Empirical Determination of a Desirable Mesh Size for the Gill-net Fishery of Oreochromis mossambicus (Peters) in a Man-Made Lake in Sri Lanka

Abstract

Experimental fishing with bottom-set gill nets of different mesh sizes was carried out in Parakrama Samudra, a man-made reservoir in Sri Lanka, May to September 1983. The optimum retention length of Oreochromis mossambicus, the dominant fish species in the reservoir fishery, was estimated for each mesh size using the Baranov-Holt method. The optimal length of 0. mossambicus is a function of mesh size and is described by the equation: Y = 3.4763 + 2.0237X (r = 0.992; p < 0.01) where Y = optimal total length in cm and X = stretched mesh size in cm. The desirable mesh size corresponding to the acceptable size of 0. mossambicus to the consumer (20-28 cm) is 10.2cm. Natural mortality (M) was estimated to be 1.10 using Loo = 31.3 cm and K = 0.48 year-1 estimated from length-frequency data of the catches. The long-term biological effects of the increase in mesh size in the gill-net·fishery on the harvests and catch rates are discussed using length-structured yield-per-recruit and biomass-per-recruit analyses based on ko and M/K for different levels of exploitation rates and different sizes of first capture corresponding to various mesh sizes.