Translocation of humpback chub (Gila cypha) and food-web dynamics in Grand Canyon National Park tributary streams
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Humpback chub Gila cypha, a morphologically unique large-bodied cyprinid, is adapted to exist in the Colorado River and it's major tributaries and is in decline throughout it's range. Conservation of humpback chub may depend on translocation into novel habitats. We evaluated humpback chub response, in terms of growth and body condition, apparent survival, and dispersal, following translocation of approximately 902 individuals into Shinumo Creek, a tributary stream of the Colorado River within Grand Canyon National Park. Also, we developed a stage-structured population model to simulate population abundance under three different translocation strategies (i.e. current, supplemental, and continuous). Finally, assessed trophic structure of among resident native and introduced fishes using stable isotope analysis of δ13C and δ15N. Low annual apparent survival estimates in 2009 (0.22 , 95% CI = 0.20- 0.24) and 2010 (0.20, 95% CI = 0.18 - 0.22) coupled with high initial dispersal rates limited the establishment of humpback chub into Shinumo Creek under the current translocation strategy and continuous translocations may be necessary. The fish community spanned two trophic positions (range = 1.60 to 3.75), which suggested omnivory was a prevalent feeding strategy among species. However, introduced fishes, including humpback chub, occupied higher trophic positions than resident natives (P < 0.001), but introduced δ 13C differed during all sampling occasions (P < 0.001), indicating diet partitioning may occur. Translocation, as a conservation tool for large-river fishes, may benefit from reducing high dispersal after release and introducing species into potential niche vacancies within aquatic food webs.
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