Effects of square mesh bunt on by-catch reduction in white shrimp Nematopalaemon hastatus

Simultaneous paired fishing comparison of modified codend against conventional codend was done with shrimp beam trawl in near shore sea off Lagos.The modified codend was designed to reduce by-catch and was made by incorporating square mesh panel at anterior bunt. Results 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 of 11-30cm were retained by the square mesh codend, while those with total length of 4-10cm were 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), llisha 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 (Cynoglossus senegalensis), Spinous fishes (Arius latiscutatus), shell fishes with morphometric body protection (Callinectes amnicola) were not significantly reduced (P> 0.05).