Selectivity Coefficient Of Wire Basket Traps For Tilapia Nilotica

Abstract

Most methods of estimating growth and mortality rates require samples representative of the population with respect to size of one or more age groups. There is no fishing gear that exhibits equal selectivity towards fish of all size even with a particular species. It is attempted in the present work to define the mesh size of wire basket traps for Tilapia nilotica before its catch data may be used for fish population studies m the Egyptian lake Borollus. Traps with different mesh sizes were tried in comparative fishing experiments. The selectivity coefficient and mean selection lengths were calculated according to Baranov's, Holt's and Olsen's methods. It is concluded that the most convenient method of calculation is that suggested by Olsen. For the proper management of Tilapia nilotica fisheries, it is recommended that the wire basket traps mesh size should not be less than 30 mm (mesh bar) to give mean selection length of 15.0 cm. It is expected according to this recommendation that the total catch of Tilapia may increase more than three times annually