7926

• UCREFRP Catalog Number: 7926
• Author: Annear, T. C. and A. L. Conder.
• Title: Relative Bias of Several Fisheries Instream Flow Methods.
• USFW Year: n.d.
• USFW - Doc Type: Cheyenne, Wyoming.
• Copyright Material: NO

pre ferred flow.

Many inves tigators have developed MF-type recommendations

each life stage, one rate of flow provides the maximum WUA which we termed
t!~~

r~ference to these preferred flows in one of several ways, despite the fact th~t

the models were not originally intended to be used for identifying single-value

MF estimates.

Two approaches to defining MF estimates were used for both

PHABSIM models in this study.

Bovee (1982) described an optimization technique for minimizing negative

impacts. This approach involves arraying WUA data for pertinent life stages of

the target species in an optimization matrix'(Table 4). The flow recommendation

is obtained by recording the minimum value in each column and then selecting the

highest of these minimum values.

Other users of PHABSIM models have occasionally identified a "significant

impact" (or minimum acceptable flow) as a 10% reduction in WUA from the recom-

mended flow.

We used this approach in combination wi th the above method to

define an MF for both IFG-2 and IFG-4 models as a (lower) flow which resulted in

a 10% reduc tion in WUA from the recommendation arrived at in the optimization

matrix. Only adult, juvenile, and fry' life stages were.used as we ~ssumed they

would be the only ones in: the stream during late summer. 'We assumed that each

life stage was of equal importance.

A second approach for ob taining MF es timates from the PHABSIM models was

developed by identifying I a flow that resulted in a statisticaly significant

,

reduction in the averag~ WUA from the preferred flow for combined adult,
i

juvenile, and fry life s,tages of the dominant trout species in each stream.

This

flow was

. I
found by using a techn1que similar to that described for wetted

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