Clearwater tributaries and invasive fishes: Summary of findings and conclusions by Rene Henery

Henery (2005) hypothesizes that clear-water tributaries may be susceptible to colonization by trout or other invasive species displaced downstream by the November 2004 flood or by the high ramping rates of the trout and tamarisk “perturbation” flows. Henery (2005) goes on to suggest that increased presence of invasive fishes in the productive clear-water tributaries of the Colorado River could pose a threat to native fishes who depend on the tributaries for crucial spawning and rearing habitat. During our trip, hook-and-line sampling and snorkeling observation at Tapeats Creek (Campos et al. 2005, this volume), Bright Angel Creek (Campos et al.2005, this volume), Havasu Creek (Campos et al. 2005, this volume), and Kanab Creek (Campos and Epstein 2005, this volume) supported these hypotheses, finding invasive fishes to be present at all locations. Invasive fishes were not, found to be present in Shinumo Creek or Elves Chasm (Campos et al 2005, this volume). However, high flows in Shinumo Creek paired with rock walls suggest that the absence of fish may have been due to scour and lack of velocity refugia. The absence of Fish in Elves Chasm remains somewhat of a mystery. However, given strong anecdotal evidence of trout in the lower Elves chasm pool the previous summer, and the abundant invertebrate life (Purdy 2005, this volume), recolonization at Elves Chasm seems likely. Though invasive fish presence in tributaries was widespread, their impact on tributary ecology remains unclear. However, the presence of carp in Havasu Creek during flannelmouth sucker spawning (Campos et al. 2005, this Volume), the presence of trout in Kanab Creek during juvenile sucker rearing (Campos and Epstein 2005, thios volume), and the observed lack of any fish in Bright Angel Creek other than invasive rainbow trout (Campos et al. 2005, this volume) all point to the potential for increased competition and predation pressures for native fishes in tributaries. At the same time, tributaries offer native fishes excellent habitat, warmer more lentic waters, a productive invertebrate foodsource, and a general refuge from the high level of disturbance daily flow oscillations have generated in the Colorado River mainstem. Given this, the need to conserve the productive remnant ecosystems the tributaries represent seems clear. Perhaps through increased research, intensive monitoring and focused management efforts such as invasive fish removal, tributary colonization by invasive fishes can be curtailed before it exacerbates the decline of the Grand Canyon’s native fishes.

REFERENCES Campos, B. Epstein, D. 2005. “Kanab Creek.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html.

Campos, B. Epstein, D., Henery, R. 2005. “Bright Angel Creek” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html.

Campos, B., Epstein, D., Purdy, S. 2005. “Tapeats Creek.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html.

Campos, B. Epstein, D., Henery, R., Purdy, S. and Wilson, D. 2005. “Havasu Creek.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html

Campos, B. Epstein, D., Henery, R., Purdy, S. and Wilson, D. 2005. “Shinumo Creek and Elves Chasm: Spring Runoff, Oscillating Flows and Fish Habitat.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html

Purdy, S. 2005. “Invertebrate abundance and diversity in Elves Chasm.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html. . Henery, R.H. 2005. “Clear-water tributaries of the Colorado River in the Grand Canyon, Arizona: stream ecology and the potential impacts of managed flow.” In. J. Mount, P. Moyle and C. Hammersmark (eds.). Ecogeomorphology of the Grand Canyon and its Tributary Streams. Davis, CA. http://watershed.ucdavis.edu/grand_canyon/history.html.