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Show At Bonneville, where volumes of water involved are too great to permit screening, one investiga- tion has shown that about 15 percent of young isalmon die as a result of the rapid pressure changes encountered as they pass the turbines at the dam. While this dam alone will probably not seriously affect the total production, new and higher dams may well eliminate most of the nat- ural salmon run. It is not felt that present ex- pensive hatchery programs which collect salmon spawn, raise the young artificially, and return them to the river, alone can maintain commercial runs indefinitely. One difficulty on the Columbia River has been the rapidity with which the program of develop- ment has proceeded. The great need for power which has developed within a decade in the Pa- cific Northwest has caused an acceleration of the construction program, leaving fisheries research far behind in planning corrective measures to adapt the salmon to the great changes taking place. The Columbia salmon difficulties have been some of the results of an early lack of a truly comprehensive plan for the river. Salmon research takes time. There is no way the natural life cycle of 2 or 3 years can be speeded, and in many cases definite statistical information can be gained only by following sev- eral generations through that cycle. Preservation of the salmon industry demands that dams bar- ring important runs be designed carefully with fish preservation in mind, and then tested over a period of several years to see whether the design is adequate to solve the problem. To make pos- sible such tests, consideration may be given to the possibility of delaying construction of new dams until the tests have been completed. Large populations of Atlantic salmon were once found in Scandinavia, Continental Europe, and the British Isles. They once ascended the Rhine into Switzerland. Today, except in re- mote places, that resource is gone in Britain and on the Continent as a result of dam building and pollution of waters. The story is similar on our East Coast. One hundred years ago, salmon were abundant from the Connecticut River to the Canadian boundary, but now they are rare. The shad and the striped bass similarly have been eliminated from many eastern streams. The so- called Colorado River salmon has already been virtually destroyed by the structures on that river. In the Pacific Coast States where in 1909, 150 million pounds of salmon were landed, today only 65 million pounds are handled. The catch may be further reduced. Diversions and the Oyster.-In the East, there is another commercial fishing problem which il- lustrates some of the subtle repercussions which river development programs have on aquatic life. In 1931, the Supreme Court refused to enjoin New York City from impounding the waters of the upper Delaware River and diverting up to 400 million gallons a day for municipal use. In its decision, however, the Court recognized that a larger diversion might seriously affect the oyster fisheries of Delaware Bay. Studies of these beds have shown that excessively decreased flows allow a slow influx of saline waters which bring certain enemy organisms within reach of oyster populations. At the same time,,deduced flows mean a re- duction in the dissoij i i the bay. This cuts down on the production of microscopic plants that constitute the oyster's diet. To make matters even more difficult, when there is an insufficient flow of warm river water, the temperature of the bay fails to rise sufficiently to induce the oyster to spawn. It is often pointed out that permanent diver- sions of large amounts of water from a stream may cause seasonal drying up, overheating, or a serious rise in pollution concentrations with consequent loss of wildlife. It is seldom fully appreciated, however, that diversions and stoppages affect not only the wildlife and fish along the stream itself, but also have complex effects on the broad tidal regions and their commercial fisheries. Gains and Losses.- -There are gains from water impoundments. Reservoirs may provide excellent fishing and serve as a temporary refuge for fish of intermittent tributary streams. They may also create waterfowl resting, feeding, and nesting grounds and public shooting areas. Animals such as muskrats may be benefited by ponded streams where relatively stable clear 262 |