Used for organisms inhabiting the open waters of the oceans and seas beyond the continental shelf, the pelagic zone. The following distinction can be made between marine birds; i.e. 1) inshore, 2) offshore and 3) pelagic marine birds. Offshore and pelagic sea birds are considered real oceanic birds. The true deep-sea or pelagic birds live beyond the continental edge (shelf) and often breed on oceanic islands, although occasionally they disperse into the waters of the continental shelf. They often depend more on squids and planktonic organisms such as crustaceans than on fish for food.