Only limited hydrographical work was carried out. Two sections were laid out, one a little north of Mayumba and one north of Port Gentil (Figure 1). Figure 2 shows these two sections together with a third one, just south of the Congo river, carried out a few days earlier at the end of the preceding survey in Angola.
The surface temperature shows only slight variations along the coast from Pointe Noire to North-Gabon and lies within the range 28-30 degr. C. The thermocline is located at around 20 m depth.
The oxygen content of the water is such that it should not limit the distribution of the fishes on the shelf. The level is above 2 ml/l down to about 200 m depth.
