La pêche crevettière en Côte d'Ivoire. Bilan 1969-1970 et perspectives

The evolution of the fishery of the pink shrimp Penaeus duorarum Burkenroad is analysed from its beginning in 1969 until the end of 1970. A rapid and general decline of the yield has been evident during this period. The actual shrimp fleet seems to be too big to allow an exploitation economically convenient of the stock.

Évaluation de la production primaire et de la chlorophylle à partir des données hydrologiques. Application au Golfe de Guinée

Quantitative relationships between nitrate distribution, chlorophyll and primary integrated values have been used to evaluate the phytoplankton abundance in the Gulf of Guinea. Data of Guinee I cruise (May-July 1968) of the R.V. Jean Charcot have been used. They show a large oligotrophic convergence area (< 250 mg C/m2/J). A relationship previously found between the depth of the nitracline (first level where the nitrate appears) and the depth of the thermal maximum gradient is confirmed. From a practical point of view, this relationship is very useful since it allows, when the biological or chemical data are not available, a rough estimation of phytoplankton integrated biomass and production in the water column, from a temperature profile.

La pollution bacterienne de la lagune et de la mer autour d'Abidjan

The total coliforms, fecal coliforms and fecal streptococci were counted over 1 year at 33 stations in the Ebrié Lagoon near Abidjan (Ivory Coast). Most of the waters show high numbers of bacteria, (D category of the American standards). For the sea-beaches, high numbers of fecal germs are found where the human population is abundant.

Biologie de la phase lagunaire de Penaeus duorarum en Côte d'Ivoire. Écologie et dynamique

Ecology and dynamics of juvenile pink shrimp Penaeus duorarum were studied from weekly sampling in the Abidjan lagoon system. After a brief description of biogeography and principal features of climate, hydrology of Ebrié lagoon and Adiopodoumé bay were considered. Shrimp distribution were connected with the main environmental factors. Precise work was done in Adiopodoumé bay, especially concerning the succession of age classes, their growth on the nursery grounds, seasonal variation in abundance, size and distribution, in relation to environmental factors. These results, and former knowledges, allowed us to propose a general pattern for pink shrimp life history in Côte d'Ivoire.

Biologie de l'Ethmalose, Ethmalosa fimbriata (Bowdich), en Côte d'Ivoire. 1 - Description de la reproduction et des premiers stades larvaires

Descriptions of spawning and larval development of Ethmalosa, up to the vitelline vesicle resorption stage, are made from plankton samplings in the Ebrié coastal lagoon and from artificially fertilized eggs. Spawning takes place from November to June in waters with salinities of 18 to 26 parts per thousand, and temperatures of 22.8 to 30.2 degrees, for 13-14 cm long fishes.

Biologie de Penaeus duorarum notialis en Côte d'Ivoire. 4 - Rélations entre la répartition et les conditions du milieu. Étude des variations du sex-ratio

The analysis of the geographic and bathymetric distribution of Penaeus duorarum and, particularly P. d. notialis off Côte d'Ivoire and in its whole distribution area leads to the definition of the adult ecological requirements (temperature, salinity, grain size and sediment composition, organic matter) and the importance of the thermocline in the bathmetric distribution. The population structure study shows: (1) variations of size with depth, (2) variations of sex ratio, with size, depth and seasons.

Récolte et traitement des données statistiques de la pêche des palangriers asiatiques dans l'Atlantique

The authors report on the computer programmes developed in the Oceanographic Research Centre of Abidjan for the collection and treatment of statistical data on the fisheries of the asiatic trawlers in the Atlantic. They provide yield by boat, by fishing sector (5 degrees x 5 degrees) and by 15 days fishing in the Atlantic.

Zooplancton et micronecton dans la région du Dôme d'Angola en février-mars 1971 et rélation avec les thons

Diurnal variations and geographic distribution of zooplankton and micronekton are studied in the Angola Dome. The small zooplankton species (Copepodids, Copepods, Amphipods, Ostracods, Chaetognaths, etc.) undertake vertical migrations within a 100 m water layer. Most of the micronekton species are below this layer during the day and move towards the surface during the night. The whole region prospected is rich in zooplankton and micronekton species that are present in the upper 100 m layer during the day. Only the South-West region is poor. On the contrary, this latter region is abundant in species that migrate below this layer during the day. The authors think there are 3 main difficulties in establishing good relationships between micronekton and tunas distribution: 1 - inability of micronekton nets to catch the tunas preys; 2 - the great diversity of tunas food; and 3 - the too large delay between micronekton studies and those of stomach contents of tunas.

Premiers résultats sur l'excrétion et la production du zooplancton de la Lagune Ebrié (Côte d'Ivoire)

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators.

Variabilité, circulation et chlorophylle dans la région du Dôme d'Angola en février-mars 1971

In February-March 1971 the hydrological conditions off Angola did not display the thermal dome mapped by Mazeika's averages (1967). Cold water cells observed are connected at the surface to a sinuous boundary between low-salinity coastal waters and high-salinity tropical oceanic waters. That boundary coincides rather regularly with an area where trades and SW winds alternate; photosynthesis growths rapidly in a thermoclinal layer that rises until 10 m of the surface but never outcrops. Below a poor and permanent homogeneous surface layer, chlorophyll concentrations show a distribution which is typical of divergence areas. Geostrophical and measured currents show off a transient process in horizontal and vertical movements, however the general curvature of the circulation is propitious to upwelling. Oxygen oversaturations of about 110%, suggest a moderate potential primary production which confirms slowness and alternation of movements. Also, the regular range of the various chemical and biological levels and moderate chlorophyll concentrations suggest an ecosystem where nutrients supply rapidly equilibrate phytoplankton consumption and not at all a 'phytoplankton bloom' area as that which exists in coastal upwelling. Values of Richardson's number show that instability becomes visible at the bottom of the euphotic layer. An evaluation of the vertical motion is inferred by the peculiar distribution and diurnal alternance of the winds shows that 'doming' structures may be sustained by local meteorological events.

Biologie de la phase lagunaire de Penaeus duorarum en Côte d'Ivoire: biométrie et croissance.

Principal biometric relations have been calculated for juvenile pink shrimp Penaeus duorarum, of Côte d'Ivoire lagoons. Growth has been studied from weekly sampling using Petersen's method and Von Bertalanffy's equation. Results are very similar to those obtained by the authors working in the same environmental conditions, especially concerning temperature.

Biomasses du phytoplancton et du zooplancton dans l'Atlantique tropical le long du méridien 1O' W (Résultats de la campagne Capricorne 7314)

The standing stock of chlorophyll, the quantities of copepods collected with a 30 liter Niskin bottle and the standing stock of zooplankton collected with a 'Bongo' net were measured from 0 to 200 m depth during a cruise along 10' W from 1' N to 12' S. These parameters are correlated to hydrological conditions measured simultaneously. 6 zonal areas have been delimited and described; the north equatorial convergence, the northern flow of the south equatorial counter-current, the trade winds drift, the south equatorial counter-current and the Benguela's drift.