Status and trends of fishes in the lower 1,200 meters of the Little Colorado River, Grand Canyon (1987-2013)

Authors: Robin J. Osterhoudt, Aaron J. Bunch

Year: 2013 (xlv)

Abstract

Hoop net monitoring of fishes in the lower 1,200 meters (m) of the Little Colorado River (LCR) in the Grand Canyon began in 1987 to assess population status and trends of the endangered humpback chub (Gila cypha) during annual spring spawning migrations. The LCR represents the primary spawning and production site in the Grand Canyon for these species. In addition to humpback chub, other native fish common in this community include flannelmouth sucker (Catostomus latipinnis), bluehead sucker (Catostomus discobolus), and speckled dace (Rhinichthys osculus). A total of 2,214 fish representing 10 species were captured during 2013 spring monitoring, with humpback chub comprising 35% of total catch. Native fishes have dominated total catch since 1987 with the exception of 1997 and 2006 when fathead minnows were the majority of total catch. Mean catch-per-unit-effort (CPUE; fish/24 hrs) for adult humpback chub (considered > 150 mm total length [TL]) dropped significantly since 1987-1988, but has shown a general increasing trend since 2006. Mean CPUE of humpback chub < 150 mm TL has increased steadily from 2010-2012. Seasonal timing of sampling, flood events, and changes in hydrology of the mainstem Colorado River may have influenced CPUEs over the last few years.