Abstract:

In a fishery, the fish catch is partly determined by the type, number and size of fishing gear, the manpower on the fishing vessel and the fishing ground. In the Lake Victoria gill net fishery these fish catch attributes are dependent on the size and mode of propulsion of the fishing boat and the mode of operation of the gill nets. This study, conducted at six fish landing sites: Masese, Lingira, Bugonga, Kasenyi, Lambu and Kasensero on the Uganda sector of Lake Victoria, investigated how the size of fishing boats, mode of propulsion of fishing boats (motorised or manual), mode of operation of gill nets (active or passive) were related to the number of gill nets, number of boat crew, fishing grounds, the quantity and species composition of the fish catch and hence the income to the fishers. There was significant increase in the overall mean number of gill nets per boats with increase in boats size (ANOVA test, F6>499 = 124.1782, P<0.05) from 20.9 + 2.3 nets in 5.0-5.9 m long boats to 88.6 + 11.8 nets in 11.0-11.9 m long boats. Bigger boats required more crew such that the number of crew increased with increase in boat size, from an average of 2 men in boats <8.0m to 3 men in large boats. The proportion of large gill net mesh sizes >127 mm (5 inch) also increased with increase in boat size from 40.4% in 5.0 - 5.9 m long boats to 100% in boats >10.0 m long. The majority of large boats >8.0 m long were motorised and fished in far offshore waters targeting Nile perch whereas nearly all boats <8.0 m long were manually powered and fished in inshore waters targeting both Nile perch and Nile tilapia. Boats operating gill nets actively fished very close to the shoreline targeting Nile tilapia. Nile perch contributed 97.7-100% of the catch in boats >8 m long whereas Nile tilapia and other fish species contributed 31.0- 59.9% in boats <8 m long. 73.6-89.0% of Nile perch caught by boats <8.0 m long were <50 cm TL whereas <17% of Nile perch in larger boats were <50 cm TL. The overall mean fish catch rates increased significantly with increase in boat size (ANOVA test, F6 5i3 = 15.0367, P<0.05) from 12.6 + 1.9 kg in 5.0-5.9 m long boats to 78.2 + 16.4 kg in 11.0-11.9 m long boats. Actively fishing boats at Masese and Lingira carried about half the number of nets carried by passively fishing boats but there were no significant differences in the average mean total weights of fish landed by both categories of boats (ANOVA test F]j81 = 3.8999, P<0.05). Thus, active operation of the gill nets raised the catch rate per net twofold from 0.43 + 0.11 kg in passively fishing boats to 0.96 + 0.15 kg in actively fishing boats. These observations indicate that full exploitation of the L. niloticus fishery of Lake Victoria up to offshore waters would require promotion of use of large motorised boats that use large numbers of large mesh sized nets and land desirable sizes of fish and putting restrictions on number of boats and/or mesh size of gill nets of manually powered boats that operate in inshore waters and land mainly immature fish. The management of the O. niloticus fishery should focus on discouraging the active operation of gill nets, reducing the number of boats operating in inshore waters and preventing further reduction of gill net mesh sizes.