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International audience; The specific stock composition and dispersion of anadromous fish species aggregations in the marine environment are poorly known, while they can play a major role in the metapopulation dynamics. Otolith microchemistry has proven to be a powerful tool to address natal origins of anadromous fish. We used archived otolith microchemistry to investigate the population-specific composition of European shads (Alosa alosa and Alosa fallax) subadults in the ocean during the 80’s. The allocation of natal origin was addressed relying on contemporary water and juveniles signatures within a Bayesian model. A great discrimination of natal origin was obtained at the Biscay Gulf scale. However, the discrimination of 80’s natal origin for the southern rivers with similar geology based on 2013 water and juveniles baselines was doubtful. Our results showed that the most abundant southern populations were dominant, suggesting that population-specific composition was related to population relative abundance. The dispersion in the marine environment was plastic; alternatively shads were found large distances away from their natal rivers, while others remained in the vicinity of their natal river plume.

International audience; Restocking measures of the endangered European eel (Anguilla anguilla) have been set up in Europe since 2011. Restocking operations are performed with glass eel postlarval stage during their upstream migration. Restocking protocols involve the collection of glass eel in estuaries, transport and marking of 30% of the glass eels with Alizarin red S before restocking. All these restocking operations such as transport, handling, osmotic and thermal shock are a potential source of physiological stress for glass eels. The objective of the present study was to investigate the inter-individual responses to stress in the structure of the otoliths of restocked fish. This was achieved using otolith and experimental science. The originality of the present study was to address restocking stress for early stages of European eels. An experimental setting was performed by rearing glass eels obtained from a restocking program during 9 months. A control group was obtained by collecting wild glass eels at the entrance of a freshwater habitat. Relying on microstructure analysis of the sagittae otoliths and biometric measures, we aimed at investigating inter-individual variabilities of glass eels during their larval and glass eel stage and verifying the presence of additional stress marks related to restocking. The present results would be useful for improving eel restocking protocols or interrogating the relevance of restocking eels programs as a measure of recovery of healthy eel populations

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International audience; Methods to study the migratory behaviourr of fish can be divided in two categories: capture-dependent (based on sampling marked or unmarked fish) and capture-independent methods, such as visual or video observation, resistivity fish counters or hydroacoustics. In this chapter we focus only on capture-dependent methods using marked fish.

International audience; Introduction, anadromous fishes: who are they? Why do they migrate? When do they migrate? How do they migrate? Insights on anadromous species conservation.

International audience; Otoliths as tracers of fish migration. Analytical techniques and equipment used to infer fish migrations and movements. Collection and preparation of samples. Investigating fish migration: data treatment. Case studies.

International audience; La compréhension des capacités de dispersion des espèces migratrices est d’importance capitale pour leur gestion. En jumelant la microchimie des otolithes aux analyses génétiques reposant sur les microsatellites, nous avons obtenu de l’information sur la capacité de dispersion immédiate et à long terme de l’alose vraie (Alosa alosa), un poisson clupéidé anadrome en déclin dans toute son aire de répartition. L’affectation de l’origine natale a été établie sur la base de la signature de l’eau et des signatures d’otolithes d’individus juvéniles et matures au sein d’un modèle bayésien. La majorité des adultes a été affectée à une rivière source avec des degrés de confiance élevés, et seulement 4 % des individus étaient d’origine indéterminée. L’origine natale obtenue des otolithes a été utilisée pour définir une ligne de base des populations en regroupant les individus de la même rivière natale plutôt que du même lieu d’échantillonnage, comme cela se fait habituellement. Si A. alosa faisait preuve d’un degré élevé de fidélité au site natal, cette espèce présentait une structure génétique faible, ce qui appuie les indices d’un flux significatif d’individus égarés entre bassins versants rapprochés ou plus éloignés. Cependant, l’égarement sur de grandes distances était probable, mais pas fréquent. Dans un contexte de changements planétaires, l’égarement constituerait un important mécanisme de dispersion qui conférerait de la résilience aux populations d’aloses vraies.; Understanding dispersal capacities for migratory species is crucial for their management. By coupling otolith microchemistry and microsatellite genetic analyses, we provided information on snapshot and long-term dispersal capacity of Allis shad, an anadromous clupeid in decline throughout its distribution range. The allocation of natal origin was obtained from water chemistry, signatures in otoliths of juveniles and spawners within a Bayesian model. The majority of adults were assigned to a source river with high degrees of confidence, only 4% were undetermined. Otolith natal origins were used to define a population baseline by grouping individuals from the same natal river and not from the same sampling location as usually done. While Alosa alosa exhibited a high level of natal site fidelity, this species showed weak genetic structure which supported the evidence of a significant flow of strayers between river basins in vicinity or at longer distances. However, long distance straying was probable but not frequent. In a context of global change, straying would be a key mechanism to drive dispersal and allow resilience of Allis shad populations.

International audience; Physical obstacles to upstream migration such as dams are a major impairment of natural colonisation and dispersion of migratory fish such as eels. Dams and obstacles increase fish energy expenditure, even when they are equipped with fish friendly devices. Besides, local accumulation of eels below dams increase the mortality associated with predation. Obstacles may also select on different traits of life history. While quantitative impact of dams is subjected to numerous studies, little is known about their intra-specific selectivity. Even the fishway efficiency analyses are scarcely hinting at their potential selective effect (Castro-Santos 2004; Noonan, Grant & Jackson 2012). The objective of this study was to pinpoint phenotypic traits predisposing glass eels to dams successful passage. In a preliminary approach we measured the transcription level of 15000 known eel genetic sequences in three main tissues (brain, liver and muscle) from wild individuals sampled on three successive river segments separated by dams. Interestingly, whereas no significant difference was observed in muscle and liver, segment-specific gene expression profiles were observed in brain. Surprisingly, the set of regulated genes was involved in synaptic plasticity, associated with animal cognition. In this study, by means of qPCR analysis of targeted genes, behavioral tests on experimental fishway and common garden experiment, the objective was to give insight into how genes related to learning and memory are associated with climbing behavior of fish.

International audience; L’anguille européenne est une espèce amphihaline à migration catadrome facultative et à reproduction panmictique dans la mer de Sargasses. La dynamique de sa population est en fort déclin depuis les années 80. Parmi les facteurs qui ont pu contribuer à la disparition de l’espèce, on peut citer la pollution, la surpêche et la fragmentation de l’habitat. Ce dernier est intimement lié à la construction des barrages aquatiques. En effet, les rivières aménagées créent un obstacle au déplacement des anguilles dans les deux sens, c’est-à-dire lors de leur migration de croissance (en amont) ou de reproduction (en aval). Beaucoup d’efforts ont été faits afin d’augmenter la transparence de ces ouvrages. Par exemple, la migration en amont des jeunes stades d’anguilles est facilitée par la construction des passes à civelles, dont le design est adapté à leur taille et comportement. D’une manière générale, l’évaluation de l’impact des barrages, mais aussi de l’efficacité des passes à civelles est quantitative, où seule la proportion des poissons présents dans la parte amont du barrage/passe est comparée au nombre des poissons présents au pied du barrage ou s’engageant dans la passe. Malheureusement, la variabilité entre les individus pour les traits comme la capacité de nage ou d’escalade, la motivation, l’activité ou le comportement exploratoire est rarement prise en compte dans ce contexte. Cependant, certains traits pourraient faciliter le succès de passage par les obstacles, ce qui aboutirait à une sélection Afin d’évaluer si les barrages exercent une pression de sélection sur les civelles migrantes, une étude qualitative à été réalisée sur des groupes des civelles présentes d’une part et d’autre des obstacles. Tout d’abord, une approche par puce ADN a été adoptée pour identifier sans à priori les traits différant entre les groupes amont et aval. Ensuite, les tests expérimentaux ont été réalisés afin d’associer le phénotype moléculaire (expression des gènes) au phénotype organismique (comportement). Parmi les trois tissus étudiés ; le muscle, le foie et le cerveau, seul ce dernier a montré des différences significatives entre les groupes amont et aval des obstacles. Les gènes surexprimés des les parties amont des barrages sont impliqués dans la régulation de la plasticité synaptique et du développement neuronal, qui à son tour sont sollicités dans les processus de cognition, apprentissage et mémorisation. Le comportement d’escalade des parois verticales, souvent effectué en dehors de l’eau, est une condition à laquelle les civelles sont soumises pour la première fois de leur vie, ce qui peut suggérer que le processus d’apprentissage s’est mis en place à ce moment précis. Un tri comportemental effectué dans les conditions expérimentales confirme en partie l’association entre l’expression des gènes de plasticité synaptique et le comportement d’escalade individuel.

Insights provided by futures analyses are becoming increasingly important for planning research activities in a rapidly changing world. Few examples exist in fisheries science. A structured methodology based on a series of facilitated workshops and consensual decisions was applied here to draw potential areas for future research on diadromous fishes circa 2030 that could be of relevance for European researchers. First, twenty drivers were identified and fell within the scope of (i) diadromous fish conservation, (ii) their place and roles in modern societies, (iii) the main features of the world of science and research, and (iv) the main characteristics of research activities on this biological group. Driver's evolvement during the past and the estimation of their potential development in the future (i.e. hypotheses) were examined. Then, the combination of drivers' hypotheses within each of the four components listed above led to micro-scenarios describing how the components could plausibly change in the next fifteen years. Finally, global scenarios were obtained by the juxtaposition of four micro-scenarios, one for each of the components. The 6 global scenarios that present possible futures for diadromous fish research were arranged in a dimensional plot, with the first axis opposing food production objectives to ecosystem preservation approaches and the second axis representing the intensity level of studies on diadromous fishes. Challenges that were identified and discussed from these global scenarios were mostly structural, intellectual and ethical, and can be useful to better inform future changes in thematic positioning, missions, boundaries, technical investments, and funding opportunities operated by laboratories or individual researchers working on diadromous fishes.

Insights provided by futures analyses are becoming increasingly important for planning research activities in a rapidly changing world. Few examples exist in fisheries science. A structured methodology based on a series of facilitated workshops and consensual decisions was applied here to draw potential areas for future research on diadromous fishes circa 2030 that could be of relevance for European researchers. First, twenty drivers were identified and fell within the scope of (i) diadromous fish conservation, (ii) their place and roles in modern societies, (iii) the main features of the world of science and research, and (iv) the main characteristics of research activities on this biological group. Driver's evolvement during the past and the estimation of their potential development in the future (i.e. hypotheses) were examined. Then, the combination of drivers' hypotheses within each of the four components listed above led to micro-scenarios describing how the components could plausibly change in the next fifteen years. Finally, global scenarios were obtained by the juxtaposition of four micro-scenarios, one for each of the components. The 6 global scenarios that present possible futures for diadromous fish research were arranged in a dimensional plot, with the first axis opposing food production objectives to ecosystem preservation approaches and the second axis representing the intensity level of studies on diadromous fishes. Challenges that were identified and discussed from these global scenarios were mostly structural, intellectual and ethical, and can be useful to better inform future changes in thematic positioning, missions, boundaries, technical investments, and funding opportunities operated by laboratories or individual researchers working on diadromous fishes.

International audience; Concepts: An installation to aprehend as an experience. Innovative technics to reveal what is not obvious. The experience of life as a migration journey. Life delimited by water milestones. Immersive experience (fish point of view?)