Spatial scale estimates of catch per unit effort of bottom trawl off Lagos Coast, Nigeria

Abstract

Bottom trawl surveys with independent observers on-board a commercial vessel of 24m length overall were conducted in the wet season of 2009 off Lagos coast. The objective was to estimate the catch per unit effort as an index of standing stock abundance at different fishing depths. Transects were established for sampling at depths of 10, 20, 30, 40, 50, 70 and 100m. Four replicate hauls were made at each of these spatial scales. A total of 103 species of fin fishes belonging to 56 families were inventorised. The number of different species of fish caught did not increase with the fishing depth (r = 0.31). However, the number of fish species was low at fishing depths of 10, 20, 70 and 100m and high at depths of 40 and 50m. At depths between 10m to 50m, the species assemblages were mainly the croaker fauna while the snapper fauna, characterized by small sized and reddish coloured fishes dominated the catch at depth of 70 to 100m. Catch per unit effort increases from 2.5 kg/minute at a depth of 10m, peaks with 7.21kg/minute at depth of 40m and falls to 2.61kg/minute at a depth of 100m. F – test detected a significant difference (P< 0.05 ) of catch per unit effort at the various spatial treatments.