Some aspects of Nile tilapia Oreochromis niloticus (L.) population characteristics in Lake Victoria, Kenya
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Some aspects of Nile tilapia Oreochromis niloticus (L.) population characteristics in Lake Victoria, Kenya. M. Njiru1*, J.B. Okeyo-Owour2, M. Muchiri3, and I. G. Cowx4 1.Kenya Marine and Fisheries Research Institute (KMFRI). P.O. Box 1881, Kenya, e-mail-kmfkisu@net2000ke.com, 2. School of Environmental Studies. Moi University P.O. Box 3900 Eldoret, Kenya. 3. Moi University. Fisheries Department P.O. Box 3900 Eldoret, Kenya, e-mail Mu-fish @net2000ke.com 4. University of Hull International Fisheries Institute, Hull HU6 7EX, UK, e-mail-i.g. Cowx @biosci.hull. ac.uk * for all correspondence
Abstract/
Length frequency data collected from commercial landings were used to estimate growth parameters, mortality (Z, F, M), growth performance index (f’) and exploitation rate (E) in O. niloticus from the Nyanza Gulf of Lake Victoria, Kenya. The asymptotic length (L¥) had mean (±S.D) of 58.78 ± 2.42 cm TL, K of 0.59 ± 0.05 yr-1, Z of 2.16 ± 0.40 yr-1, M of 1.00 ± 0.06 yr-1, F of 1.12 ± 0.34 yr-1, E of 0.51 ± 0.06 and f’ of 3.31 ± 0.04. Fifty percentage (L50) entry into the fishery had a mean (±S.D) of 26.18 ± 12.50 cm TL. A comparison with previous studies in the gulf indicates that O. niloticus is now caught at a lower mean size, K, Z, M, F, have increased and the fish is maturing earlier. These changes may point to a population under stress, but still the fish exhibits high growth performance (f’) and grows to a large size and if well manage high production can be attained. The study showed that the major threat to the Oreochromis fishery is overexploitation caused by use of illegal fishing methods leading to capture of immature fish and breeding fish. The remedial measures to sustain the fishery include imposing ban on illegal fishing methods, limiting entry to the fishery, encouraging alternative livelihood and involvement of the community in fisheries management.