Population Size and Structure of Humpback Chub, Gila Cypha, in Black Rocks, Colorado River, Colorado, 2003-2004

摘要

The Colorado River in Black Rocks was sampled in 2003 and 2004 to estimate size and structure of the humpback chub population. Sampling began in mid September and continued through October. Four sampling trips (4 days each: conducted in alternating weeks) were conducted in both years. Sampling was primarily done with multi-filament trammel nets (1-in inner mesh), although Gila captures were supplemented with electrofishing. Trammel nets were set in shoreline eddies in early morning and late afternoon. Nets were run at 1 to 2 hr intervals with 2 hrs set as a maximum interval. All Gila were removed from the nets, placed in fresh water and transported to a central processing point. In addition, the entire Black Rocks reach was sampled with electrofishing during three of four trips each year. All Gila were identified as either humpback chub or roundtail chub, checked for a PIT tag and measured (total length, 1 mm). Untagged humpback chub were equipped with a PIT tag before release; roundtail chub were not tagged. After handling, all Gila were placed in an oxygenated tank containing a mixture of salt and Stress Coat for about 1 hr as a skin treatment and to assess general health. All chubs were released at the common location and appeared healthy when released.