The North Atlantic Ocean has some of the world's busiest shipping lanes; the northern lanes are patrolled for icebergs. Commerce between the Mediterranean Sea and the NE Atlantic Ocean was initiated by the Carthaginians. From the 7th cent. A.D., Scandinavians navigated the Atlantic; they probably reached North America c.1000. Trade routes along the coast of Africa were opened by Portugal in the 15th cent. and to the Western Hemisphere by Spain after the voyages of Columbus. The Grand Banks have traditionally contained some of the world's best commercial fishing grounds, but by the early 1990s the area had been overfished, and many species were depleted.