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

prevents sediment and silt from getting
into the streambed. Buffer strips are
recommended in logging practices in the
Pacific Ilorthwest (Lantz 1971). The amount
of riparian vegetation along a grazed reach
of a Montana stream was about one-third of
that found along a natural reach of the
same stream (Fig. 8; Marcuson 1977). Lusby
(1970) reported on a 10 year study where
a grazed watershed had a greater runoff and
erosion than in an ungrazed situation.
However, the intensity of grazing, the slope
of the land, precipitation and other factors
would influence the amount of runoff that
would result from a watershed.

It is quite clear that riparian vege-
tation has a distinct influence on salmonid
habitat in streams. Any man-made alterations
in the riparian zone of streams would there-
fore have an effect on the fish populations
regardless of whether these alterations were
caused by grazing, logging, mining, or stream
channelization. The vegetation type, soil,
and precipitation as well as the degree of
the alteration would influence the effect on
the riparian zone.

Riparian vegetation can be restored
through the selection of the proper species
to be established from cuttings or seedlings
as well as determining the proper time of
Boussu (1954) reported that trout in a the year and site selection (Skovlin et al.
small stream increased 258% in weight in rea- 1977).
ches where brush Cover was added while the in-
crease was only 22.5% in reaches without PREVENTION, MINIMIZATION, OR IMPROVB~ffiNT
the addition of cover. The total number of OF MAN-MAN ALTERATIONS
trout in his study increased 159.5% in TO AQUATIC ENVIRONMENTS
reaches with added brush cover than in rea-
ches without added cover. Chapman (1966)
speculated that food and space are import-
ant in regulating the numbers of salmonids
during the spring, summer, and early fall,
but that habitat with suitable cover was
important in salmonid density during the
winter. Wesche (1974) demonstrated a direct
relation between the amount of cover and
the weight of trout per unit of area in
two Wyoming streams with the larger mean
cover rating supporting a greater weight of
fish.

Water, as all of our natural resources,
should be managed for the maximum benefit
to the American people. Today, competition
for water resources for various uses has
caused environmental problems for natural
resource managers. Partisan views such as
environmental concerns must be evaluated
against economic needs, or preservation
considered against use (McCloskey 1973).
Often ecological systems, environmental
quality, and pUblic values were damaged or
destroyed through alterations of the aquatic

NATURAL [_

GRAZED [~

. Before Fl ood

~ After Flood

o

200
VEGETATION

400 600

(m/km of Streambank)

Figure 8. Riparian vegetation along reaches of Rock Creek, Montan~ where natural condi-
tions exist and where streambanks are affected by livestock grazing. (Data from Table 5;
Marcuson 1977)

68