By William F. Royce (Auth.)

ISBN-10: 0126009503

ISBN-13: 9780126009507

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Whether the waters do support most of the earth's photosynthesis is not known because the plants are vastly different from those on land, although we guess that photosynthesis is at about the same rate per unit area. Practically all of the plants in the waters are the minute, pelagic phytoplankton that drift throughout the surface layer. The attached algae and higher plants that occur only in shallow water along the shores comprise but a minute part of the total weight of aquatic plants, although they may be important in marshes, small lakes, or streams.

The surface layer will sink when it becomes more dense than the deeper water during the seasonal temperature changes in lakes and the pole­ ward movement of water in the ocean. Once below the surface a water mass remains almost constant in temperature and salinity; these properties are called "conservative" properties since they are changed only slowly by mixing processes. The masses of water that sink in the colder oceans move slowly toward the equator, so slowly that some are estimated to have been at the surface 2000 years ago !

Most of the sounds produced by animals are of low frequency varying from about 10 to 1000 Hz (cycles/second), but some produced by mammals are of frequencies ranging up to 80,000 Hz, far above the limit of human hearing (about 10,000 Hz). Sound is important to the fisherman who uses either echo-sounding or echo-ranging equipment for either navigation or fish location. ) Echo-sounding equipment is considered essential for all high-seas vessels as a navigational aid and as a help in locating fish near the bottom (Fig.

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Introduction to the Fishery Sciences by William F. Royce (Auth.)


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