2020 |
Pham, M. H., et al. "Importance of various marine coastal habitats during the life cycle of Spratelloides delicatulus in Con Dao, the oldest MPA in Vietnam." Aquatic Conservation: Marine and Freshwater Ecosystems (2020).
Résumé: 1.Marine protected areas (MPAs) are set up to conserve biodiversity, but their design is not always based on strictly scientific considerations. Ideally, an MPA should protect all key habitats necessary for a marine species to complete its life cycle. The identification of these key habitats is complex, especially during the early life of marine fishes. 2.A widely distributed tropical and important low trophic-level fish species, Spratelloides delicatulus (Clupeidae), was used to evaluate the significance of various coastal habitats for its larvae and juveniles in the Con Dao Archipelago MPA in Vietnam. Early stages (larvae and juveniles) were sampled monthly over one year (June 2016 to May 2017) using light traps in three main habitats (seagrass beds, coral reefs and harbour). The species was identified using morphometry and DNA barcoding. Age and growth variables were estimated using otolith daily growth increments. 3.A total of 3,581 fish were caught. The species was not found in captures between January and February, directly linked to the decrease in seawater temperature and was most abundant from April to June. For a subsample of 248 fish (7–38 mm standard length), ages ranged from 7 to 108 days. 4.Captures and back-calculated birthdates using otolith daily increments showed that S. delicatulus spawns during the period of high seawater temperature, from March to October. The species colonizes all three habitats during the early stages (0–26 days old), with growth rate lowest on the seagrass beds. Nevertheless, the species occupies seagrass beds exclusively during the older stages. 5.The conservation of seagrass beds in the Con Dao archipelago is essential for protection of juvenile stages of this species but this habitat is presently not included in the MPA patches. Establishment of a continuum of protected areas linking habitats, rather than the existing patches is needed to conserve the complete life cycle of this species in the Con Dao MPA.
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2019 |
Hauser, M., et al. "Shedding light on the migratory patterns of the Amazonian goliath catfish, Brachyplatystoma platynemum, using otolith 87Sr:86Sr analyses." Aquatic Conservation: Marine and Freshwater Ecosystems (2019).
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Tessier, A., et al. "Life history traits and exploitation of Hampala barb (Hampala macrolepidota – Cyprinidae) in a subtropical reservoir (Lao PDR)." Cybium, Société Française d’Ichtyologie. 43.4 (2019): 351–365.
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Tessier, A., et al. "Life history traits of the exploited Nile Tilapia (Oreochromis niloticus – Cichlidae) in a subtropical reservoir (Lao PDR)." Cybium. 43.1 (2019): 71–82.
Résumé: Biological traits of Oreochromis niloticus were studied in order to identify potential differences between the population of the Nam Theun 2 Reservoir and other populations in Asia and in Africa. The study also aimed to characterize the demographic structure of the exploited population by fisheries in the reservoir. Toluidine-stained transverse section of otoliths from 322 specimens, collected between November 2015 and January 2017, were analysed to identify the periodicity of annulus formation and to age individuals. Length, weight, sex and sexual maturity stage were recorded. Life history traits were characterized by length-weight and length age relationships. The periodicity of annulus formation was annual, with complete formation of the translucent zone at the beginning of the warm and wet season (June and July). The length-age key has been established and was composed of 9 age classes, ranging from 0 to 8 years old. Males showed positive allometric growth whereas juveniles and females exhibited isometric growth. The study showed an asymptotic standard length of 658 mm and a low growth rate (K = 0.08 year(-1)). The sex ratio was equilibrated, and first maturity of females was at 277 mm standard length. The population was composed of individuals aged 3 years old and older, and 60% of the landings were composed of individuals aged 5 years and older. The growth rate was lower than for Asian and African populations, and the age-length key provided was specific to the studied reservoir. However, some biological traits of the O. niloticus population were similar to those found for other population in the world: (i) formation of an annual annulus during the reproduction period, at the beginning of the warm and wet season like populations from subtropical countries, and (ii) an isometric or a positive allometric growth as seen in populations that were not overexploited and were living in favourable environmental conditions. Therefore, the present study suggests that the O. niloticus population of the NT2 Reservoir was not overexploited at the time of the survey.
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Tran, N. T., et al. "Changes in environmental salinity during the life of Pangasius krempfi in the Mekong Delta (Vietnam) estimated from otolith Sr : Ca ratios." Mar. Freshw. Res.. 70.12 (2019): 1734–1746.
Résumé: Pangasius krempfi is a commercially important catfish in the Mekong River and is believed to migrate along the Mekong River basin. To verify this migration, elemental concentrations were measured in the water and in otoliths to infer the salinity of the water through the fish's lifetime. In 2017, eight element concentrations were measured along the Mekong Delta using solution-based inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of Sr, Li and Rb were strongly and positively correlated with salinity. Otoliths were taken from P. krempfi caught in the brackish waters of the lower Mekong Delta and seven element : Ca ratios were measured from the core to the otolith edge using laser ablation ICP-MS. The Sr : Ca, Ba : Ca, P : Ca and Mn : Ca ratios varied through the lifetime of the fish, but only Sr : Ca was suitable for estimating ambient salinity. The Sr : Ca profiles in otoliths were analysed and significantly correlated between individuals, with all fish hatched in water with very low levels of salinity, indicating a single freshwater spawning ground, and then living in waters with higher salinity, with two types of migration behaviour. Some individuals may return to low-salinity waters when older. These conclusions were supported by the Ba : Ca and Mn : Ca ratios. These migration patterns may have implications for fishery management.
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2018 |
Bettarel, Y., et al. "Hordes of Phages in the Gut of the Tilapia Sarotherodon melanotheron." Sci Rep. 8 (2018): 11311.
Résumé: Preliminary studies conducted on the human gastro-intestinal tract have revealed that enteric viral communities play a preponderant role in microbial homeostatis. However to date, such communities have never been investigated in the fish gut. Herein, we examined the main ecological traits of viruses in the digestive tract of a euryhaline fish, the tilapia Sarotherodon melanotheron. Individuals were collected at 8 different sites in Senegal covering a salinity gradient from 3 to 104 parts per thousand, and showing large disparities in their organic pollutant concentrations. Results showed that the gut of S. melanotheron is home to a highly abundant viral community (0.2-10.7 x 10(9) viruses ml(-1)), distinct from the surrounding water, and essentially composed of phages of which a substantial proportion is temperate (the fraction of lysogenized cells-FLC ranging from 8.1 to 33.0%). Also, a positive and significant correlation was detected between FLC and the concentrations of polycyclic aromatic hydrocarbon in sediment, while no clear relationships were found between salinity and any of the microbial parameters considered. Finally, our data suggest that virus-bacteria interactions within the fish intestine are likely sensitive to the presence of particular xenobiotics, which may compromise the balance in the gut microbiota, and subsequently affect the health of their host.
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2017 |
Cormier-Salem, M. - C., et al. "The mangrove's contribution to people: Interdisciplinary pilot study of the Can Gio Mangrove Biosphere Reserve in Viet Nam." Comptes Rendus Geoscience. 349.6 (2017): 341–350.
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Sirot, C., et al. "elementr: An R package for reducing elemental data from LA-ICPMS analysis of biological calcified structures." Methods Ecol. Evol.. 8.12 (2017): 1659–1667.
Résumé: 1. Elemental analysis of biological calcified structures (e.g. fish otoliths, mollusc shelves, coral skeletons or fish and shark bones) provides invaluable information regarding ecological processes for many aquatic species. Despite this importance, the reduction of the raw data obtained through Laser-ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) (i.e. the conversion of the machine raw signal into elemental concentrations) remains a challenge as the tools developed so far for carrying out this task have important limitations for aquatic ecologists. 2. Here, we introduce the elementr R-package which provides a handy, reliable and transparent way to reduce elemental data acquired from spot or transect LA-ICPMS analysis of biological calcified structures. This free and open-source software, implemented based on state-of-the-art literature, handles data from both standards and samples, allowing fast and simultaneous calculations of concentration for any chemical element, correction for potential machine drift, and realignment and averaging for sample replicates when needed. 3. The major attributes of elementr are: (i) its user-friendly graphical interface which provides widgets to set all the reduction settings (i.e. no programming skills are required to run it), (ii) its reactivity whereby the software continuously observes any setting change made by the user, re-calculates and displays all updated results, allowing therefore users to visually check the validity of their settings and to tune them if needed and (iii) an object oriented underlying that facilitates subsequent handling of LA-ICPMS data in R. 4. Despite the elementr design being most suited to the needs of aquatic ecologists, its use could be broadened to other research fields (i.e. geology, material engineering) due to its flexibility. Moreover, the open-source approach used for programming this software allows its expansion in order to refine calculation procedures or to add new functionalities.
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Sirot, C., et al. "Using otolith organic matter to detect diet shifts in Bardiella chrysoura, during a period of environmental changes." Mar. Ecol.-Prog. Ser.. 575 (2017): 137–152.
Résumé: Accurate knowledge on fish trophic ecology and its modifications is crucial for understanding the impact of global change on ecosystems. In this context, we investigated the value of the delta C-13 and delta N-15 of otolith soluble organic matter (SOM) for identifying temporal diet shifts in American silver perch Bairdiella chrysoura over a 30-yr period characterized by strong changes in its population size and habitats within the Terminos Lagoon (Mexico). We first compared the otolith SOM isotopic signatures from present-clay adults to those of muscle and the main local prey. Our results suggest that otolith SOM can be confidently extracted and analyzed for both present and past otoliths of this species. The mean otolith SOM signatures obtained (-15.92 +/- 1.35%, for delta C-13 and 9.38 +/- 0.93%, for delta N-15) were consistent with those of the diet as 85% of the individual signatures were included within the prey isotopic niche area. Moreover, this study supports a trophic enrichment factor between diet and otolith (TEFdiet-otolith) close to 0 for delta N-15, while for delta C-13, the TEFololith-muscle of +0.02% warrants further investigation. Then, we compared past and contemporary otolith SOM signatures to investigate temporal diet shifts in B. chrysoura. This showed that 613C and delta N-15 differed significantly between the past and present period even if the temporal shift remained relatively small (respectively +1.17%, and 0.55%). The present study substantiates the use of otolith SOM delta C-13 and delta N-15 as a proxy of fish present and past trophic position, opening the possibility for major progress in studies of temporal changes in food web ecology.
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Trape, S., et al. "Recruitment success and growth variability of mugilids in a West African estuary impacted by climate change." Estuarine, Coastal and Shelf Science. 198 (2017): 53–62.
Résumé: With the persistence of a drought since the late 1960s, some West African estuaries became permanently reversed in term of salinity gradient and hypersaline waters are present in their upstream part (salinity >60). To understand the mechanisms regulating fish recruitment intensity in these estuaries and evaluate the consequences of freshwater shortages on juvenile habitat quality, a growth study was conducted in the Saloum hypersaline estuary (Senegal). The Mugilidae fish family, highly representative of estuarine environments, was targeted and several species sampled (Chelon dumerili, Mugil bananensis and M. cf. curema sp. M). Juveniles were sampled monthly all the year round in three areas of the estuary exhibiting strongly contrasted habitat conditions. Otolith sections were used to estimate the ages, reconstruct growth trajectories, estimate the duration of the oceanic larval phase, and evaluate juvenile growth variability along the salinity gradient. Analyses revealed that the temporal recruitment variability of C. dumerili, with 2 annual cohorts, was not mainly induced by growth-selection mechanisms, but probably more by predation pressures. Juveniles exhibited significantly faster growth rates in the lower salinity suggesting that benthic food availability was a strong factor controlling habitat quality of early juveniles. Salinity had also a clear impact when reducing the growth in hypersaline conditions and/or selecting slower growing individuals. Moderate freshwater inputs positively affected the nursery function of the estuary for mugilids by enhancing the productivity of the first trophic levels. In a long term, the global change could have an impact of the mugilid fishery and its management.
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2016 |
Ba, K., et al. "Resilience of Key Biological Parameters of the Senegalese Flat Sardinella to Overfishing and Climate Change." PLoS One. 11.6 (2016): e0156143.
Résumé: The stock of the Senegalese flat sardinella, Sardinella maderensis, is highly exploited in Senegal, West Africa. Its growth and reproduction parameters are key biological indicators for improving fisheries management. This study reviewed these parameters using landing data from small-scale fisheries in Senegal and literature information dated back more than 25 years. Age was estimated using length-frequency data to calculate growth parameters and assess the growth performance index. With global climate change there has been an increase in the average sea surface temperature along the Senegalese coast but the length-weight parameters, sex ratio, size at first sexual maturity, period of reproduction and condition factor of S. maderensis have not changed significantly. The above parameters of S. maderensis have hardly changed, despite high exploitation and fluctuations in environmental conditions that affect the early development phases of small pelagic fish in West Africa. This lack of plasticity of the species regarding of the biological parameters studied should be considered when planning relevant fishery management plans.
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Cormier-Salem, M. C., and J. Panfili. "Mangrove reforestation: greening or grabbing coastal zones and deltas? Case studies in Senegal." African Journal of Aquatic Science. 41.1 (2016): 89–98.
Résumé: Besides their important contribution to global biodiversity, mangroves provide many services. Nevertheless, due to an increase of human activities and to climate change, in less than 20 years these ecosystems have lost one fifth of their global surface area. In response to this decrease, mangrove reforestation incentives have spread throughout the world. The scientific and societal legitimacy of reforestation actions still remain in question. Focusing on two case studies, the Saloum Delta and Lower Casamance, Senegal, our methodology was mainly based on the analysis of environmental narratives and discourses between 2009 and 2013, and on reforestation campaigns conducted by NGOs. We highlight the complexity of the system of values associated with the mangroves, as well as the positive and negative interactions between the services. Even although the reforestation campaigns were generally successful in terms of reforested surfaces and international visibility, they were poor in terms of biological and cultural diversities and led to spatial injustice. Moreover, the extensive reforestation with a unique mangrove species, Rhizophora mangle, was perceived as means of ‘green grabbing’, and the simultaneous buying of carbon tax by industrial conglomerates induced disempowerment of the local communities. More integrated research programmes must be developed towards the extensive knowledge of the mangroves.
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Duponchelle, F., et al. "Trans-Amazonian natal homing in giant catfish." J. Appl. Ecol.. 53.5 (2016): 1511–1520.
Résumé: 1. Knowledge of fish migration is a prerequisite to sustainable fisheries management and preservation, especially in large international river basins. In particular, understanding whether a migratory lifestyle is compulsory or facultative, and whether adults home to their natal geographic area is paramount to fully appraise disruptions of longitudinal connectivity resulting from damming. 2. In the Amazon, the large migratory catfishes of the Brachyplatystoma genus are apex predators of considerable interest for fisheries. They are believed to use the entire length of the basin to perform their life cycle, with hypothesized homing behaviours. Here, we tested these hypotheses, using the emblematic B. rousseauxii as a model species. 3. We sampled adults close to major breeding areas in the Amazon basin (upper Madeira and upper Amazonas) and assessed their lifetime movements by measuring variations in Sr-87/Sr-86 along transverse sections of their otoliths (ear stones) using laser ablation multicollector mass spectrometry (LA-MC-ICPMS). 4. We demonstrate that larvae migrate downstream from the Andean piedmont to the lower Amazon, where they grow over a protracted period before migrating upstream as adults. Contrary to prevailing inferences, not all fish spend their nursery stages in the Amazon estuary,. By contrast, the passage in the lower or central Amazon seems an obligate part of the life cycle. We further evidence that most adults home to their natal geographic area within the Madeira sub-basin. Such long-distance natal homing is exceptional in purely freshwater fishes. 5. Synthesis and applications. By using otolith microchemistry, we were able to demonstrate a seemingly compulsory basin-wide migratory life cycle of large Amazonian catfishes. This makes them the organisms performing the longest migrations ( >8000 km) in fresh waters. This exceptional life history is already jeopardized by two dams recently built in 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.
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Samba, O., et al. "Evolution of catches and variability in the life history traits of the bonga shad, Ethmalosa fimbriata (Bowdich, 1825), a highly targeted small pelagic fish in West African coastal waters." International Journal of Fisheries and Aquatic Studies. 4.5 (2016): 98–108.
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Tahri, M., et al. "Health status of the swim bladder of the European eel Anguilla anguilla in northeastern Algeria’s Lake Oubeïra." International Journal of Fisheries and Aquatic Studies. 4.1 (2016): 364–369.
Résumé: While there have many numerous studies regarding the spread of the nematode Anguillicoloides crassus
in its host, few of these have addressed the pathology itself. In the present work, we examined the status
of the swim bladders of European eels populating Lake Oubeïra, by assessment of their Swim bladder
Degenerative Index (SDI). We found that the 450 eels that we captured were aged between 19 and 79
months, and that they exhibited an extremely fast growth rate.
Our assessment of the REPRODUCTIVE capacity of the European EELs (EELREP) [13] revealed that
3.78% had not undergone sexual differentiation, while 95.78% were females, of which more than half
were silvered; and only 0.45% were silvered males. The parasitism by Anguillicoloides crassus exhibited
the following epidemiological parameters: P=50.44%, I=7.04±3.18 parasites per swim bladder, and
A=3.74±2.04 parasites per eel (the latter varies significantly with the SDI). Lastly, we noticed that 95%
of the examined swim bladders were damaged (the SDI varied between 1 and 5) and that this worm does
not spare any age group.
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2015 |
Ba, A., et al. "Slow growth of the overexploited milk shark Rhizoprionodon acutus affects its sustainability in West Africa." J Fish Biol. 87.4 (2015): 912–929.
Résumé: Age and growth of Rhizoprionodon acutus were estimated from vertebrae age bands. From December 2009 to November 2010, 423 R. acutus between 37 and 112 cm total length (LT) were sampled along the Senegalese coast. Marginal increment ratio was used to check annual band deposition. Three growth models were adjusted to the length at age and compared using Akaike's information criterion. The Gompertz growth model with estimated size at birth appeared to be the best and resulted in growth parameters of L∞ = 139·55 (LT) and K = 0·17 year−1 for females and L∞ = 126·52 (LT) and K = 0·18 year−1 for males. The largest female and male examined were 8 and 9 years old, but the majority was between 1 and 3 years old. Ages at maturity estimated were 5·8 and 4·8 years for females and males, respectively. These results suggest that R. acutus is a slow-growing species, which render the species particularly vulnerable to heavy fishery exploitation. The growth parameters estimated in this study are crucial for stock assessments and for demographic analyses to evaluate the sustainability of commercial harvests.
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Le Loc'h, F., et al. "Spatio-temporal isotopic signatures (δ13C and δ15N) reveal that two sympatric West African mullet species do not feed on the same basal production sources." J Fish Biol. 86.4 (2015): 1444–1453.
Résumé: Potential trophic competition between two sympatric mullet species, Mugil cephalus and Mugil curema, was explored in the hypersaline estuary of the Saloum Delta (Senegal) using δ13C and δ15N composition of muscle tissues. Between species, δ15N compositions were similar, suggesting a similar trophic level, while the difference in δ13C compositions indicated that these species did not feed from exactly the same basal production sources or at least not in the same proportions. This result provides the first evidence of isotopic niche segregation between two limno-benthophageous species belonging to the geographically widespread, and often locally abundant, Mugilidae family.
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Ndiaye, W., et al. "The Length-Weight Relationship and Condition Factor of white grouper (Epinephelus aeneus, Geoffroy Saint Hilaire, 1817) at the south-west coast of Senegal, West Africa." International Journal of Advanced Research. 3.3 (2015): 145–153.
Résumé: This study describes some biological parameters including length-weight relationships and condition factors of Epinephelus aeneus (Geoffroy Saint Hilaire, 1817) in the western coasts of Senegal (Joal,
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Panfili, J., et al. "Experimental evidence of complex relationships between the ambient salinity and the strontium signature of fish otoliths." Journal of Experimental Marine Biology and Ecology. 467 (2015): 65–70.
Résumé: The otolith strontium:calcium ratio (Sr:Ca) has been widely used to assess the connectivity between fish populations in ocean, estuarine and freshwater environments as the concentration of Sr in the otoliths is strongly correlated with water salinity. This correlation was tested experimentally in hypersaline conditions by submitting the extremely euryhaline tilapia species Sarotherodon melanotheron heudelotii (Cichlidae), found throughout West African continental waters and commonly used as an aquaculture species, to a strong salinity gradient (15–106). Experimental and control individuals were reared from birth in a closed system at a constant salinity of 10 and injected with oxytetracycline (OTC) to mark the otoliths at the beginning of the experiment. Randomly selected control fish were maintained for 75 days at salinities of 10–20. The remaining experimental fish were acclimated to a salinity above 100 which was reduced by 10 each week to a salinity of 20. The salinity and temperature of the water were recorded every day and the Sr concentrations in the water were measured weekly by solution-based ICP-MS. The fish from the control and experimental groups were sampled weekly and otolith transverse sections were prepared for Sr:Ca measurements by laser ablation ICP-MS. No significant difference in the otolith growth rates after OTC marking was found between the control and experimental groups (ANCOVA, p = 0.63), showing that the experimental design did not affect fish growth. The Sr concentration in the water was closely related to ambient salinity (positive linear regression, R2 = 0.96). For most of the fish tested (~ 80%), the relationship between otolith Sr:Ca and salinity was positive but nonlinear (power law, R2 = 0.77 on log–log plot). However, about 20% of individuals from both the control and the experimental groups showed consistently low Sr:Ca ratios irrespective of the salinity, suggesting that the Sr incorporation into the otoliths in these fish was strongly regulated. This shows that there is high variability between individuals in the regulation of Sr incorporation by a euryhaline species and indicates that otolith datasets for ecological applications should be interpreted with caution.
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Sirot, C., et al. "Linking temporal changes in the demographic structure and individual growth to the decline in the population of a tropical fish." Estuarine, Coastal and Shelf Science. 165 (2015): 166–175.
Résumé: The exceptional biodiversity and productivity of tropical coastal lagoons can only be preserved by identifying the causes for the decline in the populations living in these vulnerable ecosystems. The Terminos lagoon in Mexico provided an opportunity for studying this issue as some of its fish populations, in particular the Silver Perch (Bairdiella chrysoura), have declined significantly since the 1980s. Fish sampling campaigns carried out over the whole lagoon area in 1979–81 and again in 2006–2011 revealed the mechanisms which may have been responsible for this decline. Based on biometrical data for 295 juveniles and adults from the two periods and on somatic growth derived from 173 otoliths, a study of the temporal changes in the demographic structure and life history traits (individual growth and body condition) made it possible to distinguish the causes of the decline in the B. chrysoura population. Growth models for the lagoon in 1980–1981 and 2006–2011 showed no significant change in the growth parameters of the population over the last 30 years with a logistic model giving an accurate estimate (R2 = 0.66) of the size-at-age for both periods. The decline in the B. chrysoura population could not be explained by an overall decrease in individual size and condition in the lagoon, the average standard length (SL) and Fulton index (FI) having increased slightly since 1980–1981 (4.6 mm and 0.02 for juveniles and 5.42 mm and 0.07 for adults). However, the size structure of the population in the lagoon has changed, with a significant shift in the size distribution of juveniles with a marked reduction in the proportion of juveniles ≤ 60 mm in the captures (90.9% fewer than in 1980–1981). As the otolith growth rate of fish during the first 4 months also decreased significantly between the two sampling periods (−15%), it is suggested that the main reason for the decline in the abundance and biomass of B. chrysoura within this system may be that its habitats are less suitable for fish growth and survival in the initial months after settlement. Environmental conditions in the lagoon appear to allow compensatory growth of the individuals that survive this early demographic bottleneck. The key for the conservation of B. chrysoura probably lies in the identification and restoration of the habitats required by its larvae and juveniles.
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Sirot, C., et al. "Combinations of biological attributes predict temporal dynamics of fish species in response to environmental changes." Ecological Indicators. 48 (2015): 147–156.
Résumé: Assessing species vulnerability to environmental changes is a major challenge for conservation. Combinations of biological attributes have already been successfully used for this purpose, allowing large-scale prediction of inter-specific differences in demographic parameters (e.g. abundance) or endangered status. However, studies investigating whether biological attributes could be used to predict the temporal demographic responses of species in a changing environment are still scarce. In this work, we tackled this issue by taking advantage of a multi-decadal survey of concomitant changes in fish communities and environmental conditions within the Terminos lagoon (Mexico). Based on this rare dataset, we first characterized changes in abiotic parameters that occurred in this ecosystem since the 80s. Then, we adapted a multivariate index accounting for changes in both species abundance and occurrence to assess concomitant demographic changes for the 25 dominant fish species in the lagoon, classifying them into five various types of trajectories (“Increasing”, “Decreasing”, “Constant”, “Hump-shape” and “U-shape”). Finally, we assessed the accuracy in prediction of these temporal responses for all possible combinations of 15 biological attributes including taxonomy, ecological and life-history traits. Our results showed that fish specific demographic changes over the last 30 years could be accurately predicted (72% accuracy) using a combination of five biological attributes (spawning season, order, maximum salinity, width of salinity range, oocyte size) among which three could be related to the increase in average salinity occurred in the lagoon over this period. Appropriate sets of complementary biological attributes could similarly allow prediction of inter-specific differences in demographic changes in other areas, thereby offering an additional pragmatic tool for ecosystem managers to identify vulnerable species at the local scale.
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2014 |
Avarre, J. - C., et al. "Plasticity of gene expression according to salinity in the testis of broodstock and F1 black-chinned tilapia, Sarotherodon melanotheron heudelotii." PeerJ. 2 (2014).
Résumé: The black-chinned tilapia Sarotherodon melanotheron heudelotii Rüppell 1852 (Teleostei, Cichlidae) displays remarkable acclimation capacities. When exposed to drastic changes of salinity, which can be the case in its natural habitat, it develops quick physiological responses and keeps reproducing. The present study focused on the physiological impact of salinity on male reproductive capacities, using gene expression as a proxy of acclimation process. Two series of experimental fish were investigated: the first one was composed of fish maintained in freshwater for several generations and newly acclimated to salinities of 35 and 70, whereas the second one consisted of the descendants of the latter born and were raised under their native salinity. Expression patterns of 43 candidate genes previously identified from the testes of wild males was investigated in the three salinities and two generations. Twenty of them showed significant expression differences between salinities, and their predicted function revealed that most of them are involved in the osmotic tolerance of sperm cells and/or in the maintenance of sperm motility. A high level of expression variation was evidenced, especially for fish maintained in freshwater. In spite of this, gene expression patterns allowed the differentiation between fish raised in freshwater and those maintained in hypersaline water in both generations. Altogether, the results presented here suggest that this high variability of expression is likely to ensure the reproductive success of this species under varying salinities.
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2013 |
Ba, A., et al. "Reproductive biology of the milk shark Rhizoprionodon acutus (Carcharhinidae) off the coast of Senegal." African Journal of Marine Science. 35.2 (2013): 223–232.
Résumé: Despite the considerable commercial value of the milk shark Rhizoprionodon acutus (Ruppell 1837) along the Senegal coast, there are few data on its biology. Milk sharks examined in this study were caught by small-scale fisheries on the Senegalese coast from May 2009 to February 2011 at eight landing locations. Landings were higher during the warm season (May-October) (71.5%), and lower during the cold season (November-April) (28.5%). The largest landings were recorded in the central area (36.9%) and the smallest in the coastal area of the Casamance (South-West Senegal) (0.6%). The observed size of individuals ranged from 31 to 113 cm (total length, TL), and the total weight from 150 to 8 500 g. Landings mostly included small individuals with a modal size of 50 cm TL for males and 60 cm TL for females. A reduction in the size range of milk sharks in the study area was consistent with those studied elsewhere. Females were more abundant than males (sex ratio 1.65F:1M). Mature individuals were dominant at the northern landing sites whereas immature individuals were more abundant in the southern regions. Our observations suggest a possible seasonal migration towards the north for reproductive purposes. The size at first sexual maturity was 92 cm TL for females and 82 cm TL for males. The gonadosomatic index, nidosomatic index and hepatosomatic index peaked from May to August, indicating that the reproductive period is during the warm season. Milk sharks off the coast of Senegal appear to have an annual reproductive cycle. Ovarian fecundity varied from 2 to 8 follicles and uterine fecundity from 2 to 7 embryos. Parturition occurred between May and June. Moreover, the presence of mature spermatozoa in the oviducal glands during the warm season supports the notion that mating takes place during that period.
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Ndiaye, W., et al. "Changes in population structure of the white grouper Epinephelus aeneus as a result of long-term overexploitation in Senegalese waters." African Journal of Marine Science. 35.4 (2013): 465–472.
Résumé: In Senegal, a significant decrease in catches indicates that many demersal fish stocks are being overexploited. The white grouper Epinephelus aeneus, locally known as the 'thiof', is exploited by both small-scale and industrial fisheries. A 28-year database of E. aeneus catches along the Senegalese coast provided by the Centre for Oceanographic Research of Dakar-Thiaroye, and size at maturity measured in Dakar (Senegal) from monthly samples in 2010, were used to analyse changes in population structure in the area over the past 37 years. Catches from the northern fishing areas were lower than those from the southern fishing areas, and decreased steadily during the period (Kolmogorov-Smirnov test, D = 0.243, p = 0.0002). The individual mean weight of catches decreased from 1974 to 2010 (linear regression, r(2) = 0.40, n = 37) and only 60% of the individuals were mature. The calculated sizes at maturity were 49 cm total length (TL) for females and 55 cm for males, and the optimal length of capture for a sustainable fishery was 96 cm, but only 0.03% of E. aeneus caught reached this length. Most of the catch consisted of juveniles; the larger reproductive individuals had disappeared. The number of individuals caught decreased significantly between 1974 and 2010 (1974-1983, r(2) = 0.98, n = 74 674; 1984-1993, r(2) = 0.95, n = 96 696; 1994-2003, r(2) = 0.93, n = 12 619; 2004-2010, r(2) = 0.91, n = 12 887), whereas the length range remained the same (10-110 cm TL). Biological indicators clearly showed that E. aeneus stocks in Senegal are overexploited and the species is now endangered. Immediate active management of fishing pressure is needed, therefore, to maintain E. aeneus populations in the area. Our results suggest a minimum size of <50 cm should be introduced and that fishing effort should be reduced.
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2012 |
Duponchelle, F., et al. "Contrasted hydrological systems of the Peruvian Amazon induce differences in growth patterns of the silver arowana, Osteoglossum bicirrhosum." Aquatic Living Resources. 25.1 (2012): 55–66.
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Ndiaye, A., et al. "Multiparametric approach for assessing environmental quality variations in West African aquatic ecosystems using the black-chinned tilapia ( Sarotherodon melanotheron ) as a sentinel species." Environmental Science and Pollution Research. 19.9 (2012): 4133–4147.
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Panfili, J., et al. "Habitat residence during continental life of the European eel Anguilla anguilla investigated using linear discriminant analysis applied to otolith Sr:Ca ratios." Aquat. Biol.. 15.2 (2012): 175–185.
Résumé: European eel Anguilla anguilla migratory behaviour during continental life is still unclear due to the multiplicity of aquatic environments colonised by the species. In the Camargue area (NW Mediterranean), eel colonisation of the Fumemorte canal, a freshwater habitat that communicates only with a vast brackish ecosystem (the Vaccares lagoon), offers a rare opportunity to test for freshwater habitat residence during continental life. To this end, both laser ablation inductively coupled plasma mass spectrometry and electron probe micro-analysis were used to measure chronological variations of strontium concentrations (Sr:Ca) in the otoliths of 58 silver eels captured in the canal between 1997 and 2007. Comparing mean Sr: Ca ratios measured on otolith edges with the 2 analytical methods indicated that they provide comparable measurement accuracies. Linear discriminant analysis (LDA), based on the otolith Sr: Ca values corresponding to the initial entrance of the fish into the brackish ecosystem and their final capture in the freshwater canal, allowed successful discrimination of the 2 habitats and reconstruction of migratory history for all individuals. Six different migratory behaviours were identified. Eels that entered the freshwater canal did so either directly (67%) or after 1 to 2 yr spent in the lagoon (33%), with a subsequent majority of freshwater residents (55%) until their silvering. These results indicate the value of LDA for reconstructing habitat use during continental life using Sr: Ca ratios. They confirm the occurrence of freshwater residence during continental life in European eels, even in Mediterranean continental areas where brackish environments are predominant. This observed sedentary behaviour has implications for eel population management and conservation.
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Whitfield, A., J. Panfili, and J. D. Durand. "A global review of the cosmopolitan flathead mullet Mugil cephalus Linnaeus 1758 (Teleostei: Mugilidae), with emphasis on the biology, genetics, ecology and fisheries aspects of this apparent species complex." Reviews in Fish Biology and Fisheries. 22.3 (2012): 641–681.
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Yoboué, A. N., et al. "Genetic diversity and adaptability of Sarotherodon melanotheron (Cichlidae) in coastal ecosystem." Ethology Ecology & Evolution. 24.3 (2012): 230–243.
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2011 |
Mercier, L., et al. "Otolith reading and multi-model inference for improved estimation of age and growth in the gilthead seabream Sparus aurata (L.)." Estuarine Coastal and Shelf Science. 92.4 (2011): 534–545.
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2010 |
Blel, H., et al. "Selection footprint at the first intron of the Prl gene in natural populations of the flathead mullet ( Mugil cephalus , L. 1758)." Journal of Experimental Marine Biology and Ecology. 387.1-2 (2010): 60–67.
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2009 |
Diouf, K., et al. "Effects of the environment on fish juvenile growth in West African stressful estuaries." Estuarine Coastal and Shelf Science. 83.2 (2009): 115–125.
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Ouattara, N., et al. "Changes in gill ionocyte morphology and function following transfer from fresh to hypersaline waters in the tilapia Sarotherodon melanotheron." Aquaculture. 290.1-2 (2009): 155–164.
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Trape, S., et al. "Identification of tropical Eastern Atlantic Mugilidae species by PCR-RFLP analysis of mitochondrial 16S rRNA gene fragments." Biochemical Systematics and Ecology. 37.4 (2009): 512–518.
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Trape, S., et al. "Recruitment patterns of young-of-the-year mugilid fishes in a West African estuary impacted by climate change." Estuarine Coastal and Shelf Science. 85.3 (2009): 357–367.
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