Presence of Palaemon macrodactylus in a Europe estuary: evidence for a successful invasion of the Gironde (SW France)

Palaemon macrodactylus, an exotic shrimp native to the northwest Pacific Ocean, has been recorded in many estuaries along the Atlantic coast of Europe since the late 1990’s. In this study, a regular monthly survey, held since 1992 of the middle section of the Gironde estuary, revealed this species’ rapid and full colonization of the system since its appearance in samples during summer 1998. In the Gironde, the population of P. macrodactylus is self-sustaining and the species is now established there. Our study highlights two important elements that might explain its successful colonization: its ability to quickly invade a niche under-exploited by the similar native species and its greater reproductive output. The species’spatio-temporal distribution in relation to environmental variables was studied and compared with that of the native species P. longirostris. The exotic species was shown to mainly inhabit the polyhaline and mesohaline section of the estuary, which are sections generally under-exploited by females of the native species. Furthermore, fecundity analysis and larval abundance survey results revealed a higher potential fecundity and a greater proportion of larvae and juvenile stages for P. macrodactylus in the natural environment

Shark predation on migrating adult american eels (Anguilla rostrata) in the Gulf of St. Lawrence.

In an attempt to document the migratory pathways and the environmental conditions encountered by American eels during their oceanic migration to the Sargasso Sea, we tagged eight silver eels with miniature satellite pop-up tags during their migration from the St. Lawrence River in Québec, Canada. Surprisingly, of the seven tags that successfully transmitted archived data, six were ingested by warm-gutted predators, as observed by a sudden increase in water temperature. Gut temperatures were in the range of 20 to 25°C-too cold for marine mammals but within the range of endothermic fish. In order to identify the eel predators, we compared their vertical migratory behavior with those of satellite-tagged porbeagle shark and bluefin tuna, the only endothermic fishes occurring non-marginally in the Gulf of St. Lawrence. We accurately distinguished between tuna and shark by using the behavioral criteria generated by comparing the diving behavior of these two species with those of our unknown predators. Depth profile characteristics of most eel predators more closely resembled those of sharks than those of tuna. During the first days following tagging, all eels remained in surface waters and did not exhibit diel vertical migrations. Three eels were eaten at this time. Two eels exhibited inverse diel vertical migrations (at surface during the day) during several days prior to predation. Four eels were eaten during daytime, whereas the two night-predation events occurred at full moon. Although tagging itself may contribute to increasing the eel's susceptibility to predation, we discuss evidence suggesting that predation of silver-stage American eels by porbeagle sharks may represent a significant source of mortality inside the Gulf of St. Lawrence and raises the possibility that eels may represent a reliable, predictable food resource for porbeagle sharks

Réponses d'une population aux forçages environnementaux et anthropiques : le suivi à long terme de la crevette Palaemon Longirostris de l'Estuaire de la Gironde (1979-2007)

La population de la crevette blanche Palaemon longirostris, espèce résidente des estuaires faisant l’objet d’une pêche traditionnelle, est soumise à des forçages environnementaux (fluctuations naturelles du milieu, modifications du régime hydro-climatique de l’estuaire en lien avec le changement climatique) et anthropiques importants (aspiration dans les circuits du CNPE -Centre Nucléaire de production d’Electricité du Blayais-, pêche ciblée, pollutions etc.). Dans ce contexte et sur la base d’un suivi mensuel, réalisé depuis 1979, complété par des échantillonnages en 2007, cette thèse montre que cette population répond fortement aux changements environnementaux abiotiques et anthropiques. Ainsi, d’importantes fluctuations spatio-temporelles des abondances sont mises en évidence à diverses échelles temporelles, spatiales et biologiques. L’analyse de la série à long terme montre des fortes oscillations interannuelles régulières (période 5/10 ans) en partie liées aux facteurs environnementaux et aux variations du recrutement. Une diminution de l’abondance globale, ainsi qu’un déplacement vers l’amont de cette population, sont également constatés. Ce déclin est attribué aux fortes variations et nombreuses modifications des traits de vie de l’espèce –reproduction, -croissance, -mortalité, démontrées au cours de l’étude. La présence de déformations de l’exosquelette, étudiée aussi via un élevage de plusieurs mois, révèle par ailleurs, de forts impacts négatifs à l’échelle individuelle (mortalité). De plus, des simulations réalisées à partir d’un modèle matriciel de dynamique de population élaboré durant l’étude, montrent la synergie des pressions anthropiques par prélèvements (CNPE, pêche) et des forçages environnementaux, ainsi que l’importance des processus de déplacement dans le fonctionnement de cette population. Cette étude démontre finalement l’intérêt que revêt cette population et plus largement les populations de crevettes estuariennes, pour l’étude du fonctionnement et du diagnostic de l’état des écosystèmes estuariens. De nouvelles métriques originales sont proposées, lesquelles ouvrent vers la voie vers de nouveaux indicateurs.The white shrimp, Palaemon longirostris, is an estuarine species and an important fishing resource. This species therefore encounters an important environmental forcing (natural fluctuations of the environment, modifications of the hydro-climatic regime of the estuary associated with the climate change) and an anthropological forcing (drawing up by the circuits of the CNPE - Nuclear center of electricity production of Blayais-, targeted fishing, pollutions etc.). In this context and on the basis of a monthly survey in place since 1979 and completed in 2007, this study shows that this population is strongly influenced by environmental and anthropological changes. Important spatio-temporal variations in the shrimp abundance are highlighted at different temporal, spatial and biological scales. A long-term analysis underlines strong regular interannual oscillations (5/10-year period) partially linked with environmental factors and recruitment variations. A decrease in the global abundance and a movement of this population towards the upstream part of the estuary are also displayed. In this study, the decline is attributed to strong variations and numerous modifications in the life history traits of the species - reproduction, - growth, - mortality. The presence of exoskeletal deformities, alternatively studied via a rearing of several months, reveals strong negative impacts at the individual scale (mortality). Furthermore, simulations based on a population-matrix model, developed during the study, show the synergy of the anthropological pressure by capture (CNPE, fishing) and the environmental forcing, as well as the importance of movement processes in the population dynamics. This study finally demonstrates the interest of this population, and more widely of the estuarine shrimp populations, in the understanding of the functioning and the diagnosis of the estuarine ecosystem state. New original metrics are proposed, opening the way towards new indicators

Réponses d'une population aux forçages environnementaux et anthropiques :le suivi à long terme de la crevette Palaemon longirostris de l'estuaire de la Gironde (1979-2007)

The white shrimp, Palaemon longirostris, is an estuarine species and an important fishing resource. This species therefore encounters an important environmental forcing (natural fluctuations of the environment,modifications of the hydroclimatic regime of the estuary associated with the climate change) and an anthropological forcing (drawing up by the circuits of the CNPE Nuclear center of electricity production of Blayais, targeted fishing, pollutions etc.). In this context and on the basis of a monthly survey in place since 1979 and completed in 2007, this study shows that this population is strongly influenced by environmental and anthropological changes. Important spatio‐temporal variations in the shrimp abundance are highlighted at different temporal, spatial and biological scales. A long term analysis underlines strong regular interannual oscillations (5/10 year period) partially linked with environmental factors and recruitment variations. A decrease in the global abundance and a movement of this population towards the upstream part of the estuary are also displayed. In this study, the decline is attributed to strong variations and numerous modifications in the life history traits of the species reproduction, growth, mortality. The presence of exoskeletal deformities, alternatively studied via a rearing of several months, reveals strong negative impacts at the individual scale (mortality). Furthermore, simulations based on a population matrix model, developed during the study, show the synergy of the anthropological pressure by capture (CNPE, fishing) and the environmental forcing, as well as the importance of movement processes in the population dynamics. This study finally demonstrates the interest of this population, and more widely of the estuarine shrimp populations, in the understanding of the functioning and the diagnosis of the estuarine ecosystem state. New original metrics are proposed, opening the way towards new indicators.La population de la crevette blanche Palaemon longirostris, espèce résidente des estuaires faisant l'objet d'une pêche traditionnelle, est soumise à des forçages environnementaux (fluctuations naturelles du milieu, modifications du régime hydro climatique de l'estuaire en lien avec le changement climatique) et anthropiques importants (aspiration dans les circuits du CNPE Centre Nucléaire de production d'Electricité du Blayais‐, pêche ciblée, pollutions etc.). Dans ce contexte et sur la base d'un suivi mensuel, réalisé depuis 1979, complété par des échantillonnages en 2007, cette thèse montre que cette population répond fortement aux changements environnementaux abiotiques et anthropiques. Ainsi, d'importantes fluctuations spatio temporelles des abondances sont mises en évidence à diverses échelles temporelles, spatiales et biologiques. L'analyse de la série à long terme montre des fortes oscillations interannuelles régulières (période 5/10 ans) en partie liées aux facteurs environnementaux et aux variations du recrutement. Une diminution de l'abondance globale, ainsi qu'un déplacement vers l'amont de cette population, sont également constatés. Ce déclin est attribué aux fortes variations et nombreuses modifications des traits de vie de l'espèce reproduction, croissance, mortalité, démontrées au cours de l'étude. La présence de déformations de l'exosquelette, étudiée aussi via un élevage de plusieurs mois, révèle par ailleurs, de forts impacts négatifs à l'échelle individuelle (mortalité). De plus, des simulations réalisées à partir d'un modèle matriciel de dynamique de population élaboré durant l'étude, montrent la synergie des pressions anthropiques par prélèvements (CNPE, pêche) et des forçages environnementaux, ainsi que l'importance des processus de déplacement dans le fonctionnement de cette population. Cette étude démontre finalement l'intérêt que revêt cette population et plus largement les populations de crevettes estuariennes, pour l'étude du fonctionnement et du diagnostic de l'état des écosystèmes estuariens. De nouvelles métriques originales sont proposées, lesquelles ouvrent la voie vers de nouveaux indicateurs

Première observation de la crevette invasive orientale Palaemon macrodactylus Rathbun, 1902 en France (Gironde)

International audienceDuring summer 2006, the first specimens of the oriental shrimp Palaemon macrodactylus Rathbun, 1902 were identified in the Gironde Estuary (France). These specimens, which included ovigerous females, are confirmed present throughout a large part of the estuary, in large numbers compared to the local resident shrimp Palaemon longirostris Milne Edwards, 1837. Native to Asia, P. macrodactylus was first introduced in California (USA) in the 1950s, before being detected recently within several European estuaries, e.g. the Guadalquivir Estuary (Spain) and the Orwell Estuary (England). According to these records, P. macrodactylus appears to be a strong invader, able to colonise a wide geographical range

Quel avenir pour la crevette blanche?

National audienceEtude de la crevette blanche dans l'estuaire de la Gironde : espèce qui semble en déclin, dont les performances reproductives diminuent, qui a des problèmes de déformations durables, un fort taux de mortalité non naturelle face à une espèce exotique très proche moins touchée par la mortalité

Estimation de la mortalité des crevettes blanches transitant dans le circuit de refroidissement du CNPE du Blayais : Rapport définitif Mai 2006 – Juin 2007

D’après le descriptif de l’étude et en fonction des délais imposés et des moyens disponibles, l’estimation des mortalités a été réalisé selon 2 approches : - une étude qualitative : taux de mortalité immédiate et différée, - et une étude semi-quantitative : niveaux de mortalité mensuels, à relativiser au regard des autres mortalités anthropiques directes connues et du fonctionnement de la population

Biologie de la reproduction de Palaemon longirostris (Décapodes : Palaemonidés) de l'estuaire de la Gironde, avec une comparaison avec les autres populations européennes

International audienceOur study details key parameters of the reproductive biology of the shrimp Palaemon longirostris, e.g., spatio-temporal variation of the sex-ratio, migration pattern, breeding period, fecundity, size at the onset of maturity, and egg volume. While P. longirostris population was very little studied in its distribution area, our fist aim was to complete that lack of knowledge and to provide a basis for understanding its population dynamic. Finally, our results were also compared with those reported from different studies on this species within Europe, in order to test the reported latitudinal cline of reproductive parameters in decapods. During a one-year survey, P. longirostris have been collected monthly across a large part of the Gironde estuary (France). Biometric measurements and determination of sex and maturation stages were carried out on preserved subsamples. Eggs were counted and measured for ovigerous females. In the Gironde, the breeding period was restricted from March to July, and related to water temperature. The size of the ovigerous females ranged between 7.1 and 14.6 mm cephalothorax length; according to their size, these females brought between 78 and 1391 eggs (547 on average). These results were compared with available data from the literature on French or foreign populations. For two reproductive parameters a latitudinal cline was noticed: e.g., an increase of the maximum females size and a restriction of the breeding period with latitude. Due to the weakness of available data on the reproductive biology of P. longirostris, it was very difficult to compare fecundity (number of eggs brought per female) and egg volume between localities. As expected fecundity could decrease with latitude, but this trend remains to be confirmed by more extensive studies on the species populations

Déformations des crevettes de l'estuaire : un désastre pour la population ?

National audienceAnalyse des déformations externes des crevettes blanches