8096

• UCREFRP Catalog Number: 8096
• Author: American Fisheries Society.
• Title: Proceedings of the 19th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1984.
• USFW - Doc Type: March 7-8, 1984.
• Copyright Material: NO

C.C. = TH x B/H
m m
where: TH = the total microhabitat of the adult population of a stream.
m
B/Hm = the potential adult biomass that one unit of microhabitat can
support.
Quantification of microhabitat is essential in order for this equation to be
solved. PHABSIM is a method that will quantify microhabitat and relate it
as a function of discharge (Milhous et al. 1981). PHAB5IM considers the
stream hydrology and the trout preferences for the changing Physical condi-
tions (Bovee and Milhous 1978, Rovee 1978). The output of PHABSIM is a unit
of microhabitat called weighted usable area (W.U.A.) expressed as square feet
of microhabitat available per 1000 feet of stream. PNABSIM relies heavily
on the assumption that trout select their habitat primarily on the basis of
velocity, depth and substrate. An assumption of the carrying capacity equa-
tion is that adults can be recruited in excess of the available adult habitat.
The methods used to estimate trout population data are described in
Federal Aid Report F-51-R (Nehring and Anderson 1983). Since [a.U.A. is in
1000 ft. stream increments, the density and biomass were converted to
1000 ft. stream increments for uniformity in regression analysis.
RESULTS
In order for PHABSIM to be an effective indicator of available habitat,
there must be a strong relationship between W.U.A. and adult trout standing
stock. In this study W.U.A. biomass information has been gathered on ten
trout streams. Of these, six are streams with either a catch and release
regulation with zero bag ,limits or are closed to public access. Only two
of the six no-harvest streams have significant sucker populations, the North
Fork of the South Platte (50%) and the Middle Fork of the South Platte (30%)
(Table 1).
Since W.U.A. varies with discharge, it is necessary to identify a flow
that typifies the carrying capacity of the stream. Some of the candidate
flows could be: mean annual, median annual or mean winter flow. Also, the
maximum W.U.A. found could be used, avoiding the use of a specific discharge.
The maximum W.U.A, was used to express TH in the carrying capacity equation.
m
W.U.A,/adult trout (age 2+ and older in the fall) biomass regressions
were run to test for the relationship between W.U.A. and rainbow or brown
trout standing stock. The stronger correlations were found for brown trout
biomass versus brown trout W.U.A. (Figs. 1 and 2). The r value was not
significant for rainbow trout density and biomass versus rainbow trout [d. [1. A.
(Figs. 3 and 4).
Correlations by species were much better for brown trout than rainbow
trout. Apparently this is due to the more territorial and defensive behavior
of the brown trout. Also, brown trout are more resistant to angling pressure
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