Abundance, distribution and reproductive biology of two selected penaeid prawns in Tanzanian waters

Tanzania is one of the tropical countries, which practises both industrial and artisanal prawn fisheries targeting the shallow water penaeid prawns. Industrial prawn fishery takes place in three designated fishing grounds along the coast of Tanzania, namely zone 1, zone 2 and zone 3 of which in this study were considered the main sampling locations during the ship surveys conducted. On the other hand artisanal fishery is concentrated in the Ruvu estuary and along Rufiji Delta. The prawn fishery in Tanzania for the past decade has indicated serious unsustainable exploitation levels and a decline in production trends despite the reduction in fishing effort. The shallow water prawn species composition, abundance and distribution by site, zones, depth and season were assessed. Seasonal size frequency distribution, length-weight relationships, sex ratio, size at first sexual maturity, and gonad histology and growth parameters of the two prawn species (Fenneropenaeus indicus and Metapenaeus monoceros) were also studied. It was not known whether the prawn populations existing in the study area are genetically connected or distinct. To test the hypothesis that a single population exists, the mitochondrial DNA (mtDNA) sequence data were used to study the populations. From the findings of this study, it is concluded that the populations existing in the three prawn fishing grounds are not different. The study observed high exploitation levels at the two land-based sites (Bagamoyo and Nyamisati) with a slight improvement in the catch rates, which is an indicator of slow recovery of the stock. Consequently, a management strategy of extending the closed season to include the artisanal fishers’ grounds is recommended.