Predation of juvenile tiger prawns in a tropical Australian estuary

Abstract

We investigated predation of juvenile penaeids, in particular the grooved tiger prawn Penaeus semisulcatus and the brown tiger prawn P. esculentus, by sampling prawns and their potential fish predators on 2 intertidal seagrass beds in the Embley River, Queensland, Australia. Despite large differences in above-ground biomass of seagrass, these beds are both critical nursery areas for postlarval [ =3 mm CL) tiger prawns. Thirty-seven species of fish were found to eat juvenile penaeids, but 76% of P. semisulcatus and 43% of P. esculentus (numbers) were found in the stomachs of 1 species of fish (Scomberoides commersonianus). Predation levels at the 2 seagrass beds did not appear to be related to the amount of seagrass present; rather the numbers of Penaeus semisulcatus eaten by fish increased with the numbers of P. semisulcatus on the seagrass beds. Compared to the size distributions of tiger prawns resident on the seagrass, postlarval and small juvenile tiger prawns were under-represented in the stomach contents of fish and only 17 of the 287 P. semisulcatus found in fish stomachs were <=4 mm CL. Although we were unable to quantify the component of natural mortality attributable to predation by fish, we have identified the major fish predators of juvenile tiger prawns and provide evidence suggesting that fish are not significant predators of postlarval and small juvenile tiger prawns.