8167

• UCREFRP Catalog Number: 8167
• Author: Nehring, R. B.
• Title: Distribution and Abundance of the Fish Fauna in the Dolores River From McPhee Reservoir Downstream to the Dove Creek Pump Plant.
• USFW Year: 1993.
• USFW - Doc Type: Montrose, Colorado.
• Copyright Material: NO

where W = weight and L = length. Condition factors can be calculated for
individual trout species for different stations and years (Lagler 1952).
Multiplying the weight by 100 standardizes the K value at 1. A "K" value of one
is average, less than one is below average, greater than one above average. K
factors provide additional information on changes in the body condition of the
trout in the Dolores River over the past 8 years. Average condition factors for
species and stations between years are presented in Table 13.

The body condition factor data indicates (with rare ex~eption) that the
average K factors for all three species of trout were higher at all three study
sites in 1987 and 1988 compared to 1989 through 1991. The only exception is the
Metaska site which registered a large increase in 1991. The K factor decreased
for all species at all sites in 1989 over 1988. This is an indication that food
and habitat conditions were becoming inadequate at that time for the trout
density and biomass in the river (see Tables 2 through 7). This was more than
6 months prior to the reduction in flow to 20 cfs in March 1990.

The K factors were either generally constant or increased slightly after
1989 through 1990 and 1991. However, this should not be construed as an
indication of an improvrnent in trout habitat conditions in 1990 and 1991.
Rather, it is the result of the very large decreases in trout density and biomass
after the 100 day period of 20 cfs from March 1 through mid-June 1990, i.e., an
easing of overcrowding in a degraded environment. The preceding statement is
validated by the fact that the 1991 K factors for the two downstream sites were
as low or lower than in 1987-1988, despite the fact trout density and biomass are
50%-80% or more below the levels of October 1988 (Tables 2-7). In reality, it
is not surprising K factors increased somewhat during 1990 and 1991 in light of
the dramatic decrease in density and biomass since October 1989.

Normal or above normal precipitation patterns returned to the Dolores River
drainage during the 1992 and 1993 water years. As a result, total discharge into
the Dolores River from McPhee Reservoir exceeded 100,000 AF during those years
for the first time since 1989 (see Tables 1 and 15). Body condition factors for
all three species (brown, rainbow, and cutthroat trout) at all three stations in
October 1992 were the best overall since sampling began in 1986. Moreover, K
factors at the Rock Stockpile Area (RM 10) in October 1992 were the best they.
have ever been for all three species of trout (Table 13). Again, these data are
another biological indication that the overall health of the river habitat and
biota has improved dramatically with increases in stream discharge and a return
to normal or above normal precipitation patterns in 1992 and 1993.

The K factor data for July 1993 (Table 14) is even more encouraging. The
only occurrence of a K factor ~ 1.0 was for rainbow trout at river mile 11, and
this was due to a sample size of 3 and a single rainbow with a K value of 0.66,
which dramatically lowered the average. Without this anomaly, all of the average
K factors for all three species at every river segment would have been;;:: 1.0, the
first such occurrence since sampling began in October 1986. (See .Table 15 in
Nehring 1992 and Table 13 in this report). This occurred in concert with the
increases in trout density and biomass in the fall of 1992 and summer of 1993.

Once again, these data strongly support the conclusion that the health of
the aquatic habitat and biota of the Dolores River below McPhee Reservoir has
significantly improved with the return of "normal" patterns of precipitation and
run-off.

Dolores River Flows and Water Temoeratures

Dolores River Flows - All of the foregoing information, including the
original reports (Nehring 1991, 1992), provide significant insights into the
linkage between the annual discharge patterns and volumes of water in the Dolores
River and the trout population from 1986 through July 1993. The question is "how
much water is necessary to maintain a quality trout fishery in this river"

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