The effect of intensive fishing on two cichlids (Oreochromis niloticus and Astatotilapia burtoni) in Nyangara wetland at the north end of Lake Tanganyika (D. R. Congo) with fishery management implications
Keywords:
exploitation, maximal length, length frequency distribution, size at maturityAbstract
The Nyangara wetland, also known as Laguna, in the fluvial plain of Rusizi River at the northern end of Lake Tanganyika, harbours a fish fauna which offers food and income for 500 people directly or indirectly associated with fisheries. Fishing focuses mainly on two cichlids (Oreochromis niloticus and Astatotilapia burtoni) and the marbled lungfish (Protopterus aethiopicus).
Studies of population structure were based on length-frequency distributions of fish in catch samples. The size at first maturation was estimated using total length and state of gonad maturity estimated macroscopically. Minimum and maximum sizes in catches ranged from 10 to 100 mm total length in A. burtoni and from 20 to 180 mm in O. niloticus. Sizes at first maturation were 65 mm total length for female and 70 mm for male in A. burtoni and 130 mm in O. niloticus. Immature fish comprised 95 % of the catch. The majority of harvesting thus took place before the onset of maturity. In both species, the dominance of very small fish in the population structure, the reduced maximal size, and the early maturation of fish, indicated high fishing mortality.
Although further studies are needed to properly understand the effects of intensive fishing on fish populations in the Nyangara wetland, the present study suggests that the fishing community would be well-advised to follow the precautionary approach and pay more attention to the numbers and types of fishing gear, and to appropriate mesh sizes to ensure successful spawning of fish. To reduce fishing pressure, alternative sources of protein should be sought, such as pond aquaculture, agriculture and animal husbandry for example.
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