Evaluating the performance of light traps for sampling small fish and squid in open waters of the central Great Barrier Reef lagoon

Abstract

Fish representing 38 families, and lologinid squid, were caught. The fish catch was dominated by the famly Pomacentridae (63% of fish collected), with lower numbers of lethrinids (6.7%), clupeids (6.3%), mullids (3.8%), and scombrids (2.7%). Size-frequencies of the fish collected indicated that the light traps sampled late-stage larvae and pelagic juveniles exclusively. No effect of time of night on catch rate was detected. Light traps that were allowed to drift with prevailing water currents caught more fish than anchored traps; this unexpected result may be a function of the effect of current velocity on trap efficiency. Analysis of standard error/sample size curves suggested that optimum replication was achieved with 5-6 traps, but that reasonable precision could be obtained with 2-3 traps. Coefficients of variation among replicate traps were taxon-specific, ranging from 0.9 (for clupeids) to 0.2-0.1 (for pomacentrids). Light traps have considerable potential for sampling nekton that are capable of avoiding conventional towed nets. -from Author