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<br />sre endangered. Similar
<br />e used for spawning has
<br />'the Clear Lake splittail
<br />r. Reduced stream flows
<br />klta and its fish fauna.
<br />they will probably be
<br />~. Besides reducing the
<br />ie upstream penetration
<br />~ the flushing action of
<br />ase water temperatures,
<br />ranges, unless controlled
<br />;t on fishes of the Delta,
<br />i, and American shad
<br />dewatering has been the
<br />m Joaquin Valley. They
<br />nnows in the nineteenth
<br />:fore anyone was able to
<br />habitat for Sacramento
<br />;pleted native fishes.
<br />-ot used directly for one
<br />reset degree. Pollution is
<br />m Joaquin Valley, most
<br />sections of stream. The
<br />large numbers living in
<br />sewage-disposal systems.
<br />X71, the fishes inhabiting
<br />tually wiped out by the
<br />eleased large amounts of
<br />Eook place in the Pajaro
<br />;r, releasing highly toxic
<br />r 2,500 Pacific lampreys,
<br />ice in a small stream in
<br />A kill of several hundred
<br />a August 1973, when an
<br />accidentally dumped the
<br />~ nearby (H. W. Li, pers.
<br />~t isolated incidents but
<br />ystem, permanently alter
<br />wally significant to fish
<br />`rowth, inhibit reproduc-
<br />pesticides, such as DDT,
<br />snd-trout, but the subtle
<br />,clirr~ of a fish population
<br />r
<br />t
<br />CHANGE 51
<br />on pesticide levels. Equally subtle in their effects on fish populations are the rises in
<br />water temperatures caused by pumping river water through power plants as a coolant,
<br />and then returning it to the river. Small increases in stream temperatures can have
<br />severe long-term effects on the fishes. For example, striped bass spawning and
<br />migration is greatly inhibited if power plant effluent causes water temperatures to
<br />exceed 21°C (Talbot, 1966). So far, the effects of inland thermal pollution have been
<br />minimal in California, but as more power plants are built on streams with reduced
<br />flows, even lethal temperatures may be reached for many species of fish, especially
<br />trout and salmon.
<br />Another environmental change that is likely to raise water temperatures is the
<br />deforesting and overgrazing of watersheds, particularly if the practices eliminate
<br />streambank vegetation shading the water. Such changes are likely to be most
<br />significant to marginal trout streams, where summer water temperatures normally
<br />approach the upper limits for trout. The removal of watershed vegetation, especially
<br />by logging operations, is likely also to affect stream flows, increase erosion and
<br />turbidity, compact streambeds, decrease dissolved oxygen levels, and create logjam
<br />barriers to fish migration (Burns, 1972). Streams in heavily logged or grazed areas tend
<br />to have greater flows in the summer because there is less vegetation to take up the
<br />water and lose it to the atmosphere through transpiration. The depletion of the
<br />vegetation also tends to increase winter and spring runoff, resulting in more damaging
<br />floods. In some situations, vegetation removal may actually create year-round flows in
<br />normally intermittent streams, improving the streams for some fish species. The large
<br />spring floods, however, may offset any gains by increasing streambank erosion, by
<br />silting in pools and riffles (or, alternately, by scouring and compacting them), by
<br />increasing water turbidity, and by piling up barriers of fallen trees and logs. Sloppy
<br />logging practices, such as using streambeds for roadways or as dumping grounds for
<br />slash, may exaggerate these effects, just as careful logging practices, such as leaving a
<br />belt of trees along the streams, can minimize them. Thus Burns (1972) found that
<br />sloppy logging along the Noyo River, Mendocino County, caused a decrease of 42
<br />percent in young steelhead biomass and a decrease of 65 percent in young coho
<br />salmon biomass, yet careful logging along other similar streams actually increased
<br />production of these two species.
<br />INTRODUCTIONS
<br />The introduction of exotic fishes into California was both inevitable and necessary:
<br />inevitable because Western Man has seldom been satisfied with what he finds naturally.
<br />in newly settled areas, necessary because his manipulation of the waterways has made
<br />many of them unsuitable for the native fishes. The introduced freshwater fishes of
<br />California have a worldwide origin, although most of them (thirty-three species) are
<br />from eastern North America. There are two species from other parts of western North
<br />America, six species from Central and South America, two species from Africa, three
<br />species from Europe, and five species from eastern Asia.
<br />The reasons for introducing fishes are many, but there seem to be eight main ones:
<br />to improve sport and commercial fishing, to provide forage for game fishes, 'to provide
<br />4 ~
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