Gillnet selectivity of commercially important fish species in lake hashenge, Ethiopia

The present study was aimed to evaluate the selectivity of gillnets and the size at first maturity of commercially important fish species in Lake Hashenge mainly the Nile tilapia Oreochromis niloticus and common carp Cyprinus carpio. Experimental fishing was conducted using gillnets of different mesh sizes (60, 80, 100, 120 and 140 mm) in six sampling occasions from 2010 – 2011. A total of 2671 fish specimens consisting of 1184 O. niloticus and 1523 C. carpio were analyzed. Gillnet selectivity parameters for each mesh sizes were estimated for each species using the SELECT method. The size at first maturity (Lm) and its 95% CI for O. niloticus and C. carpio were estimated at 23.9 cm (23.3 – 24.5 cm), and 32.5 cm (31.6 – 33.4 cm), respectively. Results showed that a Log-normal model best described gillnets selectivity for C. carpio, while a Normal location model best described for O. niloticus. Capture probability estimates indicate that the optimum length of capture (LCAP) of 120 mm mesh net selects above the Lm value for both O. niloticus and C. carpio. Although the 100 mm mesh selects above the size of Lm value for O. niloticus, it still selects below the Lm value for C. carpio. Based on the results obtained, it was concluded that gillnets of mesh size 100 and 120 cm may safely be applied in Lake Hashenge fishery if proper level of effort is applied that ensures sustainability of both target species.