The diet of the large coral reef serranid Plectropomus leopardus in two fishing zones on the Great Barrier Reef, Australia

Abstract

The diet of Plectropomus leopardus (Serranidae, Lacepede 1802) was examined on two pairs of reefs in the Cairns Section of the Great Barrier Reef Marine Park, Australia. For both pairs, one reef was open to fishing and the other had been closed to fishing for eight years; however zoning appeared to be ineffective as there was no difference in the size structure of leopard coralgrouper populations on either open or closed reefs. Two fishing methods were used to sample reefs concurrently and the size structure and diet of P. leopardus that were speared randomly (n=587) were compared to samples caught by line (n=85). Adult P. leopardus were highly piscivorous (96% of prey was fish by number), and two families of fishes, Pomacentridae and Labridae, composed approximately half of their diet tinder of relative importance=48.4%). Numerical composition of fish in the diet varied significantly among reefs, but there were no patterns related to reef closures when fish prey were classified by taxa or by their habitat. Fishes categorized as living in the demersal reef habitat were the dominant prey consumed, followed by midwater fishes. When the data from reefs were pooled, the abundance of families in the diet differed between locations (north and south) but not between fishing zones. Dietary overlap was high between the different fishing zones and was very high in relation to naturally occurring spatial and temporal variability in the diet of I! leopardus found in other studies. With line fishing larger and hungry fish are caught, and the few data on natural prey suggest tentatively that line catches are biased toward I! leopardus feeding on pelagic fishes. The coral reefs and surrounding waters provide the major food source of Fl leopardus,:whereas sandy areas are much less important. Our data suggest that the coral trout fishery is resilient to changes in abundances of particular prey species because the diet of P. leopardus is broad and because the two major prey families are diverse and abundant on coral reefs.