We analysed the patterns of variation that characterize 33 catch time series of large pelagic fishes exploited by the Japanese and Taiwanese longline fisheries in the Indian Ocean from 1968 to 2003. We selected four species, the yellowfin (Thunnus albacares), the bigeye (T. obesus), the albacore (T. alalunga), and the swordfish (Xiphias gladius) and aggregated data into five biogeographic provinces of Longhurst (2001). We carried out wavelet analyses, an efficient method to study non-stationary time series, in order to get the time-scale patterns of each signals. We then compared and grouped the different wavelet spectra using a multivariate analysis to identify the factors (species, province or fleet) that may influence their clustering. We also investigated the associations between catch time series and a large-scale climatic index, the Dipole Mode Index (DMI), using cross wavelet analyses. Our results evidenced that the geographical province is more important than the species level when analyzing the 33 catch time series in the tropical Indian Ocean. The DMI further impacted the variability of tuna and swordfish catch time series at several periodic bands and at different temporal locations, and we demonstrated that the geographic locations modulated its impact. We discussed the consistency of time series fluctuations that reflect embedded information and complex interactions between biological processes, fishing strategies and environmental variability at different scales.

Yield-per-recruit models are often used to provide management guidance for the efficient use of a fish cohort and to estimate the biological reference points, such as F0.1 or FMAX. Although model parameters are usually age-specific, these parameters are thought to be more likely related to length than age. In this study, age- and length-structured models are compared in calculating yield per recruit, F0.1, and FMAX at which the yield per recruit is maximized. Using a Monte Carlo simulation approach, I also compare differences in effects of uncertainties of the model parameters on yield-per-recruit analysis and estimation of F0.1, and FMAX using age- and length-structured models. This study shows that differences are small in estimating yield per recruit, F0.1, and FMAX using two types of models when there are no error variances in the model parameters. However, such differences increase with the uncertainties of the model parameters. The yield-per recruit, F0.1, and FMAX estimated using the age-structured model tend to have smaller values and variations compared with those estimated using the length-structured model. This study indicates that although the length-structured model can better incorporate the information observed from fisheries, age-structured yield-per-recruit model can provide estimates of yield per recruit, F0.1, and FMAX, more precisely and more conservatively, and thus is preferred from the conservation viewpoint in fisheries management.

A scattering layer consisting mainly of krill (Meganyctiphanes norvegica) was studied with a submersible transducer, to assess the behaviour of individual organisms in situ by means of split-beam target tracking. Individuals were resolved and tracked, but a rapid increase in average swimming speeds with depth suggested that inaccuracies in the angular estimates affected the estimates. Attempts were made to smooth the tracks during post-processing. Smoothed speeds suggested that most (>78%) invertebrates swam at speeds below 12 cm s–1 (mode ~4 cm s–1), with components of speed larger in the horizontal plane than in the vertical.

The objective of this study was to investigate the effect on Mullus barbatus (red mullet) codend selectivity by increasing the codend mesh size or reducing the number of meshes in the codend circumference. This was performed through experimental sea trials and computer simulations. The sea trials were carried out in the Adriatic Sea using a polyamide codend in order to assess its selectivity, to record morphological (height, width and length) and population size structure parameters of red mullet (Mullus barbatus). The selectivity process in the codend was also simulated with an individual-based model (PRESEMO) and a finite element model (FEMNET) to calculate the codend shapes. By adjusting the behavioural description of red mullet in the simulation, the model results reached an agreement with the experimental results. Next these, behavioural parameters were used in the simulation model to predict the effect of changing mesh size and number of meshes around in new codend designs. The predicted effect and the benefit of enforcing these designs on catch efficiency below and above minimum landing size (MLS) were investigated. The results confirm that the reduction of number of meshes in the codend circumference will be more beneficial than increasing the mesh size.

Schooling fish may aggregate in very high densities covering very small areas. Thus the probabilityof hitting such high-density spots during a large-scale sampling is very low. The sampling fluctuations of the tail of the histogram are thought to be very significant. The stock biomass estimate and its precision rely greatly on how precisely the tail of the histogram can be sampled. In order to acquire elements for improving survey designs and abundance estimators wc study here the relation in space that the high values have with the other values. A disjunctive kriging approach is used. Different quantiles of the histogram are coded by indicators. The spatial structure of each indicator and its spatial covariation with the others are studied by computing experimental indicator variograms and cross-variograms. Such analysis is applied to dissect finely the spatial structure of a Norwegian herring stock sampled acoustically. It is shown that when going from low-density areas to high-density ones, intermediate values are not necessarily crossed. Thus a particular disjunctive kriging model with no transition in space is well adapted to the herring data. The model is based on the regressions of each indicator on the one immediately below it. In the model one can estimate the probability for the fish density to trespass a given cut-off at a given location when knowing that the density trespasses lower cut-offs at surrounding points. It is shown on the data that the high densities are structured and show small aggregations. Then it is shown that having trespassed a certain cut-off, i.e. inside the corresponding areas in space, the high-density aggregations can be considered to be positioned independently from the other values. These areas, where the structuring of the high values is not correlated to the structuring of the other values, are mapped using the fitted disjunctive kriging model. The implications for survey designing of the existence of such areas and of their geometry are discussed. Also discussed is the possibility of stratifying the data in spatially uncorrelated boxes when deriving the biomass estimate and its precision, on the basis of an observed spatial non-correlation property between the spatial distribution of different quantiles.

Fluxes of nutrients (NH4+, NO3-, PO43- and Si(OH)4) were studied on an intertidal mudflat in Marennes-Oléron Bay, France, at two different seasons and at different times of the emersion period. Fluxes through the sediment-water interface were both calculated from vertical profiles of nutrient concentration in pore-water (diffusive fluxes, JD) and measured in light and dark benthic mini-chambers (measured fluxes, J0). Results indicate that ammonia was mainly released in summer while nitrate was mainly taken up in late winter. This uptake from the overlying water was probably due to the coupling of nitrification-denitrification within the sediment. The J0/JD ratio further indicates that bioturbation likely enhanced ammonia release in summer. Concerning phosphate, the comparison of diffusive and measured fluxes suggests that PO43- could be assimilated by the biofilm in winter while it was released in summer at a high rate due to both bioturbation and desorption because of the relative anoxic conditions in summer. Silica was always released by the sediment, but at a higher rate in summer. Statistically significant differences in measured fluxes were detected in dark chambers at different times of low tide, thus suggesting a short-term variability of fluxes. Microphytobenthos preferred ammonia to nitrate, but assimilated nitrate when ammonia was not available. It also turned out that benthic cells could be limited in nitrogen during low tide in late winter. In summer, ammonia was not limiting and microphytobenthic activity significantly decreased the measured flux of NH4+ in the middle of low tide when its photosynthetic capacity was highest.

Despite many previous studies on the life history of the squid Loligo forbesi, the roles of internal and external factors in growth and maturation have not previously been investigated in detail. The present study takes advantage of the availability of statistical techniques, namely generalised additive models, which permit simultaneous evaluation of the effects of multiple explanatory variables while avoiding the need to assume linear relationships. This has the further advantage that the size of body parts can be entered directly into the models rather than expressed as indices (e.g., gonado-somatic index). The present analysis is based on measurements taken from monthly market samples during 1989-1991 and aims to infer patterns of reproductive and somatic investment though comparison of large numbers of individuals at different (post recruit) life-cycle stages. Results indicate that, once the effect of body size is removed, gonad weight in both sexes is affected by month and digestive gland weight, consistent with seasonal triggering of maturation, and with energy for gonad growth being derived from food. There is also evidence of a negative relationship between somatic and ovary growth in females, possibly indicating remobilisation of somatic tissue to grow the ovary. In males, relationships between variables tended to have more complex forms, probably related to the existence of two or more growth patterns leading to different sizes at maturity. As found in previous work, maturation begins around 1-2 months earlier in males, suggesting that sensitivity to external triggers is controlled by a sex-dependent internal factor.

As marine protected areas (MPAs) are increasingly being utilised as a tool for fisherymanagement, their impact on the food web needs to be fully understood. However, little isknown about the effect of MPAs on fish assemblages, especially in the presence ofdifferent life history and ecological traits. Modelling the observed changes in fishpopulation structures may provide a mechanistic understanding of fish assemblage dynamics.In addition, modelling allows a quantitative estimate of MPA spill-over. To achieve thispurpose, we adapted an existing ecosystem model, OSMOSE (Object-oriented simulator ofmarine biodiversity exploitation), to the specific case of the presence of fish withmultiple life histories. The adapted model can manage 4 main categories of life historyidentified in an estuary MPA: fish that (1) spend their entire life cycle locally, (2) arepresent only as juveniles, (3) enter the area as juveniles and stay permanently exceptduring reproduction periods, which occur outside the estuary, and (4) are presentoccasionally and for a short time for foraging purposes. To take into account thesespecific life-history traits, the OSMOSE code was modified. This modelling approach wasdeveloped in the context of the Bamboung Bolong MPA, located in a mangrove area in theSine-Saloum Delta, Senegal. This was the ideal case to develop our approach as there hasbeen scientific monitoring of the fish population structure inside the MPA before fisheryclosure, providing a reference state, and continuous monitoring since the closure.Ecologically similar species were pooled by trophic traits into 15 groups that represented97% of the total biomass. Lower trophic levels (LTL) were represented by 6 compartments.The biomass of the model species was calibrated to reproduce the reference situationbefore fishery closure. Model predictions of fish assemblage changes after fishery closurecorresponding to the Bamboung MPA creation scenario were compared to field observations;in most cases the model reproduces observed changes in biomass (at least in direction). Wesuggest the existence of a “sanctuary effect”, that was not taken into account in themodel, this could explain the observed increase in biomass of top predators not reproducedby the model. Finally, the annual MPA fish spill-over was estimated at 11 tons (~33% ofthe fish biomass) from the model output, mainly due to diffusive effects.

This study was designed to specify the testosterone (T), estradiol-17β (E2) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) variations during the pre-ovulatory period in female Eurasian perch, Perca fluviatilis, and also examine the ovarian synthesis of 17,20β-P and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S). Five females (100–300 g) were collected from a concrete pond from the Lindre Center (Moselle, France) between March and April 1999, three times a week, and sex steroids measured. Two females were also collected from the Lindre pond on three dates (18 February, 14 and 23 March) for an in vitro study. Significant plasma 17,20β-P peaks were measured for the first time in this species reaching 3.5 ng ml–1. However, the synthesis and release of 17,20β-P in blood seems to not be synchronized with the final maturation and ovulation stages. The in vitro study showed that ovaries at the pre-ovulatory stage produce some 17,20β-P but no 20β-S from a tritiated precursor (17-P-3H). 17,20β-P is produced after 30 min and is still present in the medium after 2 h of incubation, but is no longer detectable after 4 h. Some other non-identified compounds were synthesized at this stage suggesting that 17,20β-P was quickly metabolized. Moreover, the plasma level increases, observed in spawned females suggest that this steroid might be involved in the oviposition process. These results suggest a role for 17,20β-P in the final stages of oocyte development.

The behaviour and spatial distribution of tuna, aggregated beneath fish aggregating devices (FADs), have been studied through ultrasonic tagging experiments but, surprisingly, very few studies on FADs have used underwater acoustic devices. We present techniques, and their limits, incorporating a scientific echo sounder connected to a split-beam transducer to observe and characterise tuna aggregations around FADs, and propose a general approach for future studies. Experiments were conducted in French Polynesia between December 1995 and February 1997. Two methods, echo-counting and echo integration, were used. Echo-counting is possible when individual fish are sufficiently scattered so that each target can be discerned. On the other hand, echo integration can be used with both scattered and aggregated fish schools. The knowledge of tuna target strength is useful for separating targets for echo-counting, and essential for obtaining absolute estimates of densities by echo integration. Sonar performances and settings should be considered when choosing the most suitable method to determine fish density or assessing spatial structure of a tuna aggregation. These techniques allow one to study an entire tuna aggregation, its behaviour in space and time at very fine time–space scales (about a nautical mile and over a few hours), and open up a new scientific field to study the spatial structure and behaviour of tuna aggregations around anchored or drifting FADs.

We investigated spatial patterns of stony corals, molluscs and echinoderms among six habitat types within the lagoons of six atolls in the Tuamotu Archipelago (French Polynesia). Percent cover (stony corals only), abundance and richness were recorded within habitat types delineated by specific geomorphological features. Among six habitat types defined a priori, four encompassed distinct assemblages of corals and molluscs: (1) pinnacles possessed maximum richness, abundance and coverage, (2) passes showed relatively high abundance and coverage, (3) lagoon floors were marked by the commonness of a few coral genera, and minimum mollusc abundance and richness, and (4) inner reef flat stations, independent of their location in front of spillways, motu or rim zones, had low cover, abundance, and richness. While habitat associations were similar for stony corals and molluscs, echinoderms were preferentially found on the inner reef flat facing the rim. Lowest echinoderm abundances and species richness were recorded on pinnacles and in the vicinity of the pass. Such small-scale spatial heterogeneity appears to be one of the distinctive characteristics of coral communities in French Polynesian reefs. These results, along with those of the TYPATOLL program, demonstrate the importance of both local and regional factors in determining the diversity and structure of coral assemblages. Habitat fidelity was weak: many species/genera were poorly represented among habitats and restricted to a few atolls, while others were present across all lagoons and habitats. Therefore, marine protected areas design based solely on representativeness will require the protecting the vast majority of lagoon habitats.

Despite the importance of the dredge fishery in Portugal, few studies have focused on bycatch and discard mortality. Catches from three types of dredge: north dredge (ND); grid dredge (GD); and traditional dredge (TD), currently used in the Spisula solida (Bivalvia: Mactridae) fishery, were compared in order to characterize bycatch and to estimate discard mortality. In TD and ND, the catch was retained in a net bag, whereas in the GD a metallic grid cage was used. Tows were carried out on sandy bottoms at depths ranging from 5 to 10 m. Bycatch differed significantly between dredges. The ratio of bycatch abundance to S. solida was 0.22:1 for ND, 0.10:1 for GD and 0.33:1 for TD. The weight ratio was 0.15:1, 0.14:1 and 0.32:1 for ND, GD and TD, respectively. Although a lower bycatch was observed for GD, higher mortality (ND: 10%; TD: 20%; GD: 36%) was estimated for this dredge. However, taking into consideration the fishing yields obtained for each dredge combined with the fact that this fishery is managed by daily quota per vessel, our results showed that, at daily quota level, discard mortality was lower when GD was used. Our study suggests that in output-controlled fisheries, there are obvious advantages in developing dredges with rigid retention structures, such as metallic grids, because these are more selective and efficient than dredges that use net bags. At species level, the bycatch mortality to attain quota varied among dredges. A “selective” and persisting significant removal of bycatch species from biota may change benthic community structure. Therefore, clam fisheries should apply exploitation strategies that are goal-oriented and adaptive to the evolution of the macrofauna communities, which might include the use of different dredge types, thereby diversifying the bycatch and consequently avoiding the cumulative removal of specific macrofauna taxa.

Anti-proteinase activity was demonstrated in the seminal plasma of cyprinid fish species (bream, chub, ide, dace, asp, goldfish, roach, common carp) using electrophoretic techniques combined with a detection method based on inhibition of bovine trypsin. We found species-specific protease inhibitors in the seminal plasma of cyprinids. At least three bands of protease inhibitors with different migration rates could be identified by native PAGE. Higher variability was characterized for bands with slower migration rates. Visualization of inhibitors after SDS-PAGE under non-reducing conditions allowed estimation of their molecular weights. Apparent molecular weights were within the range of 51–59 and 47–54 kDa for the bands with slower and moderate migration rates, respectively. The molecular weight of fast migration bands for roach and common carp were estimated to 23 and 30 kDa, respectively. Inhibitors of common carp seminal plasma differed in their affinity toward serine proteases. Three inhibitors in common carp seminal plasma could be visualized using cod and bovine trypsin, but only two inhibitors (of high molecular weight) were recognized with chymotrypsin. There were differences in anti-proteinase activity and seminal plasma protein concentration in relation to the origin of common carp seminal plasma (breeding lines) and time of milt collection (spawning vs. post-spawning season).

The experiment was conducted for 122 days in central Thailand to test rearing of hybrid catfish in cages in earthen ponds, where tipalia (Oreochromis niloticus) was stocked to utilize the waste products derived from intensively reared catfish. Catfish fingerlings (13-17 g size) was stocked in plastic net cages at a density of 275 fish/m3. Six earthen ponds (250 m2-110 m3 each) were used to suspend the cages in two loading densities as experimental treatments: 880 and 1760 catfish/pond. Each loading density was replicated in 3 ponds. Each pond was stocked with 440 sex-reversed male tilapia of 6-7 g size in open water, giving the catfish and tilapia stocking ratios of 2:l and 4:1, respectively. Catfish was fed twice daily at 3-10% body weight per day with commercial floating pellets containing 25-30% crude protein. Wate quality was analyzed bi-weekly for concentration of dissolved oxygen, ammonia and chlorphyll a.

Results showed that there was no significant difference (p < 0.05) in catfish growth rate and survival between the two loading densities. The mean weight gain of harvested catfish was 259.5 ± 34.5 g and 255.2 ± 8.4 glfish, giving the total net yield of 218.0 ± 26.8 kg and 391.5 ± 88.0 kg per pond in low and high loading density, respectively. Tilapia was harvested with mean weight of 172.3 ± 37.8 g and 297.5 f 32.0 glfish, and the net yield of 68.1 ±13.6 and 86.0 ± 27.2 kg/pond for low and high loading catfish density treatment, respectively. Chlorophyll a and total ammonia concentrations differed greatly between the two treatments. Early morning dissolved oxygen (DO) declined steadily both treatments over the culture period.

Cette étude d'écophysiologie a été réalisée sur l'huître japonaise (Crassostrea gigas) cultivée en baie de Marennes-Oléron (France) en mai 1992. Les mesures sont effectuées dans des conditions alimentaires naturelles au cours de trois cycles de mesure (a, b, c) à des coefficients de marée de 49,57 et 88. La matière particulaire totale est mesurée en continu durant les cycles de marée. La fonction de consommation est calculée selon une nouvelle formulation prenant en compte un "échappement particulaire" précédant le tri pré-ingestif et représentant une perte passive de particules de petites tailles entraînées par la masse d'eau à travers le filtre branchial. La comparaison des fonctions de consommation et d'absorption de la matière organique totale et de la chlorophylle a, montre des différences significativement supérieures pour la charge particulaire de 55 mg.l−1 (c) comparée aux autres conditions (a, b) de charges particulaires inférieures à 30 mg.l−1. La comparaison des coefficients de sélectivité et des taux d'absorption de la chlorophylle a, (43,3 et 81,6 %), respectivement, supérieurs à ceux de la matière organique totale (33,4 et 68,7 %),respectivement, montre le tri de la matière organique effectué par l'huître. Le bilan énergétique calculé prend en compte le matériel d'origine phytoplanctonique et le matériel organique total. Les potentiels de croissance ainsi obtenus de 0,88-11,60 et 47,60 J.h−1.g−1 respectivement pour les conditions à 13,5–28,9 et 54,6 mg.l−1 de charge particulaire totale, traduisent une forte variabilité journalière d'énergie disponible pour la production organique dans le milieu naturel. Ces résultats sont cohérents avec les résultats de croissance d'huîtres en élevage dans la baie de Marennes-Oléron.

Une description chronologique du développement embryonnaire et larvaire du poisson-chat africain Heterobranchus longifilis (Clariidae) a été effectuée jusqu'à l'âge de 17 jours. Une comparaison avec le développement ontogénique d'un autre Clariidae, Clarias gariepinus, a été faite. Les deux espèces présentent de grandes similitudes dans leur développement et diffèrent surtout par la genèse de la nageoire dorsale, unique et allongée chez C. gariepinus, plus courte et suivie d'une grande nageoire adipeuse chez H. longifilis. Les limites inférieure et supérieure de tolérance thermique des œufs de H. longifilis ont été déterminées. Elles se situent entre 22 et 24 °C et entre 34 et 35 °C respectivement, aucune éclosion n'étant obtenue à 21 °C comme à 36 °C. L'optimum thermique pour lequel les pourcentages d'éclosion sont les plus élevés se situe entre 25 et 29 °C. Cet intervalle de température est donc recommandé pour l'incubation des œufs dans la pratique piscicole. La durée de l'incubation varie avec la température. L'éclosion des œufs se situe entre 26 à 33 heures et 14 à 18 heures après la fécondation pour des températures d'incubation de 25 et 33 °C respectivement.

The bigeye cigarfish (Cubiceps pauciradiatus) is a small pelagic nomeid of the tropical world ocean, often recovered in the stomach contents of top predators such as tunas, billfishes and marine mammals. In the Indian Ocean, a few studies have investigated the biology and the ecology of this species that is one of the most abundant fish of the intermediate trophic levels. In this paper, we investigated the spatial distribution of C. pauciradiatus in the Indian Ocean using pelagic trawl catches carried out between 20°N and 45°S, and the importance of bigeye cigarfish in the diet of 9 piscivorous fishes sampled by different fishing gears in the western part of the Indian Ocean. The highest densities were observed along the eastern coast of Africa and in the Arabian Sea (87 000 individuals per square nautical mile) during the South-West Monsoon and in the eastern part of the Seychelles archipelago (62 200 ind. square nmi) during the North-East Monsoon. Small sized bigeye cigarfish (20–80 mm SL) was a regular and abundant prey (20 to 200 ind. per stomach) for schooling predators exploited by purse seine fishery such as large yellowfin and bigeye tunas chasing prey near the sea surface. Large sized bigeye cigarfish (61–150 mm SL) occurred in small numbers (3 to 20 ind. per stomach) in the stomach contents of swordfish and of large yellowfin and bigeye tunas caught by longline sets at great depths. Large concentrations of bigeye cigarfish occurred in zones of high productivity, and that species constituted seasonally a strong link in the transfer of energy from low to high trophic levels in this part of the Indian Ocean.

La notion de qualité des postlarves de crevettes pénéides, qui sous-entend un potentiel de survie, est un paramétre resté longtemps subjectif. Les critères zootechniques et les observations visuelles ne sont pas des paramètres suffisants pour apprécier la condition physiologique des postlarves à la sortie de l'écloserie. La résistance aux chocs de salinité est un critère représentatif de l'état des postlarves. Cette étude a pour but de présenter un modèle de régression non linéaire à deux variables (taille, salinité) de la résistance des postlarves Penaeus vannamei à des chocs de salinité. Entre le 2e et le 20e jour après la métamorphose 5 chocs de salinité. (20, 15, 10, 5 et 2 ‰) sont testés chaque jour, avec respectivement 50 postlarves par salinité. Le taux de survie est enregistré après 2 heures. Parallèlement, la croissance des postlarves en élevage est étudiée par la mesure quotidienne de 30 animaux. La tolérance à la salinité des postlarves P. vannamei augmente avec la taille qui s'accroit d'une façon linéaire.

Results of an annual survey of fishing activities and catches in the Gambia estuary (200 km long), carried out from June 2001 to May 2002, indicated that fishing effort targets mainly (66% of fishing trips) shrimps. As a result of the globalisation of fish markets, the fishery has become a quasi mono-exploitation of shrimp for exporting. At the opposite, fishing activities focusing on fish were low and carried out with large and medium mesh drift nets, gill nets and surrounding nets (17% of fishing trips), handlines and longlines (15%). The annual catch, estimated at 2350 tonnes for the estuarine part of the River Gambia, consisted of 1800 t of fish and 550 t of shrimp. Stownets were the most efficient gear accounting for 50% of the total production (550 t of shrimp and 600 t of fish) while other significant techniques were mainly drift nets (21%), longlines (11%) and gillnets (5%). Fish catches were composed with 55 fish species among which 16 species accounted for 90% of the annual catch. The average catch length of these first sixteen species was 295 mm, clearly demonstrating that fishing for fish was targeting large fish. The effects of the targeted shrimp exploitation resulted in a low fishing effort for fish leading to low fish landings and consequently to an under exploitation of fish resource in the Gambia estuary.

About 60 papers and reports dealing with heavy metal contents in different eel species were reviewed in order to document various patterns of uptake, elimination and accumulation of these metals and to underline their detrimental effects (lethality, histo-pathology). Two main toxicological topics were considered: observations on contaminant levels in eels taken from the wild, mainly from contamined waters, and experimental studies under laboratory conditions.