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

(1962), Schenberger and Funk (1971), Smith
and Larimore (1963), Stroud (1971), Stroud
(1972), Warner and Porter (1960), Wene and
Wickleff (1940), and Whitney and Bailey
(1959) .

The effects of channel alterations on
fish populations in thirteen Montana streams
was documented by Peters and Alvord (1974).
Natural reaches o~ these streams contained
nearly 3.5 times the number and nearly 9
times the biomass of trout when compared
with altered reaches (Fig. ~). In addition,
the natural reaches contained over 10 times
the number and nearly 10 times the biomass
of mountain whitefish Iprosopium williamso-
nil than altered reaches. In Idaho, natur-
al stream reaches contained between 1.5 and
112 times the biomass (average B) of game
fish when compared to altered reaches (Geb-
hards 1970). Over a third (39%) of the
length of 45 stream channels surveyed in
Idaho (1,831 km or 1,138 mil has been alter-
ed and fish production was believed to re-
main 80-90% below the original levels up to
86 years after the alteration. Similar
relationships apparently hold for warmwater
fish species since Tarplee et al. (1971)
reported that fish over 6 in in length were
75% lower in number in altered reaches of
coastal plain streams in North Carolina.
The standing crop of invertebrates was 8
times greater in natural portions of the
~1issouri River (Morris et a1. 1968).
Yerke (1971) has stated the importance of
preserving the pre-existing hydraulic gradi-
ent when stream channels are relocated. By
working with a stream and not against it,
biologists and engineers can perhaps even
improve the habitat for fish when stream
channels are moved.

Dams

In the arid and semi-arid western
states, the economy depends upon storage
of water from the annual runoff for use at
another time of the year. As a result,
reservoirs have been fuilt for supplying

water for agricultural, industrial, and
municipal uses. In other parts of the
country, dams are built to supply hydro-
electric power without much consumptive use.
Additional dams are contemplated to be built
in the future. For example, a three-fold
increase in the demand water for municipal
use is anticipated to accomodate the 253%
increase in the urban population of the
Colorado River Basin (Crawford and Peterson
1974). In addition, large quantitites of
water will be needed for steam-generating
plants, development of coal through gasifi-
cation, extraction of other minerals such
as trona, and development of the oil shale
deposits in this part of the country (Cran-
dall1974). The impoundment of streams
causes changes in the sediment load, water
temperature, water quality, and streamflow
and changes of stream environments into re-
servoir environments. Often the building
of a dam is an irreversible process that
should be carefully considered in future
water development. The fishery that is
generated from the reservoir may not re-
place the stream fishery that may be lost.
Utah, for example, only contains about 60
milea of Class 1 trout streams.

Trout production in 105 Idaho reser-
voirs appeared to be limited by the follow-
ing factors: (1) paucity of spawning or
nursery areas (69.5%); (2) drawn down
(62.0%); (3) competition (51.9%); (4) temp-
erature (31.4%); (5) food supply (19.0%);
and (6) dissolved oxygen (15.2%) (Gebhards
1975). When streams are impounded, those
species that can best adapt to the newly
environmental conditions usually explode
in numbers. Often various species of
minnows and suckers will populate the reser-
voirs in western United States and are
believed to be competitors with game spe-
cies. Because of the lack of spawning
or nursery areas and the competition from
undesirable species, wild trout only com-
pose 20% of the total catch in 6.1% of 916
reservoirs in the mountain region of the

. - Natural II - Altered
878~ [ TROUT [.,. ] 344~
~
.m [ ~ WHITE. r:- ]
FISH 1065%
4 3 2 1 0 0 I 2 3 4 5
BI~4ASS (kg XIO) NUMBER OF FISH (XIOO)

Figure 4. The effect of stream channel alterations on fish populations in thirteen Mon-
tana streams. (From Peters and Alvord 1964)

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