Chwaka Bay (Zanzibar, East Africa) as a nursery ground for penaeid prawns

Abstract

The penaeid prawns are recruited in the sheltered sandy beaches and mangrove areas of Chwaka Bay (Zanzibar) at post-larval stage (7 mm). Year round incursions with a maximum during the warmer months of December to March were observed. February to March is considered as the peak recruitment period. Out of six species of penaeids represented in the area, Penaeus latisulcatus (75%) and Penaeus indicus (15%) were dominant. The recruitment pattern indicated greatest incursions of post-larvae with the flood spring tides of the night when the tidal flow is strong. The juvenile population of P. latisulcatus is distributed in those intertidal sandflats with a rich growth of seagrass and P. indicus in the muddy areas of mangrove forests. P. indicus showed affinity for euryhaline conditions, whereas P. latisulcatus showed no preference for lower salinity. Provision of food and shelter are considered as important factors for their nursery dependence. P. latisulcatus attained a size of 60–70 mm in five to six months and P. indicus 110–120 mm in six to eight months during their nursery phase. These juvenile penaeids were found to be omnivorous, feeding on animal products, plant material and detritus. The maturing P. latisulcatus emigrate back to the sea when they are about 65 mm, whereas P. indicus move out at about 120 mm. A positive correlation between post-larval recruitment and juvenile abundance was observed.