COMPARISON OF CATCH EFFICIENCY AND SELECTIVITY OF ENTANGLING NETS: GILLNETS AND TRAMMELNETS IN LAKE KAINJI, NIGERIA

Abstract

The relative catch performance and selectivity of gillnets and trammel nets were investigated in 12 sampling stations on Lake Kainji, Nigeria.3 types of nets with dimensions 50m x 3m were constructed using 76mm and 178mm meshsizes for two type of gillnets, 76mm and 178mm meshsizes for the lint and armour nets of the trammelnets respectively. The stations, with a distance of about 1225m from each other were located at the lower basin of the lake. All the nets were randomly ganged together to form a fleet of nine nets each, and were set twice in each of the 12 stations which gave a total of 24 fishing operations. A total of 365 fish weighing 88.9kg and belonging to 16 different species were caught in all the nets. The trammel had the highest catch by number and weight constituting 60% and 69.22% of the total catch respectively with a relative species diversity index of .82. This was followed by 76mm gillnet which constituted 38.63% by number, 28.09% by weight, 0.69 relative species diversity index. The 178mm gillnet had the least percentage catch of 1.37% and 2.9% by number and weight respectively with 0.25 relative species diversity index. The master selectivity curves of the 76mm gillnets and trammelnets for the four most abundantly caught species (Oreochromis niloticus, Citharinus citharus, Sarotherodon galilaeus and Synodontis membranaceous) were bell shaped. The minimum selection length for these species caught were the same for each .net The trammel net had a wider selection range that skewed to right, a higher modal and median length indicating larger individual species being entangled in the net. The cost benefit analysis showed that the relative efficiency of the trammel nets was high enough to compensate for the extra cost incurred on them.