PREDATION ON PENAEID PRAWNS BY FISHES IN ALBATROSS BAY, GULF OF CARPENTARIA

Fishes were trawled from Albatross Bay, on the west coast of Cape York, north Queensland (12-degrees-45'S'; 141-degrees-30'E) during 4 yr, from August 1986 to April 1989. Penaeids were the first or second most important prey item by dry weight in 14 of the 34 penaeid-eating fish species, and in 12 of the species by frequency of occurrence. Eighteen species of Penaeidae were identified in fish stomachs. The five commercially important species comprised over 70% by dry weight of all the penaeids eaten by all the fishes, Metapenaeus ensis, Penaeus semisulcatus and P. merguiensis comprised 22, 28 and 11%, respectively. Commercially unimportant penaeids comprised 85% by numbers of all penaeids eaten. Larger fishes ate larger penaeids, mainly commercially important species, while smaller fishes ate smaller penaeids, mainly commercially unimportant species. All penaeid-eating fishes also ate some teleost prey and many were primarily piscivorous. Most penaeid-eating fish species took more benthic prey than bentho-pelagic and pelagic prey combined. The fishes with the strongest predation impact on commercially important penaeids were Caranx bucculentus and four species of elasmobranchs. The highest impact on commercially unimportant penaeids was made by several species of smaller but abundant fishes. An overall annual estimate of 2950 t yr-1 of commercially important penaeids is eaten by all fishes, a much higher figure than the average 870 t yr-1 taken by the fishery. This study highlights the need for accurate measurement of the abundance of penaeid predators as well as analyses of their diets when assessing the impact of predators on prawn stocks.