The Pelagic Fish Community of the Polar Frontal Zone off the Kerguelen Islands

Abstract

Because of the clearly observed increase of the majority of fur seal and penguin populations in the Southern Ocean new developments in marine studies are attempting to quantify the impact of predators on marine resources. The predation in the subAntarctic zone of this ocean is directed mainly to the mesopelagic fish as noted from studies at the breeding sites of predators. Guinet et al. [1], studying the Indian sector of the Southern Ocean, have estimated that the annual consumption of marine seabirds and fur seals off the Kerguelen Islands was about 1.8x10 super(6) tonnes during 1985, including 26 % (0.46x10 super(6) tonnes) of Myctophidae. At that time they considered that the king penguin (Aptenodyptes patagonicus) population (173 000 pairs) takes about 146 236 tonnes of Myctophidae annually. The nearby Crozet Islands, sheltering 1 771 000 king penguins, consume about 744 700 tonnes of myctophids [1]! The potential impact of these top predators on the marine resources can be estimated when the world population size is considered. These birds are recognized to be the most specialized in the predation of mesopelagic fish, specially the Myctophidae [2-5]. However no real-time study of the pelagic fish community present in the foraging range of a top predator has ever been published. A joint ornitho-ichthyological study in summer, in the offshore Polar Frontal Zone near the eastern coast of the Kerguelen Islands (distance: 20 - 110 miles; bottom depth: 450 - 2300 m), was the first to investigate the pelagic fish community of the upper water column. The aims were to study the distribution and abundance of the prey and to test whether predators could be used as bioindicators of the marine resources. Only the fish results were presented subsequently.