|
<br />.
<br />
<br />~
<br />I
<br />
<br />{~~
<br />
<br />,--:
<br />
<br />:~
<br />
<br />HUMPBACK CHUB SPECIES ACCOUNT
<br />
<br />~
<br /><,0-
<br />'"
<br />
<br />j
<br />
<br />>
<br />~,
<br />
<br />Distribution and Abundance
<br />
<br />The humphack chub (HBC; Cyprinidae: Gila~) is an endemic fish species in
<br />the Colorado River hasin. The HBCwas taxonomically descrihed by Miller
<br />(1946), and was listed as an endangered species in 1968. Stream alteration,
<br />including flow modification, diversion for irrigation, channelization, and
<br />introduction of non-native fish species, have he en suggested as responsible
<br />for declining populations of HBC throughout the Colorado River hasin (Valdez
<br />1995). Five HBC populations remain in canyon-bound reaches of the upper
<br />Colorado River basin: Black Rocks (upper Colorado River), Westwater Canyon
<br />(upper Colorado River), Cataract Canyon, Desolation/Gray canyons (Green River)
<br />and in the Yampa River.
<br />
<br />~ ...
<br />
<br />','
<br />
<br />f
<br />"
<br />~(~;
<br />
<br />;{'.
<br />:"';'
<br />~
<br />('
<br />
<br />?Ji,':
<br />;~:,
<br />
<br />The Grand Canyon population is the only successfully reproducing HBC
<br />population in the lower Colorado River basin (Kaeding and Zimmerman 1983;
<br />Valdez 1995). Valdez (1995) identified nine distinct aggregations in the
<br />mainstream Colorado River downstream from Glen Canyon Dam, including: 30-Mile,
<br />Little Colorado River inflows, Lava/Chuar to Hance Rapids, Bright Angel Creek
<br />mouth, Shinumo Creek mouth, Stephens Aisle, Middle Granite Gorge, Havasu Creek
<br />mouth and Pumpkin Spring. From 3000 to 3500 adult HBC occupy the mainstream
<br />Colorado River, and these are largely concentrated within i 4.2 miles of the
<br />mouth of the Little Colorado River (Mile 61; Valdez 1995), the largest sub-
<br />population.
<br />Habitat use by HBC varied between age classes and by time of day. YOW1g HBC
<br />in the mainstream commonly use return current channels and other backwater
<br />habitats (Maddux et al., 1987); however, HBC use of backwater habitats in
<br />Grand Canyon has been compromised by fluctuating flows and cold-stenothermic
<br />releases which reduce warming and create unstable conditions. In addition,
<br />backwater habitat area has been reduced and backwaters have aggraded through
<br />siltation under Interim Operations in Grand Canyon (McGuinn-Robbins 1995).
<br />
<br />~,~.:.
<br />;:t:
<br />co;::;
<br />~
<br />;"',~;
<br />(>Ji
<br />~
<br />f>i'
<br />f:~
<br />
<br />,:.0;
<br />~~'
<br />;i
<br />~i',
<br />:'';'
<br />~::
<br />
<br />Subadult HBC in the Colorado River mainstream often use irregular shorelines
<br />as habitat, and adult HBC often occur in or near eddies (Valdez 1995). Adult
<br />radio-tagged HBC demonstrated a consistent pattern of greater near-surface
<br />activity during the spawning season and at night, and day-night differences
<br />decreased during turbid flows (Valdez 1995) .
<br />
<br />~:',"!.
<br />r-^:;
<br />k}
<br />(.;'"
<br />f:';"
<br />f.\.
<br />f':'
<br />,,,,:'
<br />~. "
<br />ftj
<br />l~p;
<br />t;1
<br />('
<br />di
<br />~','"
<br />,~ ,
<br />.y
<br />~~~
<br />t!5#,
<br />I
<br />~
<br />~
<br />r~~;
<br />~.
<br />ti;~
<br />f~~
<br />
<br />Life Requisites
<br />
<br />The life 'history and ecology of HBC in Grand Canyon has been intensively
<br />studied (Suttkus and Clemmer 1977, Kaeding and Zimmerman 1983, Carothers and
<br />Minckley 1981, Maddux et al., 1987, Gorman 1994, Valdez 1995). A key issue is
<br />lack of recruitment to the adult population as reflected by low survivorship
<br />of young fish (Valdez, 1995). Individual adult HBC demonstrate high microsite
<br />fidelity (Valdez 1995), hut young HBC may drift for relatively long distances
<br />(Tuegel 1995) . Mainstream Colorado River HBC in Grand Canyon spawn primarily
<br />in the lower nine miles of the Little Colorado River from March through May.
<br />
<br />',:
<br />.
<br />.
<br />
<br />8
<br />
|