8019

• UCREFRP Catalog Number: 8019
• Author: Montana Department of Fish, W., and Parks.
• Title: Kootenai River Fisheries Investigations, Final Completion Report.
• USFW Year: 1983.
• USFW - Doc Type: \
• Copyright Material: NO

an overall increase in the density of invertebrates. The number of stoneflies
and caddisflies has decreased dramatically at this site since impoundment,
while the densities of mayflies and dipterans appear to have increased
substantially. Species collected in pre-impoundment studies, but not
in this study, are listed in Table 7.

Biomass measurements are not directly comparable since we used volumetric
analyses in order to preserve the specimens. The percent composition
can be used for comparative purposes. The trend is the same as the density
trend; a very marked decrease in stonef1ies and caddisflies 2nd a six-
fold increase in mayflies and 2.5-fo1d increase in dipterdns.

Comparisons of 1970 and 1980 Data on the Fisher River

Comparison of our data with a 1970 study of the Fisher River (May
1972) indicates that there have been similar changes in the relative
percent composition by density and biomass of insect orders in the Fisher
River in the last 10 years. A comparison of the percent composition
of annual means in density and biomass at two stations from the 1970
study and from our study site on the Fisher River (Table 8) indicates
a decrease in the importance of stoneflies and caddisflies and an increase
in dipterans. This is likely due to long-term changes associated with
channelization of the Fisher River at the time Libby Dam was constructed,
and other changes associated with logging or agriculture in the Fisher
River drainage.

Comparisons of Present Populations of Invertebrates in Kootenai and
Fisher Rivers

A notable feature of the benthos in the Kootenai River was the paucity
of stonef1ies which generally comprise less than 0.1 percent of the density
of benthic invertebrates (Table 4). There were no species of stonefly
common in the Kootenai River as opposed to about 14 species which were
common in the Fisher River. Seventeen species of stonef1ies were collected
in the Kootenai River compared to 23 species in the Fisher River and
42 species in the partially regulated Flathead River. Their absence
may be related to changes in the substrate, to higher fall and winter
water temperatures, or to availability of oxygen (see later section of
possible problems with low dissolved oxygen).

Shifts in the species composition of mayflies were found with increasin9
distance downstream from the dam and between regulated and control sites
(Tables 9 and 10). Two species of mayflies (Ephem~etla in~~ and
Ba~ tnieaudat~) predominate near the dam. They are species with
several generations per year, and apparently are prolific enough to with-
stand population losses due to frequent stranding and downstream drift
caused by flow fluctuations. The heptageniid mayflies (Epeo~~, Rhit~ogena)
were found in very low numbers near the dam, but increased at the downstream
stations. They were far more abundant in the Fisher River than in the
Kootenai River (Table 10). Rapid water fluctuations and increased algal
growths probably impair the efficiency with which they can maintain their

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