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

Abstract

Seasonal, diel and tidal cycles of beam-trawl catches of juvenile tiger prawns, Penaeus semisulcatus, from an intertidal seagrass bed in the Embley River, Gulf of Carpentaria, were studied at three-week intervals 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. semisulcatus juveniles were caught during the day, and more were caught around 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°C. These findings, and practical considerations, suggest that to study long-term changes in relative abundance of juvenile P. semisulcatus with beam trawls, sampling should be completed at night and during the early part of the flood tide.