Audrey Darnaude - Academia.edu (original) (raw)
Papers by Audrey Darnaude
Marine Ecology Progress Series
The oxygen isotopic ratio of fish otoliths is increasingly used as a 'natural tag' to assess prov... more The oxygen isotopic ratio of fish otoliths is increasingly used as a 'natural tag' to assess provenance in migratory species, with the assumption that variations in δ 18 O values closely reflect individual ambient experience of temperature and/or salinity. We employed archival tag data and otoliths collected from a shelf-scale study of the spatial dynamics of North Sea plaice Pleuronectes platessa L., to examine the limits of otolith δ 18 O-based geolocation of fish during their annual migrations. Detailed intra-annual otolith δ 18 O measurements for 1997−1999 from individuals of 3 distinct sub-stocks with different spawning locations were compared with δ 18 O values predicted at the monthly, seasonal and annual scales, using predicted sub-stock specific temperatures and salinities over the same years. Spatio-temporal variation in expected δ 18 O values (−0.23 to 2.94 ‰) mainly reflected variation in temperature, and among-zone discrimination potential using otolith δ 18 O varied greatly by temporal scale and by time of year. Measured otolith δ 18 O values (−0.71 to 3.09 ‰) largely mirrored seasonally predicted values, but occasionally fell outside expected δ 18 O ranges. Where mismatches were observed, differences among sub-stocks were consistently greater than predicted, suggesting that in plaice, differential sub-stock growth rates and physiological effects during oxygen fractionation enhance geolocation potential using otolith δ 18 O. Comparing intra-annual δ 18 O values over several consecutive years for individuals with contrasted migratory patterns corroborated a high degree of feeding and spawning site fidelity irrespective of the sub-stock. Informed interpretation of otolith δ 18 O values can therefore provide relatively detailed fisheries-relevant data not readily obtained by conventional means.
Reliable assessment of fish origin is of critical importance for exploited species, since nursery... more Reliable assessment of fish origin is of critical importance for exploited species, since nursery areas must be identified and protected to maintain recruitment to the adult stock. During the last two decades, otolith chemical signatures (or…
Marine Ecology Progress Series, 2021
Marine Biology
For many jellyfish, the magnitude and timing of medusae blooms are recognized to result from the ... more For many jellyfish, the magnitude and timing of medusae blooms are recognized to result from the benthic stage dynamics. However, information on the scyphistomae of jellyfish populations in the wild remains scarce. Here, bi-mensual underwater photoquadrat surveys were combined with scyphistomae sampling and observation to describe the annual (February 2017-January 2018) benthic stage dynamics and asexual reproduction strategy of Aurelia coerulea in the Thau lagoon (43°25′31.1″N; 03°42′0.9″E). Our results revealed unexpected seasonal patterns of variation: scyphistoma coverage peaked in the spring (11.6 ± 3.7% on 21st April) and was minimal in the summer and autumn (1.4 ± 1.3% on 10th October). The increase in scyphistoma coverage mainly resulted from an intense production of buds between February and April during the spring rise in water temperature (peak of 12,800 buds m −2 on 21st April), but scyphistoma coverage appeared to be negatively influenced by the interaction of high summer temperatures and salinities. Strobilation was observed from November to April. It peaked on 17th November, with 33.1% of the scyphistomae strobilating and an average production of 19,100 strobila disks m −2. However, the low scyphistoma coverage at this time of the year (< 2%) likely limited the intensity of ephyrae liberation and the subsequent medusae bloom. The final population size of A. coerulea thus results from a complex interaction of abiotic and biotic factors. Our results bring into question how the different populations of Aurelia spp. will respond to the predicted global warming scenarios.
Aurelia aurita ecology is well known. However, critical periods of its life cycle have been overl... more Aurelia aurita ecology is well known. However, critical periods of its life cycle have been overlooked, such as polyps, which are crucial in shaping blooms intensity. Thau lagoon, a coastal lagoon in Northwestern Mediterranean, offers an ideal framework to investigate the life cycle of the species. Here we study the benthic and pelagic dynamics of A. aurita in Thau lagoon over a 4-year period, focusing on the sources of population growth and mortality. Field surveys were conducted to assess benthic population distribution, settlement surfaces, density and budding. Pelagic abundances and growth were also monitored. Mortality was assessed by complementary methods consisting in molecular analysis of fish gut contents and predation experiments using Sparus aurata. The results of this study show that the dynamics of the species is mainly shaped by temperature, while the benthic phase further benefits from habitat modification. In situ, Sarpa salpa was confirmed as a predator of A. aurita...
Estuarine, Coastal and …, 2011
Accurate knowledge of fish age and growth is crucial for species conservation and management of e... more Accurate knowledge of fish age and growth is crucial for species conservation and management of exploited marine stocks. In exploited species, age estimation based on otolith reading is routinely used for building growth curves that are used to implement fishery management models. However, the universal fit of the von Bertalanffy growth function (VBGF) on data from commercial landings can lead to uncertainty in growth parameter inference, preventing accurate comparison of growth-based history traits between fish populations. In the present paper, we used a comprehensive annual sample of wild gilthead seabream (Sparus aurata L.) in the Gulf of Lions (France, NW Mediterranean) to test a methodology improving growth modelling for exploited fish populations. After validating the timing for otolith annual increment formation for all life stages, a comprehensive set of growth models (including VBGF) were fitted to the obtained ageelength data, used as a whole or subdivided between group 0 individuals and those coming from commercial landings (ages 1e6). Comparisons in growth model accuracy based on Akaike Information Criterion allowed assessment of the best model for each dataset and, when no model correctly fitted the data, a multi-model inference (MMI) based on model averaging was carried out. The results provided evidence that growth parameters inferred with VBGF must be used with high caution. Hence, VBGF turned to be among the less accurate for growth prediction irrespective of the dataset and its fit to the whole population, the juvenile or the adult datasets provided different growth parameters. The best models for growth prediction were the Tanaka model, for group 0 juveniles, and the MMI, for the older fish, confirming that growth differs substantially between juveniles and adults. All asymptotic models failed to correctly describe the growth of adult S. aurata, probably because of the poor representation of old individuals in the dataset. Multi-model inference associated with separate analysis of juveniles and adult fish is then advised to obtain objective estimations of growth parameters when sampling cannot be corrected towards older fish.
ICES Journal of Marine Science
Partial migration, where migrant and resident organisms coexist within the same population, has b... more Partial migration, where migrant and resident organisms coexist within the same population, has been found in many fishes. Although it seems obvious that different life cycles exploit habitats and food webs differently, few assessments about the trophic consequences of partial migration are available. To unveil part of this complexity, we combined otolith chemistry with stable isotope analyses data for hind-casting Merluccius australis habitat use and diet composition at age. By providing detailed information about lifetime variability in diet, trophic position, and prey demand of four M. australis life-cycle types, we show that these groups feed differentially in estuarine and oceanic habitats throughout their ontogeny. Although trophic positions were similar between habitats for juvenile and subadults, substantial differences between life-cycle types were found regarding lifetime diet and trophic demand. Thus, the more abundant and heavily exploited oceanic stock of M. australis w...
Oecologia, 2004
The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lion... more The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lions (NW Mediterranean) was analysed using carbon-and nitrogen stable isotopes along the flatfish food webs. Off the Rhone River, the main terrestrial (river POM) and marine (seawater POM) sources of carbon differed in δ 13 C (-26.11‰ and −22.36‰, respectively). Surface sediment and suspended POM in plume water exhibited low δ 13 C (-24.38‰ and −24.70‰, respectively) that differed more from the seawater POM than from river POM, demonstrating the dominance of terrestrial material in those carbon pools. Benthic invertebrates showed a wide range in δ 15 N (mean 4.30‰ to 9.77‰) and δ 13 C (mean −23.81‰ to −18.47‰), suggesting different trophic levels, diets and organic sources. Among the macroinvertebrates, the surface (mean δ 13 C −23.71‰) and subsurface (mean δ 13 C −23.81‰) deposit-feeding polychaetes were particularly 13 C depleted, indicating that their carbon was mainly derived from terrestrial material. In flatfish, δ 15 N (mean 9.42 to 10.93‰) and δ 13 C (mean −19.95‰ to −17.69‰) varied among species, indicating differences in food source and terrestrial POM use. A significant negative correlation was observed between the percentage by weight of polychaetes in the diet and the δ 13 C of flatfish white muscle. Solea solea (the main polychaete feeder) had the lowest mean δ 13 C, Arnoglossus laterna and Buglossidium luteum (crustacean, mollusc and polychaete feeders) had intermediate values, and Solea impar (mollusc feeder) and Citharus linguatula (crustacean and fish feeder) exhibited the highest δ 13 C. Two different benthic food webs were thus identified off the Rhone River, one based on marine planktonic carbon and the other on the terrestrial POM carried by the river. Depositfeeding polychaetes were responsible for the main transfer of terrestrial POM to upper trophic levels, linking sole population dynamics to river runoff fluctuations.
Precise knowledge of lifetime migrations is vital in exploited fish species, since all essential ... more Precise knowledge of lifetime migrations is vital in exploited fish species, since all essential habitats must be protected to maintain sustainable stock levels. The present study used multi-element otolith fingerprints of the gilthead sea bream Sparus aurata (L.) to discriminate its main juvenile and adult habitats in the Languedoc-Roussillon region (Gulf of Lions, northwest Mediterranean) and infer the lifetime migrations of 12 individuals from the area (11 from the present day and 1 from the Roman era). This allowed for the first time the identification of key habitats for the successful completion of the species' life cycle in the Gulf of Lions, and the connectivity between them. Our results revealed that lagoon use by S. aurata is probably ancient (> 2500 yr) and confirmed its current commonness. Yet, although most observed migration patterns were in accordance with the migratory behavior previously described for the species, strong inter-individual variations and new patterns in habitat use were detected. At the juvenile stage, a preference for shallow lagoons with low salinities was evidenced. Nevertheless, the first year of life can also be successfully completed in marine conditions. At the adult stage, lagoon use was shown to occur until at least age 4 yr, with periods of lagoon residency of up to 11 mo in a year, often including winter months. Because overwintering in the lagoons was previously thought to be impossible for S. aurata due to low temperatures, this finding has important implications for future stock management, especially since the species breeds in winter.
Limnology and Oceanography
Genes
Understanding the genetic underpinnings of fitness trade-offs across spatially variable environme... more Understanding the genetic underpinnings of fitness trade-offs across spatially variable environments remains a major challenge in evolutionary biology. In Mediterranean gilthead sea bream, first-year juveniles use various marine and brackish lagoon nursery habitats characterized by a trade-off between food availability and environmental disturbance. Phenotypic differences among juveniles foraging in different habitats rapidly appear after larval settlement, but the relative role of local selection and plasticity in phenotypic variation remains unclear. Here, we combine phenotypic and genetic data to address this question. We first report correlations of opposite signs between growth and condition depending on juvenile habitat type. Then, we use single nucleotide polymorphism (SNP) data obtained by Restriction Associated DNA (RAD) sequencing to search for allele frequency changes caused by a single generation of spatially varying selection between habitats. We found evidence for mode...
ICES Journal of Marine Science
Partial migration, where migrant and resident organisms coexist within the same population, has b... more Partial migration, where migrant and resident organisms coexist within the same population, has been found in many fishes. Although it seems obvious that different life cycles exploit habitats and food webs differently, few assessments about the trophic consequences of partial migration are available. To unveil part of this complexity, we combined otolith chemistry with stable isotope analyses data for hind-casting Merluccius australis habitat use and diet composition at age. By providing detailed information about lifetime variability in diet, trophic position, and prey demand of four M. australis life-cycle types, we show that these groups feed differentially in estuarine and oceanic habitats throughout their ontogeny. Although trophic positions were similar between habitats for juvenile and subadults, substantial differences between life-cycle types were found regarding lifetime diet and trophic demand. Thus, the more abundant and heavily exploited oceanic stock of M. australis w...
Background. Otolith microchemistry applications of finite mixture distribution models (FMDM) desc... more Background. Otolith microchemistry applications of finite mixture distribution models (FMDM) describe mixed stocks using three sets of parameters: proportional contributions (pi), baseline parameters (θi) and number of contributing nursery origins (c#). Under ideal scenarios, c# is known and all potential sources are sampled to produce source-based ^θi estimates. Hence, ^pi is the only parameter vector estimated by FMDM from the mixed-data. If some/all nursery areas are unknown or not sampled, some or all θi and c# need to be also estimated from the mixed-data. Our goal here was to assess bias and variability in ^pi, ^θi and ^c# when estimated by FMDM, under a range of data availability scenarios. Methods. We used a comprehensive Sparus aurata dataset, tat contained otolith elemental ratios from 301 young of the year, sampled at four nursery origins, in three highly contrasting years. Using bootstrap resampling (n=1000) we produced artificial source- and mixed-samples. Source-sample...
Aquatic Conservation: Marine and Freshwater Ecosystems
The fish assemblages of two shallow soft-bottom areas located in the Gulf of Fos (NW Mediterranea... more The fish assemblages of two shallow soft-bottom areas located in the Gulf of Fos (NW Mediterranean) were studied by means of 57 trawl surveys carried out on both seasonal and diel scales between 1983 and 1985. A total of 47 fish species was recorded, with a mean density and biomass of 650 individuals ha-1 and 2.67 kg ha-1 , respectively. Most of the fluctuations observed were on the spatial scale. Strong differences in fish assemblages were observed between the two areas, with both higher species richness and biomass in the outer part of the gulf (La Gracieuse), while a higher density of individuals characterised its inner part (Bay of Carteau). This spatial pattern was due to a small number of species, such as the gobiids Gobius niger and Pomatoschitus minutus in Carteau, and the flatfish Arnoglossus laterna, Buglossidium luteum and Solea solea in La Gracieuse. These differences were probably induced by differences in the hydrological and benthic characteristics of the two study areas. Decreases in species richness, density and/or biomass were observed in both areas over the study period, although this trend was not significant in all cases. These decreases may have been linked to interannual variations in the mean flow rate of the Rhône River (-28.1% between 1983 and 1985), which might have induced a decrease in the density of benthic invertebrate populations. We suggest that a similar reaction occurred in fish populations, as most of them are known to feed on these invertebrates. Diel patterns did not reveal any significant trends. However, an increase in density and biomass at sunset, and a decrease before sunrise were observed in summer in both areas, and the presence of certain specific species was recorded in catches at determined hours of the diel cycle. These observations were likely due to the activity cycles (diurnal vs. nocturnal) of the fish species. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS demersal ichthyofauna / Gobiidae / Pleuronectiforms / spatial distribution / temporal variations Résumé − Variations spatio-temporelles des assemblages de poissons dans des petits fonds meubles de Méditerranée (golfe de Fos, France). Les communautés de poissons des fonds meubles de deux secteurs du golfe de Fos ont été étudiées par 57 chalutages, réalisés en différentes saisons et à différentes heures du nycthémère, entre 1983 et 1985. Un total de 47 espèces de poissons a été recensé, avec une densité et une biomasse moyennes de 650 individus ha-1 et 2,67 kg ha-1 , respectivement. L'essentiel des différences observées est lié à la distribution spatiale des espèces, avec une forte distinction entre les deux secteurs: la richesse spécifique et la biomasse ont été plus fortes à l'extérieur du golfe (La Gracieuse), alors que la densité a été plus forte à l'intérieur (baie de Carteau). Cette ségrégation
Limnology and Oceanography
Journal of Applied Ecology, 2016
Running head: Trans-Amazonian natal homing in giant the Madeira River, which block a major migrat... more Running head: Trans-Amazonian natal homing in giant the Madeira River, which block a major migration route and access to a substantial part of their spawning grounds. Major impacts can be anticipated from the current and forthcoming hydroelectric development in the Amazon basin, not only on the populations and fisheries of this apex predator, but also on Amazonian food webs through trophic cascades.
Marine Ecology Progress Series
The oxygen isotopic ratio of fish otoliths is increasingly used as a 'natural tag' to assess prov... more The oxygen isotopic ratio of fish otoliths is increasingly used as a 'natural tag' to assess provenance in migratory species, with the assumption that variations in δ 18 O values closely reflect individual ambient experience of temperature and/or salinity. We employed archival tag data and otoliths collected from a shelf-scale study of the spatial dynamics of North Sea plaice Pleuronectes platessa L., to examine the limits of otolith δ 18 O-based geolocation of fish during their annual migrations. Detailed intra-annual otolith δ 18 O measurements for 1997−1999 from individuals of 3 distinct sub-stocks with different spawning locations were compared with δ 18 O values predicted at the monthly, seasonal and annual scales, using predicted sub-stock specific temperatures and salinities over the same years. Spatio-temporal variation in expected δ 18 O values (−0.23 to 2.94 ‰) mainly reflected variation in temperature, and among-zone discrimination potential using otolith δ 18 O varied greatly by temporal scale and by time of year. Measured otolith δ 18 O values (−0.71 to 3.09 ‰) largely mirrored seasonally predicted values, but occasionally fell outside expected δ 18 O ranges. Where mismatches were observed, differences among sub-stocks were consistently greater than predicted, suggesting that in plaice, differential sub-stock growth rates and physiological effects during oxygen fractionation enhance geolocation potential using otolith δ 18 O. Comparing intra-annual δ 18 O values over several consecutive years for individuals with contrasted migratory patterns corroborated a high degree of feeding and spawning site fidelity irrespective of the sub-stock. Informed interpretation of otolith δ 18 O values can therefore provide relatively detailed fisheries-relevant data not readily obtained by conventional means.
Reliable assessment of fish origin is of critical importance for exploited species, since nursery... more Reliable assessment of fish origin is of critical importance for exploited species, since nursery areas must be identified and protected to maintain recruitment to the adult stock. During the last two decades, otolith chemical signatures (or…
Marine Ecology Progress Series, 2021
Marine Biology
For many jellyfish, the magnitude and timing of medusae blooms are recognized to result from the ... more For many jellyfish, the magnitude and timing of medusae blooms are recognized to result from the benthic stage dynamics. However, information on the scyphistomae of jellyfish populations in the wild remains scarce. Here, bi-mensual underwater photoquadrat surveys were combined with scyphistomae sampling and observation to describe the annual (February 2017-January 2018) benthic stage dynamics and asexual reproduction strategy of Aurelia coerulea in the Thau lagoon (43°25′31.1″N; 03°42′0.9″E). Our results revealed unexpected seasonal patterns of variation: scyphistoma coverage peaked in the spring (11.6 ± 3.7% on 21st April) and was minimal in the summer and autumn (1.4 ± 1.3% on 10th October). The increase in scyphistoma coverage mainly resulted from an intense production of buds between February and April during the spring rise in water temperature (peak of 12,800 buds m −2 on 21st April), but scyphistoma coverage appeared to be negatively influenced by the interaction of high summer temperatures and salinities. Strobilation was observed from November to April. It peaked on 17th November, with 33.1% of the scyphistomae strobilating and an average production of 19,100 strobila disks m −2. However, the low scyphistoma coverage at this time of the year (< 2%) likely limited the intensity of ephyrae liberation and the subsequent medusae bloom. The final population size of A. coerulea thus results from a complex interaction of abiotic and biotic factors. Our results bring into question how the different populations of Aurelia spp. will respond to the predicted global warming scenarios.
Aurelia aurita ecology is well known. However, critical periods of its life cycle have been overl... more Aurelia aurita ecology is well known. However, critical periods of its life cycle have been overlooked, such as polyps, which are crucial in shaping blooms intensity. Thau lagoon, a coastal lagoon in Northwestern Mediterranean, offers an ideal framework to investigate the life cycle of the species. Here we study the benthic and pelagic dynamics of A. aurita in Thau lagoon over a 4-year period, focusing on the sources of population growth and mortality. Field surveys were conducted to assess benthic population distribution, settlement surfaces, density and budding. Pelagic abundances and growth were also monitored. Mortality was assessed by complementary methods consisting in molecular analysis of fish gut contents and predation experiments using Sparus aurata. The results of this study show that the dynamics of the species is mainly shaped by temperature, while the benthic phase further benefits from habitat modification. In situ, Sarpa salpa was confirmed as a predator of A. aurita...
Estuarine, Coastal and …, 2011
Accurate knowledge of fish age and growth is crucial for species conservation and management of e... more Accurate knowledge of fish age and growth is crucial for species conservation and management of exploited marine stocks. In exploited species, age estimation based on otolith reading is routinely used for building growth curves that are used to implement fishery management models. However, the universal fit of the von Bertalanffy growth function (VBGF) on data from commercial landings can lead to uncertainty in growth parameter inference, preventing accurate comparison of growth-based history traits between fish populations. In the present paper, we used a comprehensive annual sample of wild gilthead seabream (Sparus aurata L.) in the Gulf of Lions (France, NW Mediterranean) to test a methodology improving growth modelling for exploited fish populations. After validating the timing for otolith annual increment formation for all life stages, a comprehensive set of growth models (including VBGF) were fitted to the obtained ageelength data, used as a whole or subdivided between group 0 individuals and those coming from commercial landings (ages 1e6). Comparisons in growth model accuracy based on Akaike Information Criterion allowed assessment of the best model for each dataset and, when no model correctly fitted the data, a multi-model inference (MMI) based on model averaging was carried out. The results provided evidence that growth parameters inferred with VBGF must be used with high caution. Hence, VBGF turned to be among the less accurate for growth prediction irrespective of the dataset and its fit to the whole population, the juvenile or the adult datasets provided different growth parameters. The best models for growth prediction were the Tanaka model, for group 0 juveniles, and the MMI, for the older fish, confirming that growth differs substantially between juveniles and adults. All asymptotic models failed to correctly describe the growth of adult S. aurata, probably because of the poor representation of old individuals in the dataset. Multi-model inference associated with separate analysis of juveniles and adult fish is then advised to obtain objective estimations of growth parameters when sampling cannot be corrected towards older fish.
ICES Journal of Marine Science
Partial migration, where migrant and resident organisms coexist within the same population, has b... more Partial migration, where migrant and resident organisms coexist within the same population, has been found in many fishes. Although it seems obvious that different life cycles exploit habitats and food webs differently, few assessments about the trophic consequences of partial migration are available. To unveil part of this complexity, we combined otolith chemistry with stable isotope analyses data for hind-casting Merluccius australis habitat use and diet composition at age. By providing detailed information about lifetime variability in diet, trophic position, and prey demand of four M. australis life-cycle types, we show that these groups feed differentially in estuarine and oceanic habitats throughout their ontogeny. Although trophic positions were similar between habitats for juvenile and subadults, substantial differences between life-cycle types were found regarding lifetime diet and trophic demand. Thus, the more abundant and heavily exploited oceanic stock of M. australis w...
Oecologia, 2004
The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lion... more The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lions (NW Mediterranean) was analysed using carbon-and nitrogen stable isotopes along the flatfish food webs. Off the Rhone River, the main terrestrial (river POM) and marine (seawater POM) sources of carbon differed in δ 13 C (-26.11‰ and −22.36‰, respectively). Surface sediment and suspended POM in plume water exhibited low δ 13 C (-24.38‰ and −24.70‰, respectively) that differed more from the seawater POM than from river POM, demonstrating the dominance of terrestrial material in those carbon pools. Benthic invertebrates showed a wide range in δ 15 N (mean 4.30‰ to 9.77‰) and δ 13 C (mean −23.81‰ to −18.47‰), suggesting different trophic levels, diets and organic sources. Among the macroinvertebrates, the surface (mean δ 13 C −23.71‰) and subsurface (mean δ 13 C −23.81‰) deposit-feeding polychaetes were particularly 13 C depleted, indicating that their carbon was mainly derived from terrestrial material. In flatfish, δ 15 N (mean 9.42 to 10.93‰) and δ 13 C (mean −19.95‰ to −17.69‰) varied among species, indicating differences in food source and terrestrial POM use. A significant negative correlation was observed between the percentage by weight of polychaetes in the diet and the δ 13 C of flatfish white muscle. Solea solea (the main polychaete feeder) had the lowest mean δ 13 C, Arnoglossus laterna and Buglossidium luteum (crustacean, mollusc and polychaete feeders) had intermediate values, and Solea impar (mollusc feeder) and Citharus linguatula (crustacean and fish feeder) exhibited the highest δ 13 C. Two different benthic food webs were thus identified off the Rhone River, one based on marine planktonic carbon and the other on the terrestrial POM carried by the river. Depositfeeding polychaetes were responsible for the main transfer of terrestrial POM to upper trophic levels, linking sole population dynamics to river runoff fluctuations.
Precise knowledge of lifetime migrations is vital in exploited fish species, since all essential ... more Precise knowledge of lifetime migrations is vital in exploited fish species, since all essential habitats must be protected to maintain sustainable stock levels. The present study used multi-element otolith fingerprints of the gilthead sea bream Sparus aurata (L.) to discriminate its main juvenile and adult habitats in the Languedoc-Roussillon region (Gulf of Lions, northwest Mediterranean) and infer the lifetime migrations of 12 individuals from the area (11 from the present day and 1 from the Roman era). This allowed for the first time the identification of key habitats for the successful completion of the species' life cycle in the Gulf of Lions, and the connectivity between them. Our results revealed that lagoon use by S. aurata is probably ancient (> 2500 yr) and confirmed its current commonness. Yet, although most observed migration patterns were in accordance with the migratory behavior previously described for the species, strong inter-individual variations and new patterns in habitat use were detected. At the juvenile stage, a preference for shallow lagoons with low salinities was evidenced. Nevertheless, the first year of life can also be successfully completed in marine conditions. At the adult stage, lagoon use was shown to occur until at least age 4 yr, with periods of lagoon residency of up to 11 mo in a year, often including winter months. Because overwintering in the lagoons was previously thought to be impossible for S. aurata due to low temperatures, this finding has important implications for future stock management, especially since the species breeds in winter.
Limnology and Oceanography
Genes
Understanding the genetic underpinnings of fitness trade-offs across spatially variable environme... more Understanding the genetic underpinnings of fitness trade-offs across spatially variable environments remains a major challenge in evolutionary biology. In Mediterranean gilthead sea bream, first-year juveniles use various marine and brackish lagoon nursery habitats characterized by a trade-off between food availability and environmental disturbance. Phenotypic differences among juveniles foraging in different habitats rapidly appear after larval settlement, but the relative role of local selection and plasticity in phenotypic variation remains unclear. Here, we combine phenotypic and genetic data to address this question. We first report correlations of opposite signs between growth and condition depending on juvenile habitat type. Then, we use single nucleotide polymorphism (SNP) data obtained by Restriction Associated DNA (RAD) sequencing to search for allele frequency changes caused by a single generation of spatially varying selection between habitats. We found evidence for mode...
ICES Journal of Marine Science
Partial migration, where migrant and resident organisms coexist within the same population, has b... more Partial migration, where migrant and resident organisms coexist within the same population, has been found in many fishes. Although it seems obvious that different life cycles exploit habitats and food webs differently, few assessments about the trophic consequences of partial migration are available. To unveil part of this complexity, we combined otolith chemistry with stable isotope analyses data for hind-casting Merluccius australis habitat use and diet composition at age. By providing detailed information about lifetime variability in diet, trophic position, and prey demand of four M. australis life-cycle types, we show that these groups feed differentially in estuarine and oceanic habitats throughout their ontogeny. Although trophic positions were similar between habitats for juvenile and subadults, substantial differences between life-cycle types were found regarding lifetime diet and trophic demand. Thus, the more abundant and heavily exploited oceanic stock of M. australis w...
Background. Otolith microchemistry applications of finite mixture distribution models (FMDM) desc... more Background. Otolith microchemistry applications of finite mixture distribution models (FMDM) describe mixed stocks using three sets of parameters: proportional contributions (pi), baseline parameters (θi) and number of contributing nursery origins (c#). Under ideal scenarios, c# is known and all potential sources are sampled to produce source-based ^θi estimates. Hence, ^pi is the only parameter vector estimated by FMDM from the mixed-data. If some/all nursery areas are unknown or not sampled, some or all θi and c# need to be also estimated from the mixed-data. Our goal here was to assess bias and variability in ^pi, ^θi and ^c# when estimated by FMDM, under a range of data availability scenarios. Methods. We used a comprehensive Sparus aurata dataset, tat contained otolith elemental ratios from 301 young of the year, sampled at four nursery origins, in three highly contrasting years. Using bootstrap resampling (n=1000) we produced artificial source- and mixed-samples. Source-sample...
Aquatic Conservation: Marine and Freshwater Ecosystems
The fish assemblages of two shallow soft-bottom areas located in the Gulf of Fos (NW Mediterranea... more The fish assemblages of two shallow soft-bottom areas located in the Gulf of Fos (NW Mediterranean) were studied by means of 57 trawl surveys carried out on both seasonal and diel scales between 1983 and 1985. A total of 47 fish species was recorded, with a mean density and biomass of 650 individuals ha-1 and 2.67 kg ha-1 , respectively. Most of the fluctuations observed were on the spatial scale. Strong differences in fish assemblages were observed between the two areas, with both higher species richness and biomass in the outer part of the gulf (La Gracieuse), while a higher density of individuals characterised its inner part (Bay of Carteau). This spatial pattern was due to a small number of species, such as the gobiids Gobius niger and Pomatoschitus minutus in Carteau, and the flatfish Arnoglossus laterna, Buglossidium luteum and Solea solea in La Gracieuse. These differences were probably induced by differences in the hydrological and benthic characteristics of the two study areas. Decreases in species richness, density and/or biomass were observed in both areas over the study period, although this trend was not significant in all cases. These decreases may have been linked to interannual variations in the mean flow rate of the Rhône River (-28.1% between 1983 and 1985), which might have induced a decrease in the density of benthic invertebrate populations. We suggest that a similar reaction occurred in fish populations, as most of them are known to feed on these invertebrates. Diel patterns did not reveal any significant trends. However, an increase in density and biomass at sunset, and a decrease before sunrise were observed in summer in both areas, and the presence of certain specific species was recorded in catches at determined hours of the diel cycle. These observations were likely due to the activity cycles (diurnal vs. nocturnal) of the fish species. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS demersal ichthyofauna / Gobiidae / Pleuronectiforms / spatial distribution / temporal variations Résumé − Variations spatio-temporelles des assemblages de poissons dans des petits fonds meubles de Méditerranée (golfe de Fos, France). Les communautés de poissons des fonds meubles de deux secteurs du golfe de Fos ont été étudiées par 57 chalutages, réalisés en différentes saisons et à différentes heures du nycthémère, entre 1983 et 1985. Un total de 47 espèces de poissons a été recensé, avec une densité et une biomasse moyennes de 650 individus ha-1 et 2,67 kg ha-1 , respectivement. L'essentiel des différences observées est lié à la distribution spatiale des espèces, avec une forte distinction entre les deux secteurs: la richesse spécifique et la biomasse ont été plus fortes à l'extérieur du golfe (La Gracieuse), alors que la densité a été plus forte à l'intérieur (baie de Carteau). Cette ségrégation
Limnology and Oceanography
Journal of Applied Ecology, 2016
Running head: Trans-Amazonian natal homing in giant the Madeira River, which block a major migrat... more Running head: Trans-Amazonian natal homing in giant the Madeira River, which block a major migration route and access to a substantial part of their spawning grounds. Major impacts can be anticipated from the current and forthcoming hydroelectric development in the Amazon basin, not only on the populations and fisheries of this apex predator, but also on Amazonian food webs through trophic cascades.