9385

• UCREFRP Catalog Number: 9385
• Author: Hawkins, J.
• Title: Responses by Flaming Gorge Technical Integration Team to April 4, 2000, Minority Report from John Hawkins
• USFW Year: 2000.
• USFW - Doc Type: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Gorge Dam ‎(hereafter the Flow Report.
• Copyright Material: NO

recommendations made in our report are within the range of flows presented as "optimum" in the
Rakowski and Schmidt report.

Comment:
Tyus and Haines (1991) captured young Colorado pikeminnow for 9 years when mean base
flows rangedfrom about 1400 cft - 5500 cft during August through September. Regression
analysis revealed that young pikeminnow relative abundance and size increased as mean flow
decreased, although lower flows (below 1400 cft) similar to natural pre-dam conditions were not
examined. In addition, they attributed the reduced abundance and growth of young pikeminnow
in 1983 and 1984 to the abnormally high summer flows from Flaming Gorge Dam. Bestgen
(1997) used Tyus and Haines' data and additional data from ISMP collections from 1986 to
1995 to evaluate the effects of summer flows (July and August) on recruitment. He found above
average recruitment when summer discharge ranged 1800 to 2650 cft (50-75 cms; Flow Report
Page 4-32). July and August flows that Bestgen evaluated often included part of the descending
limb of the hydrograph and it is unclear how the results of this analysis relate to lower base
flows that occur later in summer, autumn, and winter.

Response: These data indicate that the base flows we recommend in average and moderately wet
years are not too high as is maintained in the minority report. Direct measures of recruitment
such as provided by these studies are perhaps better indicators of suitability than are relationships
between backwater area and flow.

Comment:
The above studies are far too mixed in their results to clearly support the Flow Report's
recommendation of range of mean base flow magnitudesfrom 1500 to 2400 cft (43 - 67 cms)
during average years, the 900 to 3000 cft (25- 85 cms) spread from dry to wet years, or the
specific apportionment of that range to match the width of the hydrologic categories. The results
from these studies may actually point to base flow magnitudes that more closely resemble the
natural hydrograph. The Flow Report's base flow recommendations provide too great a spread
in mean magnitudes especially during average water years (Excel Figure 2). The maximum
recommended flow in average years (2400 cft) is 185% or almost double the flow that occurred
in pre-dam conditions (1296 cft). Average years, with their more regular occurrence, are when
base flow magnitudes need to be the most optimum for the fish. Except during wet years, the
lower range of the recommended base flow magnitudes provide conditions that more closely
resemble pre-dam natural conditions.

Response: Many of the reports that we examined in developing the report provided mixed
results. This is really to be expected given the complex nature of the river system and the life
cycle of the species. To overcome this we used a lines-of-evidence approach to develop flow
recommendations. We believe that the base flow recommendations included in the report are
supported by the existing information. That is not to say that there is not some associated
uncertainty. Contrary to the statement in the minority report, we do not believe that the studies
may actually point to base flow magnitudes that more closely resemble the natural hydro graph;
none of the studies indicated that this is the case. The statement that the maximum

4