Indicios preliminares de variaciones ontogenéticas y espaciales en las señales isotópicas y elementales de otolitos de Solea solea del Golfo de León (Mediterráneo noroccidental)

Knowledge of fish life cycles is important for exploited species. In the Mediterranean Sea, catches of common sole (Solea solea) have fluctuated widely since the 1970s. Solea solea displays an ontogenetic shift in habitat: sole larvae are marine, juveniles inhabit shallow marine waters and coastal lagoons and adults inhabit deeper marine waters. Although the results of this study were obtained using only a small set of individuals, the otolith elemental composition and isotopic ratios were investigated for the three life stages (post-larval, juvenile and adult) in order to acquire a better knowledge of the variability in environmental conditions experienced by the common sole at each life stage in the NW Mediterranean. Moreover, this study provides the first evaluation of the potential of whole otolith microchemistry for investigating habitat connectivity in sole populations from the Gulf of Lions. The elemental and isotopic signatures of otoliths of post-larvae captured in various environments appear to show variations related to the River Rhône inputs (high Ba/Ca and low Sr/Ca ratios). Juveniles appear to show significant variations in otolith elemental and isotopic compositions depending not only on the physico-chemical properties of water in the nurseries they inhabit (Rhône River, Thau or Mauguio lagoons), but also as a result of variations in the chemical composition of their surrounding sediments and in their benthic prey. Adults exhibit otolith differences for isotopic ratios only, which is probably linked to the River Rhône inputs. Finally, several significant relationships were observed between otolith elemental composition and fish size in specimens captured at the River Rhône mouth. However, these variations seem to be an indication of the composition acquired in each environment rather than a sign of ontogeny.El conocimiento del ciclo de vida es importante para las especies comerciales de peces. En el mar Mediterráneo, las capturas de lenguado común (Solea solea) han fluctuado ampliamente desde la década de los 70. Solea solea presenta un cambio de hábitat ontogenético, las larvas son marinas, los juveniles viven en aguas marinas y en lagunas costeras, y los adultos viven en aguas marinas más profundas. Aunque los resultados de este estudio fueron obtenidos usando sólo un número pequeño de individuos, la composición de elemental los otolitos y las relaciones isotópicas fueron investigados en las tres etapas de vida (post-larval, juveniles y adultos) con el fin de adquirir un mejor conocimiento de la variabilidad en las condiciones ambientales que experimenta el lenguado común en cada etapa de la vida en el mediterráneo noroccidental. Por otra parte, este trabajo permite una primera evaluación del potencial de toda la microquímica de otolitos para la investigación de la conectividad del hábitat en las poblaciones de lenguado en el Golfo de León. Las señales elementales e isotópicos de los otolitos de las post-larvas capturadas en diferentes entornos muestran variaciones en relación a los materiales aportados por del río Ródano (alta relación Ba/Ca y baja relación Sr/Ca). Los juveniles parecen mostrar variaciones significativas en la composición elemental e isotópica de los otolitos dependiendo no sólo de las propiedades físico-químicas del agua en los viveros que habitan (Thau, Mauguio o el río Ródano), sino también como resultado de las variaciones en la composición química de los sedimentos circundantes y de su presa béntica. Los adultos presentan únicamente diferencias en las relaciones isotópicas de los otolitos, que está probablemente vinculado a por materiales aportados por el río Ródano. Por último, se observaron varias relaciones significativas entre la composición elemental de los otolitos y el tamaño de los peces en las muestras capturadas en la desembocadura del río Ródano. Sin embargo, estas variaciones parecen ser una indicación de la composición adquirida en cada entorno, más que ser debidas a la ontogenia

Macroparasite communities in European eels, Anguilla anguilla

European eel parasites, in particular invasive species, are suspected to play a role in the decline in the populations of their host. The aims of this work were to describe the parasitic fauna of eels in French Mediterranean lagoons and to study the epidemiological trends of the invasive helminth species, the nematode Anguillicola crassus and the monogenean Pseudodactylogyrus spp., in regard to spatio-temporal dynamics, host biological characteristics and parasite community. A total of 418 eels was sampled in eight lagoons between March 2003 and June 2005. Our results revealed a total macroparasite richness of 23 species: 1 Monogenea, 13 Digenea, 2 Cestoda, 3 Nematoda, 2 Acantocephala and 2 Crustacea. We found no variation in A. crassus abundance in Salses-Leucate lagoon in the same month across years. However, the nematode abundance was higher in eels caught in summer than in those caught in winter. Pseudodactylogyrus sp. was not found in Salses-Leucate lagoon, except in July 2004. Comparisons between the lagoons on the same date showed that they could be separated into two groups for both species' abundance: Grau-du-Roi, Mauguio, Palavas and Vaccarès lagoons, where abundance was rather high, against Bages-Sigean, Pierre-Blanche, Salses-Leucate and Thau lagoons, where abundance was rather low or nil. We found significant negative relationships between A. crassus abundance and the length and age of eels. We also found a significant positive relationship between A. crassus and Pseudodactylogyrus sp. abundance. Finally, our results showed significant positive relationships between both A. crassus and Pseudodactylogyrus sp. abundance and the abundance of the digeneans Prosorhynchus aculeatus and Lecithochirium gravidum. We discuss the results in regard to the dynamics of invasions, the characteristics of the parasite life cycles and the ecology of eels

Macroparasite communities in European eels, Anguilla anguilla, from French Mediterranean lagoons, with special reference to the invasive species Anguillicola crassus and Pseudodactylogyrus spp.

European eel parasites, in particular invasive species, are suspected to play a role in the decline in the populations of their host. The aims of this work were to describe the parasitic fauna of eels in French Mediterranean lagoons and to study the epidemiological trends of the invasive helminth species, the nematode Anguillicola crassus and the monogenean Pseudodactylogyrus spp., in regard to spatio-temporal dynamics, host biological characteristics and parasite community. A total of 418 eels was sampled in eight lagoons between March 2003 and June 2005. Our results revealed a total macroparasite richness of 23 species: 1 Monogenea, 13 Digenea, 2 Cestoda, 3 Nematoda, 2 Acantocephala and 2 Crustacea. We found no variation in A. crassus abundance in Salses-Leucate lagoon in the same month across years. However, the nematode abundance was higher in eels caught in summer than in those caught in winter. Pseudodactylogyrus sp. was not found in Salses-Leucate lagoon, except in July 2004. Comparisons between the lagoons on the same date showed that they could be separated into two groups for both species' abundance: Grau-du-Roi, Mauguio, Palavas and Vaccarès lagoons, where abundance was rather high, against Bages-Sigean, Pierre-Blanche, Salses-Leucate and Thau lagoons, where abundance was rather low or nil. We found significant negative relationships between A. crassus abundance and the length and age of eels. We also found a significant positive relationship between A. crassus and Pseudodactylogyrus sp. abundance. Finally, our results showed significant positive relationships between both A. crassus and Pseudodactylogyrus sp. abundance and the abundance of the digeneans Prosorhynchus aculeatus and Lecithochirium gravidum. We discuss the results in regard to the dynamics of invasions, the characteristics of the parasite life cycles and the ecology of eels

Macroparasite communities in European eels, <i>Anguilla anguilla</i>, from French Mediterranean lagoons, with special reference to the invasive species <i>Anguillicola crassus</i> and <i>Pseudodactylogyrus</i> spp.

European eel parasites, in particular invasive species, are suspected to play a role in the decline in the populations of their host. The aims of this work were to describe the parasitic fauna of eels in French Mediterranean lagoons and to study the epidemiological trends of the invasive helminth species, the nematode Anguillicola crassus and the monogenean Pseudodactylogyrus spp., in regard to spatio-temporal dynamics, host biological characteristics and parasite community. A total of 418 eels was sampled in eight lagoons between March 2003 and June 2005. Our results revealed a total macroparasite richness of 23 species: 1 Monogenea, 13 Digenea, 2 Cestoda, 3 Nematoda, 2 Acantocephala and 2 Crustacea. We found no variation in A. crassus abundance in Salses-Leucate lagoon in the same month across years. However, the nematode abundance was higher in eels caught in summer than in those caught in winter. Pseudodactylogyrus sp. was not found in Salses-Leucate lagoon, except in July 2004. Comparisons between the lagoons on the same date showed that they could be separated into two groups for both species' abundance: Grau-du-Roi, Mauguio, Palavas and Vaccares lagoons, where abundance was rather high, against Bages-Sigean, Pierre-Blanche, Salses-Leucate and Thau lagoons, where abundance was rather low or nil. We found significant negative relationships between A. crassus abundance and the length and age of eels. We also found a significant positive relationship between A. crassus and Pseudodactylogyrus sp. abundance. Finally, our results showed significant positive relationships between both A. crassus and Pseudodactylogyrus sp. abundance and the abundance of the digeneans Prosorhynchus aculeatus and Lecithochirium gravidum. We discuss the results in regard to the dynamics of invasions, the characteristics of the parasite life cycles and the ecology of eels

Silver eel population size and escapement in a Mediterranean lagoon: Bages-Sigean, France

Much concern has been raised about the decline in the European eel (Anguilla anguilla) population. European management plans for the recovery of the stock are now in preparation, the main objective being to increase the escapement of the potential spawners (silver eels) in each basin to allow 40% of the pristine biomass to escape. However, there are relatively few studies on silver eel escapement and production, and no recent measurement of escapement in lagoons, habitats which support large silver eel sub-populations in the Mediterranean region. A mark-recapture study was carried out in autumn 2007 in order to estimate the number of silver eels migrating from the Bages-Sigean lagoon in the South-West of France. The migrating population, mostly males between 36 and 42 cm, was estimated to be around 1 120 000 eels (30 kg.ha(-1)). The exploitation rate by professional fishermen was around 20% (6 kg.ha(-1)), leading to an escapement level of 80% (24 kg.ha(-1)). The results are discussed regarding the available data in the literature on silver eel escapement.Le déclin de l'anguille européenne Anguilla anguilla est très préoccupant et chaque pays européen a maintenant le devoir de préparer un plan de gestion pour la reconstitution du stock. Le principal objectif est d'assurer un taux d'échappement d'au moins 40 % de la biomasse pristine des anguilles argentées (futurs géniteurs) vers leur lieu de reproduction. Cependant, très peu de recherches ont été menées sur l'estimation du stock et du taux d'échappement des anguilles argentées et aucune estimation récente du taux d'échappement n'avait encore été réalisée en Méditerranée. Cette étude de marquage-recapture a été réalisée en automne 2007 dans le but d'estimer la quantité d'anguilles argentées migrantes de la lagune de Bages-Sigean. La population migrante, principalement des mâles entre 36 et 42 cm, a été estimée à 1 120 000 anguilles (30 kg·ha–1). Le taux d'exploitation par les pêcheurs professionnels évalué à 20 % (6 kg·ha–1) laisse suggérer un taux d'échappement de 80 % (24 kg·ha–1). Les résultats sont discutés au regard de la littérature disponible sur l'échappement des anguilles argentées

Tissus durs et âge individuel des vertébrés

Ce travail présente l'état actuel des connaissances sur l'évaluation de l'âge des anguilles. L'application des méthodes classiques de scalimétrie et d'otolithométrie révèle l'existence de difficultés d'interprétation des structures. Des méthodes plus discriminantes (MEB, analyse chimique) sont susceptibles de fournir des informations permettant d'apprécier les dépôts journaliers et de mieux cerner le passé biologique inscrit avec précision dans l'otolithe de l'anguille. (Résumé d'auteur

Contribution de l'otolithométrie à l'étude de la dynamique de la migration larvaire de l'anguille européenne (Anguilla anguilla)

L'originalité de l'anguille européenne réside dans son aire de ponte unique : la Mer des Sargasses, qui implique de longues migrations transatlantiques. La première d'entre elles, à destination des côtes européennes, concerne les deux stades larvaires : leptocéphales et civelles transparentes. Cette migration larvaire demeure mal connue du point de vue spatio-temporel (durée et voies empruntées). Une étude microstructurale des sagittae de civelles transparentes a permis, non seulement de décrire les étapes antérieures de la vie larvaire marine, mais aussi, d'estimer l'âge absolu des civelles par comptabilisation de l'ensemble des accroissements journaliers. Une telle connaissance permet de déduire la période de ponte des anguilles argentées en Mer des Sargasses