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.
