The central part of the Gulf of Guinea, flanked by the productive areas of Mauritania Angola, has proved to be very poor in fishery resources (Williams, 1968). The côte d'Ivoire-Benin and the Gabon-Cabinda (Southern sector) shelves are enhanced by the seasonal upwelling of the deep Atlantic waters, but marine productivity in the remaining sectors, unaffected by this phenomenon (southern Sierra Leone-Liberia) is extremely low.
While this low productivity could be explained to some extent by the Gulf of Guinea's hydrographic regime, affected by a relatively stable, shallow thermocline, the almost permanent presence of warm, low salinity tropical waters and the narrow continental shelf, the major factor determining stock abundance and distribution would be this seasonal upwelling in the central part of the Gulf.
Even though global bathymetric fish distribution patterns appear to be influenced by trophic factors, these seasonal variations may modify the behaviour of some species, e.g., the sciaenids, causing them to migrate to the coast during the cold season in search of warmer waters. Others (sparids , for instance), although also affected by the hydrological seasons, might become more accessible to capture as a result of their migratory breeding habits.
Although the marine fauna of the Eastern Tropical Atlantic is poorer in demersal species than other tropical zones, data collected by bottom trawling surveys, especially the 1963-64 Guinean Trawling Survey, nevertheless show this fauna to be homogenous.
A number of stocks have been defined (Longhurst, 1969) on the basis of factors such as ecological characteristics, bottom types, hydrological conditions and the depths at which they occur (Fager and Longhurst, 1968). Artisanal and industrial fisheries operating in the target area, from Sierra Leone to Ghana, focus mainly on the sciaenid, lutjanid and sparid stocks, coastal penaeids, pelagics and various species of rays and sharks.
All these fisheries are multispecific, which makes them difficult to assess and manage. Latest analyses of the state of demersal resources by CECAF Resources Assessment Working Groups have shown moderate or severe overfishing of some coastal stocks, including penaeids, which declined sharply in Côte d'Ivoire in 1981-82. First estimates of these same stocks in Ghana confirmed this trend. In 1962, demersal species, especially croakers (Pseudotolithus), in the 0–40 m depth stratum in Sierra Leone, were declared overexploited, and productivity in côte d'Ivoire and Ghana seems to have declined since the appearance of dense concentrations of Balistes in 1969.
The level of exploitation of coastal demersal stocks (0–50 m) throughout the region would appear to be in the vicinity of (but usually below) the estimated mean maximum potential, while stocks in the deep part of the shelf (50–120 m) are fished only on a seasonal basis and those on the slope are unexploited.
For this reason the CECAF Resources Assessment Working groups insist that a shift in fishing effort toward the relatively deep-swimming (below 50 m) sparid stocks and utilization of less economically valuable species or discards (e.g., Balistes), would significantly increase production.
A number of species could also constitute new fishery resources, among which the red crab (Geryon maritae) which has already been the object of various studies in Côte d'Ivoire and is currently the target of one Japanese vessel's apparently successful fishing. It is assumed to be equally abundant in all countries of the region.
Yields of the deepwater rose shrimp (Parapenaeus longirostris) would not, however, appear to be sufficient to sustain a fishery (the situation in Liberian waters supports this view). Nematocarcinus sp., another crustacean, abundant between Lagos and Monrovia, is of little value at present because of its small size.
Also cited for its abundance below 60 m on the coasts of Ghana, is Ariomma bondi.
Lack of general data on fishery resource potential, especially in the deep shelf and slope, recently prompted CECAF Resources Assessment Working Group on Demersals to recommend that stratified trawling surveys be carried out.
