Stock Assessment and Estimation of Maximum Sustainable Yield for Tilapia Stock ( Oriocromis niloticus) in Lake Hawassa, Ethiopia

Abstract

The study was conducted on Lake Hawassa, one of the series Ethiopian rift valleys lakes. Data were collected from the area where fish are landed at one major landing site called fish market informally known as Amora Gedel, for one year (365days) on a daily basis. The length composition of tilapia caught by the fishery, total tilapia yield, fishing effort expanded as well as the price of tilapia and the cost of fishing operation were the basic information collected from the site. The aim of the analysis was to assess sustainability of fish stock, fishing level and to predict optimum yield and the bio-economic features of Lake Hawassa fisheries. Jones length based cohort analysis Model and length-based Thompson and Bell yield Prediction Model have been employed to estimate the maximum sustainable yield and maximum economic yield with their corresponding effort level. The estimated current annual yield was 182.94 tons of tilapia with the annual sale value of 4,158,760 ETB and 3,199,210 ETB of net profit for the fishermen cooperative. The predicted value of MSY was 186.72 tons/yr and this is obtained at fishing mortality factor of 1.6. And also MEY was 178.20 tons/yr and this is obtained at fishing mortality factor of 0.8. The fishery sector was found inefficient; the production was below its maximum sustainable yield level. Therefore harvest level should increase to its maximum sustainable yield level this might be possible by reducing the operating cost in order to increase both the level of yield as well as the net profit gained by the fishery sector