Seasons are the main motor of natural phenomena in biology, such as climate-driven currents in the ocean. Thus each year a flood of over half a billion sardines assemble in sea-darkening schools near the South African and Angolan coast. It draws equally epic armies of fish-eaters. The ablest hunters, first of all dolphins, spot the prey first, and are followed by others who fish at sea, like whales and sharks, from land and by air, many in colonies, like seals, as a stable food source to feed their young. Fishing techniques vary widely, most recent and devastating being those of man.