Prediction of yield and optimum fishing effort for the Tilapia (Oreochromis niloticus, Linnaeus, 1758) stock of lake Hawassa, Ethiopia.

Abstract

Oreochromis niloticus (Tilapia) is the major commercially exploited species in Lake Hawassa that contributes more than 85% of the total annual landings from Lake Hawassa. On the other hand its potential is not rigorously studied so far in Lake Hawassa and in the other lakes as well. In the present study the Schaefer and Fox models were used to predict the Maximum Sustainable yield (MSY) and optimum fishing effort (fMSY) of tilapia in Lake Hawassa using catch effort data collected over a period of 9 years (2005-2013). Accordingly The MSY of tilapia in Lake Hawassa is around a 500 tones / year and the optimum level of fishing effort to be expanded on the stock should be below 1000 nets per day. The current yield estimate is by half less than that of the yield predicted during the early 1990’s, which is 900 tones/year (LFDP, 1993). This shows that the tilapia stock of Lake Hawassa is overfished. Accordingly, seasonal closure and enforcement of minimum mesh-size regulations as well as a limitation of the number of gillnets should be implemented on the lake in order to protect the stock from depletion.