Gillnet selectivity of Lake Tana piscivorous fish: Labeobarbus megastoma

Gillnet selectivity parameters and its impacts on the population of the Lake Tana Labeobarbus megastoma , were estimated from fishery-independent catches in multi-panel gillnets with stretched mesh sizes ranging from 60 to 140 mm. Selectivity on L. megastoma was assessed using the PASGEAR software. Five different functional models; normal location, normal scale, gamma, log-normal and bi-modal were used to fit the selectivity curves to the catch data. It was shown that the bi-modal function was the best fit to the data. For the bi-modal selectivity curves, the optimum lengths (100% retention probability) for the 60, 80, 100, 120 and 140 mm mesh sizes were 24.18 cm, 32.24 cm, 40.3 cm, 48.36 cm and 56.42 cm, respectively. Considering the size at first maturity (L 50 %), 100 mm mesh size was found to be the most adequate mesh for exploiting the minimum allowable landing size (35 cm). Key words/phrases: Bi-modal, Labeobarbus , Lake Tana, Selectivity