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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)

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.

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.

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.

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.

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.

Sampling was conducted in the Northwater Polynya (between 70°20' and 77°20'N), on 17 and 19 May 1991. At each of the 14 sampling stations, CTD profiles were recorded from surface to bottom and nutrients and phytoplankton were determined at four depths down to 30 m. The presence, between 220 and 400 m, of water temperatures > 0°C is an indication that, in winter, the West Greenland Current enters the Northwater along the Greenland coast. The worm water is progressively mixed as it moves northward and eastward. It was thus hypothesized that sensible heat is as an important factor in keeping the Northwater open. Measured chemical and biological variables were quite homogeneous on the vertical down to 30 m and they showed longitudinal gradients. From east to west, the average concentrations of nutrients increased (phosphate from 0.5 to 1.4, nitrate from 3.7 to 10.8, and silicate from 6.8 to 34.2 mmol/m3), whereas the areal concentrations of phytoplankton decreased (from 47 to 9 x 10 to the ninth power cells/m2 and from 506 to 50 mg Chla/m2). Nutrient ratios indicated possible silicon deficiency in the easternmost part of the polynya. Diatoms dominated cell numbers (greater or equal to 87% at all stations). Concentrations of the three nutrients were inversely correlated with both Chla and cell numbers. The Y-intercepts of regressions of Chla on nutrients provided an estimate of potential maximum biomass in the upper 30 m, which was ca. 600 mg Chla/m2, or lower if there was silicon limitation. The overall picture was that of a diatom bloom, moving westward and progressively exhausting the nutrients. Initiation of the bloom appeared to have been linked to the absence of sea ice. A source of heat for this would have been the above sensible-heat process. (Résumé d'auteur)

We monitored the feeding success (percent feeding incidence at length and mean feeding ratio at length) of Arctic cod (Boreogadus saida) and sand lance (Ammodytes sp.) larvae in relation to prey density, light, temperature and potential predator density under the ice cover of southeastern Hudson Bay in the spring of 1988, 1989 and 1990. Both prey density and light limited larval fish feeding. The relationship between feeding success and actual food availability (nauplii density X irradiance) was adequately described by an Ivlev function which explained 64 and 76% of the variance in Arctic cod and sand lance feeding success respectively. By affecting both prey density and irradiance, the thickness of the Great Whale River plume (as defined by the depth of the 25 isohaline) was the main determinant of prey availability. Arctic cod and sand lance larvae stopped feeding when the depth of the 25 isohaline exceeded 9 m. Limitation of feeding success attributable to freshwater inputs occurred exclusively in 1988, the only time when the depth of the 25 isohaline exceeded the 9 m threshold. The close dependence of larval fish feeding success on the timing of the freshet and plume dynamics suggests a direct link between climate and survival of Arctic cod and sand lance larvae. The actual impact of climate fluctuations and/or hydro-electric developments on recruitment will depend on the fraction of the larval dispersal area of the two species that is affected by river plumes.

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.

The distribution of zooplanktonic prey of fish larvae was examined in three bays and two lagoonal stations in the Southwest lagoon of New Caledonia. Water column conditions were characterized by increasing chlorophyll a and particulate organic matter (POM) concentrations from the lagoon to the estuarine bay. The mean zooplankton settled volume and total density were significantly higher in the estuarine bay, reaching 35.1 mL m(-3) and 3.5 x 10(5) individuals m(-3), respectively. The total zooplankton density also progressively increased along the sampling period. The composition of assemblages differed between the lagoon and the bays, and was similar in the three bays. Wind speed, surface temperature, chlorophyll a and POM explained these variations, as revealed by a co-inertia analysis (COIA). The prey preferred by fish larvae, i.e. small crustaceans and small copepods, were more abundant in bays. Sheltered bays, most influenced by terrigenous inputs, are likely to provide the best feeding conditions.

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 first step in building predictive models of larval fish assemblages is to identify the main environmental parameters which influence their spatial and temporal structure. In this study, multivariate regression trees (MRT) were used to classify hierarchically the effects of large-scale meteorological factors and small-scale water column factors on pre-settlement larval fish assemblages at two sites in the lagoon at New Caledonia, southwest Pacific. The environmental conditions at one site were highly variable spatially and temporally, but varied little at the other. In spite of these differences, MRT models revealed that identical forcing factors influenced the structure of larval fish assemblages at both sites, with a similar hierarchy, but a different statistical efficiency. At a large spatial scale, the seasonal variabilities in sun hours and wind (speed and/or direction) explained 14% and 64% of the structure of larval fish assemblages at the sites of high and low variability, respectively. At a small spatial scale, the seasonal variability in mean surface water temperature, followed by the concentration in Chl a, explained 22% and 62% of the structure of assemblages at the sites of high and low variability, respectively. The Dufrene–Legendre index matched characteristic families of larvae to each set of environmental conditions, and illustrated the role of sheltered, Chl a enriched, coastal waters in producing a families-rich assemblage of fish larvae, some species of which are targeted by fishing. This study shows that it may be possible to use environmental data, and predictions computed from MRT to design spatially explicit models of larval fish distribution in coral-reef lagoons.

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.

The effects of artificially low runoffs in the Sinnamary River, French Guiana, South America, on flow patterns and on richness and abundance of young fish in Venus Creek, one of its main downstream tributaries were examined. After Petit-Saut dam's gates were closed, the areas adjacent to this tributary were never once flooded for the entire duration of the rainy season. The daily maximal averages of water speed at the tributary's mouth were found to be significantly increased. Young fish sampled using light-traps were less abundant and less diverse after dam closure. Young Characiformes appeared to be the most affected by these flow disturbances. These findings enabled us to develop a conceptual model of the consequences of impoundment on young fish assemblages through the modifications of tributaries and associated floodplains hydrology. Because of flow reduction in the river during the first year of impoundment, young fish that previously had a tendency of being trapped in tributaries and flooded areas were then at risk of being flushed away. The pattern of flow release by dam operations is known to be very different from natural flow variations. The consequences for downstream tributaries will be similar to those of channelization: lack of adjacent flooding areas and higher rates of downstream water transfer. How the recovery of downstream fish assemblages will occur is discussed. © 1998 John Wiley & Sons, Ltd.

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.