Mathew Ogalo Silas - Fisheries Biology and Management

Mathew is supervised by Jeppe Kolding.

Excluding the Islands, Tanzania has a coastline of about 800 kilometers endowed with valuable marine fisheries resources including prawns. There are six dominant prawn species; Penaeus indicus, P. monodon, P. semisulcatus, P. latisulcatus, P.japonicus and Metepenaeus monoceros, all with significant economic value. Tanzania’s prawn fishery industry is the most important of the marine fisheries in terms of income and export value (Ngusaru, 2000) .

Commercial prawn fisheries started in 1980’s in three fishing grounds (Bagamoyo/Saadani, Rufiji delta and Jaja/Kilwa) before that it was mainly done by artisanal fishers.

Fisheries research in Tanzania has been conducted since the beginning of the century, however at a slow pace and Tanzanian wild prawn stocks potential are not well known as only a few research programmes have been conducted on the fishery. Some of these researches included;

Preliminary assessment for the shallow water shrimp trawl fishery of Tanzania (Sanders, 1989) he used catch and effort data, possibility of minimizing juvenile prawns and finfish in the catches of trawlers at Bagamoyo/Wami area by incorporating rigid separator grids in the commercial trawls (Mahika, 1992), assessment on the by-catch composition of finfish in the shrimp fishery (Nkondokaya, 1992) investigation of  the species composition, distribution and abundance in Bagamoyo and Rufiji delta (Bwathondi et al., 2002), assessment of crustacean resources in the Rufiji – Mafia channel (Nhwani et al., 1993), preliminary work on the abundance and reproductive biology of the Penaeid prawns of Bagamoyo coastal waters (Teikwa and Mgaya, 2003). Assessment of Tanzanian prawn fishery resources (Mwakosya, 2004 )

 FAO (1970) estimated a potential of 2,000 metric tones. In early 1980s there was an intensive fish stock assessment that was done by FAO research vessel “Fridjoft Nansen” that determined among other resources the potential prawn fishery resource along the Tanzanian coast at 1000metric tones. The Ministry of Natural Resources and Tourism, in collaboration with the South West Indian Ocean Project (1990) estimated an MSY of 1,050 metric tones, having surveyed 859 shrimp-fishing units. TAFIRI in 2001 conducted a survey of the resources, and gave an estimation of 497 metric tones of the prawn stock.

The inshore fishery recently has been showing signs of being overexploited (Ngusaru, 2000). This can be seen easily with declining trend in annual catch and Catch rates from 63.2kg/hr (Nhwani et al., 1993) to 4.68 kg/hr (Bwathondi et al., 2002).

This MSc thesis will evaluate and analyse all fisheries independent data from past years to closure of fishery together, so as to get general trend and conclusive result and explanation on status of prawn stock biomass from available data of three Prawns important fishing grounds using swept area method, the estimates will be compared with the stock abundance of the earlier assessment which used the same method  i.e. (Bwathondi et al., 2002) and (Mwakosya, 2004 ).

Species composition and distribution of an area will be established and compared with that of (Bwathondi et al., 2002), species composition of the by-catch will also be established and compared with that of  (Nkondokaya, 1992).

The aim of the project, and possible parts/sections of the aim

• To estimate biomass of prawns in three fishing grounds of Tanzanian Coastal line using fisheries independent data.
• To determine variation in species composition and distribution in the fishing grounds.
• To determine the magnitude of fish by-catch in shrimp trawl surveys.