Impacts of fishing gears, fishing methods and fishing effort in the fisheries of Lake Victoria and proposals for management

摘要

The initial subsistence fisheries of Lake Victoria were dominated by two indigenous tilapiines, Oreochromis esculentus (Graham 1929) and Oreochromis variabilisudBoulenger 1906, exploited with simple fishing crafts and gears that had little impact on the fish stocks (Jackson 1971). Commercial fisheries, targeting the tilapia fishery,udstarted at the beginning of the 20th Centurywhen cotton flax gillnets were first introduced in 1905 into the Nyanza Gulf in Kenya. Gillnets were quickly adopted around the whole lake and consequently, the native methods of fishing soon died out (Jackson 1971).udFollowing the introduction of gillnets, fishing boats and their propulsion methods were also improved. These improvements in fishing capacity coincided with developmentudof urban centres and increasing human population around the lake, which increased the demand for fishery products. To satisfy the increasing demand, fishing effort increased greatly during the 20th century, despite the decline of catch per unit of effort (CPUE) (Jackson 1971; Ogutu-Ohwayo 1990). The initial catch rates of 127mm (5 inch) mesh size gill nets in the tilapia-based fishery, in 1905, was in the range of 50 to 100 fish per gillnet of approximately 50 m in length. However, twenty years later, the catch rates of gillnets of the same mesh size had declined to about six fish per net and gillnets of smaller mesh sizes, which had better catch rates, had been introduced suggesting overfishing (Worthington and Worthington, 1933).