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8. SPARID COMMUNITIES IN THE NORTHERN CECAF AREA

As a result of the Guinean Trawling Survey in 1963 and 1964 and subsequent surveys, Longhurst (1969) provided some definitions of fish communities for the waters of the Gulf of Guinea (including Guinea and Guinea Bissau), based on the occurrence of species in trawl catches. The occurrence of certain species appeared to be related to the type of bottom. Amongst others, Longhurst described two sparid communities, one living above and the other below the more or less permanent thermocline in the Gulf of Guinea.

Fish communities have also been defined by Domain (1985 and in Table 61) during the Working Group on the Mauritanian marine resources and referred to during the CECAF ad hoc Working Group on demersal resources of Mauritania, Senegal and The Gambia (FAO, 1984a). Summaries of these results with reference to sparid species are presented in Tables 60, 61 and 62. For the continental shelves of Mauritania, Senegal and The Gambia, this community was subdivided by bottom type.

The important bottom types distinguished on the continental shelf are soft deposits, hard bottoms (characterized by the presence of detritic sand and flat rocks) and rocky bottoms.

The sparids communities may be found down to 70 or 80 metres depth. The continental edge community occurs between 80 and 200 m on muddy, muddy sand or sandy mud bottoms. The juveniles of some members may be found in shallower waters.

According to Domain, the sparid community is composed of species with a preference for cold waters. The distribution of the community on the shelf therefore depends on the depth of the thermocline and on the positions on the fronts separating the warm and the cold waters.

The distribution of the several communities on the Mauritanian and Senegambian shelf is shown in Figures 10 and 11. The fish communities of the region from 20–26°N have been studied by Mennes (1985), who distinguished 7 fish communities of which 3 contains sparid species (see Appendix 9).

For the Moroccan region (34.1.1)no fish communities have been described.

Analysing the species lists for the existing communities, it is remarkable that some species which certainly do occur in the region, are not included. The descriptions of the communities are based on the results of trawling operations on boards research vessels. Rocky untrawlable grounds are hardly covered by research surveys, and, therefore, species associated with these grounds are missing in the descriptions. A good example is Spondyliosoma cantharus, which is the target species of the trap fishermen fishing around Cape Bojador. Their catches consist of 70% of this species (Balguerias, 1983). Other sparid species, such as Diplodus cervinus cervinus and Diplodus sargus cadenati, which are not mentioned in existing communities, and S. cantharus are members of the serranid community which may be found on rocky untrawlable grounds (van der Knaap, in preparation).


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