The following summary of biological data is mostly based on the report by Ssentongo, Ajayi and Ukpe (1983).
The available data indicate that the distribution of a number of demersal fish species is limited by the depth of the thermocline and is influenced by the type of bottom deposits and the depths on the continental shelf.
The distribution of demersal fishes indicates discrete ecological fish communitites each of which are fairly homogeneous. There is also ecological and microgeographical heterogeneity of fish communities.
The following demersal fish stocks are distributed on the continental shelf :
the estuarine and creek sciaenid subcommunity (exploited by canoe fishermen) ;
the offshore suprathermocline sciaenid subcommunity (on soft deposits) ;
the shallow suprathermocline sparid subcommunity (on sandy, corally and rocky substrates) ;
the deep subthermocline sparid subcommunity (on both hard and soft deposits).
Estuarine and creek sciaenid subcommunity
The demersal fish community inhabiting the estuaries, creeks and other coastal brackishwater consists of a number of species. The estuarine sciaenidae (croakers) are dominated by Pseudotolithus elongatus whose bathymetric distribution extends to 20 m depth. But P. sengalensis and P. typus also occur in the estuaries. Secondly, the family Polynemidae (threadfins) contributes significantly to estuarine and creek fisheries, but it is not yet possible to determine the exact magnitude of Galeoides decadactylus, Polynemus quadrifilis and Pentanemus quinquarius, stocks which are harvested from brackishwater area. Other marine species in this sector include : Pteroscion peli (drum), Lutjanus dentatus (snapper), Cynoglossus (soles), Pomadasys jubelini (grunters), Penaeus notialis (Southern pink shrimp), the marine and estuarine Parapenaeopsis atlantica (Guinea shrimp), Palaemon sp. (white shrimp).
Offshore suprathermocline sciaenid subcommunity
The dominant element of this fish community are : Arius, Pseudotolithus spp., Drepane africana, Pomadasys jubelini, Pentanemus, Galeoides, Cynoglossus, Polynemus and Pteroscion peli. The offshore suprathermocline community occurs along the coast above the 40 m depth contour except in a few soft and rocky bottom areas occupied by the sparid community.
Shallow water suprathermocline sparid community
The sandy and rocky bottom sparid community consists of Sparus caeruleostictus, Pagrus gibbiceps, Pagellus coupei, Dentex spp., Lutjanus sp. and Epinephelus.
Deep water subthermocline sparid subcommunity
The deep water sparid community occurs on both sandy and muddy bottoms below the thermocline, down to the edge of the continental shelf. This fish community is comprised of Dentex congoensis, Dentex filosus, other Dentex spp., Pagellus bellottii and Pseudupeneus prayensis.
Eurybathic fish species
Those demersal species having a large vertical range of distribution on the Nigerian continental shelf are : Cynoglossus, Brachydeuterus auritus, Raja spp. and the penaeid shrimps.
The ecological and biological characteristics of demersal species inhabiting the waters of Cameroon and Nigeria are given in Annex 6.
Information on length/age frequencies, sex ratio, mean size, etc., of individual species in the catch made by canoe fishermen and inshore trawlers is very scanty, not is there data on selectivity of mesh sizes used in the creeks and the shallow inshore waters, thus the length/age structure of fish caught using the various mesh sizes is unknown. But a number of estimated population parameters which can be used to assess fishing trends are given in Table 21.
Njock and Djama (Annex 7) presented data on the biology of the second most important species in the Cameroonian catches, Pseudotolithus elongatus. From the monthly length frequency distribution in the catches growth parameters, and mortality coefficients (using Pauly's methods) were calculated, as well as the length/weight relationship.
Surface temperatures, salinities, conductivity and dissolved oxygen, pH as well as plankton composition have been studied along a transect northwest from the Cape Nachtigal, Cameroon (Ikome, 1985). Data for the period July 1984-March 1985 are summarized in Table 22.
Based on the results of exploratory surveys carried out in Cameroonian waters (OMBANGO, 1962–1963 ; FIOLENT, 1976), Villegas and Garcia (1983) produced a modified bottom chart (Figure 4a). They also produced maps showing the demersal fish assemblages and the distribution of the main components (Figure 4b).
