7809

• UCREFRP Catalog Number: 7809
• Author: Wydoski, R. S.
• Title: Responses of Trout Populations to Alterations in Aquatic Environments
• USFW Year: 1978.
• USFW - Doc Type: A Review, reprinted from John R. Moring, ed., Proceedings of the Wild Trout - Catchable Trout Symposium.
• Copyright Material: NO

affects the physiological processes, such
as metabolism and osmoregulation, that
produce stress in the fish; resulting in
mortality by direct toxicity or indirectly
by increased predation or susceptibility
to disease. The dissolved gases below dams
often become supersaturated with ni~rogen,
resulting in gas-bubble disease in fish
(Rucker 1972). In summary, fish must con-
tinually adapt to environmental changes
(such as ion composition of the water, dis-
solved gases, light, pressure, and other
factors), migrate, or die. Furthermore,
successful species must be sufficiently
plastic in their characteristics to environ-
mental changes so that they can adapt mor-
phologically, physiologically, or behaviorly
to environmental changes (Warren 1971).
See the keywords of Fish Physiology, Water
Quality Criteria, and Water Qual~t~ Pollu-
tion for references that w~ll prov~de fur-
ther information on this important topic.

The U. S. Geological Survey (1974)
considered sedimentation to be one of the
largest pollutants in streams. It is par-
ticularly important in reservoirs (Dendy
1958) since the suspended material settle
as the hydraulic gradient decreases due to
impoundment. The net result is that reser-
voirs become filled with organic material
that lowers the dissolved oxygen or inert
sandy deposits that converts the bottom of
the reservoir into a sterile, biologically
poor environment for aquatic organisms.

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Hence, the productivity diminishes with age
in reservoirs and man-induced sedimentation
increases the rate of aging in reservoirs.

Increases in the fine sediments in
spawning gravel has been shown to decrease
the survival of various salmonid alevins
(Fig. 7 - Bjornn 1969; Hausle and Coble
1976; and Phillips et al. 1975). Although
various experiments demonstrated the de-
crease in survival as the percentage of
fine sediments was increased, these values
varied somewhat but were rather consistent
considering that three genera of fish were
used in the experiments; about 50% mortality
occurred when the fine sediments were be-
tween 30 and 50% (Fig~ 7). The mortality
of cutthroat trout (Salmo clarki) eggs was
45% in the pre-eyed stage and 30% in the
eyed stage from a stream in northcentral
Utah where heavy sedimentation from grazing
Occurred (Platts 1958). Platts reported
that the mortality of cutthroat trout eggs
was between 4.5 and 29% for a stretch in the
same stream where sedimentation and grazing
was less intense. Hansen and Alexander
(1976) demonstrated that the experimental
addition of sand to a rtichigan stream in-
creased t~e gradient and width of the
stream and reduced the depth and amount of
pool area. Such physical changes in a
stream have been shown to have pronounced
impacts on the biota of a stream (Elser
1968; Etnier 1972; Lewis 1969; Ward 1976).
Numerous references are provided under the

Figure 7. Survival to emergence of salmonid alevins in relation to the percentage nf
fine sediments in the gravel. (Data from Bjornn 1969 - A in legend; Phillips et al.
1975 - B in legend; and Hausle and Coble 1976 - C in legend)

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