Closed Population Estimates of Humpback Chub, Gila cypha, in the Little Colorado River, Grand Canyon, AZ

Authors: David R. Van Haverbeke

Year: 2010 (xlii)

Abstract

Since 2000, a series of two-pass, closed mark-recapture efforts have been conducted in the spring and in the fall in the Little Colorado River (LCR) to track the abundance of humpback chub (HBC). Preliminary results indicate that during spring 2010 the estimated abundance of HBC >=150 mm in the lower 13.57 km of the LCR was 8,099 (SE = 522). Of these fish, it was estimated that 6,311 (SE = 480) were >=200 mm. These numbers indicate a continuing increase in the abundance of the spring LCR HBC spawning population. Fall results for 2010 are not yet available, however, during fall of 2009, the estimated abundance of HBC >=150 mm in the lower 13.57 km of the LCR was 3,982 (SE = 480). Of these fish, it was estimated that 1,572 (182) were >=200 mm. These numbers also suggest an increasing trend in the LCR population of HBC. Between 2003 and 2009, 1,643 HBC (50-131 mm TL) were translocated from the lower reaches of the LCR to above a travertine structure known as Chute Falls. Since 2006, mark-recapture efforts have been conducted in the reaches of the LCR above 13.57 km, largely in order to track the translocated HBC. Study results continue to suggest that most of the translocated fish are dispersing downriver in the LCR.