Synthèse des travaux effectués au CRO sur les végétations envahissantes flottantes (1985-1990). Propositions et recommandations

The present document represents a synthesis of the scientific knowledge gathered by the CRO in the years 1985-1990, and related to the proliferation of aquatic macrophytes, commonly called floating aquatic weeds, in the Ebrié lagoon.

Incidences de la modification de la circulation des eaux sur l'hydrochimie et le degré de contamination bacterienne d'un estuaire eutrophe tropical

In order to control the proliferation of floating aquatic vegetation in Côte d'Ivoire, a coastal inlet, allowing a direct communication between the Comoe river and the ocean, was created in September 1987. The impact of this operation on the hydrochemistry (salinity, nutrients, algal biomass) and the bacterial contamination level was studied in the area close to the Vridi canal.

Les effets de la réouverture de l'embouchure du fleuve Comoé sur le végétation littorale lagunaire (Lagune Ebrié - Côte d'Ivoire)

The results of floristic data collected during two surveys in the eastern region of Ebrié lagoon in 1987 (before the reopening of the inlet) and in 1988 (after the reopening of the inlet) are discussed in this article. Salinity increase (from 4‰ to 30‰) as a result of the reopening in September 1987 of the channel of Comoé river, profoundly modified qualitatively and quantitatively, the plant population. Floating or fixed macrophytes have been completely destroyed. Mangrove forest being the hydrophytic belt of the lagunar rives.

Analyse des effets de l'ouverture du chenal de Grand Bassam (estuaire du fleuve Comoé, Lagune Ebrié) sur la macrofaune benthique lagunaire

This paper presents the results of a comparative study of three series of samples collected in the area near the Bassam channel before, six and twenty months after its opening in September 1987. Observed effects are the decrease in the abundance and the modification of the benthic macrofauna composition. These effects appeared to be definitive, without recovery of the most abundant species Corbula trigona. Most differences noted in the population structure are due to the increase of the salinity and at a least degree to the modification of the nature of the sediment.

Influence de la réouverture du canal de Bassam sur la pêcherie de crabes de Vitré II en Lagune Ebrié (Côte d'Ivoire)

This work is the result of one year of investigation from May 1987 to June 1988 among fishermen of Vitré II village located in the eastern region of the Ebrié lagoon.

Communication mer-lagune: impact d'une réouverture sur l'ichtyofaune de la lagune Ebrié (Côte d'Ivoire)

The artificial reopening of the lagoon inlet, made in Grand-Bantam in September 1987 in order to reduce the aquatic weeds proliferation, induced some environmental and fish communities alterations in the eastern part of the Ebrié lagoon (Côte d'Ivoire). A preliminary field survey made in May 1988 shows an increase in the salinity rate and an increase of the marine component among fish communities, when compared to the former ecological state of this lagoon area (reference data of 1980 and 1981).

Phytotoxicité du glyphosate sur la Jacinthe d'eau (Eichhornia crassipes, Solms)

The toxicity of the herbicide glyphosate was tested on water hyacinth (Eichhornia crassipes) samples cultivated in glass aquariums. The lowest dose (0.09 g.m-2) leads to an increasing plant growth rate. This growth rate decreases with intermediate doses (0.18 and 0.36 g.m-2), the consequence of which is to increase stolons (vegetative reproduction). On the other hand, the dose of 0.72 g.m-2 leads to a total and irreversible destruction of plants.

Note sur les baleines échouées en estuaires artificiels en Côte d'Ivoire

Stranded whales in estuarine waters were identified in Côte d'Ivoire: the Spermwhale, Physeter catodon L. 1758 and the Finwhale, Balaenoptera physalus L. 1758.

Étude préliminaire sur l'incorporation de liants dans un aliment composé pour poisson d'élevage en Côte d'Ivoire

Artificial feeding constitutes a very important aspect for intensive fish culture. Then, the physical properties, particularly water stability of feed, wider influence the fish production. By trying to find some answers to these problems, a preliminary study on water stability has been conducted at the LAYO aquaculture research station. This work consisted in incorporating different types of binders available in tropical countries in fish pellets of 3.5 mm and 6.0 mm diameters in order to identify an efficient binder allowing the improvement of the water stability of feed. From this experiment, it comes out that the use of wheat flour (A1) gives excellent quality pellets followed by cassava flour residue (A3). Moreover, this study shows that it exists an influence of the diameter on the crumbling of the pellets.

Élevage du silure Heterobranchus longifilis Val. en bassins sans renouvellement d'eau: effets de l'évolution de quelques paramètres chimiques de l'eau sur la croissance et la survie

African catfish (Heterobranchus longifilis Valenciennes, 1840), with a mean weight of 37 g, were raised in 4 m3 concrete tanks, with or without water changes at densities of 10 and 20 fish per m3. The results indicate that, although the low water needs of this catfish offer hope for the productions of 150 tons/hectare/year, water quality must always be monitored.

Bilan des recherches sur la crevette rose Penaeus duorarum notialis de Côte d'Ivoire et conséquences en matière d'aménagement

A summary of results obtained from 1969 to 1977 is given. It concerns the biology of the species (ecology and distribution of the adults, behaviour and diel variation of catch rates, reproduction and larval migration, juveniles migration and recruitment at sea, sexual maturity, growth and mortality by marking experiments) and the history of the fishery (catches, efforts, seasonal variations of catch rates). The combined use of a dynamic pool model of Ricker and a production model of Fox leads to the evaluation of the potential of the stock. The simulation of different and combined fishery strategies on adults at sea and juveniles in lagoons, allows the evaluation of the consequences (in yield, value, biomass and potential fecundity) of the different proposed management procedures (reductions in fishing effort, closed seasons on both fisheries).

Étude quantitative de l'upwelling sur le plateau continental ivorien

A wind-driven upwelling occurs on the continental shelf of Ivory Coast during the northern summer months; by studying the average conditions in the wind field, it has been found that in steady state the vertical speed upwards does not exceed 70 cm per day. The vertical flow per km super(2) is estimated in 46 m super(3)/s for a channel 50 m depth and in 92m super(3)/s for a channel 300 m depth. This study does not include the inclination of isopycnes in geostrophic adjustment with the variations of the Guinea current.

Résultats du groupe de travail FAO/COPACE sur l'évaluation des stocks démerseaux côtiers du secteur Côte d'Ivoire - Congo

The exploitation rate of demersal stocks in the Côte d'Ivoire-Congo area is in most cases below the level permitting maximum sustainable yield. Any increase in total catch would be achieved through an increase in catch per effort which implies bigger mesh sizes than those in use now (40-45 mm). A first step would be to fix the minimum legal mesh size to 60 mm. New, probably limited resources (crab, squids, benthic sharks) are to be sought along the continental slope.

Notes sur l'écologie de quelques taxons du zooplancton de Côte d'Ivoire. 1 - Ostracodes, Cladocères et Cirripèdes

Seasonal variations of abundance and vertical distribution over the shelf are investigated for Ostracoda, Cladocera and Cirripede larvae. The main characteristics of the environment are the periodical enrichments mainly caused by upwellings, secondly by the river floods. Ostracoda abundance variations approximately follow phytoplankton outburst. Breeding occurs all over the year. Their vertical distribution is correlated with a discontinuity layer. Diurnal migration, when it occurs in warm season consists in an upward movement during the night towards surface layers. The Ostracoda inhabit bottom layers during the day and migrate at night in intermediate and surface layers. For the main two species of Cladocera, Penilia avirostris and Evadne tergestina, abundance periods follow upwellings, especially during the main cool season. However, Cladocera can grow in low salinity but rich waters. On average Penilia inhabits more superficial waters in cold than in warm seasons. Cirripede nauplii and cypris are more abundant off rocky coasts. Their maxima are in the upwelling periods.

Note sur les biomasses pélagiques évaluées par écho-intégration dans la zone équatoriale du Golfe de Guinée: premiers résultats

An Echo-Integration survey on the equator made during he GARP Atlantic Tropical Experiment indicated an important biomass in the layer 0/100m. The changes of that biomass have been connected to hydrological conditions. Measurements of target strength have been made, and the biggest schools have been measured.