In this study, the remuneration system applied in the French Guyana shrimp fishery is analyzed in relation to the market changes that this fishery has experienced since 1985. The contract used for the crew members is not the classical share contract usually observed in fisheries. It is a piece rate wage with quality-bonuses. In the classical contract theory literature the piece rate contract is thought to avoid effort shirking but to induce quality shirking. The bonuses are introduced here in order to limit the quality shirking which may occur during grading and storing operations on board. The skippers' contract also differs from the share contract. It is based on remuneration parameters controlled by the companies. By changing these parameters between 1987 and 1991, the companies led the skippers to modify their fishing strategies and especially to concentrate their efforts towards small sized shrimp. The companies thus became able to respond to the increasing demand for small shrimp categories which characterises the French market. The evolution of the spatial distribution of the fleet effort over the same period is consistent with this hypothesis: the fleet has moved towards fishing zones where small shrimp are known to be in abundance.

Cette étude s'appuie sur l'utilisation successive de plusieurs méthodes d'analyses multivariées pour réaliser une typologie de la flottille chalutière du port de Sète, principal port de pêche français de la Méditerranée. Les unités de pêche étudiées sont représentées à l'aide d'un profil annuel de la composition spécifique de leurs débarquements. Cinq stratégies de pêche ont ainsi pu être identifiées. La mise en œuvre d'une méthode de segmentation permet une caractérisation formelle de ces différentes stratégies à l'aide d'objets symboliques. Les stratégies sont étudiées en référence à plusieurs caractéristiques générales couramment utilisées en gestion des flottilles de pêche (puissance, longueur, âge du bateau, etc.). L'analyse typologique mise en œuvre au cours de l'étude permet de caractériser nettement deux grandes logiques d'exploitation, l'une orientée vers la recherche d'un très petit nombre d'espèces (Engraulis encrasicolus, Sardina pilchardus), l'autre déterminée par une grande diversité des captures. Elle permet également d'apprécier comment les captures d'espèces peu représentées dans certaines stratégies peuvent contribuer significativement à l'exploitation d'une ressource.

The purse-seiners of the Java Sea use light and fish aggregating devices (FAD) to concentrate and catch small pelagic fish (Decapterus sp., Amblygaster sirm, Sardinella gibbosa). This sets a question about the interaction between fish and fishing vessels. Relevant estimates of fishing mortality and fishing effort require an understanding of this interaction. To gain information on this relationship, acoustic surveys were performed on the fishing grounds and the present paper analyses these data. Using acoustic surveys, the fish density was measured and the number of schools was counted per sea surface unit. The fishing vessels were located by radar. Acoustic data were stratified into two groups, one where fishing vessels were present and the other where they were not. This stratification was tested for by resampling the data. Day and night sampled data were analysed in each strata separately. Variograms were computed to characterise spatial structure both for the fish and the purse-seiners. Contingency tables between number of schools and fish density were computed to characterise the relation between biomass and schools for the day and the night when seiners are absent or present. At night, in the absence of purse-seiners, the number of schools increase and fish rise from the bottom. In areas where purse-seiners are present this natural phenomenon is stronger. It also changes the spatial structure both of the fish density and the school abundance. The spatial structure of the vessels is similar to that of the fish density. The fishermen seem to be able to detect by day fish concentrations which will be fished later by night.

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transfer of brown trout to sea water, in order to compare nitrogen utilisation in the two species. Apparent protein digestibility (ADC), nitrogen (ammonia and urea) excretion, protein productive value (PPV) and actual observed nitrogen mass balance were determined. Rainbow trout raised in fresh water had a higher growth rate (1.1 vs 0.8%.d−1), better food conversion ratio (0.7 vs 1.0), better ADC (91 vs 85%) and PPV (45 vs 35%) and lower ammonia excretion rates than brown trout reared in fresh water. Transferring brown trout to sea water induced lower PPV (30%) and ammonia and urea excretion. Salinity did not modify metabolic efficiency in brown trout. Fat content was higher in brown trout (7.7-8.9% ww) than in rainbow trout (5.7-7.6% ww). Nitrogen mass balance indicated that compounds other than ammonia and urea were produced in higher quantities by seawater brown trout. Behaviour, less domestication and specific ability to utilise protein could explain the differences between the two species.

The study of abundance of small-bodied species of fish such as minnow is important because these species play an important role in the food-web dynamics of small streams. In this work, we propose the use of an Artificial Neural Network (ANN) to the modelling and prediction of abundance in minnow Phoxinus phoxinus using 10 environmental microhabitat variables: distance from the bank, percentage of boulders, pebbles, gravel, sand, mud, marl, cover respectively, depth and velocity. A total of 372 points were randomly chosen from a total of 465 electrofished point samples to establish a ANN model. A validation holdout of the training of the ANN was undertaken with testing on 93 other sampling points. On the test set, the prediction performance was 92%. Our study showed the advantages of the back-propagation procedure of the neural network in the field of stochastic approaches to ecology of coarse fishes. The limitations of the neural network approaches as well as statistical and ecological perspectives are discussed.

L'étude de la maturation et de la ponte de l'huître creuse Crassostrea gigas, s'intègre dans une large problématique visant à comprendre les causes de mortalité qui surviennent épisodiquement dans le bassin de Marennes-Oléron au printemps et en été. Un conditionnement thermique et alimentaire des élevages permet d'obtenir simultanément des huîtres à tous les stades de maturité sexuelle. Le calcul des taux de filtration, consommation, absorption et respiration permet d'estimer le potentiel de croissance, et donne le bilan énergétique des huîtres aux différents stades sexuels. Les réponses physiologiques sont semblables pour des huîtres mâles ou femelles. La filtration de 2,4 à 2,6 1.h−1, passe à 1,8 1.h−1 à un stade de maturation avancée. La prise de poids liée au développement des gonades ne semble pas avoir d'effet sur le taux de filtration. Les huîtres de 2,5 ans présentent un bilan énergétique déficitaire (–15 J.h−1) à un stade de maturation avancée. Ce déficit est confirmé (–90 J.h−1) sur des huîtres de 1,5 ans au même stade de maturation. En revanche, les huîtres immatures, en début de maturation ou en post-ponte, ont un potentiel de croissance compris entre 110 et 170 J.h−1 . Le déficit énergétique observé au stade de maturation avancée relève essentiellement de la fonction d'absorption qui chute de façon importante en période de forte gamétogenèse. L'étude de la respiration permet de définir une allométrie particulière à la croissance gonadique avec un coefficient d'allométrie de 0,574. La faiblesse physiologique des huîtres, observée à un stade de maturation avancée, doit être prise en compte dans la recherche des facteurs responsables des mortalités printanières et estivales affectant les cheptels en élevage dans le bassin de Marennes-Oléron.

The ultrastructure of spermatozoon and sperm production were observed in wolffish (Anarhichas lupus), a species with internal fertilization, from a broodstock. The mature spermatozoon has an elongated head, eccentric flagellum, and comparatively well developed middle piece. Based on the observations of sperm cells with the optical microscope, the mean lengths of spermatozoon head and flagellum were 3.3 and 21.2 μm respectively. A high variability of sperm cell size was observed due to the presence of spermatids and degenerated spermatozoa in the ejaculate. In most males, sperm production was registered throughout the whole year with a peak in December and January. Sperm production decreased to the end of the breeding season. The difference in volumes of ejaculate and sperm concentrations between males kept at two light cycles (18D: 6L and 6D: 18L) was not significant. Features of wolffish sperm are compared with data reported in the literature on other internally and externally fertilizing fish.