Nsinda, P E.

Tanzania Fisheries Research Institute (TAFIRI), P. O. Box 475, Mwanza, Tanzania.

Catch and effort assessment for Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin) of Lake Victoria, Tanzania

A study on the catches, effort, and size distribution of the three commercially important fish species, Lates niloticus, Oreochromis niloticus and Rastrineobola argentea potentially fished by artisanal fishermen of Lake Victoria, Tanzania was done from October 1997 to December 2000. Consistent monthly sampling started in 1999. The number of total boats on beach, boats that went out fishing, and sampled boats were recorded. This in turn was used for calculation to gate the estimated annual total landings using data from a recently conducted frame survey. Gear type and size were noted. The catches were sorted into species and recorded accordingly.

The Catch per Unit Effort (CPUE) for O. niloticus in 1999 and 2000 increased from 22.3 to 24.3 kg boat-1 day-1 and an estimated annual total catch was 26,489,100 and 15,584,900 metric tons respectively. In the same period, R. argentea catch rates increased from 194.7 to 298.3 kg boat-1 day-1 with an estimated total annual catch of 136,594,000 and 154,673,300 metric tons respectively. L. niloticus caught in gill net with a motorised boat during this period had considerable higher CPUE (72 to 75 kg boat-1 day-1) than either sails (37 to 17 kg boat-1 day-1) or paddleboats (25 to 29 kg boat-1 day-1). Estimated total landings for Nile perch dropped from 103,138,700 to 85,458,600 metric tons during the surveyed periods.

Range of 1"-9" mesh size gill nets were used to catch O. niloticus, nevertheless, 5" and 7" nets prevailed in the fishery. Hand lines and long lines with hook size numbers 7 to 12 were also used. The harvested fish were above LM50 i.e.>30 cm Total Length (TL). Lates niloticus was caught in gill nets ranging from 4.5" to 7" and long lines of hook size numbers 7 to 13. The mean length captured by gill netting was 46 cm TL and 55 cm by long lining. Rastrineobola argentea caught in seine nets (5 mm) and lift nets (10 mm) exhibited a modal length of 52 mm TL. Relatively small size dagaa were caught at the end of November through March.

The use of encircling gill nets and splashing to capture O. niloticus should be abandoned. The majority of L. niloticus harvested were below the size at maturity. This indicates prevalent high fishing pressure in the fishery. It is suggested that long lines with size <9 should be encouraged rather than gillnets with 5" mesh size. A size distribution of the exploited R. argentea in both lift nets and seine nets had a modal length above 50 mm TL. This is the size above the LM50 of R. argentea, hence, the 5 mm mesh size can be set as a minimum size for dagaa fishing nets in the Tanzanian waters.