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

,1 analyses if it,met any
lditions: (1) 25 percent
m backwaters, concav-
embayments and grav-
~rcent or more of data
60 percent or more of
ation of 1 and 2 above.
:at constraint was im-
the species expe~ts fe~t
.tics of habitats Identl-
Land 2 could not pres-
l. This general habitat
to 8 of the 18 curve sets
~ three species, which
,pecies experts recom-
e of these curve sets un-
lbitats are characterized
LeIs.
on of workshop 2, the
ld participants felt that
nown about the biology
IlSed by the endangered
lshes to declare the 51
project as final. Instead,
o identify these 51 curv~s
rves," feeling that addl-
>n was being gathered
research projects.
,0 recognized that other
meters besides depth, ve-
'ate are likely to be im-
re fishes of the Colorado
.tem, for example, cover
est in the traditional sense
anks and vegetation as in
n. Rather, it may be de-
ity for concealment from
structure such as vertical
alus slopes, or instream
rocks, sand bars, and rock
~ts recognized the need to
cover as a microhabitat pa-
e fish.

, Refinement

lrkshop 2, all curve sets
(pert consensus were re-
led to the species experts
participants for final ~p-
ment. Comments were In-
a final report (Valdez et al.
as distributed to all inter-

This project resulted in 14 51 curves on
riverine habitat for humpback chub in the
Upper Colorado River Basin (Figures 2-6).
These were developed for four life stages
identified by the experts as larvae (<21
mm total length); young-of-the-year, YOY
(21-74 mm); juvenile (75-259 mm); and
adults (>260 mm). One curve set, consist-
ing of depth, velocity and substrate 51
curves, was developed for each life stage;
no substrate curve was developed for lar-
vae.

Larvae

Very little is known about recently-
hatched humpback chub. The experts be-
lieved that larvae use habitat similar to that
of larval Colorado squawfish, for which
there were substantial data (Table 1; Figure
2). They agreed that the depth and velocity
used by larvae of the two species was prob-
ably similar, but felt that humpback chub
probably use a different substrate, as in-
dicated by the rocky regions in which the
juveniles and adults occur; no substrate cri-
teria were developed for the larval stage.
Thus, the depth and velocity 51 curves ap-
plied to larval humpback chub were the
same as those developed for larval Colo-

RESULTS

rado squaw fish, but a very low confidence
rating (0) was given to this curve set be-
cause the data were originally developed
for another species. The velocity curve was
hand-drawn through the data to represent
high use of zero velocity areas by larvae.
The experts felt that these 51 curves should
only be applied to rearing and nursery areas
in the Upper Colorado River Basin, and
only at the onset of spawning and imme-
diately after. The experts did not recom-
mend use of this 51 curve set because 89
percent of the data came from backwaters
(general habitat constraint applied). The
experts recognized the need to more thor-
oughly describe the habitat used by young
humpback chub, but also acknowledged the
problem of distinguishing, in the field and
laboratory, the young of the species from
other closely-allied sympatric chubs.

Young-Of-The-Year

The small amount of field data describ-
ing the microhabitat of YOY humpback
chub allowed for only a low confidence
rating (C) for this curve set (Figure 3). The
small amount of data for this life stage is
caused by the difficulty in definitively dis-
tinguishing the humpback chub from the

TABLE 1
Depth, velocity and substrate statistics associated with 51 curves for the four life stages of
humpback chub in the Upper Colorado River Basin.

Parameter Larvae YOY
Depth (feet)
Observations 1,498 71
Mean 1.4 2.1
Variance 1.7 1.1
Minimum 0.1 0.1
Maximum 8.3 5.1
Velocity (feet per second)
Observations 1,512 67
Mean <0.1 0.2
Variance <0.1 0.1
Minimum 0.0 0.0
Maximum 0.3 1.0
Dominant substrate NO SI/SA

a NO = substrate not developed for this lifestage.
51 = silt, SA = sand, BO = boulder, BE = bedrock.

January 1990 I

[ R. A. Valdez et al.

Green

Juvenile

Colorado I
Yampa

Adult

34
2.3
1.0
0.1
4.4

44
11.1
78.3
1.0
35.1

286
10.3
65.2
2.5
40.1

74
0.6
0.3
0.0
2.6
51/SA

74
0.6
0.3
0.0
2.6
BO/BE

274
0.6
0.4
0.0
3.9
BO/SA

37 I'I~