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Gill net selectivity and
catch rates of pelagic fish in tropical coastal lagoonal
ecosystem
B. E. Emmanuel*, L. O.
Chukwu and L.O. Azeez
Department
of Marine Sciences, Faculty of Science, University of Lagos,
Lagos, Nigeria.
*Corresponding author. E-mail:
monetemi@yahoo.com.
Accepted
26 September, 2008 |
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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.
Key
words:
Gill net
designs, characteristics, catch composition, selectivity,
lagoon.
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