Contribution of Caridina nilotica (Roux) in the Dagaa Fishery in Lake Victoria, Tanzania

Abstract

The contribution of Caridina nilotica in the Rastrineobola argentea (dagaa) fishery was assessed at nine beaches in the Tanzanian part of Lake Victoria from May, 2001 to April, 2002. Additional data on dagaa and Caridina catches from Sweya beach between October, 2000 and April, 2001 were also included. Two main methods are used to catch R. argentea and Caridina in the Tanzanian waters of Lake Victoria: mosquito seine nets (5 mm and 10 mm mesh sizes) and catamaran lift nets (8 mm mesh sizes). The majority of the beaches used mosquito seine nets as the main gear; lift net fishing was dominant at Igombe and Busekera beaches.

Between May, 2001 and April, 2002, 157,390 t of dagaa were harvested in the Tanzanian waters of Lake Victoria; mosquito seine nets harvested 139,674 t (89%) compared with 17,716 t by lift nets (11%). CPUE was 244 and 337 kg boat^{− 1} day^{− 1} respectively for lift nets and mosquito seine nets. A total of 17,326 t of Caridina was harvested in the Tanzanian waters of Lake Victoria during the same period. More Caridina was harvested by mosquito seine nets (95%) than by lift nets (5%). Catch-per-unit-effort (CPUE; kg boat⁻¹ day⁻¹) for Caridina ranged between 1.87 and 45 kg boat⁻¹ day⁻¹, and varied with respect to location, time and fishing method. Sweya beach exhibited the highest CPUE and the lowest was at Nyangómbe beach. High CPUEs for Caridina were found during the rainy season at Sweya, Igombe, Kome and Busekera beaches. The rest of the beaches exhibited high CPUE during the dry season. CPUE of Caridina in lift nets was greater than in mosquito seines at Igombe and Busekera beaches. However, CPUE for dagaa at Igombe was higher for mosquito seines than lift nets. Reasons for these differences are unknown but probably relate to the location of fishing, particularly between inshore and offshore locations. Haplochromine cichlids were also abundant in the R. argentea catches at Igombe beach. The highest CPUE for haplochromines was at Igombe in January, 2002 and the lowest in June, 2001 (average CPUE for haplochromine cichlids at Igombe was 736 ± 746 kg boat⁻¹ day⁻¹ for lift nets). The total haplochromine catch for the region was estimated at 53,446 t. The carapace length (mm CL) distribution of Caridina in R. argentea commercial catches ranged between 1.5 mm CL and 8 mm CL depending on the gear used.

Keywords:

• Catch rates
• effort
• exploitation
• Rastrineobla argentea