Most people are familiar with mackerel from the fish store, and particularly as a goldish-brown smoked fish. Live mackerel are metallic blue-black with a silver-white belly. They are rapid predator fish and eat mainly zooplankton. In the summer months, they swim in large schools in the upper water column, hunting copepods, gammarids, fish larvae and other such organisms. After spawning in the summer, they also hunt herring, sprat and lesser sandeel, bringing them closer to the coast. There have been reports of schools of mackerel 9 by 4 kilometers in size and 40 meters deep. Mackerel are heavily fished by trawlers in the northern North Sea and the northeast Atlantic waters.