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International audience; Dams and other man-made barriers impair upstream fish migration and thus threaten fish populations that need access to upper river reaches to complete their life cycle. For many years, fishways have been used to mitigate this impact. Fishways around the globe are typically built based on recommendations made for northern hemisphere species, particularly salmonids. These recommendations do not consider the locomotor characteristics and skills of other species, especially those living in the tropics. Among tropical species, freshwater eels and gobies of the Sicydiinae subfamily are important cultural and economic species that are particularly sensitive to the impact of man-made barriers. Our experimental study aimed to test different substrates and slopes for ramp-like fishways adapted to tropical eels and sicydiines. Among the five substrates tested for 368 eels Anguilla marmorata, elastomer pins appeared to be the most efficient. Elastomer pins also appeared to be more efficient than the fine concrete which is currently used in fishways for sicydiines (Sicyopterus lagocephalus, N = 1797, and Cotylopus acutipinnis, N = 1303). The slope had a lesser effect on the climbing success of sicydiines compared to substrate type, except for gradients greater than 50° that induced a slight decrease in success. Our results indicated that ramp-like fishways fitted with 1.0 cm diameter elastomer pins, positioned in staggered rows with a diagonal spacing of 1.3 cm, wetted with low-flow and angled less than 50°, are well adapted to accommodate the different locomotor characteristics and skills of tropical eels and sicydiines.

Water warming induced by human activities can impact fish larvae survival, notably because it influences larval development and prey abundances. Amphidromous gobies of the subfamily Sicydiinae are particularly sensitive to this threat as the newly hatched free embryos are poorly developed and the first feeding opportunity only occurs after they reach the ocean. Here, we studied how water temperature (21, 23, 25, 29 and 31 degrees C) impacts early development stages of Sicyopterus lagocephalus in both freshwater and marine aquaria (salinity 35). We monitored survival time, larval condition and the occurrence of critical developmental events such as mouth opening, yolk sac and oil globule resorption. In freshwater, the survival exceeded 150 hours at 21 degrees C, while it dropped below 50 hours at 31 degrees C. In seawater, the larval development of unfed larvae was significantly affected by temperature, survival time being greatly reduced in warmer waters. Accounting for the observed duration between mouth opening and the resorption of the oil globule, we estimated that larvae need to find suitable prey in seawater within a short time: around 30 hours during the peak of reproduction in summer. Otherwise, their endogenous reserves become depleted and their condition degrades. This study emphasises the sensitivity of free embryos to stream flow alterations, which contributes to the increase in water temperature and to the slowing down of larvae drift to the ocean. We conclude that once in seawater the temperature and feeding conditions experienced by amphidromous larvae are critical for survival.

Madagascar is a marine biodiversity hotspot. A recent checklist recorded 1689 marine or transitional water fish species, 2.5% being endemic. To date, studies in this country were mostly focused on adult fishes using morphological-based identification. The early life stages of fishes remain largely understudied. The present work aimed to improve knowledge of fish biodiversity in Madagascar by focusing on post-larval reef fishes and settled juveniles in seagrass meadows of southwest Madagascar by using either species identification keys or DNA barcoding. Up to 119,500 individuals were collected, and 1096 individuals were successfully barcoded. We identified 387 species—85 through their morphology (with 58 unsuccessfully sequenced) and 302 by using CO1 barcoding corresponding to 302 barcode index numbers (BINs). This study added 27 new BINs for the BOLD database, 120 new for Madagascar, but only 159 were assigned a precise species name. By referring to the updated checklist of Madagascar fishes, 10 new species were detected for Madagascar. This number will probably increase when all the barcoded specimens become assigned to precise species names. These preliminary findings stress our poor knowledge of marine fish biodiversity in Madagascar and demonstrate the relevance of DNA barcoding in improving this knowledge.

International audience; Determining the relative importance of niche‐ and dispersal‐based processes in the structuring of animal communities is central in ecology. Freshwater fish and crustacean communities of small tropical islands can bring new insights for understanding these processes as all their species present a pelagic larval stage which gives them important dispersal capacities. Consequently, we hypothesized that dispersal‐based process may be preponderant for structuring these communities from the regional to the local, that is, survey site, scales. Gradient forest analyses allowed us to model the effect of 12 environmental variables on freshwater taxa abundances in two southwestern Indian Ocean islands: Mayotte (26 taxa) and Reunion (21). A total of 153 surveys in Mayotte and 266 in Reunion were used for building the models. Despite the strong heterogeneity of environmental conditions between the two islands, the main factors structuring freshwater fish and crustacean communities in both islands were the elevation and the slope of the sites. The observed structure appeared more pronounced for predatory species than for primary consumers and omnivores. As predators generally have limited locomotor capacities, it is concluded that dispersal‐based process structures these communities not only at large geographical scales but also at the intra‐watershed scale, by limiting the inland penetration (or dispersion) of species in relation to their locomotor capacities. However, more knowledge concerning ecological traits and taxonomic status of many species is needed to confirm this assumption.; Une des questions centrales en écologie consiste à déterminer l'importance des processus de niche et de dispersion dans la structuration des peuplements faunistiques. L’étude des peuplements de poissons et de crustacés d'eau douce des petites îles tropicales peut apporter de nouveaux éclairages pour comprendre ces processus. En effet, ces espèces présentent toutes une phase de développement larvaire en milieu marin qui augmente fortement leurs capacités de dispersion. Nous avons donc émis l'hypothèse que les processus de dispersion ont un effet majeur sur la structure des peuplements à l’échelle régionale, mais également à l’échelle locale, c'est‐à‐dire celle du site d’étude. Des analyses de type « gradient forest» nous ont permis de modéliser l'influence de 12 variables environnementales sur les fluctuations d'abondance des taxons d'eau douce de deux îles du sud‐ouest de l'océan Indien: Mayotte (26 taxons) et la Réunion (21 taxons). Au total, 153 inventaires à Mayotte et 266 à La Réunion ont été pris en compte dans les modèles. Malgré l'hétérogénéité marquée des conditions environnementales entre les deux îles, les principaux facteurs structurant les peuplements de poissons et de crustacés étaient similaires, à savoir la pente du site d'inventaire et son altitude. De plus, la structuration des peuplements de prédateurs était plus marquée que celle des consommateurs primaires et des omnivores. Comme la plupart des prédateurs ont des capacités locomotrices limitées, nous avons conclu que les processus de dispersion jouent un rôle prépondérant dans la structuration de ces peuplements que ce soit à large échelle ou à l'intérieur des bassins versants. En effet, les faibles performances locomotrices des prédateurs peuvent limiter leur capacité à coloniser (ou se disperser vers) les zones amont des cours d'eau. Cependant, des connaissances plus approfondies concernant le statut taxinomique et l’écologie de plusieurs de ces espèces seraient nécessaires pour confirmer cette hypothèse.

This study investigates how age at first maturity of two tropical amphidromous spe‐cies Sicyopterus lagocephalus (Pallas, 1770) and Cotylopus acutipinnis (Guichenot, 1863) varies in relation to their larval and juvenile life history. Reproductive stage was estimated based on histological observation of ovaries of more than 200 females of each species caught monthly over 1 year. The age of fish was estimated by interpret‐ing the daily increments deposited on otoliths during the oceanic larval phase, and the juvenile phase in the river. The age at first maturity was approximately 9 months for S. lagocephalus and 7 months for C. acutipinnis, corresponding to approximately 70–130 and 90–130 days after they returned to freshwater respectively. For both species, the time spent in freshwater before maturity was significantly influenced by the duration of the pelagic larval stage at sea (PLD) and the season of return in freshwater. Individuals with a long PLD, or returning in freshwater during the warmer season, maturated faster once in freshwater. This reproductive advantage may mini‐mise the risk of extirpation due to catastrophic events at each generation and thus probably benefits amphidromous species living in very unpredictable tropical rivers.

International audience; Amphidromous fish species reproduce in rivers, and their larvae immediately drift to the sea after hatching. Most of these larvae survive in freshwater for a few days only, rapidly reaching sea water is thus essential. Being of small size, especially among species of the Sicydiinae subfamily, the larvae possess poor swimming abilities; their drift dynamics is considered to be mainly passive and influenced by flow conditions. The influence of daily fluctuations in flow regime on Sicyopterus lagocephalus (Sicydiinae) larval drift patterns was studied using drift nets at three sites along the dammed Langevin River in Reunion Island. The river flow was stable at the upstream site when frequent anthropogenic river flow fluctuations were observed at the two sites downstream to the dam. Weak diel larval drift dynamics were detected at the upstream site and the first site under anthropogenic river flow conditions. In contrast, larval drift dynamics at the most downstream site was strongly influenced by anthropogenic daily fluctuations of discharge: the abundance of drifting larvae increased with peaks of discharge, regardless of the time. As higher mortality rates of drifting larvae were observed during discharge peaks, the benefit of a more rapid travel to the ocean associated with these peaks should be lower than expected. It is concluded that peaks of discharge increase the number of larvae drifting to the sea probably due to higher physical constraints on the egg clutches, but also decrease the chance of survival for larvae that may be nonfully developed.

International audience; Otolith microchemistry can provide crucial information to address gaps of knowledge in spatio-temporal ecology of fish species. However, understanding the seasonal variability of water chemistry and its effect on otolith signatures is needed to interpret fish movements. Otolith multi-elemental signatures were used to examine the diadromous migration and small-scale movements of a tropical goby (Sicyopterus lagocephalus) within a watershed in La Réunion Island, Indian Ocean. The elemental ratios Sr:Ca, Ba:Ca and Sr:Ba recorded monthly in the water of nine sampling sites varied between localities and were correlated with otolith signatures, whereas the Mg:Ca signature was not. The incorporation of some trace elements in otoliths was influenced by the size of fish and site where they were caught, reflecting an effect of endogenous and exogenous factors. Despite these sources of variation, the elemental signatures did not overlap for three river sections distributed along the 26-km-long watershed. The diadromous migration and fish lifetime movements between these river sections were reconstructed using an original process based on random forest analysis. This approach revealed distinct migratory behaviours after fish entered in the river, with some individuals progressing slowly in the watershed whereas other rapidly reached the upper localities. As adults, S. lagocephalus showed a restricted exploratory behaviour and a strong site fidelity to a particular part of the watershed. The detection of adult movement was typically only between adjacent locations and is possibly explained by shifts in local intraspecific hierarchies and/or displacement during extreme discharge caused by cyclones.

The species richness of communities should largely depend on habitat variability and/or on habitat state. We evaluated the ability of habitat variability and habitat state to predict the diversity of juvenile neo-tropical fish communities in creeks of a river floodplain. The young-fish fauna consisted of 73 taxa, and samples were well distributed over a wide range of relevant temporal and spatial habitat variability. We were unable to demonstrate clear patterns of richness in relation to temporal and spatial habitat variability (if habitat state variables were not included), regardless of the temporal variability scale, the grouping of sites (up- and downstream sites differed in temporal variability patterns) taxonomic units or life stages considered. Using stepwise multiple regression, 36% of the variance in species richness was explained for all data, and at best 47% was explained for all taxonomic units at upstream sites using temporal and spatial habitat variability and habitat state (bank length, mean width, mean water level before fishing and/or water turbidity). Using Monte Carlo simulations, we blindly predicted 31% (all data) and at best 37% (all upstream taxa) of the observed variance in species richness from these model types. This limited precision is probably because rare species produced most of the richness patterns in our creeks. The prediction of these rare species is generally difficult for various reasons, and may be a problem in many ecosystem types. (Résumé d'auteur)

The aim of this study was to evaluate the efficiency of geometric morphometrics for describing the body shape of fish larvae and juveniles, and identifying them to species, in comparison with traditional linear measurements. Species of emperor fishes (Perciformes: Lethrinidae, genus Lethrinus) were chosen as the model group, as the late larval and early juvenile stages in this genus are particularly difficult to identify. Forty-five individuals of different species of Lethrinus were collected from the south-western lagoon of New Caledonia between May 2005 and March 2006. The individuals were first identified to species by their partial cytochrome-b gene sequence. They were then morphologically characterized using eight linear measurements and 23 landmarks recorded on digital photographs. Except for a small proportion of individuals, geometric morphometrics gave better results to distinguish the different species than linear measurements. A 'leave one out' approach confirmed the nearly total discrimination of recently settled Lethrinus genivittatus and Lethrinus nebulosus, whereas traditional identification keys failed to distinguish them. Therefore, geometric morphometrics is a promising tool for identifying fish larvae and juveniles to species. An effective approach would require building image databases of voucher specimens associated with their DNA barcodes. These images could be downloaded by the operator and processed with the specimens to be identified.

International audience; Freshwater gobies of tropical islands are amphidromous: adults reproduce in rivers and larvae passively drift down to the sea immediately after hatching. Describing the phenology of this larval drift is essential to understanding the population dynamics of amphidromous gobies and to developing ecologically based recommendations for managing the watersheds. The larval drift patterns of two amphidromous gobies of Réunion Island, Sicyopterus lagocephalus and Cotylopus acutipinnis, were studied on a monthly basis for 1 year using plankton nets at two sites on the Mât River, located 20 km and 7 km from the river mouth. Genetic analyses showed that larval assemblages were dominated at 90% by S. lagocephalus, although the proportion of C. acutipinnis increased during early summer. Our findings highlighted a marked larval drift peak in full austral summer. The diel larval drift dynamic was described using periodic linear models. A diel pattern was only observed downstream, peaking a few hours after sunset. Finally, this study presents a new approach that improves standard methods for sampling and analyzing larval drift of amphidromous species.

Processes occurring at the end of the larval stage are of major importance in shaping spatial structure of fish assemblages in coral reefs. However, because of the difficulty in identifying larvae to species, many studies dealing with these stages are limited to the family level. It remains unknown if variation in the spatial structure of coral-reef fish assemblages across life stages can be detected at such a coarse taxonomic level. Two different surveys conducted in a similar area of New Caledonia, Southwest Pacific, provided the opportunity to compare the structure of coral-reef fish assemblages collected as pre-settlement larvae, juveniles and adults along a coast to barrier reef gradient. Adult and juvenile fish were sampled using underwater visual counts (UVC) during the warm seasons of 2004 and 2005. Pre-settlement larvae were sampled with light-traps during the same seasons. In order to standardize data between sampling methods, analyses were conducted on the relative abundance (for larvae) and density (for juveniles and adults) of 21 families commonly collected with both methods. Relative abundances/densities of families were analysed as a function of life stage (larvae, juveniles or adults), large-scale spatial location (coast, lagoon or barrier) and years (2004, 2005) using non-parametric multidimensional scaling (nMDS) and permutational multivariate analysis of variance (permanova). Kruskal–Wallis tests were then used to examine differences among life stages and locations for individual families. Different levels of spatial and temporal variability characterized fish assemblages from different life stages, and differences among life stages were detected at all locations and years. Differences among life stages were also significant at the level of individual families. Overall results indicate that studies conducted at the family level may efficiently reveal changes in coral-reef fish spatial structure among successive life stages when large spatial scales are considered.

International audience; Species identification is fundamental to address questions about community ecology, biodiversity, conservation and resource management, at any life history stage. Current studies on fish larval ecology of tropical species are hampered by the lack of reliable and effective tools for identifying larvae at the species level. Emperors and large-eye breams comprise fish species from the perciform fish family Lethrinidae. They inhabit coastal and coral-reef habitats of the tropical Indo-Pacific, and they are important fishery resources. Their taxonomy is considered difficult and identification to species is often problematic. Lethrinidae larvae and juveniles can be identified on the basis of meristic counts at the subfamily level, but no further. In this study, we developed a set of polymorphic PCR markers (size polymorphisms at the intron regions from 4/5 nuclear protein-coding genes and single-strand conformation polymorphism of a 205-bp fragment at the mitochondrial 16S rRNA locus), to characterize 341 specimens from 21 Lethrinidae species from New Caledonia (southwestern tropical Pacific). A genetic data-bank was constructed using the genotypes screened from the multiple gene loci of adult or sub-adult specimens used as references for these species. The 16S rRNA gene fragment was able to differentiate species for the genus Lethrinus, but it provided little diagnostic resolution among different species within the genus Gymnocranius. A combination of the 16S rRNA marker and 4 nuclear markers developed herein allowed to sort out species within Gymnocranius spp. from New Caledonia. Using genotype distributions at nuclear loci to test for reproductive isolation, we found that three apparently undescribed large-eye bream species may exist, provisionally referred to as Gymnocranius sp. A, sp. B and sp. C. Subsequent genotyping of 137 Lethrinidae larvae collected from the bays of the Noumea peninsula, New Caledonia, found a total of three species (Lethrinus genivittatus, L. olivaceus and Gymnocranius sp. A).

This study examines the diet of nine taxa from seven families of pre-settlement coral-reef fish larvae collected in the lagoon of New Caledonia, south-west Pacific. Chesson's index of electivity indicated that the major prey groups in the diets, i.e. small copepods, small unidentified crustaceans and eggs, were positively selected by all larvae, provided they were at least 150 microm wide. This result emphasizes the role of larvae's behaviour on their feeding.

Coral reefs are one of the most diverse ecosystems on Earth. They are currently exposed to increasing levels of anthropogenic perturbations. Several recent reviews point to the lack of good indicators for these perturbations especially to monitor their effects on fish populations or fish assemblages. The SW lagoon of New Caledonia is an ideal location to test indicator species in this context as contrasting sites are present within a small geographical range. This study analysed fish from four sites, one with heavy industrial pollution, another dominated by domestic waste, a third with historic mining activities, and the fourth as a control. The butterfly fish, Chaetodon speculum, was chosen to determine C. speculum's potential as an indicator species due to its link to coral, its sedentary behaviour and its wide geographical distribution. The size distribution, growth rate, age distribution and whole otolith composition were analysed at each site. Age and mean growth rate were analysed from daily increments of the otoliths. The concentrations of eight elements (Li, Mg, Co, Ni, Cu, Rb, Sr, and Ba) were measured by ICP-MS in the otoliths of a subset of individuals. The sites under anthropogenic impact were distinct from the control site by fish size frequencies, age distributions, and the chemical content of their otoliths. The chemical elements Mg, Co, Ni, Cu, and Rb showed differences amongst sites. Fish belonging to the sites furthest from Noumea could be discriminated in nearly 80% of samples or 60% of the cases when otolith weight or fish age respectively were taken into account. Ni concentrations of the otoliths were also higher in the bays where water concentrations of this element were known to be higher, but these differences were no longer significant once corrected for otolith weight. These results should be mitigated by the fact that: (1) despite significant differences between sites in age distribution and size frequencies there were no differences in growth rates or body condition; (2) differences in age or size were not correlated to perturbation levels; and (3) discrimination between sites based on chemical levels in the otoliths, even though significant, was not sufficient to identify the origin of the fish at a level useful for screening tests. The hypothesis that environmental differences between sites would be reflected in the otolith chemical composition is therefore not fully supported by our results.

We investigated the diversity of patterns of habitat use by juveniles of coral reef fishes according to seasons and at two spatial scales (10–100 m and 1–10 km). We conducted underwater visual censuses in New Caledonia's Lagoon between 1986 and 2001. Co-inertia analyses highlighted the importance of mid-shelf habitats at large spatial scale (1–10 km) and of sandy and vegetated habitats at small spatial scale (10–100 m) for most juveniles. Among all juvenile species, 53% used different habitats across seasons (e.g. Lutjanus fulviflamma and Siganus argenteus ) and 39% used different habitats as they grow (e.g. Lethrinus atkinsoni and Scarus ghobban ). During their ontogeny, at large and small scales, respectively, 21% and 33% of the species studied showed an increase in the number of habitats used (e.g. L. fulviflamma , L. atkinsoni ), 10% and 3% showed a decrease in the number of habitats used (e.g. Amphiprion melanopus , Siganus fuscescens ), 23% and 3% showed a drastic change of habitat used (e.g. S. ghobban , Scarus sp.) whereas 46% and 61% showed no change of habitat used (e.g. Lethrinus genivittatus , Ctenochaetus striatus ). Changes in habitat use at both small and large spatial scales occurred during the ontogeny of several species (e.g. S. ghobban , Scarus sp.). Results pointed out the different spatial and temporal scales of juvenile habitat use to account for in conservation decisions regarding both assemblage and species-specific levels.

Ten atolls of contrasting morphology and low human pressure were investigated in the Tuamotu Archipelago (French Polynesia) during the research program "Typatoll". This program produced large data sets about species richness of undisturbed fish assemblages and environmental data recorded at three spatial scales. Multivariate analyses defined six groups of transects of similar multi-scale environmental characteristics. Smoothed histograms (spectra) of species richness were plotted for each group of transect according to six size classes, six diet classes and six life-history classes of fish assemblages. The shape of spectra among groups of transects was then modelled through a single equation, determined by goodness-of-fit techniques. The height of each spectrum was then predicted by General Linear Model. Kolmogorov-Smirnov tests showed no significant difference between predicted and observed distributions of species richness. This two-phase model allowed predicting the diversity structure of undisturbed reef fish assemblages from few environmental data for the first time in the Pacific region. The resulting model will provide an efficient tool for detecting anthropogenic effects on the diversity of reef fish assemblages in atolls of the archipelago. This modelling approach could be adapted to provide a tool for the evaluation of variables affecting diversity of coral reef fish assemblages whatever the habitat they live in, and more generally the diversity of any other highly diversified tropical communities. (c) 2006 Elsevier B.V. All rights reserved.

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Noumea by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July-August to more than ten in October-November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries.

The otolith micro-increment technique was applied to assess the growth trajectory of early stages of the neotropical catfish Megalechis thoracata in Kaw Swamp, a coastal swamp in French Guiana, and two contrasting habitats in Suriname: the coastal Lelydorp Swamp with standing water and a rain-forest creek with running water, the Maykaboeka Creek. Daily deposition of increments on the lapilli was validated for the first 35 d after hatching and the innermost increments were deposited from hatching onwards. The natural habitats of M. thoracata in French Guiana and Suriname showed considerable variation in physico-chemical characteristics of the water, density of food organisms and fish fauna. Instantaneous growth rates and size-at-age differed significantly among two vegetation types in Kaw Swamp (3.5% d-1 and 4.1% d-1), Lelydorp Swamp (3.0% d-1) and Maykaboeka Creek (2.5% d-1). Spearman's rank correlation coefficient between instantaneous growth rates and environmental parameters differed significantly from 0 only for water temperature. Hatch date analysis revealed an extended spawning season from January to June in the rain-forest creek.

The growth of most mensural characters of Krobia guianensis and Crenicichla saxatilis during early development was explained by a split regression indicating inflection in allometry at specific standard lengths. Double-centred PCA revealed morphological transformations during ontogeny mostly under the influence of the maximum body depth and the maximum caudal peduncle width, the area of the caudal fin and the horizontal diameter of the eye contributing also, but to a lesser extent. Young K. guianensis switched to larger prey at the end of the period when the growth of most of their studied mensural characters demonstrated an inflection, but young C. saxatilis changed their diet at a much smaller size than that at which an inflection occurred. However, in the lower reservoir sites, most young juveniles of K. guianensis and C. saxatilis did not switch to larger items during their ontogeny and micro-crustaceans occurred more frequently in their diet. It is hypothesized that the low net energy gained when eating such small prey may explain why the young of both species were thinner at these sites than in their undisturbed habitats. If food resources of young cichlids do not improve in the Petit-Saut reservoir, it is hypothesized that these species will develop stunted populations there.

SUMMARY 1. We investigated which environmental parameters control the variation in density, in space and time, of young stages of fish in tributaries of a natural and a flow-regulated section of the Sinnamary River, French Guiana. 2. The density of the progeny in most taxa varied in space and/or time. However, most non-Perciformes responded differently to space and/or time in the two sections. 3. Oxygen, turbidity and habitat structure (i.e. bank length, occurrence of undercut bank, richness in litter, vegetation and substratum) were important, as was the position of the sampling site relatively to the main channel in the downstream tributaries, in explaining the variation of density in space in both sections. Both habitat complexity and distance from the main channel protect young fish against unpredictable flow releases downstream from the Petit Saut dam. 4. Hydrological events played an important role in the temporal variation in densities of many fish taxa. The density of most early life and many juvenile stages (mostly Characiformes) was positively related to hydrological events. 5. Some fish taxa had reproductive habits which were relatively independent of abiotic factors, such as flow variability, and the density of their progeny did not vary with time. 6. The nursery areas of more than 45% of species in the Sinnamary River have been degraded by flow regulation.

A total of 1468 young fish representing 66 taxa from the Sinnamary River, French Guiana was classified by complete cluster analysis of mean relative body width and mean relative body height into four groups. These had anguilliform, disciform, flat or intermediate body shapes and belonged chiefly to Gymnotiformes, Perciformes, Siluriformes and Characiformes, respectively. Several of the taxa shifted from one to another body shape during ontogenesis. Seven diet groups were defined by complete cluster analysis. Among these, six groups were represented by carnivorous fish. The three most frequent groups had diets of (1) mainly insect larvae and small crustaceans, (2) insect larvae, and (3) predominantly terrestrial insects. The majority of the fish taxa showed ontogenetic diet shifts. Carnivorous fish usually switched from small-size prey, such as small crustaceans, to intermediate-size prey, such as insect larvae and/or to large-size prey, such as insects and/or fish. However, taxa differed in their capacities to switch from small prey to intermediate and/or to large prey. Taxa of different body shapes had significantly different diets. Disciform fish fed mainly on aquatic insect larvae and terrestrial insects but also, in small amounts, on small curstaceans. Most anguilliform taxa ate insect larvae. Individuals belonging to the depressiform or intermediate morphotype had varied diets ranging from plant debris and substratum to fish.

We examined fish community structure and habitat use at the start of the dry seasons: (1) in 10 tributaries of the River Sinnamary (French Guiana) before and after the start of dam operation, and (2) in 10 upstream tributaries and at 10 littoral sites in the newly-created reservoir after the start of operation to assess the impact on fish juveniles of a hydroelectric dam built on the river's lower section. After the first year of dam operation, juvenile fish communities downstream of the dam showed an important decrease of the relative abundance of Characiformes, and Perciformes dominated. Principal components analysis revealed a distinct upstream-to-downstream progression in the juvenile fish communities with post-reservoir downstream and reservoir sites representing transitions between the upstream and pre-reservoir downstream sites. Canonical correspondence analysis and electivity indices of fish-habitat associations revealed three relatively distinct groups of sites, corresponding to the downstream, reservoir and upstream taxa. The proportion of juveniles presenting higher-than expected frequencies (Fisher's exact test) towards local environmental variables was higher for taxa more often caught in upstream sites. Inversely, juvenile taxa more frequently observed in downstream and reservoir sites appeared less selective towards local environmental characteristics. In the downstream reaches of the river, hydrodam operation is expected to drive the fish community towards a new biologically accommodated state where tolerant species will dominate and sensitive species will be lacking.

International audience; The objectives of this paper are (1) to present VideoSolo, a new autonomous video system; and (2) to show its relevance through the analysis of temporal variability of fish populations at different temporal scales of years, days and hours. The underwater video system VideoSolo, designed for use in remote places, combines advantages in comparison to older systems necessitating the presence of a ship and whose autonomy is generally limited in time due to biofouling. All these issues have been resolved in VideoSolo, a fully autonomous long-term system, programmable, easy to set up and deploy (the housing weighs only 3 kg). It has sufficient energy storage and an anti-biofouling system in the form of its hydro-wiper, enabling continuous operation for up to one month. The experiment was conducted in a remote place (Glorioso Island, SW Indian Ocean) where the system was installed in front of the same coral colony (1 m2) at a depth of 8 m. Data was recorded in May for two subsequent years and six times per day (between 6 am and 4 pm). The analysis of the video sequences enabled the recording of 6224 individuals of 75 species belonging to 16 families over 41 days of experiment. At a small spatial scale, fish assemblages were variable over time at the three temporal scales studied. The number of individuals and species observed was variable between years whilst the number of individuals observed per day remained relatively stable through time. When occurrences were considered, less variation was observed between years. Analyses of temporal fish variability on the most abundant families revealed that the abundances of Acanthuridae, Labridae, Scaridae and resident Pomacentridae were significantly different between years and inversely so for the non-resident Pomacentridae. When the diurnal variations of fish assemblages were considered, the abundances differed significantly over time for Acanthuridae, higher in the morning (6 am and 9 am), and for Scaridae, higher at sunrise (6 am) and sunset (4 pm). The abundances of Pomacentridae and Labridae were stable from sunrise to sunset. The variability between years could be linked to events such as recruitment whilst daily variations could be more related to the effects of tidal cycles whose effects may have created periodic feeding opportunities. VideoSolo has demonstrated its efficiency and has remarkable potential in the field of aquatic biology in any location, as no human presence is required for it to work.

Invertebrates represent an essential component of coral reef ecosystems; they are ecologically important and a major resource, but their assemblages remain largely unknown, particularly on Pacific islands. Understanding their distribution and building predictive models of community composition as a function of environmental variables therefore constitutes a key issue for resource management. The goal of this study was to define and classify the main environmental factors influencing tropical invertebrate distributions in New Caledonian reef flats and to test the resulting predictive model. Invertebrate assemblages were sampled by visual counting during 2 years and 2 seasons, then coupled to different environmental conditions (habitat composition, hydrodynamics and sediment characteristics) and harvesting status (MPA vs. non-MPA and islets vs. coastal flats). Environmental conditions were described by a principal component analysis (PCA), and contributing variables were selected. Permutational analysis of variance (PERMANOVA) was used to test the effects of different factors (status, flat, year and season) on the invertebrate assemblage composition. Multivariate regression trees (MRT) were then used to hierarchically classify the effects of environmental and harvesting variables. MRT model explained at least 60% of the variation in structure of invertebrate communities. Results highlighted the influence of status (MPA vs. non-MPA) and location (islet vs. coastal flat), followed by habitat composition, organic matter content, hydrodynamics and sampling year. Predicted assemblages defined by indicator families were very different for each environment-exploitation scenario and correctly matched a calibration data matrix. Predictions from MRT including both environmental variables and harvesting pressure can be useful for management of invertebrates in coral reef environments.

With 4 figures and 1 table in the text 0. R.S.T.0.M. F~i~tis 5~~~m~n~~i~~ NQ : 42 344 B Abstract CDk An improved version of the quatrefoil light trap was tested in a tributary of the Sin- namary River, French Guiana, South America, at the beginning of the rainy season. The entire trap was simplified to lower the cost and increase the reliability of the entire system in harsh field work conditions. The major improvement was an inexpensive electronic light-switch that automatically lighted the lamp at dusk and turned it off at down allowing deployment of numerous traps over large distances. Most of the 648 in- dividuals caught in the 76 samples were Characiformes larvae, juveniles, and small adults. Some Clupeiformes, Siluriformes, Cyprinodontiformes, Syngnathiformes and Perciformes were also caught but no Gymnotiformes were represented in the samples. Light traps appear useful to sample in their microhabitat neotropical young and small fishes of several taxonomic groups.

In ice-covered southeastern Hudson Bay (northern Quebec, Canada) the production of suitable zooplankton prey for manne fish larvae was simdar withln and outside the area covered by the Great Whale h v e r plume Within the plume however, hght attenuahon by the turbld surface layer reduced the foraging efficiency of first-feeding Arctic cod Boreogadus s a ~ d a nd sand lance Ammodytes sp larvae In daytime, first-feeding larvae accumulated at the pycnocline where food availability (l e light X prey density) was maximum Below the pycnocline, the average number of prey lngested by indiv~dual arvae (foraging gain) decllned with depth At night, fish larvae and their prey redistnbuted more uniformly over the water column, suggesting a similar passive response to the turbulence field In the absence of a light gradient The observed Ideal free distributions (IFDs) were better explained by unequal foraging abilities of the larvae than by density-dependent interactions among the assemblage of planktonic predators

The relationship between fish larvae and their zooplanktonic prey has not been fully explored for late-stage larvae of coral-reef fish in lagoonal environments. However, compared to most temperate taxa, these larvae are characterized by strong sensory and swimming abilities, which may influence their feeding behaviour in the water column. The present study aims to determine the relative importance of the water column and zooplankton variables for the structure of pre-settlement larval fish assemblages within a single season in three bays of the coral reef lagoon of New Caledonia, southwest Pacific. The structure of larval assemblages was found to be explained better by water column variables in two out of the three bays examined. Zooplankton variables only played a role in one bay out of the three, probably due to the lower variability in the water column variables. Moreover, the relationship between total larval fish abundance and zooplankton density was not significant in any of the three bays. These results suggest that the relationship between late-stage coral-reef fish larvae and their prey: 1) is difficult to detect at small spatial and temporal scales, 2) is probably complex and non-linear, 3) depends on environmental conditions, and 4) probably varies between fish taxa. La relación entre las larvas de peces y sus presas zooplanctónicas sigue siendo poco estudiada para las larvas en últimas fases de desarrollo de peces coralinos en ambientes lagunares. además estas larvas se caracterizan por tener grandes habilidades natatorias y sensoriales respecto a la mayoría de peces en mares templados, habilidades que pueden influenciar su comportamiento alimenticio en la columna de agua. El presente estudio tiene como objetivo determinar la importancia relativa de las variables de la columna de agua y del zooplancton sobre la estructura de las larvas de peces próximas al asentamiento durante una única estación y en tres bahías de la laguna coralina de Nueva Caledonia en el Pacífico sur. La estructura de los grupos de larvas de peces se explica mejor por las variables de la columna de agua en dos de las tres bahías estudiadas, pero las variables zooplanctónicas desempeñan un papel importante en la tercera bahía, seguramente debido a la mayor variabilidad de las condiciones de la columna de agua. La relación entre la abundancia total de las larvas de peces y la densidad total del zooplancton no fue significativa en ninguna de las tres bahías. estos resultados sugieren que la relación entre las larvas de peces coralinos en última fase de desarrollo y sus presas es 1) difícilmente detectable a tan pequeña escala espacial y temporal, 2) probablemente compleja y no lineal, 3) variable según las condiciones medioambientales y 4) probablemente variable según los taxones.

Due to an increasing emphasis for fish population survey and regulation, efficient tools for evaluating the abundance and diversity of fish from various life stages are needed, especially for coral reef species that present a high taxonomic diversity. The characteristics of six different techniques used for sampling pelagic larvae (a plankton-net and two light-traps), newly settled juveniles (one type of artificial reef), and older juveniles (an underwater seine net in seagrass and macroalgal beds, and rotenone poisoning in coral patches) are described in this study. Larvae belonging to 70 families and juveniles belonging to 34 families were collected. An analysis of similarity (ANOSIM) showed that the taxonomic composition of assemblages collected with the plankton-net and the two light-traps were overlapping but clearly different, due to the higher occurrence of Gobiidae in the plankton-net and of Pomacentridae in both light-traps. Larvae being 2–4 mm standard length (SL) dominated in the plankton-net, whereas larvae being 9–11 mm SL dominated in both light-traps. Pomacentridae juveniles were more abundant in rotenone samples, whereas Labridae dominated in the underwater seine. Juvenile fish collected with the artificial reefs, the underwater seine, and rotenone poisoning largely overlapped in size, with mean sizes of 22, 38, and 33 mm SL, respectively. Seven families were caught by the six sampling techniques, but with unequal success. This study provides ecologists and managers with a unique review of six techniques for sampling a wide range of developmental stages of young fish in different habitats of a coral reef lagoon.

The feeding ecology of whitefish, Coregonus, larvae in oligotrophic Lake Sarnen and eutrophic Lake Hallwil is presented, taking into consideration the size of the prey ingested in relation to the mouth size of larvae and to the availability of zooplankton. When larvae grow from 10 to 16 mm their mouth width increases from 500 to 1000 μm while their gape height, with the mouth open at 45 and 90°, increases from 200 to 400 μm and from 400 to 700 μm, respectively, whichever lake is considered. The differences found in the mean prey width between the two lakes arise in part from the composition of diets, and in part from differences in size of the available prey organisms. Whatever the origin of the larvae and the taxon we consider, larvae seem to ingest the most abundant prey size without selecting the biggest ones available even if, from a mechanical point of view, they would be able to ingest them. Taking into account the generally low density of zooplankton in the uppermost layer of the lake, we conclude that whitefish larvae eat in the manner such as to decrease the cost of prey capture, in terms of energy and time, by choosing the more abundant prey available.

Ciguatera Fish Poisoning (CFP) is a tropical syndrome well known in remote archipelagos where the population is still dependent on fish resources. In order to assess the ciguatera risk in two islands of French Polynesia, Tubuai (Australes) and Nuku Hiva (Marquesas), a study was carried out on both Gambierdiscus populations as well as on various fish species using the receptor-binding assay (RBA) to detect and quantify ciguatoxins. Relationship between RBA data and size or weight of fish was evaluated, and when only few individuals for a particular species were available the trophic level was used to help comparisons between studied areas. According to epidemiological data, toxic versus safe areas were explored and compared in both islands. In Tubuai Island, Gambierdiscus cells were surprisingly absent in the north area, considered as a toxic area, but almost 94% of fishes were classified as RBA. In contrast, the south area, supposed to be safe, was evolving to be a risky area because of the presence of Gambierdiscus cells and 74% of fishes being RBA(+). In Nuku Hiva Island, Gambierdiscus cells were present in the toxic areas, Anaho, Taiohae and Taipivei, with two toxic blooms in Anaho Bay, but none in Terre Deserte, the fishing area of this island. With RBA data, fishes were analyzed to be RBA(+) at a high percentage in Anaho and Taiohae, higher than in Taipivei and Terre Deserte areas. In general, our findings were congruent with epidemiological data and the knowledge of local people only for risky fish species.

Competent larvae of 4 tropical reef fish species, i.e. two pelagic spawners (Parupeneus barberinus and Acanthurus triostegus ) and two benthic spawners (Abudefduf sexfasciatus and Dascyllus aruanus ) were collected over two years in Wallis Islands, in order to compare 1) their size and age at settlement, 2) the variability of these parameters and 3) their spatial and temporal variations. The larvae were collected in three sites approximately 10 km apart in September 2002, December 2002, March 2003 and June 2003. The otoliths were examined to obtain early life history information: pelagic larval duration and timing of settlement. Size at settlement varied from 3 mm for A. sexfasciatus , D. aruanus and A. triostegus to 10 mm for P. barberinus . For the benthic spawners, settlement occurred after 17 and 19 days within a narrow age interval (7 to 9 days) and mainly in the middle of the interval. For the pelagic spawners, settlement occurred later (after 35 and 42 days), within a larger age interval (13 days). These estimates are lower than those from other locations in the Pacific but their range is larger. Size at settlement differed significantly between sampling sites only for D. aruanus and between surveys only for A. sexfasciatus . Age at settlement differed significantly between sampling sites only for A. sexfasciatus and between surveys only for D. aruanus . For the pelagic spawners the variability of size and age within site and survey was up to ten times greater than for the benthic spawners. This flexibility would be an advantage for larvae of the pelagic spawners that have to travel greater distances to settle.

We examined the factors controlling fish species richness and taxa-habitat relationships in the Malmanoury and Karouabo coastal streams in French Guiana between the short and long rainy seasons. The aims were to evaluate the environnemental factors that describe species richness on different scales and to define the ecological requirements of fish taxa in the two streams at that period of the year. We sampled ten regularly spaced freshwater sites in each stream with rotenone. We caught a total of 7725 individuals representing 52 taxa from 21 families and 6 orders. More taxa were caught in the Malmanoury (n = 46) than in the Karouabo stream (n = 37). These values augmented by the number of fish taxa caught only by gill nets in a parallel survey fitted very well to a log-log model of fish richness versus catchment area in Guianese rivers. Most of the fish taxa encountered in the Malmanoury and Karouabo streams were of freshwater origin and nearly all the fish species caught in these two small coastal streams were also found in the nearby Sinnamary river with the exceptions of the cichlid #Heros severus$ and the characid #Crenuchus spirulus$. Moreover, no significant relationship was found between a size-independent estimate of fish richness and distance from the ocean. Thus, despite their coastal position, the Malmanoury and Karouabo streams contained fish assemblages with strong continental affinities. At a local scale, independently of site size, those with relatively more habitat types harbored a relatively greater number of fish taxa. Canopy cover, water conductivity and bank length were the most important environmental variables for fish assemblage composition at that period of the year. Oxygen and vegetation participated also in defining fish habitat requirements but to a lesser extent. (Résumé d'auteur)

In ice-covered southeastern Hudson Bay (northern Quebec, Canada), the foraging of first- feeding Arctic cod Boreogadus saida and sand lance Ammodytes sp. was adversely affected by the plume of the Great Whale River. Before the freshet, manne fish larvae and their potential prey were marginally more abundant offshore where porous sea ice supported the development of ice algae than inshore where freshwater ice prevented algal growth. Larval fish foraging under the ice appeared limited by prey availability in the diluted (S < 5 %o), 5 m thick, surface layer and by light availability in the underlying marine waters. Arctic cod larvae which avoided the freshwater surface layer did not feed. The more euryhaline sand lance were present in the surface layer and fed to some limited extent until the freshet when further light attenuation by the turbid waters of the expanding plume completely halted their foraging activity, Feeding resumed in sand lance and started in Arctic cod at the ice break- up when the fragmentation of the ice cover and the vertical mixing of the plume allowed light to penetrate at depth. An anthropogenic reduction of the Great Whale River discharge in spring would generally improve local feeding conditions for manne fish larvae that occur under the ice. The impacts of such a reduction on the productivity of the coastal zone in summer remain to be assessed.

Artificial habitats provide a unique opportunity to investigate how habitat characteristics structure juvenile fish assemblages after settlement. We quantified the differences between assemblages of juvenile fish on artificial substrates moored in macroalgal beds, seagrass beds or coral patches over two temporal scales that corresponded to a short (48 h) and a longer (>2 weeks) immersion time, respectively. The highest abundances were obtained from artificial habitats moored in seagrass beds, whatever the immersion time was. Total abundances of juveniles increased 3-fold between a short and a long immersion, suggesting a net accumulation of individuals with time. Moreover, significant differences in juvenile fish assemblage structure were observed between habitats and between immersion times. Artificial habitats may reflect species-specific habitat preferences at settlement at a meso-scale; however, caution must be paid to the effects of ambient habitat and post-settlement processes on juvenile fish assemblages observed on artificial habitats.

Bernard Hugueny, ORSTOM, Ecologie des eaux douces et des grands fleuves, Universite Claude Bernard, 43, Bd du 11 Novembre 1918, F-69622 Villeurbanne Cidex, France. Luis Tito de Morais, ORSTOM, BP 1434 Bouake 01, the Ivory Coast. Sylvie Mirigoux, ORSTOM, Ecologie des eaux douces et des grands fleuves, Universite' Claude Bernard, 43, Bd du 11 Novembre 1918, F-69622 Villeurbanne Cidex, France. Bernard de Mirona and Dominique Ponton, ORSTOM, Route de Montabo, BP 165, F-97323 Cayenne C&dex, Guyane Frantaise.

Whitefish larvae (Coregonus sp.) were caught at regular intervals in 1986 and 1987 in oligotrophic Lake Sarnen, and in 1987 in eutrophic Lake Hallwil.

We studied the synchronism between the seasonal occurrence of fish larvae and their prey in ice-covered southeastern Hudson Bay, Canada, in spring 1988, 1989 and 1990. Arctic cod #Boreogadus saida$ and sand lance #Ammodytes$ sp. larvae hatched several weeks before ice break-up and fed primarily on copepod nauplii. The timing of 50% yolk resorption was the same every year (11 to 18 May for Arctic cod and 5 to 11 June for sand lance) but the availability of copepod nauplii varied substantially between years, both in magnitude (7-fold) and timing (4 to 6 wk). Interannual differences in the under-ice abundance of nauplii were linked to variations in the abundance of female cyclopoid copepods, and appeared unrelated to the timing of the ice-algal or phytoplankton blooms. Interannual differences (2- to 4-fold) in the feeding success of fish larvae (percent feeding incidence at length and mean feeding ratio at length) were related to the availability of copepod nauplii. Consistent with the match/mismatch hypothesis, the fixity of the spawning season in relation to a variable cycle of prey abundance accounted for the observed variations in feeding success and apparent growth (length at date) of fish larvae. Yet, in this particular ecosystem, a match or mismatch between Arctic cod or sand lance larvae and their prey may depend more on the dynamics of cyclopoid copepods during the previous winter than on the timing of the spring algal blooms. (Résumé d'auteur)

In the ice-covered southeastern Hudson Bay (northern QuCbec, Canada), marine fish exhibited 2 distinct reproduction strategies. Sand lance Amrnodytes sp. and Arctic cod Boreogadus saida produced large numbers of small larvae that hatched before the ice break-up when the abundance of prey (copepod eggs and nauplii) was low. Feeding incidence was low and the larvae fed on relatively small prey. A morphometric index of condition suggested that the 2 species suffered from starvation at first feeding. This critical period was approximately synchronized with peak abundance of prey, possibly an adaptation to minimize starvation mortality. Shchaeidae and Cottidae produced small numbers of large larvae that fed efficiently on relatively large prey before yolk resorption. These larvae emerged after the ice break-up, when phytoplankton production was well under way and prey were abundant. Interannual variations in the timing between first feeding and the production of prey could influence recruitment in sand lance and Arctic cod but are unlikely to affect the early survival of Stichaeidae and Cottidae.