SEASONAL, DIEL AND TIDAL VARIATION IN BEAM-TRAWL CATCHES OF JUVENILE GROOVED TIGER PRAWNS, PENAEUS-SEMISULCATUS (DECAPODA, PENAEIDAE), IN THE EMBLEY RIVER, NORTH-EASTERN GULF-OF-CARPENTARIA, AUSTRALIA

Seasonal, diel and tidal cycles of beam-trawl catches of juvenile tige r prawns, Penaeus semisulcatus, from an intertidal seagrass bed in the Embley River, Gulf of Carpentaria, were studied at three-week interva ls between August 1981 and August 1982. Two seasonal peaks in catches of P. semisulcatus were recorded around November and April. Split-plot analysis of variance showed that after seasonal variation was removed , catches were influenced by day-night and tidal cycles. Few P. semisu lcatus juveniles were caught during the day, and more were caught arou nd low tide than around high tide. Results from drop-trap sampling at low tide showed that juvenile P. semisulcatus remained in the seagrass bed even when it became exposed and the water temperature exceeded 35 -degrees-C. These findings, and practical considerations, suggest that to study long-term changes in relative abundance of juvenile P. semis ulcatus with beam trawls, sampling should be completed at night and du ring the early part of the flood tide.