9520

• UCREFRP Catalog Number: 9520
• Author: Haines, G. B., D. Irving and T. Modde.
• Title: White River Base Flow Study for Endangered Fishes, Colorado and Utah, 1995-1996.
• USFW Year: 2004.
• USFW - Doc Type: 5D,
• Copyright Material: NO

productivity during base flow period (i.e., cover 95% of the surface area), flows of 400-500 cfs

are needed; and ifflows fall below 161 cfs, riffle habitat declines rapidly. However, between 1923

and 1997 baseflow (August through October) discharge in the White River (Watson gage) has

only dropped below 200 cfs less than 5% of the time. Further, baseflow discharge on the White

River (Watson gage) has been below 150 cfs less than 1 % of the time.

Finally, we point out that under the current flow regime (the past 20 years), the Colorado

pikeminnow population has done well in the White River. Preliminary population estimates

suggest that the density in the White River are two or three times the density in the Yampa River

(Bestgen et al. 2002), and Interagency Standardized Monitoring Program suggests that Colorado

pikeminnow numbers have increased in recent years (1986-2000) and that the White River has

increased most of all (McAda 2002). Irving and Modde (1994) suggested that Taylor Draw Dam

may concentrate fish by preventing upstream movement and may have increased the prey base

downstream and artificially increased carrying capacity for large predators such as Colorado

pikeminnow. Or perhaps the relatively large base flows, at least compared to the near by

Duchesne River, may attract more fish. Unfortunately, w~ do not yet know why it attracts so

many Colorado pikeminnow.

CONCLUSIONS

1. There is a great deal of uncertainty in the precision, interpretation, and scope of this study, but

listed below are the results we found.

19