7945

• UCREFRP Catalog Number: 7945
• Author: Bovee, K. D. and T. Cochnauer.
• Title: Development And Evaluation Of Weighted Criteria Probability-Of-Use Curves For Instream Flow Assessments
• USFW Year: 1977.
• USFW - Doc Type: Fisheries, Instream Flow Information Paper No. 3.
• Copyright Material: NO

Most present-day methods of assessing flow address only one, or
occasionally two, of the above species classes. Frequently, a par-
ticular life history stage, or a certain time period is singled out as
being critical for the continued well-being of a fish population. A
flow recommendation for a relatively long time period may be based on an
a riori assumption about critical conditions for a small and rather
definite time period. For example, spawning success is commonly con-
sidered a critical factor in the maintenance of a fish population, but
habitat evaluations for fry and juvenile-fish are almost universally
neglected.
It must be recognized that regardless of the methods or the bio-
logical criteria employed, there are always assumptions of which the
biologist must be aware. Some assumptions are expressed, while others
are implied, and each exerts an influence on the conduct of the study
and its eventual defense. Value judgements which should be made during
any streamflow assessment involves these assumptions; i.e., whether or
not the assumptions appear logical and are acceptable for the case at
hand, and the ability of the field practitioner to logically defend
the assumptions.
The types of criteria concerned herein are termed elective criter-
ia. The expressed assumption is that the distribution and abundance
of any species is not primarily influenced by any single parameter of
streamflow, but related by varying degrees to all hydraulic parameters.
It is further assumed that a species will-elect to leave an area when
streamflow conditions become unfavorable, and will generally not vol-
untarily remain in the area until conditions become lethal.
Probability curves are based on the assumption that individuals of
a species will tend to select the most favorable conditions in a stream,
but will also use less favorable conditions within a defined range,
with the probability of use decreasing as conditions approach the end
points of the total range (Figure 1). These curves are integral to the
use of the IFG Incremental Instream Flow Method, which will be de-
scribed under a separate title, available from the Cooperative In-
stream Flow Service Group. Instream Flow Information Paper 8 (in
preparation).
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