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

Table 14. Brown, rainbow, and cutthroat trout body condition factors (K) for the
Dolores River by stream segment during July 1993.

River Mile Brown Trout Rainbow Trout Cutthroat Trout
1 1.0865 1.1121 1.0993
2 1.1636 1. 0894 1. 0093,
3 1.1508 1.0901 1. 2200
4 1.1080 1. 0537 ------
5 1. 2289 ------ 1. 0469
6 1.1362 1.0500 1.0403
7 1.1555 1. 0935 1.0772
8 1.1922 1. 2028 ------
9 1.2782 1.1716 1.1531
10 1.1978 1. 2151 ------
11 1.3000 0.9388 ------
12 1.1412 1.0400 ------

The data in Table 15 summarizes the history (1984-1993) of water storage
in and downstream releases from McPhee Reservoir compared to the response of the
downstream trout population. The data for 1988 through 1991 provide insight into
what are the minimal water requirements of the aquatic ecosystem in this stream.
It is noteworthy that the trout population was still increasing in density and
biomass in 1988 and 1989 when downstream water deliveries still exceeded 100,000
AF/water year. A severe decline in the trout population took place between
October 1989 and 1990 when the annual downstream releases dropped to 37,700 AF.
Only 14,300 AF were delivered to the river between March 1 and September 30,
1990. Included in this 7-month period was the 100-day period (March 6 - June 14)
when the flow was 20 cfs. Moreover, the trout population continued in a state
of decline through October 1991, despite the increase in annual discharge to
50,800 AF for the 1991 water year. Only when the total annual releases increased
to more than 100,000 for the 1992 and 1993 water years did the trout population
density and biomass parameters once again increase (Table 15).

Interrelationships between Water Temperature and Discharge - The data in
Table 16 summarize the interraction(s) between water temperature and discharge
for the Dolores River below McPhee Dam. In 1990, when stream discharge ranged
from 20 to 70 cfs between April and October, there were many days when water
temperatures at the Bradfield Bridge reached daytime maximums of 70 - 74 F, and
daytime mean temperatures were ~. 66 F. The summer of 1991 was a much cooler
summer than 1990. Correspondingly, the numbers of days with water temperatures
stressful to trout decreased. In 1992, Dolores River stream flows increased with
the return of normal precipitation patterns and daytime maximum water
temperatures rarely exceeded 70 F at Bradfield Bridge, while the mean temperature
reached 66 F only once.

Air and water temperature and flow records for April 1 through August 4,
1993 (provided by the USBOR-DPO staff) indicate that mean daily water
temperatures at the Bradfield Bridge never reached 63 F during that period.
Similarly, daytime maximum water temperatures never reached 69 F. The stream
discharge in the Dolores River during this time period was rarely less than 100
cfs and probably not less than 94 cfs for a 24 hour average discharge.

It is important to note that the discharge and temperature records indicate
that maximum water temperatures at McPhee Dam ranged between 50 and 61 F during

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