How to increase the fisheries yield in low productive marine environments

The study of a complex of artificial structures (man-made reefs) established in the coastal waters of Israel, where primary productivity is low, is discussed. The results may point to several ways to increase the fish yield in low-productive marine environments. One direction is the artificial enrichment of the man-made structures with surplus nutritious materials, which increases the recruitment of some highly commercial fish like large groupers. Another approach may incorporate the intensive rearing of commercial species, such as gilthead sea bream, in cages in the framework of the reef. In this way the cages can be anchored to the reef, and any excess food fed to the caged fish, together with the excretion of these animals, will enrich it. An additional source is species with high market prices which use the reef just for shelter during part of the day or season while foraging over an area much larger than the reef itself during the rest of the time. The Mediterranean slipper lobster is a good example of such an organism. Another possible way to improve fisheries in sucn regions may be the utilization of acoustic signals in combination with partial artificial enrichment to attract commercial species to special underwater traps.