7860

• UCREFRP Catalog Number: 7860
• Author: Douglas, M. E. and P. C. Marsh
• Title: Population Estimates/Population Movements of
• USFW Year: 1996
• Copyright Material: YES

16

COPEIA, 1996, NO.1

DOUGLAS A

N~~r::- -
I DESOlAnON CN ~

( CATARACT ) \
\, CANYON ~

I VmGIM R.
I

A ARIZONA

Fig. 2. (A) Map of the
of the lower Little Color;
Coconino County, AZ) tc
Park, Coconino County,

cussed in the context 0
in 1963 to impound 1
ern extent of Grand (

Fig. I. (Top) An adult female humpback chub (Gila c)'pha) captured by trammel net at confluence of Little
Colorado and mainstream Colorado rivers (Grand Canyon National Park, Coconino County, AZ). (Bottom)
Adult male humpback chub (Gila r)'pha) captured by hoop net in Little Colorado River near Salt Trail Camp,
12.8 km above confluence (Navajo Indian Reservation, Coconino County, AZ).

ument, respectively); the Colorado River in Utah
above Lake Powell (Canyonlands National Park);
and the Colorado River above its junction with
the Green River [between confluences of the
Dolores (in eastern Utah) and Gunnison rivers
(in western Colorado; Fig. 2A)]. Gila c)'pha was
also within other canyon-bound reaches of the
Colorado River, as documented from archae-
ological remains (Miller, 1955; Miller and Smith,
1984; Sigler and Miller, 1963).
Gila c)'pha was the last fish to be described
from the mainstem Colorado River (Miller,
1946), the type specimen caught in 1932 by
angling within Grand Canyon National Park
[(GCNP) at Bright Angel Creek, now 141.3 riv-
er kilometers (RKM) below Glen Canyon Dam
(Carothers and Brown, 1991:95)]. The largest
population of G. c)pha is in the Marble Canyon
section of GCNP, at the junction of the Little
Colorado (LCR) and mainstem Colorado rivers,
99 RKM below Glen Canyon dam (Fig. 2B).

MATERIALS

Although the life history of G. c)pha is enigmatic
(discussed in Douglas, 1993), the Grand Canyon
population is least known of al!. For example,
chub inhabiting the Colorado River at the LCR
confluence were not even recognized as a re-
producing population until 1975 (R. R. Miller,
field notes, Special Col!., Hayden Library, Ar-
izona State University, unpub!.). Even then their
numbers were not considered substantial; the
largest population of G. c)'pha at that time was
believed to inhabit the Colorado River near
Grand Junction (based upon 32 specimens cap-
tured in 1974;]. E.Johnson, Bur. Land Manag.
Tech. Note 280, 1976, unpuh!.).
This study was undertaken to estimate num-
bers of adult G. c)'pha within the LCR, define
the nature and extent of their movements with-
in that river (where reproduction occurs an-
nually), and test the hypothesis that both local
movements and residency are restricted to the
reproductive period. Habitat use is then dis-

Stud)' river.- The LC
eastern and northern,
Mexico and flows 41 ~
confluence with the
Coconino County, AZ
the LCR is seasonally
390 km, a result of IT
and water impoundm
of the century (Miller.
the lower 21 km is pc
groundwater springs
of the Black Mesa no
AZ. The largest of th
LCR RKM 21; Fig. 21
6.6 mS /sec Oohnson ;
The LCR at base fI
exceeds 5000 umho
forming. Carbonate I
and in the water colu
river a distinct turqw
position (a function 0
tosynthetic activity of
produces an intrical