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Cast net design characteristics, catch composition and selectivity in tropical open lagoon


BE Emmanuel
LO Chukwu
LO Azeez

Abstract

Cast net design characteristics, construction, operational techniques and selectivity in Lagos lagoon, Nigeria was examined between September and December 2005. Netting materials for cast net
construction in Lagos lagoon were monofilament nylon, poly-ethylene (PE) and polyester (PES). The conventional ratio 1:2 of the number of meshes in the length of the apical panel to the second was not
adopted by the fishermen. The cast net length was 1.77 m and net mouth area was 4.99 m2. Twenty-one fish species belonging to 19 families were caught during the study period. Sarotherodon melanotheron was numerically most abundant in Lagos lagoon. Numerically, more fish specimens were caught at night than daytime. The higher the effort (throw) the more the cast net catches. The condition factor (K) of fishes in the lagoon ranged between 0.27 and 3.0. The crustacean had the overall highest condition factor. A total of 1,501 specimens (30 kg) at N 4, 500 (USD 32.14) were caught for 11 trips (247 casts) for 38.7 h. The Catch Per Unit Effort (CPUE) (number of catch per cast) ranged between 0 and 6; the average number of cast per hour was 6. Cast net was not species specific. The smallest fish (S. melanotheron) had a burst speed of 51 cm per second while the largest (L. falcipinnis) had a maximum burst speed of 262 cm per second. Cast net was selective for shallow water species. Cast nets durability ranged from 3 months to 3 years depending on the netting material and the environment where it is operated.