The distribution of larval and pelagic juvenile fish was investigated along 2 cross shelf transects in the central Great Barrier Reef (GBR) lagoon, during October to December 1988 and October 1989 to January 1990. One transect originated just north of Cape Cleveland and extended out in the direction of Lodestone Reef (Transect LR), while the second transect originated near Cape Bowling Green and extended in the direction of Davies Reef (Transect CB).
During the first survey season, 4 stations were located 8 km apart along each transect. The distance between the 4 stations was extended to 16 km for the second survey season, to span the width of the GBR lagoon. The sampling period was chosen to coincide with peak spawning of most fish species in the region and sampling equipment was deployed within a 10 day period either side of the new moon. Each transect was sampled between 1 and 3 times each month.
At each station, 6 light traps were deployed 200-300 m apart, approximately 1 m below the surface and allowed to drift with the water mass. Traps were set up to fish for 1 hour, emptied and redeployed at the next station on the transect. While the traps were fishing, three 10 minute plankton tows were carried out in the immediate vicinity of the light traps. Plankton nets, fitted with a digital flowmeter, were set to fish between 0.5 and 2 m below the surface and towed at between 0.5 and 1.0 m/s. Samples were immediately preserved in 80-90% alcohol.
Fish collected in the plankton nets were identified to family level, while fish collected in the light traps were identified to the lowest possible taxa. Fish were also measured under a stereo dissecting microscope with an ocular micrometer.
The effect of time of night on catch rate was investigated for 4 nights at the 16 m station on the LR transect during October and November 1990. Four traps were fished within the the same general area for 1 hour at three times during the night (19:30 to 20:30h, 23:30 to 00:30h and 03:30 to 4:30h).
Comparisons between anchored and drifting light traps were made on three occasions. On each occasion, 6 traps were set in a line perpendicular to the prevailing current direction. Alternating traps were then either anchored to the bottom or allowed to drift with the water mass and the traps fished for 1 hour.