Assessment of fish by-catch species from coastal artisanal shrimp beam trawl fisheries in Nigeria

Abstract

Abstract An observer programme that incorporated both fisheries-dependent and -independent surveys with fishers, was conducted to identify and quantify by-catch species from artisanal and nearshore shrimp beam trawl fisheries off Lagos, Nigeria. Catches were sampled from 62 replicate landings by five boats from January to December 2002. Twenty-five species belonging to 20 families of fish targeted in other inshore/offshore commercial fisheries constituted the by-catch species. Target shrimps Nematopalaemon hastatus (0.5–1.5 cm CL) are smaller in size than important commercial species (4–30 cm TL), which occur as juveniles on their nursery grounds. The percent of weight compositions of commercial by-catch species are: Pseudotolithus elongatus (19.89%), P. senegalensis (13.69%), Ilisha africana (8.85%), Pentanemus quinquarius (4.95%), Callinectes amnicola (3.27%), Pseudotolithus typus (2.75%), Galeoides decadactylus (2.26%), Cynoglossus senegalensis (1.43%) and Chloroscombrus chysurus (1.05%). By-catch species having total length of 11–30 cm are marketable and consumed, while a length range of 4–10 cm, which constitute 75%, is discarded ashore, thus resulting in high biodiversity loss. A t-test comparison of by-catch species weight, with weight of target shrimps was significant (P