WSP05885

• File Number: 8240.200.38.A
• Description: Coordinated Reservoir Operations
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1998
• Author: CWCB
• Title: 1998 Coordinated Reservoir Operations Bypasses for Endangered Fish - Annual Summary of Operations for 1998 to Benefit the Endangered Fishes of the Upper Colorado River Basin
• Water Supply Pro - Doc Type: Publication

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Peter Evans, Director

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Fish and Wildlife Service biologists report that the combination of a high peak (29,900 cfs in the 15-
Mile Reach) in 1995, which stayed above 20,000 cfs until mid July, followed by a moderately high
peak in 1996 resulted in very successful Colorado pikeminnow reproduction in 1996. This same
pattern also occurred in the mid-1980's when two moderately high years (1985 and 1986) fell on the
heels of 2 flood years (1983 and 1984) resulting in high reproduction and later strong recruitment to
the adult population (early 1990's). While it will take several years to confirm, it is anticipated that
1996 will also become a strong year class. There has been a steady increase in adult Colorado
pikeminnow in the Colorado River between 1991 and 1998, particularly in the upper reach, from
Westwater Canyon to Palisade (see Figure. 2), including the 15-Mile Reach. This has primarily
resulted from recruitment of the strong year classes of the mid-1980's mentioned above, but also
from some year classes hatched in the early 1990's_

As the number of adults increases in the 15-Mile Reach, the importance of meeting the flow
recommendations there becomes greater, i.e., when numbers are low, reproduction primarily limits
the ability of the population to increase; when numbers become high, the amount of suitable habitat
becomes limiting (carrying capacity may be reached). The flow recommendations were designed to
maximize the amount of optimum habitat for adults and thereby increase the carrying capacity there.
The flow augmentation from Ruedi and Wolford Mountain Reservoir was critical in providing
adequate habitat for the Colorado pikeminnow that inhabit the 15-Mile Reach and in making room
for additional adults this year. Flows in late summer 1998 would have dropped off dramatically in
mid-September to about 660 cfs without the augmentation of flows that we were able to provide.

Responses of the fish community to flow augmentation are difficult if not impossible to quantify on a
short-term basis. As described above, the objective is to provide room for a growing population of
Colorado pikeminnow, which we appear to now have, and in the future, for razorback suckers if
augmentation efforts prove successful. Annual reports for four studies dealing with the 15-Mile
Reach in 1998, including the population abundance survey described above, are included for your
revIew.

After preparing these reports for the past several years it has become apparent that the requirements
for reporting need to be revised to include a period of time necessary to detect a biological response.
The Service believes reporting back to the CWCB and Reclamation every 5 years would provide a
sufficient time period to identify changes in the 15-Mile Reach and in the fish populations. Thus, we
recommend that the next report be prepared in 2003. This would capture a time period when more
effort has gone into meeting Service flow recommendations for the 15-Mile Reach starting in 1998
and would include the benefits of flow augmentation provide by the Programmatic Biological
Opinion for the Reach. This time period would also coincide well with the biannual checkpoints
identified in the Opinion.

The Service continues to believe that flow augmentation from these reservoirs has been an important
step in improving habitat conditions in not only the l5-Mile Reach but also the reaches downstream.

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