9473

• UCREFRP Catalog Number: 9473
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flows Investigations.
• USFW Year: 2001.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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INTRODUCTION
Habitat loss is one of the single greatest causes of declines in populations of native

fishes in North America (Williams et al. 1989). The need to preserve minimum stream flows

was recognized by the state of Colorado with the passage of Senate Bill 97 in 1973. Espegren

(1998) states that most in stream flow water right filings in Colorado have been for protecting

minimum flow for cold water (headwater) habitats. The most common methodologies used in.

Colorado are the R2Cross method (Nehring 1979) and Instream Flow Incremental

Methodology (IFIM) (Bovee 1982). IFIM estimates the amount of usable habitat for fish as a

function of discharge by combining habitat suitability curves with the hydraulic model. The

habitat component of the model has received much criticism because of assumptions implicit

with using suitability curves and assumptions of positive relationships between habitat

availability and fish abundance. Validation of these assumptions have been obstacles for

successfully using IFIM to model minimum flow impacts on large warm water rivers of the

west slope (Rose and Hahn 1989).
Currently there is no standardized approach to establish minimum flow needs on warm

water river sections, and the use of sophisticated models appear to be required in high profile

situations (Espegren 1998). Warm water fish assemblages appear to require a more intensive

approach to instream flow modeling compared to cold water fish communities. Warm water

river reaches tend to be lower gradient and have higher channel complexity and sediment

loads. Warm water fish populations tend to have higher species diversity. Also habitat

suitability curves derived from microhabitat observations do not adequately describe habitat

use for many warm water species. A broader community-level perspective, as opposed to an

indicator species approach, may be required to protect all habitats of a functioning warm
water stream ecosystem.

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