International audience; This study examined stocking with three early life stages of brown trout, Salmo trutta L., in the context of rehabilitating a native lineage. Experimental sections in five streams were stocked successively with three stages (I: unfed fry at the end of the reabsorption phase, II: fed fry measuring 2–3 cm and III: fed fry measuring 4–5 cm) derived from a hatchery stock bred from wild spawners. The three stages were distinguished by single or multiple fluoromarking of the otoliths with alizarin redS. The index of relative stocking efficiency was greater for stage II than for stage I in all sections and equivalent or greater than that for stage III. Stage II achieved significantly larger mean length and weight in autumn than stage III stockings.

This paper deals with the analysis of images of biological tissue that involves ring structures, such as tree trunks, bivalve seashells, or fish otoliths, with a view to automating the acquisition of age and growth data. A bottom-up template-based scheme extracts meaningful ridge and valley curve data using growth-adapted time-frequency filtering. Age and growth estimation is then stated as the Bayesian selection of a subset of ring curves, which combines a measure of curve significativity and an a priori statistical growth model. Experiments on real samples demonstrate the efficiency of the proposed data extraction stage. Our Bayesian framework is shown to significantly outperform previous methods for the interpretation of a data set of 200 plaice otoliths and compares favorably with interexpert agreement rates (88% of agreement to expert interpretations)., Cet article traite de l'analyse des images de tissus biologiques à des fins d'automatisation de l'acquisition des données d'âge et de croissance. Nous développons une approche générale pour l'extraction et l'interprétation des structures géométriques concentriques dans les images de tissus biologiques, tels que les troncs d'arbres, les coquilles de bivalves et les otolithes de poissons. La première étape permet d'identifier des courbes signficatives correspondant aux crêtes et aux vallées dans l'image. Elle intègre un filtrage adapté, fonction d'un a priori sur la croissance. Dans un second temps, l'estimation de l'âge et de la croissance est formulée comme un problème de sélection bayésienne d'un sous-ensemble pertinent de courbes parmi l'ensemble des courbes extraites. Des résultats obtenus sur des images de différents tissus démontrent l'efficacité de notre méthode d'extraction des structures d'intérêt. De plus, l'évaluation du schéma bayésien d'interprétation pour un ensemble de 200 otolithes de plie valide notre approche en termes d'amélioration des résultats antérieurs obtenus par des approches automatiques et en termes de comparaison aux taux d'agrément inter-experts de 88 %.

The West-African neighbouring Gambia and Saloum estuaries function in different ways, the first being normal (saltier waters in the lower river, salinity range 0-38) and the second being inverse (saltier waters in the upper river, salinity range 36-90). The common cichlid species Sarotherodon melanotheron was collected in both systems over 16 months (June 2001 to September 2002) at five locations. We quantified reproductive traits from macroscopic examination of the gonads, oocyte counts and measurements, and growth from interpretation and measurements of an otolith sub-sample. There was a clear seasonal cycle of reproduction in the estuaries with a peak at the beginning of the wet season (May-July). Size at maturation was smaller in the more saline environment, the Saloum, for both females (170 mm in Gambia and 131 mm in Saloum) and males (162 and 113 mm respectively). The relative fecundity was lower and the oocyte size was bigger in the freshwater location of the Gambia river. Growth, estimated by counting the annual opaque zones on whole otoliths, was reduced in the hypersaline environment of the Saloum (L ∞ = 198 mm, K = 0.26). Differences are less obvious between the growth in the Gambia (L ∞ = 238 mm, K = 0.21) and that in the Saloum with a salinity of less than 60 (L ∞ = 244 mm, K = 0.22). All these observations suggest that S. melanotheron is able to withstand saltier environments by limiting its growth, reducing the size-at-maturity, and changing its fecundity, but the most profound changes are only visible in hypersaline conditions.

The direct effects of reproduction (energy expenditure for gametogenesis) were studied in gonadectomized Oreochromis niloticus females, incapable of reproducing. The indirect effects of reproduction were studied in intact females that had either mouth brooded their eggs or not. In gonadectomized females the slowing of growth observed in the marginal zone of their otoliths coincided with the time of gonad regeneration. The responses were very varied in the group of intact females. In these females, there was less otolith growth and more checks were observed on the otoliths. The results showed that reproduction influenced-the growth of fish and their otoliths leading to a significant underestimate of the number of primary increments during this period of life.

Nile tilapia Oreochromis niloticus, initial age 12 days, were given an unrestricted (NR) or restricted (R) ration over 93 days which resulted in fish of very different sizes although the body condition factor (K) and the viscero-somatic index (IV) remained almost unchanged. In a second stage (64 days) each group (NR & R) was divided into three subgroups that were subjected to 0 (NR0, R0), 15 (NR15, R15) and 30 (NR30, R30) days of food restriction, respectively. The impact of the different treatments on the somatic growth during the second stage of the experiment had an effect, with a highly significant difference between the mean ± S.D. masses (MT) in the different subgroups (NR0= 115.0 ± 26.6 g; NR15 = 94.8 ± 24.9 g; NR30 = 56.3 ± 28 g; R0 = 76.4 ± 20.1 g; R15 = 72.l ± 17.6 g; R30 = 43.6 ± 17.2 g). Similarly, K and IV decreased. Irrespective of the initial feeding condition, the width of the otolith microincrements started to decrease at the end of the first or second day of restricted feeding. In the subgroups given a restricted food ration for 30 days (NR30 and R30), this decrease reached a plateau at about day 30, which was maintained even when the restriction had ended. This slowed growth did not lead to any marked halt in microincrement formation, since there were no significant differences (ANOVA; P>0.05) in the numbers of increments counted in the various subgroups. The results show that in 153 day old fish, a period of severe food restriction, even if prolonged (15 to 30 days), had no influence on the timing of the laying down of microincrements but only affected their growth.

The embryonic past of glass eels vas studied from the interpretation of microstructures registered on otoliths. The aim of this work is to put in evidence possible seasonal modifications of the growth of otoliths so that differences between otoliths of glass eels caught off marine and estuarine environment. So during the season 1999-2000, from November till March, otolith sampling was realised in the Southwestern part of France, in an estuarine and coastal zone. We observed a spatial and temporal evolution of proportions of the three various types of otoliths taken into account. Glass eels sampled at sea sometimes have a mark on their otoliths indicating the transition in the estuary, especially at the end of the fishing season. Measures of growth marks of otoliths showed that there were no seasonal differences during phases of the transoceanic migration and the crossing of the continental shelf. The radius of otoliths of glass eels sampled at sea was significantly smaller than those sampled in estuary. These results translated homogeneous environmental modifications met by the various larvae groups during the oceanic crossing and during the principal migration season as well as a turn over of these groups during the transition between marine and continental environment., Le passé larvaire des civelles est étudié à partir de l'interprétation des microstructures inscrites sur les otolithes. L'objectif de ce travail est de mettre en évidence d'éventuelles modifications saisonnières de la croissance des otolithes ainsi que des différences entre les otolithes des individus capturés en milieux marins et estuariens. Ainsi, au cours de la saison 1999¿2000, de novembre à mars, un échantillonnage d'otolithes est réalisé dans le Sud-Ouest de la France, en zones côtières et estuariennes. On observe une évolution spatiale et temporelle des proportions des trois différents types d'otolithes pris en compte. Les civelles capturées en mer présentent parfois sur leurs otolithes une marque de transition en estuaire, surtout en fin de saison de pêche. Les mesures des marques de croissance des otolithes montrent qu'il n'existe pas de différences saisonnières au cours des phases de migration transocéanique et de la traversée du plateau continental. Le rayon des otolithes de civelles capturées en mer est significativement plus petit que celui des civelles capturées en estuaire. Ces résultats traduisent des conditions environnementales homogènes rencontrées par les différents flux de larves pendant la traversée océanique au cours de la saison ainsi qu'un brassage de ces flux lors de la transition entre le milieu marin et le milieu continental.

Sole nurseries are located in the main bays and estuaries of the Bay of Biscay, where juveniles from the same stock. concentrate and constitute temporarily isolated groups. This context being favourable for elemental analyses of juvenile otoliths this study has been initiated with the aim of obtaining environmental imprints of the main nurseries of origin of juveniles recruiting to the adult stock, and of evaluating the relative contribution of these nurseries to the stock. The objectives were to compare (i) the otolith elemental imprints obtained by sampling juveniles in the Loire and the Gironde nurseries, and (ii) two multi-element analysis techniques: laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and solution-based ICPMS (SB-ICPMS) adapted to small volumes. Depending on the fish origin, differences in Sr and Rb concentrations were shown using LA-ICPMS. Comparisons between the antero-dorsal and postero-ventral sites from where otolith material was ablated also suggested a spatial heterogeneity in otolith composition at least for some metals. From linear discriminant analyses, 73 % and 79 % of individuals (bootstrap estimations) were correctly classified with respect to their origin from the composition of the antero-dorsal and postero-ventral areas, respectively. The SB-ICPMS analysis was more powerful, which resulted in an 89 % rate of correct classification from a 2-variable model (Mg and Cd), whereas a 5-variable model (Li, Mg, Rb, Cd, Th) resulted in a 91 %, rate of correct classification (bootstrap estimations). These results confirm that sole juveniles from the main estuaries of the French Atlantic coast could be discriminated by the elemental fingerprints of their otoliths., Les nourriceries de la sole sont localisées dans les principales baies et estuaires du golfe de Gascogne où les juvéniles se concentrent et constituent des groupes du même stock, temporairement autonomes, caractérisés par leurs traits démographiques. L'isolement des juvéniles dans des zones sous diverses influences continentales offre un contexte propice à l'analyse élémentaire de leurs otolithes. Cette méthode permet de rechercher les éléments traces susceptibles de représenter une signature environnementale de la nourricerie afin de tenter une estimation des proportions relatives de juvéniles (recrutement) issus de ces nourriceries et rejoignant le stock d'adultes. Pour définir les bases de la méthode, nous avons comparé (i) les signatures élémentaires obtenues pour les otolithes de juvéniles prélevés sur les nourriceries de Loire et Gironde, et (ii) les potentialités de deux techniques de la spectrométrie de masse à plasma inductif (ICPMS) reposant, l'une sur des prélèvements par ablation laser d'échantillons solides (LA-ICPMS) et l'autre, sur le dosage d'échantillons mis en solution (SB-ICPMS), dosage adapté à de très petits volumes. Les concentrations en Sr et Rb mesurées en ablation laser (LA-ICPMS) diffèrent avec l'origine des juvéniles. La comparaison des données acquises sur les aires antéro-dorsale et postéro-ventrale de l'otolithe suggère par ailleurs, pour certains métaux au moins, une hétérogénéité spatiale de composition de l'otolithe. À partir d'analyses linéaires discriminantes, 73 % et 79 % des individus ont été correctement classés (bootstrap estimations) selon leur origine à partir de la composition élémentaire des otolithes dans les aires antéro-dorsale et postéro-ventrale respectivement. L'analyse SB-ICPMS, plus sensible du fait de limites de détection très basses, s'avère beaucoup plus performante. Sur la base des concentrations en Mg et Cd, on obtient 89 % d'échantillons biens classés (bootstrap estimation). Ce taux s'élève à 91 % en utilisant un modèle discriminant à cinq variables (Li, Mg, Rb, Cd, Th). L'ensemble des résultats confirme que les otolithes des juvéniles de la sole s'imprègnent d'éléments traces authentifiant la nourricerie d'où ils sont issus, ce qui devrait permettre de retracer l'histoire récente des sub-adultes migrant vers les frayères.

Plusieurs populations de Sardinelles (#S. aurita$ et #S. maderensis$) existent probablement le long de la côte d'Afrique de l'Ouest. A présent elles sont disséminées surtout selon les aires de ponte et de nourriceries. Les études antérieures basées sur les caractéristiques de reproduction et croissance tendent à montrer cinq populations et peut être des sous-populations. Bien que ce soient les analyses génétiques d'échantillons individuels qui puissent fournir des discriminations dans l'absolu, certaines nouvelles méthodes d'analyse des tissus calcifiés (otolithes par exemple) pourraient fournir des résultats comparables ou complémentaires. Deux types de méthodes sont utilisées à cet effet : (1) l'analyse numérique de la morphométrie des otolithes, ou (2) l'analyse microchimique des éléments à l'état de traces dans les otolithes. La microchimie semble particulièrement prometteuse car la composition élémentaires des otolithes semble étroitement liée aux conditions de l'environnement du poisson. (D'après résumé d'auteur)

La détermination de l'âge des poissons selon le nombre de marques déposées sur les pièces dures du corps, notamment les écailles, les otolithes, les os operculaires est bien connue. Toutefois, il est nécessaire d'établir la périodicité annuelle ou saisonnière du dépôt de telles marques. Les premières observations d'écailles de #S. aurita$ semblent montrer l'existence de deux cycles annuels de croissance. Ce phénomène s'expliquerait par l'existence des upwellings mineur et majeur qui constituent deux périodes favorables à la croissance. Néanmoins plus de 18 mois d'observation sur les écailles seront nécessaires pour rejeter ou accepter cette hypothèse d'un double cycle annuel de croissance. (Résumé d'auteur)

A method to assist the reading of calcified structures with digital images is proposed. An a priori growth pattern is introduced in the image processing to take into account both the variability of the ring size and the non-linearity of their growth. The introduction of biological knowledge is performed within a demodulation processing using the reciprocal growth function. The ring number is estimated by spectral analysis. The constraints introduced by the growth model are weak since they are restricted to the definition of L0, in the case of an exponential model, or of L∞ in the case of a Von Bertalanffy model. When applied to larval Dover sole otoliths (Solea solea) results close to the expert's are obtained. In the case of saithe otoliths (Pollachius virens) the mean discrepancy with the expert's, i.e. 1.5 years, can be assigned to the lack of processing of marginal rings and to the inadequacy of the morphogenesis model on which the processing algorithm is based. This approach which is only founded on the dynamic features of the "biological signal", will have to be completed in future work with the introduction of structural information., Une méthode d'aide à la lecture de pièces calcifiées par traitement d'images numériques est proposée. Un modèle de croissance a priori est intégré dans le traitement de l'image afin de prendre en compte à la fois la variabilité de la taille des "anneaux" et la non linéarité de leur croissance. Cette intégration est réalisée dans un traitement de démodulation à l'aide de la loi de croissance réciproque. L'estimation du nombre d'anneaux est ensuite réalisée par analyse spectrale. Les contraintes introduites par la prise en compte du modèle sont faibles puisque limitées à la définition du L0, dans le cas d'un modèle exponentiel, du L∞ dans le cas d'un modèle de Von Bertalanffy. Appliquée à des otolithes de larves de soles (Solea solea) cette méthode permet d'obtenir des résultats proches de ceux de l'expert. Dans le cas des otolithes d'adultes de lieu noir (Pollachius virens), la différence moyenne de 1,5 ans avec les experts doit être imputée à l'absence de traitement adéquat des anneaux marginaux tant qu'à l'inadéquation du modèle de morphogenèse sur lequel repose l'algorithme de traitement. Cette approche, uniquement fondée sur les caractéristiques dynamiques du "signal" biologique, devra être complétée par la prise en compte d'informations structurelles auxquelles se réfèrent habituellement les lecteurs.

Several methods are used for age determination of eels in the French mediterranean lagoons (observation of the whole otolith after clearing, grinding and polishing, dyeing, SEM and image analysis). Two types of otoliths are observed depending on the width of the growth rings which is probably related to the environmental conditions. Furthermore, the growth checks are located nearby or inside the opaque rings. A computer assisted method is developed, with reference to the other methods, with the aim of improving the efficiency of collecting and processing age and growth data. With further developments and increasing knowledge of life-history of elvers and juvenile eels, it seems possible to use an image analysis system for ageing eels in lagoons. Nevertheless, the most important point is to validate the results before using them for growth populations studies. (Résumé d'auteur)

Age determination for #Diagramma pictum$, (n=102), were conducted using three methods. The two first methods are based on the counts of annuli on respectively whole otolith cross sections. The third method use the decrease of otolith daily growth increment (DGI) density with age. The growth curves found with the first two methods are comparable and similar to previous results. However, the analysis of life history traits such as size at first reproduction indicates that these methods are likely to underestimate growth. The use of DGI density yields a faster growth curve. To establish this curve the relationships liking fish size to otolith radius and DGI density to otolith radius are needed. The final growth curve is particularly sensitive to changes in these previous relationships. For this reason all sizes should be well represented in the sample. This method is not recommended for fish with large seasonal growth variations but could produce good DGI measurements for those species which have only a small zone of readible otolith. (Résumé d'auteur)