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

Abstract

Light traps were used to sample small fish and squid from open waters in the central Great Barrier Reef lagoon. A total of 7203 fish, representing some 38 families, and 706 lologinid squid were caught during sampling periods October to January, 1988 to 1990. The fish catch was dominated by the family 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 errorkample size curves suggested that optimum replication was achieved with 5 to 6 traps, but that reasonable precision could be obtained with 2 to 3 traps. Coefficients of variation among replicate traps were taxon-specific, ranging from 0.9 (for clupeids) to 0.2-0.1 (for pomacentrids). These values compare favourably with those obtained from trawl nets. Light traps have considerable potential for sampling nekton that are capable of avoiding conventional towed nets.

Colonization patterns of reef fish larvae to the lagoon at Moorea Island, French Polynesia

“…Recruitment patterns at different time and space scales have been estimated using in situ censuses on newly settled fishes (Williams 1983, Eckert 1984, Sale et al 1984. Light trapping has also been used recently to catch larvae on or near reefs (Doherty 1987, Milicich 1988, but this technique relies upon an active process at night (positive phototropism) which can vary between species and developmental stages (Thorrold 1992).…”

Light traps for sampling marine biodiversity

“…No difference in time of night catches for larval fish Thorrold [60] There were two peaks in catch rates of invertebrates, one near dusk and one near dawn…”

“…Anderson et al [48] Light traps that were allowed to float with current had higher catch rates Thorrold [60] Turbidity Catch rate decreased with increasing turbidity for larval fish Lindquist and Shaw [86] Sampling duration, and time of day and night…”

“…The turbidity affects the distance the light reaches and the composition of the water may affect what wavelengths are transmitted [59]. Increased current can lower catch rates [40,42,60]. Fast currents can make it impossible for less mobile species to reach or enter the trap, even if they are attracted by the light [48].…”

Behavioral observations of an upcurrent reef colonization event by larval surgeonfish Ctenochaetus strigosus (Acanthuridae)

“…Planktonic larvae have been sampled with a variety of towed nets, but net avoidance by large 1a.rvae has always hindered the results concerning late-stage presettlement fishes (Choat et al 1993). Light aggregating devices (nightlights and light-traps) have also been used to sample late-stage larval fishes in the proximity of reefs (Victor 1983, Doherty 1987, but these methods are selective for certain taxa (Thorrold 1992, Choat et al 1993. Recently developed techniques now allow one to sample presettlement larvae during the actual transition period of reef colonization.…”