Surrounding nearly all continents is a shallow extension of that landmass known as the continental shelf. This shelf is relatively shallow, tens of meters deep compared to the thousands of meters deep in the open ocean, and extends outward to the continental slope where the deep ocean truly begins.

Sediment from the erosion of land surfaces, washed into the sea by rivers and waves, nourishes microscopic plants and animals. Larger animals then feed upon them. These larger animals include the great schools of fish, such as tuna, menhaden, cod and mackerel, which we catch for food.

The continental shelf regions also contain the highest amount of benthic life (plants and animals that live on the ocean floor).

Information provided by: http://www.onr.navy.mil