Charles Schmitz, age 14, of Middletown, Ohio, for his question:
WHAT ARE FISHERIES?
The word fisheries applies to both the commercial enterprises that harvest fish and shellfish from waters, and to the waters themselves where such fishing takes place. Fisheries are mostly marine but also exist on large lakes and rivers.
The most productive fisheries extend outward from coastlines as far as the continental shelf, an average of about 50 miles from the shore. They are less thin 650 feet deep, but due to favorable currents and temperatures and abundant plant life, they hold most of the oceans' fish.
The rich North Atlantic fisheries are found along the North Sea, the west coast of Great Britain and the continental shelf of Iceland. Those of North America include the Grand Banks off Canada and the Georges Banks off New England.
Rich fisheries are found off the southwestern United States and Peru, in the Bering Sea, in the Gulf of Alaska and off the coasts of Japan.
The two kinds of finned fish taken from saltwater fisheries are the pelagic species and the demersal species.
Pelagic fish frequent near surface water, usually migrate seasonally and travel in schools. They include tuna, salmon, anchovy, pilchard, sardine, menhaden, mackerel and the herring types.
Demersal or groundfish frequent the ocean bottoms and are less gregarious. They include cod, halibut, sole, haddock, hake and flounder.
Shellfish and other invertebrates are taken in the shallower waters. Those of greatest commercial importance include oyster, clam, scallop, lobster, crab, shrimp and squid. Although they constitute more than 90 percent of the mass of animal life in the ocean, they make up only a small percent of the food harvested.
Commercial fishermen use nets that are either pulled close to the surface or trawled along the bottom. The most effective surface net is the purse seine, a long, curtain like net that hangs into the water from floats. It is towed by a skiff in a circle around a school of fish and then drawn shut at the bottom, like a purse, with a rope.
The gill net is made with mesh size just large enough for the head of the fish to pass through and the gills to hook into the mesh. Gill nets are most often left to drift on the surface for pelagic fish but are also anchored on the bottom for groundfish.
The otter trawl dredges scatted bottom feeders such as cod and is the most important net for commercial fishing. It is used in deep water and is towed by two long cables. Near the mouth of its sock shaped net are two otter boards, or vertical vanes, that pull sideways and hold the mouth open when towed.
Longlines, which are used to catch both surface fish (such as tuna) and groundfish (such as halibut), are long, heavy ropes to which are attached auxiliary lines with baited hooks. They are attached to moored buoys or trolled from vessels and then hauled in by winches.