Laserfiche WebLink
<br />4 . Executive Summary <br /> <br />80C at the dam to l60C at Diamond <br />Creek. Despite the warming, the <br />numbers of humpback chub--and <br />other warmwater species--did not <br />increase in a downstream direction, <br />Suitable habitat was largely <br />unoccupied in the lower reaches of <br />Grand Canyon, apparently because of <br />low food availability and competition <br />from warmwater non-native fishes. <br />These alien species dominated fish <br />biomass and thus energy flow <br />through the aquatic ecosystem (Fig. <br />S). <br /> <br />Final Report <br /> <br />1.8 <br /> <br />Number of Species <br /> <br />14 D Naliw <br />.. Non-Naliw <br />12 - Species Dillersily Index <br /> <br /> <br /> <br />:II 10 <br />U <br />GI <br />Q. <br />~ 8 <br />o <br />j 6 <br />E <br />:I <br />Z <br /> <br />4 <br /> <br />2 <br /> <br />o <br />GC-LF 1 <br /> <br />200 <br /> <br />180 <br /> <br />160 <br /> <br />140 <br /> <br />60 <br /> <br />40 <br /> <br />20 <br /> <br />o <br />GC-lF 1 <br /> <br />1.6 <br /> <br />1.4 )( <br />GI <br />" <br />1,2 .E <br />i:' <br />.; <br />.. <br />GI <br />> <br />o,a ~ <br />GI <br />0.61 <br />en <br /> <br />0.4 <br /> <br />0,2 <br /> <br />o <br /> <br />2 <br /> <br />4 5 6 7 <br />Geomorphic Reach <br /> <br />8 <br /> <br />11 <br /> <br />The largest aggregation of humpback <br />chub, and the major reproducing <br />population in Grand Canyon, was <br />located in the lower 14.9 kin of the <br />LCR and adjacent 13.5 kin of the <br />mainstem Colorado River (6.9 kin <br />upstream and 6.6 kin downstream of <br />the LCR inflow). This area supports l'I 120 <br />the only self-sustaining population in i 100 <br />the canyon and provides a profile of lI:: ED <br />life histoI)' requirements for the <br />species in Grand Canyon. The LCR <br />is a warm tributary sufficiently large <br />to contain ample habitat for <br />spawning, nurseries for young, and <br />maintenance of subadults and adults <br />and it provides reliable food <br />resources for fish. This food supply <br />is supplemented by high volumes of <br />terrestrial insects and allochthonous <br />material during floods. The LCR <br />provides suspended sediment to the <br />mainstem that helps maintain fish <br />habitat (i.e., sand deposits) and increases the <br />frequency and duration of turbidity. Humpback <br />chub appear to use turbidity as a cover element <br />during feeding and possibly for protection from <br />, aquatic and avian predators. <br /> <br />9 <br /> <br />10 <br /> <br />3 <br /> <br />ON:til.e <br />III N:ln-Nctil.e <br /> <br />Biomass <br /> <br />2 <br /> <br />456 7 <br />Geomorphic Reach <br /> <br />8 <br /> <br />11 <br /> <br />9 <br /> <br />10 <br /> <br />3 <br /> <br />Fig. 5. Number of species, species diversity, and biomass of native <br />and non-native fish species by geomorphic reach from Lees Ferry to <br />Diamond Creek. Data for Glen Canyon Dam to Lees Ferry (GC-LF) <br />from Arizona Game and Fish Department (1993). <br /> <br />The adjoining reach of the mainstem is equally <br />important to this population in that it provides <br />suitable sub adult and adult habitat, greater living <br />space than the LCR, and regular supplies of food <br />produced locally and transported from upstream. <br />The channel in this reach has a high frequency of <br />debris fans and associated recirculating eddies, a <br />habitat type selected by adults; 88% of adults <br /> <br />captured and 74% of radio contacts were from these <br />eddy complexes, Adults occupy low-velocity <br />vortices in these eddies where food is entrained, and <br />where adults may use a soaring behavior that <br />enables them to feed with relatively little energy <br />expenditure. <br /> <br />The present distribution of humpback chub in Grand <br />Canyon is believed to be the remnant of a more <br />dispersed historic distribution that probably <br />extended 455 kin, from the Paria River (RM 0) to <br />Grand Wash (RM 283). As in other canyon regions <br />(e.g., Desolation/Gray Canyon, Cataract Canyon, <br />Westwater Canyon, Yampa Canyon), predam <br />