7908

• UCREFRP Catalog Number: 7908
• Author: Valdez, R. A. and R. J. Ryel.
• Title: Life History and Ecology of the Humpback Chub ‎(
• USFW Year: 1995.
• Copyright Material: NO

Final Report

Executive Summary . 15

If humpback chub were spawning in the mainstem
prior to Glen Canyon Dam--as they presently do in
all other populations in the basin--egg deposition
likely occurred when temperatures were suitable,
probably late May to early July. One of three
explanations may account for the disparity in timing
between predam and present spawning events and
spawning activity in the LCR

a spring plume of 20 0 C to a mainstem temperature
of 10 0 C, sufficient size and temperature of some
plumes may persist under various mainstem flows to
allow fish to age and acclimate to suboptimal
temperatures. If young fish reach sufficient size to
survive the thermal transition (i.e., about 50 mID
TL), their chances of swvival probably remain low
because of the large numbers of mainstem predators
and lack of suitable habitat in the vicinity of Fence
Fault.

Under interim flows, the existing
thennal regime finally reaches the
lower range of suitable spawning
temperature for humpback chub
of 160C about 385 km (240 mi)
downstream of the dam (i.e.,
below Diamond Creek) but only
during the months of July and
August. The remainder of the
year, the temperature of the
Colorado River in this region is
too cold for significant swvivaI
of eggs or larvae of humpback
chub. Some very localized
reproduction may be occurring in
the mainstem, most likely at
tributary or spring inflows, but
the numbers of young fish
produced and surviving is
probably insignificant to the
continued existence of the species
in Grand Canyon.

Spawning by humpback chub in
the LCR is timed to occur when
temperatures of that tributary are
within the suitable range of 16 to
220C, from April through May
(Fig. 14). Kaeding and
zmmnennan(1983)reportedthat
mean female gonadosomatic
indices and ovary diameters of
humpback chub in the LCR,
mainstem, and LCR inflow were
highest between early February
and late April 1980, indicating
that most spawning probably
occurred in March, April, and
May,

1. Humpback chub in Grand Canyon did not
spawn in the mainstem prior to Glen Canyon

A. Suitable Temperature Zones for Humpback Chub
(Predam Conditions)
30 Jan Feb Mar A r Ma Jun Jul Au Se Oct Nav Dec 86
Spawning/lncubaUon LarvallPostJarvel Optimum growth
Zone (16-22. C) Development Zone juvenile/adult
25 (anomolies@ 15 & 25" C) (16-22. C) 77
~ 20 68 ~
3
e 'C
C1)
::l ii1
.. 15 59
l!! ...
c
CD a
0-
E -
~ _m TOlllp8IaIuro CIl 50 0
{!!. 10 .:!!
PIt...... _lbHy"..,.) 41
5
0 Sep Oct Nav Dee 32
Jan Feb Mar Apr May Jun Jul Aug
Time
B. Suitable Temperature Zones for Humpback Chub
(Postdam Conditions)
30 Jan Feb Mar A r Ma Jun Jut Au Se Oct Nav Dee 86
LarvaVPostlarvel Optimum growth
Development Zone juvenile/adult
25 (anomolies@ 15 & 25" C) (16-22. C) 77
U 20 68 ~
0 3
-
e "CI
C1)
::l ii1
.. 15 59
ca ...
.. c
CD Cil
0-
E -
50 0
~ 10 .:!!
LCR 41
5 Glen Canyon Dam
LCR near outflow
0 Jan Feb Mar Apr May Jun Sap Oct Nav Dec 32
Jul Aug
Time

Fig. 14. Suitable and optimal temperature range for spawning by
humpback chub compared to predam temperature of the Colorado River
at Phantom Ranch (A), and the temperature of the LCR and postdam
Colorado River at Glen Canyon Dam, LCR, and Diamond Creek (B).