PhD Dissertations

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Browsing PhD Dissertations by Subject "Shrimp fisheries"

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    Abundance, distribution and reproductive biology of two selected penaeid prawns in Tanzanian waters
    (University of Dar es Salaam, 2016) Mwakosya, Catherine Adam
    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.
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    Impact of climate change and variability on coastal penaeid shrimp abundance in Rufiji delta, Tanzania
    (University of Dar es Salaam, 2016) Bwire, Masinde Kahitira
    An improved understanding of how key environmental factors drive the abundance and, thus, influence the catch of shrimps is important to prevent a decline or even collapse and to mitigate adverse effects of environmental change including climate change through fishery management. Primary and historical data of shrimp catches, rainfall, flows of the Rufiji River and temperatures were used to assess impact of climate variability on catches of coastal panaeid shrimps in the Rufiji delta. Fishing systems and socio -economic characteristics of shrimp fishers were also examined. Generally, both catches and environmental variables showed temporal variability and strong connectivity among them. Analyses of trend patterns, timing events and intensities for seasonal and interannual variability confirmed that climatic related factors influence the observed declining trends of shrimp catches in the Rufiji delta. Catches were observed to reach maximum peak during May, whereas rainfall and flows of the Rufiji River attain their maximum peaks during April of each year. Timing (phases) events and amplitude (intensities) in rainfall and river flows showed highest positive correlation with catches of coastal panaeid shrimps. Shrimp fishers had generated and adopted their own strategies to deal with a certain degree of variations in their local climate. Some of the adaptation strategies noted include shifting to new fishing areas, diversification of target species, switching and adjusting gear types, and acquiring non-fishing small scale works. This study provided the first scientific results showing drive-response relationship between climate factors and coastal panaeid shrimp catches and lays guiding foundation for formulations of climate resilience management policies of coastal penaeid shrimp fishery in Tanzania.