7399

• UCREFRP Catalog Number: 7399
• Author: Valdez, R. A., P. B. Holden and T. B. Hardy
• Title: Habitat Suitability Index Curves for Humpback Chub of the Upper Colorado River Basin
• USFW Year: 1990
• USFW - Doc Type: Rivers
• Copyright Material: YES

HUMPBACK CHUB ADU (260+mm)
, (1,9.0.40.1.1.0.20.0) 20
a.. n . 286
16
z ~
0 a..
~ z
w
... 10 ;:)
::::i 0
w
j: 0.4 rr
;:) ...
6
0.2
0
10 20 30 40
DEPTH (leet)
, (1,0.27,3.9,1.0,60.0) 40
a.. n . 274
Z 30
0 0.8 ~
~ z
... w
::::i 20 ;:)
j: 0.4 0
;:) w
rr
...
0.2 10
0 0
0.0 1.0 2.0 3.0 4.0
VELOCITY (lpa)
o.a
z
0 o.a
~
...
::::i 0.4
j:
;:)
0.2
0

CL SI SA GR RU BO BE OT
SUBSTRATE

FIGURE 6. Raw data and interim suitability in-
dex curves for depth, velocity, and substrate for adult
humpback chub (n = number of observations or in-
dividual fish).

by the adults was similar although discon-
tinuous. They also decided to pool the data
for all gears, although there was concern

that electrofishing data may reflect a fish
forced to move from preferred microhab-
itat to the capture site. Of equal concern
was the belief that passive gears such as
trammel and gill nets may intercept fish
moving between desired microhabitats.
Although radiotelemetry data were pre-
ferred, there were insufficient numbers of
observations for 51 curve development, and
the conventional gear data were also used.
Because the microhabitat data were se-
cured from different gear types, the curve
set received a confidence rating of B. The
average depth used by adults was 10.3 feet
with a maximum of 40.1 feet, and average
velocity was 0.6 fps with a range of 0 to
3.9 fps (Table 1; Figure 6). The depth curve
was dramatically modified by the experts
to reflect adult use of all water depths
greater than about 7.2 feet. The experts felt
that the smaller sample size from greater
depths reflected gear inefficiency and not
reduced use by the fish. Although the
species is known to inhabit regions with
depths of 40 feet or greater, the experts felt
that electrofishing was consistently effec-
tive to only about 10 feet depth, while gill
and trammel nets were difficult to set ef-
fectively at the greater depths, and radio-
telemetry transmission was reliable from
only about 12 feet of depth. Most of the
data from the greater water depths resulted
from netting and angling captures. The
adults were found over boulders and bed-
rock with intervening deposits of silt and
sand. The curve set for adults was applied
to the Upper Colorado River Basin from
March to November and was not restricted
by the general habitat constraint. No
spawning curve was developed for this
species because the experts felt that not
enough was known about its spawning ac-
tivities.

DISCUSSION

The 51 curves developed from this proj-
ect were based on the best field data and
information available for the humpback
chub in the Upper Colorado River Basin.
These curves were developed by species
experts through consensus and peer re-
view, and reflect the microhabitat data col-
lected in the upper basin from 1964 through
1986. Readers should be cautioned that the
species experts classified these as "interim

I~ 40

51 curves" and presently recommend ap-
plication of the adult curve set, recogniz-
ing that much information still needs to
be gathered on the rare fishes of the upper
basin. The experts recommended refining
these curves as more data become avail-
able.
The process by which these 51 curves
were developed is recommended in deal-
ing with large volumes of pre-existing mi-

Rivers · Volume 1, Number 1

J an uary 1990

crohabitat informat
many literatu~e ~Ot
concept of asslmlla
uation by a panel I
sound in that it aIle
by the experts with~
amounts of time to 1
the data. The idea I
which experts and I
equal opportunity tl
worked well. HOWl
participants felt tl
should have been h,
use of the 51 curves i
and generation of
This would have ~
voice their judgml
soundness of the st
lationships.

Armour, C. L., R.
cedures (HE!
sources. Was}
Bovee, K. D. 198:
methodology
Wildlife Serv
-. 1986. Dl
stream flow i:
ington, DC: l
Bovee, K. D., ani
probability-o
Fish and WH
Crance, J. H. 191
Inland stocks
82110.85).
-. 1987. H
nique. North
Glova, G. J. 1982
16-27 in R. .I-
Zealand Min
47).
Haan, C. T. 1977
Holden, P. B. 19
Green River,
Larimore, R. W.,
fishes. F isheri
Linstone, A. A., ,
Wesley.
Milhous, R. T. 1
Levine, editc
Society for C
Milhous, R. T., [
simulation sJ
Orth, D. J., and (
ommending
413-445.

I R. A. Valdez et c