Long-Term Monitoring of an Endangered Desert Fish and Factors Influencing Population Dynamics

Abstract The lower perennial corridor of the Little Colorado River in Grand Canyon, Arizona, is numerically dominated by endemic desert fishes and therefore significant for conservation of these species. From 2000 to 2012, the U.S. Fish and Wildlife Service conducted monitoring of native fishes in the Little Colorado River near its confluence with the Colorado River. The primary focus of these efforts was to estimate the spring and fall abundance of native fishes, especially the federally endangered humpback chub Gila cypha. Because humpback chub in Grand Canyon are influenced by operations of Glen Canyon Dam, our efforts provide managers of the Glen Canyon Dam Adaptive Management Program with abundance estimates and trends of humpback chub in the Little Colorado River, the most important tributary in Grand Canyon for spawning and production of this species. From 2001 to 2006, the spring abundance estimates of humpback chub ≥150 and ≥200 mm remained relatively low (≤3,419 and ≤2,002 fish, respectively), t...