By–catch reduction in the white shrimp, Nematopalaemon hastatus fishery of Nigeria using codend with square mesh panel
Simultaneous paired fishing comparison of modified codend against conventional codend was done with shrimp beam trawl in nearshore sea off Lagos, Nigeria. The modified codend was designed to reduce by-catch and was made by incorporating square mesh panel at anterior bunt. The result showed that the square mesh codend significantly reduced the by-catch of juvenile fishes up to 39.35% (T-test, P < 0.05; 0.01) with no significant loss (2.9%) in the quantity of the target shrimps Nematopalaemon hastatus (P < 0 .05; 0.01). Commercially important by-catch species having a total length range of 11 to 30cm were retained by the square mesh codend, while those with total length of 4 – 10cm were highly reduced eg; Pseudotolithus elongatus (43.96%, P < 0.05, 0.01), P. senegalensis (49.03%, P < 0.05; 0.01), P. typus (36.29%, P< 0.05; 0.01), Ilisha africana (39.09%, P< 0.05; 0.01), Pentanemus quinquarius (41.02%, P<0.05; 0.01), Galeoides decadactylus (48.80%, P< 0.05; 0.01), Lutjanus dentatus (48.98%, P<0.05; 0.01), Drepane Africana (43.13%, P< .0.5;0. 01), Chloroscombrus chrysurus (55.29%, P< 0.05; 0.01), and Selene dosalis (34.60%, P< 0.05; 0.01). At family level, reduction in the number of 8 out of 13 important by-catch families analyzed were significant, e.g.; Clupeidae, Trichiuridae, Sciaenidae, Serranidae, Polynemidae, Carangidae and Lutjanidae (P< 0.05; 0.01). The number of flattened fishes, eg; Cynoglossus senegalensis, Spinous fishes, e.g.; Arius latiscutatus, shell fishes with morphometric body protection eg Callinectes amnicola were not significantly reduced (P> 0.05). The economic and biological implications of the result are discussed:
Key words: Square mesh, By-catch, Nearshore, Shrimp, Beam trawl, Nigeria.