ABSTRACT

The Benue River fishery is yet to be investigated beyond frame surveys and hence the need to assess the catch efficiency of operational gears that exploit the resources with a view to predicting its status. The Lower Benue River was sampled at the Abinsi and Makurdi fishing ground on longitudes 7^o 47’N and 6^o48’E for 12 months. Sampling started in July 2010 and ended in June 2011. Four fishing gears (castnet, dragnet, gill set net and hook and line) were assessed for their efficiency. A total of 5,853 specimens from 88 species in 22 families were caught. Castnet had the highest catch for both dry seasons (25%) and wet seasons (22.6%), drag net ranked second with 22.8% and 10.87%, gill net (2cm-5cm) ranked third and recorded higher catches in the wet season (7%), than the dry season (6.6%). Hook and line that was ranked least also recorded higher catches in wet season (3.2%) than in dry seasons1.8%. Individual species that constituted up to 5% of the total catch for each gear in any particular season were considered as highly selective for it and are used to compare efficiency among the gears. Twenty three (23) species were recorded in these categories. They included Alestes baremose, Tilapia zillii, Brycinus nurse, Synodontis clarias, Citharinus citharus, Lates niloticus, Mormyrus rume, Hepsetus odoe, Hermichromis bimaculatus, Heterobranchus bidorsalis, Bagrus filamentosus, Mormyrops angulloides, Mormyrops macrophthalmus, Auchinoglanis occidentalis Hydrocynus brevis, Synodontis courteti and labeo coubie. The most dominant species in numbers included Tilapia zilii (413), Alestes baremose (405), Synodontis clarias (309), Lates niloticus (237), Synodontis batensoda (230), Hydrocynus brevis (206). Species with the highest biomass (wt in kg) included Labeo cubie (107.3kg) Lates niloticus (89.5kg), Hydrocynus brevis (67.3kg), Alestes baremose (60.4kg) and Hepsotus ode (59.1kg). The longest lengths and highest weights were observed in Labeo cubie (71cm and 8.5kg), and were caught by dragnet, next were Hydrocynus brevies (61cm and 4.5kg), caught by gill net and Bagrus filamentosus (61cm and 2.3kg) and caught by dragnet.  The seasonality of the gears showed that castnet and gill net were all season gears but with some limitations. Dragnet was more effective in dry season but its present operational conditions does not favour resource conservation concept. The most efficient gears in the wet seasons were the gill net and hook and line which recorded low catches but caught bigger species with higher biomass (high commercial value). Water parameters were observed and the average depth of the river was 11M. The velocity of water recorded ranged between 25 and 35 m/minute. Other mean water parameters recorded were dissolved oxygen 7.9±0.49 mg/l, temperature 25 ± 2.06(^oC) and turbidity 51.0 ±2.0. (cm). Among the water parameters recorded, only temperature and turbidity showed significance difference in the different seasons. DO showed significance difference in relationship to fish distribution in the dry season p<0.5. The parameters indicated that the river water was at optimal conditions for high productivity. The ongoing human activities (as observed) are enhancing aquatic ecosystem degradation via land development which does not support fish productivity. There is need for the enforcement of existing regularity laws to check the trend. It is recommended that mesh sizes of fishing nets below 2cm should be restricted for use in the area especially for cast and Drag nets. There is need for constant monitoring of the fishing activities and the hydrographic parameters in the area.