Abundance and Reproductive Biology of the Penaeid Prawns of Bagamoyo Coastal Waters, Tanzania
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The coastal waters of Bagamoyo in Tanzania constitute an important penaeid prawn trawling ground. Despite the high economic value attached to this resource, the biological information necessary for its sustainable exploitation is scanty and fragmented. The present study was therefore designed to investigate the species composition, population abundance and reproduction of the penaeid prawns in Bagamoyo coastal and nearshore waters. Samples were obtained monthly for a period of one year from inshore waters adjacent to the Ruvu Estuary while additional samples were bought at the beach from artisanal fishermen. In the laboratory, samples were identified to the species level. Four penaeid species, Fenneropenaeus indicus (formerly known as Penaeus indicus [Farfante and Kensley, 1997]), Penaeus monodon, P. japonicus, and Metapenaeus monoceros were found in the Ruvu Estuary and nearshore waters. Fenneropenaeus indicus was the most abundant, and more so during the rainy season than the dry season. The sex ratio in F. indicus was found to vary significantly from the theoretical 1:1 ratio while that of P. monodon did not vary significantly from 1:1. The average size at first maturity was different within sexes. For F. indicus males and females carapace length was 3.4 and 3.9 cm respectively. For P. monodon it was 3.58 and 4.3 cm for males and females respectively. Fecundity ranged from 40,000 to 222,000 eggs for F. indicus and 72,000 to 314,000 eggs for P. monodon. Fecundity increased with prawn size, suggesting that much of the available energy in larger prawns is devoted to egg production rather than growth.