Cooperative Fish and Wildlife Research Units Program: Arizona
Education, Research and Technical Assistance for Managing Our Natural Resources

On request by the Environment and Natural Resources Division of the Department of Justice, in the adjudication of water rights in the case of In re: Aravaipa Canyon Wilderness Area (W1-11-3342), in the General Adjudication of All Rights to Use Water in the Gila River System and Source, Ariz. Sup. Ct., Case Nos. W1-W4, we report hydrological requirements for native fish in Aravaipa Canyon, Arizona. The fisheries requirements were derived from existing literature, aided by the authors’ experience studying fish communities in Arizona, Nevada, California, Eastern Washington, and Mexican deserts. We compiled numerous studies from peer-reviewed and “grey” (e.g., agency reports) literature to help determine habitat requirements for each native fish species in Aravaipa Creek throughout their ontology. Further, we analyzed existing literature to document effects of altered hydrographs on long term viability of fish communities. This information shows that fishes of the Aravaipa fish community use a variety of habitats in the creek and all parts of the natural hydrograph are important to various species and life stages. Unaltered flow conditions are especially important for desert fishes that have evolved under the natural hydrographs of desert streams. All native species require habitats and stream conditions that result from floods in early spring. These floods are key trigger events that 1) signal native species the start of their growing and reproductive seasons, 2) create habitat heterogeneity that favors the appearance of food resources and nesting habitats for these species, and 3) aid in providing the main channel with nutrients derived from inundated areas, that will be used by all components of the in-stream foodwebs, including native fishes. Maintenance of low flows during the dry season are key to the reproductive success of numerous native species, as most larval fish require 1) areas with low water velocities and fine sediments, 2) areas with warm temperatures relative to the rest of the channel in which to grow, 3) areas where algal growth provides them with food resources and coverage, and 4) cover from terrestrial and aquatic predators. The periodic flooding typical of desert streams during early spring and the monsoon season is important for displacing non-native fish predators and competitors and depressing their populations. Native fishes are adapted to flash flooding characteristic of desert streams. Those nonnative fishes typically stocked into Southwestern streams have been introduced from habitats outside the desert (e.g. lakes and backwaters of large river systems) that are characteristically more stable and do not experience the degree of flash flooding present in desert systems. Modifying the natural hydrograph will result in the disappearance of the flow conditions required by native species to survive in the long term. We conclude that long term viability of valuable native Aravaipa Creek fishes requires that the natural hydrograph is maintained unaltered. A report was prepared for this work, and in 2015 Scott Bonar prepared for trial, appeared in a court deposition, and appeared as an expert witness on a trial regarding the matter in Phoenix. The trial concluded, and final written arguments were presented to the court in February, 2016. However, the court has not yet provided a decision on the case. Partners include the USFS and USDOJ.