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African Journal of Biotechnology

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Gill net selectivity and catch rates of pelagic fish in tropical coastal lagoonal ecosystem

BE Emmanuel, LO Chukwu, LO Azeez

Abstract


The fish species and size selectivity of gillnets design with monofilament nylon polyethylene netting materials were investigated in Lagos Lagoon, Nigeria between September and December 2005. The
gillnets floats and sinkers were improvised from rubber slippers and lead metallic objects which were attached at intervals of 1.35 to 2.0 m with hanging ratios of 45.2 and 51.7%. The number of miles per
stapling distance was three. A total of sixteen fish species belonging to 14 families were caught and Ethmalosa fimbriata was numerically most abundant. The highest numbers of fish species were recorded during the dry season month of November. The higher the fishing effort the more the gillnet catches. More fishes were caught during daytime than at night. The effect of gillnet fishing activities on fish communities includes a decrease in their abundance, changes in age structure, size composition and species composition. The overall length sizes of the fish caught were comparatively small. Gillnets used were highly selective for smaller size of fish and were easily damaged by crabs, tugs and engine powered canoes. Fishes with head and body girths smaller than 126 mm which were not gilled, wedged or entangled by the gillnets are assumed to have escaped. The condition factor (K) of fishes in the
lagoon ranged between 0.11 and 1.3 while a mean condition factor of 47.78 was recorded for swimming crab Callinectes amnicola. The gillnet price per kg of fish was (N150.00 or $1.07) while the price of fish
per trip was N477.27 or $3.41). The durability of the nets depends on its continual and timely mending and maintenance.



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