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10.1 Spawning periods and areas

The relationship between the spawning period of several sparids, Dentex angolensis, Pagellus bellottii and Sparus caeruleostictus and temperature variations has been studied by various authors. In the north of statistical division 34.3.1, for example, where the seasonal temperature changes are very marked, two separate spawning periods can be observed, corresponding to the periods of changes in temperature in April–June and October–November. South of Dakar, where seasonal temperature changes are less pronounced, spawning periods are of longer duration.

For P. bellottii, it has been observed that the spawning period changes with latitude from outh to orth ; first spawning occurs off Dakar in April ; off Kayar in May-; off Saint-Louis in June and off Mauritania in July. This shift in spawning period does not appear to be due to a migration of adult fish towards the North, since no corresponding shift in CPUE is observed in April-June. Instead, the abrupt temperature change seems to initiate the spawning process.

The spawning period of Dentex macrophthalmus is in the cold season from January to April.

The various spawning areas are not known in all cases. In the case of Sparus caeruleostictus spawning takes place at 20–40 m depth. P. bellottii spawns in shallow waters of 50 m depth, after which the adults return to the 70–80 m depth zone.

10.2 Recruitment

Franqueville (1983 and Appendix 5) describes for P.bellottii the existence of four nursery areas in statistical division 34.3.1 (Mauritania to Guinea). The length of the spawning season increases from North to South and juvenile survival is more affected by this than on temporary bad weather or other ecological conditions. As a result outhern stocks tend to be much less subject to fluctuations in abundance than the Northern ones.

10.3 Gear selectivity

The Working Group compiled selectivity data for 14 fish species studied during several surveys between Morocco and Senegal as published by Ikeda (1973), Abbess (1974), Franqueville and Lhomme (1979), Delgado de Molina and Goni (1981) and Delgado et al. (1982), Franqueville (1983) and Mennes (1984).

All these authors used the covered codend method, and Table 63 summarizes for each species studied the following parameters mesh size between knots, nominal mesh size, mesh size opening (as measured by a standard gauge, pressure 4 or 5 kg soaked net). L25, L50, L75 are the fork lengths (in centimetres) at which 25, 50 and 75% are retained, and are determined by reading values from a selection curve. Ls is the estimate of L50 determined by the Gulland method. b is the selection factor in the equation Ls = b.m. (m is mesh size expressed in cm). is the mean selection factor for each area.

10.4 Other biological data

Growth, mortality and length/weight parameters for sparids in the northern CECAF areas are summarized in Tables 64 and 65. Table 74 summarizes the availability of statistical and biological data and the recommendations for further work formulated by the Working Group.

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