Population dynamics of Hyporhamphus limbatus (Beloniformes, Hemiramphidae) in two lowland reservoirs of Sri Lanka

Abstract

Although Hyporhamphus limbatus is found in several lowland reservoirs of Sri Lanka, due to gear restrictions imposed through fisheries regulations, this species remains unexploited or under-exploited in spite of having a good consumer preference. Population dynamics of H. limbatus in two Sri Lankan reservoirs, namely Minneriya and Udawalawe were investigated in the present study. Length frequency data of H. limbatus caught in shore seine nets of mesh sizes 1 mm, 5 mm and 7 mm were analysed using FiSAT software package and the von Bertalanffy growth parameters were estimated for non-seasonalised growth. Asymptotic total length was 155.4 mm for Minneriya and 156.4 mm for Udawalawe. Growth constants of H. limbatus for Minneriya and Udawalawe were 1.37 and 1.09 year-1 respectively. High total mortality rates (4.90 in Minneriya and 3.01 in Udawalawe), which are equivalent to production/biomass ratio indicate that both stocks can withstand heavy fishing. Relative yield-per-recruit (Y'/R) analyses indicate that at present these stocks are under-exploited and that by increasing size at first capture to about 70 mm, Y'/R can be optimized at the exploitation rate of 0.6. The shore seine nets of 5 mm mesh sizes can be used to exploit H. limbatus in both reservoirs. However, juveniles of exotic cichlids and other non-target species caught in the nets are needed to be released back to reservoirs.