The diurnal vertical behaviour of yellowfin tuna observed from sonic tagging experiments in the western Indian Ocean (Comoros archipelago) is compared with the vertical profiles of temperature and dissolved oxygen concentration. Two different behavioural situations: off-FAD and FAD-associated yellowfin tuna, are characterized by the relationships between swimming depth and vertical structure of temperature and dissolved oxygen concentration (i.e.depth and thickness of the mixed layer, of the thermocline layer and of the oxycline) observed in the tracking area. Gradients of both paramelers are shown to be the key factors which determine the vertical swimming behaviour. From an analysis carried out on the whole oceanographic data set of the Western Indian Ocean, oxyeline is found to match with the depth of the 4.2-4.3 ml.1−1 dissolved oxygen concentration.

Vertical distributions of yellowfin tuna, for both off-FAD and FAD-associated situations, are modelled by using normal-derived distributions. These models indicate the probability of the presence of yellowfin tuna, related to the vertical profiles of temperature and dissolved oxygen concentration. A single mode distribution is fitted to describe the FAD-associated situation, and a bi-modal one for the off-FAD situation. Positions of the modes are determined by the relationship between the vertical swimming behaviour and the position of either maximum gradient of temperature or dissolved oxygen concentration. An iterative calculation of normal distribution standard error is conducted to adjust the shape of the eurve to cover the entire layer in which yellowfin tuna is considered to be present. Both models were applied in a remote area, east of the Seychelles, where purse seine catches are important. The predicted vertical distribution seems to be realistic and matches the observations given by echosound pictures of tuna schools obtained in the same area by purse seiners.

Freshwater fishing is highly developed in the Amazonian basin, and the problems of managing the fish resource are becoming increasingly acute. The global model of exploited stock dynamics has proved inadequate for explaining the variations observed in catches from one year to the next. Following the results of recent studies in maritime fishing, this work aims to identify the contribution of environmental variables (hydrological parameters have been selected) to the explanation of variations in the abundance of the exploited fish community. An abundance index is calculated based on the catch per unit of effort statistics and the surface of the considered basin. Using a 12-year time series, the results show that the effect of the fishing effort on the index of abundance is negligible when viewed alongside the flood regime parameters for the years prior to the catch. The effects revealed are, in chronological order of appearance: 1) a positive effect of the water level during the flood regime peak three years previous to the catch, probably associated with recruitment for a number of species; 2) the effect of the water level during its rise two years before the catch, which may well be related to competition phenomena; and 3) the effect of severe low-water levels two years before the catch, possibly due to mass natural mortality during the severest periods of low-water. Because there are complex migratory movements of fish populations either side of low-water periods, only the estimated biomass during the flood appears to be an accurate reflection of the mean biomass in the environment. Linear models are presented, where the abundance index is a function of the hydrological parameters previously identified. The model with 3 variables corresponding to the 3 evidenced effects, explains more than 83% of the variations in the annual abundance indices.

The Boreoatlantic gonate squid Gonatus fabricii is the most abundant squid in the offshore arctic and subarctic waters of the northern Atlantic. Adults are common in midwater while juveniles occur in surface waters close to the continents. As part of a research project focussing on the interactions among fish stocks off West Greenland we examined squid collections sampled with small pelagic nets in summer 1989 and in summer and autumn 1990 off Southwest Greenland. G. fabricii was by far the most abundant cephalopod species caught. We recorded a total of 698 juvenile specimens. During the summer cruise in 1989 the mantle lengths varied from 6 to 35 mm (n = 84); in summer 1990 they ranged from 10 to 48 mm (n = 542) with significantly larger body sizes in the southern part of the region. In autumn 1990 the mantle lengths ranged from 19 to 64 mm (n = 72) with largest animals again at the southern sampling sites. The data suggest growth rates for juvenile G. fabricii off West Greenland of 4 to 5.5 mm per month between July and November 1990.

Une méthode d'ajustement de l'analyse des cohortes, combinant calcul en mode inverse et calcul en mode direct, est présentée ; elle permet d'analyser l'évolution des puissances de pêche par flottille et par âge, à partir de la matrice des capturabilités nominales. La méthode est appliquée aux deux principales flottilles exploitant l'albacore dans l'Atlantique Est, entre 1980 et 1990 : les senneurs franco-ivoiro-sénégalais (FIS) et les senneurs espagnols. A l'aide d'un modèle linéaire généralisé, les puissances de pêche globales sont décomposées en deux termes : puissances locales et efficiences globales. Les évolutions tendancielles des trois grandeurs, puissances globales, puissances locales et efficiences globales, par catégorie d'âge ou en moyennes, sont analysées en calculant des taux d'accroissement inter-annuels sur des intervalles pluriannuels. Les changements de tactiques de pêche sont étudiés au travers des corrélations entre puissances de pêche résiduelles appliquées à des groupes d'âge différents.

Les résultats obtenus sont peu sensibles aux paramètres introduits lors de l'ajustement de l'analyse des cohortes. Sur l'ensemble de la décennie, un accroissement des puissances de pêche globales moyennes est mis en évidence, avec un taux estimé à 17 et 9 % par an pour chacune des flottilles FIS et espagnole respectivement. Cet accroissement est lié à une forte augmentation des puissances de pêche globales appliquées aux adultes, alors que celles appliquées aux juvéniles semblent en diminution. Les changements de l'efficience de pêche globale jouent un rôle essentiel dans le cas de la flottille FIS. Trois schémas type d'évolution, traduisant des stratégies de pêche différentes entre flottilles et entre périodes, sont définis ; l'impact des changements de tactique de pêche est souligné. Les raisons susceptibles d'expliquer les variations des puissances de pêche sont discutées, ainsi, plus généralement, que les potentialités et limites de la méthode d'analyse utilisée.

This presentation describes a series of experiments designed to study the biology and fisheries of decapod crustaceans in the Western Mediterranean in the framework of research programmes carried out by Instituto de Ciencias del Mar (CSIC) in Barcelona. The results have been used to highlight the importance of bio-ecological studies on commercial species in instituting fisheries management programmes. A series of examples are used to demonstrate how integrating knowledge of the effects of biological and ecological aspects (growth, reproduction, migrations, aggregations, environmental factors, sexual dimorphism, behaviour, etc.) in the fisheries, is essential to avoid sampling errors and errors in stock assessment. Finally, potential directions for future research in this area are discussed.

The farming of freshwater crayfish (astaciculture) is mainly carried out in the southern states of the USA, and in Australia and Europe. Production levels vary with climate but are in the region of 40 000 to 60 000 tonnes per annum. In addition, at least an equivalent amounts is harvested from the wild, particularly in North America, China, Australia, Kenya, Turkey and Europe. Crayfish farming is usually either of an extensive (ranching) or semi-intensive nature, intensive methods being infrequent, except for the rearing of juveniles for stocking (or restocking of natural waters depleted of crayfish). As crayfish do not have larvae and are polytrophic, they are relatively easy to rear, although fecundity is much lower when compared with other cultured crustaceans. At least 85% of world production is based on the red swamp crayfish, Procambarus clarkii, mainly from Louisiana and other southern USA states, but also from China, Kenya and Spain, where it has been introduced. In Australia, three species are of aquacultural importance, the yabbie, Cherax destructor; the marron, C. tenuimanus; and the red claw, C. quadricarinatus. Some very large production units have been built but none have lived up to their promise. The red claw is thought to have considerable aquacultural potential, but, being a tropical species, needs warm water for good growth. In Europe, the only endemic species cultured to any extent is the noble crayfish, Astacus astacus, mainly as juveniles for restocking. It fetches a higher price than other crayfish. The North American signal crayfish, Pacifastacus leniusculus, has been introduced to most European countries, but farmed production is relatively low. About 98% of crayfish consumed in Europe come from extensive systems or the wild harvest. European crayfish markets were upset by the collapse of the Turkish crayfishery (based on Astacus leptoductylus) due to overfishing and disease in the mid-1980s. The environmental impact of crayfish farming is most noticeable in Europe. Crayfish plague, introduced from North America last century, has devastated populations of the native species in many countries. Its spread has been exasperated by the translocation of foreign crayfish (and probably by fish) for aquacultural purposes. In addition, introduced crayfish frequently escape into the wild and form large populations, often in direct competition with native species. Burrowing and prolific species, such as P. clarkii, can also do considerable environmental damage.

Larvae of the African River Prawn Macrobrachium vollenhovenii, indigenous to West Africa, were reared at various salinities (0-32‰). A salinity range of 16-24‰ was found most suitable with highest survival and growth, and lowest number and duration of instars. Freshwater was lethal already to zoea I - larvae. A mass culture experiment demonstrated the aquaculture potential of this Macrobrachium species. Larval rearing to postlarvae was possible applying the same methods as for M. rosenbergii. Detailed descriptions of rearing techniques are provided.

Observations of acoustic images made along a transect perpendicular to the Coast, off Villefranche-sur-Mer, allow one to recognize the hydrological zone corresponding to a surface density gradient characterizing the Ligurian Sea front (Mediterranean Sea). Combinations of statistical and geometrical parameters from the digitized echoes enable discrimination between different classes of patches in relation to the frontal structure during one transect recorded on December 20, 1990. Patch recognition is based on the extraction of the general trend of each column and each row of the digitized data matrix by Eigenvector filtering. Multivariate analysis (principal component analysis and discriminant analysis) run on a 650 patches × 19 variables matrix shows a high negative relation between statistic and geometric parameters of the patches. The two main discriminant parameters are shape and echo strength of patches. From the convergence of our results in the Ligurian front with those of previous works made in other frontal region, it is suggested that this method could be generalized for quantifying and standardizing studies of the patchiness of plankton.

Foraging activities of goosanders (Anatidae, Mergus merganser) were studied in relation to seaward migration of smolt in the River Halselva in northern Norway, 1987-1989. Birds aggregated in the estuary in June, during mass migration of smolts. When present in the estuary males and femalesspent 28.7 and 35.6% of their time feeding. Only 15% of dives resulted in birds' bringing prey to the surface and about 25% of prey found in goosander stomachs were salmonids. For hatchery-reared smolts released in the estuary, average length taken did not differ from that available; for wild smolts of Arctic char, however, smaller fishes than those available were taken. For 1989, we estimate that goosanders took 1% of the hatchery-reared smolts released in the estuary, and 2% of the wild smolts when smolts passed the estuary during seaward migration. As it is likely that less fit smolts (e.g. sick, injured, small) are most prone to predation, we argue that such a level of predation on migrating smolts from goosanders has only a minor impact on salmonid production. Suggestions to reduce predation are discussed.

Daytime 38 kHz mean volume backscattering strength (MVBS) of small pelagic fish in the Gulf ofSt. Lawrence was recorded at 60-m intervals along a regular network of 11 parallel transects in August 1991. Profiles of temperature, salinity, density and transmittance were collected on a grid of 44 punctual stations along the transects. The MVBS was contagiously distributed and autocorrelated for al1 transects. No significant monotone relationship with any of the environmental variables was evidenced, except that the highest concentrations of fish were located over shallow bottoms. The anisotropic variogram of MVBS indicated three different scales of spatial structures: an unresolved small-scale variability, which accounted for only 7.7% of variance, and two structure components of along-transect scales of ~500 m (~40%) and 15 km (~50%). The theoretical variograms deduced for larger echo-integration units (EIUs) than the recorded 60-m unit, provided a good fit to the corresponding experimental variograms up to EIU of 1920-m, when the disturbing effect of outliers on the variograms was removed. Global estimates and maps produced with 240-m and 1920-m EIU data were almost identical, showing that no significant loss of information was caused by increasing the EIU. Asymmetric confidence intervals of the global estimates are obtained using two variograms, one controlled for the effect of the outliers, the other one not controlled. In an effort to take the relation of MVBS with the bottom depth into account, four differentkriging methods were compared: ordinary kriging, kriging with the bottom depth or its indicator-transform as external drift, and 3-D ordinary kriging with depth as the third dimension. Because of the weak relation of MVBS with the bottom depth, ordinary kriging had the best performance. Results are discussed in the context of applications of geostatistics to estimation and mapping of acoustic survey data.

The effect of electrical stimulation on the quality of P. setiferus sperm cells was studied during the regeneration of the spermatophore. The proportion of the animals that responded to electroejaculation was quantified and the number of live, abnormal and dead cells, as well as the relationship between the number of cells and body weight, were taken into consideration as indicators of the effect of manipulation during stimulation. It was found that electrical stimulation caused some degree of spermatophore expulsion in 78% of the cases. Total expulsion of the spermatophores occurred in only 8.3% of the cases. A logistic curve was adjusted to the relationship between the number of sperm cells and the weight of the shrimp. After regeneration no curve was adjusted to the relationship. Eighty per cent of the stimulated shrimp regenerated the spermatophore in a maximum of 168 h. Fifty per cent regeneration was obtained in 96 h after stimulation. A decrease in the number of live cells from 26.8 to 7.6 million and an increase in abnormal (from 0.02 to 3.92 million) and dead (from no cells dead to 4.6 million) respectively, were registered for regenerated animals. Necrotic areas in 60% of the ampulae of regenerated shrimps were also observed. Bacteria associated with the necrotic ampulae was observed when counting sperm. As the spermatophore of this species is complex, it is necessary to search for a way to reduce the stress produced by the handling of the ampulae so as to avoid altering the reproductive capacity of the shrimp.

Vitellogenin (VTG) was isolated from the haemolymph of Penaeus vannamei by a three stepprocedure including ultracentrifugation, gel filtration and ion exchange chromatography. VTG wasused to raise polyclonal antibodies that were purified by ion exchange chromatography. A two stepcompetitive assay was developed in which VTG could be quantitated by its capacity to inhibit thebinding of antibody to the VTG previously adsorbed onto a solid phase. Sensitivity from equilibriumand from non-equilibrium assays was 41 and 2.3 ng/ml respectively. Estimates of within-assay andbetween-assay variabilities of standard curves were 4.2 and 9.6% respectively. The inhibition curves for dilutions of haemolymph from vitellogenic females, egg yolk extracts and purified vitellin (VTL) were parallel to the standard VTG curve, haemolymph from immature females and males showed no cross-reactivity. The antibodies directed against VTG recognize but partially VTL as shown by displacement curves. Recovery tests were near 100%. Thus the procedure was considered to be suitable for the measurement of haemolymphatic VTG. The VTG enzyme-linked immunosorbent assay (ELISA) developed in this study was validated by detecting physiological VTG changes in female shrimps after being fed squid extracts.

For centuries, several species of prawns and crabs have been raised from wild-caught juveniles in coastal brackish-water fish ponds in various countries of south east Asia. The Indonesian "tambaks" are well known examples of such traditional practices. In western countries, since the turn of the century, advances of marine biology and fast increase of marine fisheries enabled the development of large-scale production and release of larval stages of American and European lobsters in a fruitless attempt to restock natural populations. After the Second World War, the increasing demand for crustaceans in United States and Japan was satisfied by opening new prawn fisheries all over the world. A major breakthrough was achieved with the development of hatchery technologies for the penaeid prawn Penaeus japonicus (Hudinaga, 1942 in Japan) and the caridean prawn Macrobrachium rosenbergii (Ling, 1969 in Malaysia), which occurred during the first decades of the second half of this century. Together with the increasing market demand in developed countries for sea food, this led to a considerable interest of both public agencies and private investors in marine shrimp and prawn culture. In western countries, a large number of pioneering commercial ventures, often based on assumptions not scientifically founded, failed. Nevertheless, the aquaculture production of prawns mainly based on wild-caught juveniles increased in South-East Asia and Central America during the 1980s. This overall positive trend should not hide important failures which occurred at a local scale, such as the Taiwanese crisis of 1988 due principally to environmental degradation, resulting in severe disease problems and a near collapse of the farming activity. Following the early period of hatchery technology development, the major scientific achievements were related to food requirements and formulation of compound diets for larvae, juveniles and adults and to a better knowledge of diseases caused by bacteria and several viruses which have been identified from hatcheries and intensive farming ponds. Additional new technological advances have emerged from recent research in the fields of physiology (endocrinology) and genetics. By far, the major part of the world production of marine crustaceans relies on penaeid prawns and, to a lesser extent, on Macrobrachium species. However, some other species of marine crustaceans have potential for aquaculture.

The economic aspects of marine crustacean aquaculture should be considered together with those of the fishing industry: market prices are rather similar, depending on the quality of the product. The balance between market demand and production is an important constraint which, in turn, establishes the success of prawn farming. Since the early 1980s, crustacean aquaculture has increased tremendously in both Asiaand America: the world production for 1991 approximated 700,000 tons, with more than 600,000 tonsfrom penaeid prawn culture.

Bien que la chitine soit synthétisée par un grand nombre d'espèces animales, unicellulaires ou métazoaires, appartenant notamment aux groupes zoologiques de la lignée des Coelomates Spiralia, la production de chitine en milieu marin est essentiellement due aux Crustacés. Une étude comparée des quelques données analytiques disponibles a permis de tenter de calculer les valeurs de biomasse et de production de chitine dans quelques grands types d'écosystèmes marins, et d'évaluer ainsi l'importance quantitative de la chitine dans les cycles biogéochimiques du carbone et de l'azote. Les principales données actuellement disponibles concernent le plancton de la baie de Calvi (Corse) en Méditerranée, le krill arctique et antarctique, une population de langoustes des côtes de l'Afrique du Sud, et les communautés benthiques infralittorales à algues photophiles des côtes rocheuses de la Corse. Dans tous les cas, la production de chitine a pu être estimée à environ 1g par an et par m2 de substrat rocheux ou de surface océanique. Sur base de ces valeurs de production et de l'étendue relative des principaux écosystèmes marins, la productiontotale annuelle de chitine par les crustacés marins a été évaluée à ± 2,3 milliards de tonnes.

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.

The toxicity of five cryoprotectants – methanol, DMSO, glycerol, ethanediol and sucrose – on different development stages of zebrafish embryos was investigated. Embryos were exposed to a range of cryoprotectant concentrations for 30 min at room temperature. Post-heart beat stage embryos were more resistant to cryoprotectants than carly embryonic stages. The maximum non-toxic concentrations of cryoprotectants on heart beat stage embryos were 2 M methanol, 2 M DMSO, 1 M glycerol, 2 M ethanediol and 0.5 M sucrose. Gradual stepwise addition did not reduce toxicity. Heart beat stage embryos survived 2 M methanol at room temperature for up to 5 hours, whilst DMSO and ethanediol were toxic after 3 and 1 hour exposure respectively. The effect of the nature and concentration of cryoprotectant, equilibrium time, and cooling rate were investigated during cooling to –30 °C. Methanol was more effective than either DMSO or ethanediol for zebrafish embryo cryopreservation and 0.3 °C/min was found to be the optimum cooling rate. Two-step addition of cryoprotectants, with the higher concentration of cryoprotectants added at 0 °C, improved the results. The best embryo survivals obtained after cooling were 94% at – 10 °C, 72% at – 15 °C, 43% at –20 °C, and 8% at –25 °C, no embryos hatched following cooling to –30 °C. Ice formation within the egg was found to be the main factor affecting survival of the embryos.

The phospholipid composition and fatty acid characteristics of diacyl and plasmalogen forms ofphosphatidylcholine and phosphatidylethanolamine of sperm of five marine and five freshwater speciesof fish have been determined. There was considerable variation in composition within each group offish, which obscured any differences which are related to the osmotic environment. Since such factors as temperature, nutrition, etc. probably greatly influence the lipid composition, we failed to determine a relationship between osmolality and phospholipid composition. We have also found certain phospho-lipid peculiarities, characteristic of sperm of various species of fish.Nevertheless, as we have found previously, the molar ratio of cholesterol to phospholipids in fishsperm is determined by the salinity of the habitat.