- 1.) Determine the fish communities in Shinumo Creek
- 2.) Determine outmigration of HBC translocated in these tributaries
- 3.) Determine if translocated humpback chub movement out of Shinumo Creek is related to hydrology, water temperature, season, and year
- 4.) Estimate survival and growth of HBC remaining in the tributaries
- 5.) Identify if any niche shifts occurs in the food web after non native fish removals.
We examined humpback chub response, in terms of growth and body condition, apparent survival, and dispersal, following translocation of approximately 300 individuals annually in June 2009, 2010, and 2011 into Shinumo Creek, a tributary stream of the Colorado River within Grand Canyon National Park. Therefore, we also evaluated trophic structure of the Shinumo Creek fish community to determine potential diet overlap among native and non-native fishes. Growth of translocated humpback chub in Shinumo Creek was consistent among year classes and sampling periods with no evidence low condition indicating humpback chub were effectively exploiting food resources. About 42% of translocated humpback chub left Shinumo Creek with approximately 33% of humpback chub leaving within the first few days after translocation indicating dispersal immediately following translocation was high. Also, larger individuals at translocation had a higher probability of dispersal. Stable isotope analysis indicated omnivory was prevalent throughout the fish community which spanned two trophic positions (range = 1.60 to 3.75). However, introduced fishes (i.e. rainbow trout and humpback chub) occupied higher trophic positions than resident natives. Stomach content analysis revealed macroinvertebrates dominated rainbow trout diets with relatively few fish in stomachs (i.e. piscivory rate = 4.2%). Successful establishment of humpback chub populations into Colorado River tributaries may depend on alternative release strategies (e.g. soft releases) which may decrease initial dispersal and continued removal of rainbow trout freeing potential diet sources including both aquatic and terrestrial invertebrates and fish. Coupling food web analysis with more traditional assessments of translocation studies (i.e. survival analysis, growth, and dispersal) can reveal potential niche vacancies or overlap with non-natives in receiving systems that may influence establishment and increase success of translocation as a conservation tool for large-river fishes.