Assessment of Maximum Sustainable Yield and Optimum Fishing Effort for the Nile Tilapia (Oreochromis niloticus L.) in Lake Chamo, Ethiopia
The study was conducted to estimate the maximum sustainable yield (MSY) and optimum level of fishing effort for Nile tilapia (Oreochromis niloticus) stock in Lake Chamo, Ethiopia. Data were collected from eight major landing sites of Lake Chamo for three days in a week for ten months (February to November, 2018). The total length, sample weight and total weight of O. niloticus caught by the fishermen and the fishing effort were the basic information collected from these sites. Totally, 7,570 O. niloticus samples were collected in 120 days. The FiSAT software was used to determine von Bertalanffy growth and mortality parameters. Jones length based cohort analysis model and length-based Thompson and Bell yield prediction models were employed to estimate the maximum sustainable yield. The estimated growth parameters; asymptotic length that the fish attains at an older age(L∞) and growth constant(k)of O. niloticus were 55 cm and 0.37 yr-1, respectively. Overall about 11 million O. niloticus populations were estimated to exist in the lake. The estimated current annual yield was 290.1 tons per year for O. niloticus fisheries of the lake. However, the predicted value of MSY was 313 tons per year obtained at fMSY of 136,249 nets. The length at first maturity (L50) was 39.6 and out of the total annual catch 93.1% were below their respective size of maturity. Thus, the current yield reduction might be due to growth overfishing with reduced mesh sizes. As reported in the earlier studies and according to the finding of this investigation, the catch and yield of Lake Chamo is in the state of reduction through year. Unless the lake is properly managed, the future yields of Lake Chamo will be declining that may lead the resources depletion. Co-management practices, using the recommended mesh size and level of effort (number of nets) should be considered for the sustainability of the resources.