Monitoring of Humpback Chub, Gila cypha, Bluehead Sucker, Catostomus discobolus, and Flannelmouth Sucker, Catostomus latipinnis, in the Little Colorado River, Grand Canyon, AZ

Authors: VanHaverbeke, D. Randy*, Young, Kirk, Stone, Dennis, Pillow, Michael

Year: 2015 (xlvii)

Abstract

Since 2000, a series of two-pass, closed Chapman Petersen 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 and native suckers. During spring 2015 the estimated abundance of Humpback Chub &#62 150 mm in the lower 13.57 km of the LCR was 3,999 (SE = 314). Of these, it was estimated that 3,078 (SE = 246) were adult fish (&#62 200 mm). The 2015 fall Humpback Chub abundance estimates are being generated. After experiencing a significant decline in abundance during the mid-1990s, Humpback Chub remained at low but stable abundances in the LCR for a number of years. After 2006, both the spring and fall abundances of humpback chub in the LCR significantly increased and remained at significantly higher levels. However, the spring 2015 estimates were significantly lower than those of the past several years for reasons unknown. In addition, Bluehead and Flannelmouth suckers underwent significant increases in abundance during the post-2006 spring seasons, but have since declined. The overall results suggest that sometime during the mid-2000s, conditions were favorable for all three large bodied native fishes in Grand Canyon. These favorable conditions are thought to be related to warmer water temperatures experienced in the Colorado River because of drought and a system-wide decline of non-native salmonids in the Colorado River. In addition, it is thought that benefit may have accrued to Humpback Chub because of translocation efforts within the Little Colorado River, and because of LCR hydrologic conditions.