Roslyn Bishop, age 17, of Manuels, Newfoundland, Canada, for her question:

Do ocean currents affect fisheries?

Indeed they do. The Atlantic fishermen from the Maritime Provinces can thank the cool Labrador Current for filling their nets. The fishermen in the Pacific waters off Peru can thank the cool Humboldt Current. Sunlit coastal waters and other factors also affect fisheries. But these factors are less important than the right kind of ocean current. And, of course, there are reasons why this is so.

The sea is a hungry world where large creatures feed on smaller ones. This food chain is the vital factor that supports everything that lives in the ocean. And like all other great systems of nature, it also links all the sea dwellers, directly or indirectly. If all the sardines were removed, dozens of larger and still larger species would go hungry. Naturally, this food chain has a beginning    and the first link is plankton. The main ingredients in this basic seafood are diatoms and other microscopic plants and animals that thrive best in chilly waters. The great plankton eating whales migrate to the Arctic and Antarctic in time for the rich plankton seasons.

Smaller fishes and the larger fishes that feed on them also swarm there to feast in the thriving meadows of plankton    and on each other. You might suppose that most of the world's fish abound in polar waters. However, the sea has a way to distribute at least a good many of them to other locations. The sun and the winds, the rotating earth and other great forces conspire to keep the ocean waters circulating. One feature is the ocean currents, great rivers of water moving on scheduled routes through the seas.

The Gulf Stream, bearing fishy populations from southern seas, sweeps north along the Atlantic coast of North America. The Labrador Current sweeps down from the Arctic. It carries Greenland icebergs and teeming populations of fish from the plankton rich polar seas. The two opposite currents meet and collide where the seabed rises off the Grand Banks. No wonder this region supports one of the richest fisheries in the whole world. Two different ocean currents deposit their assortment of fishes right on its doorstep. The crowded region is a rather shallow strip of water, curving 500 miles around the seaward side of Newfoundland. Swarms of seabirds hover and swoop, showing fishermen where the fishing is likely to be best.

Moving waters and shallow waters also encourage teeming fish populations. Fish require molecules of free oxygen from the water and the sea dissolves most of its oxygen from the air. Tossing, swirling waves are richer in oxygen and hence more likely to support fish. The food chain of the ocean depends on microscopic algae and other plants    and plants require sunlight to manufacture their food. Sunlight pierces only 1,000 feet or so through surface water and plants cannot live below this level. Fish populations also thrive where mineral rich water wells up from the deeper levels of the ocean. This occurs off the coast of Peru, which some say is the richest fishing area in the world.

There are, of course, plenty of fish and other sea dwellers out there in the middle of the deep ocean. However, there are far more in the shallow, sunlit waters of the continental slopes around the shores. A few inlets around the world are neglected by tides and ocean currents. In these stagnant waters, the fish are suffocated, either by choking vegetation or lack of oxygen.