Abundance Trends and Status of the Little Colorado River Population of Humpback Chub

Abstract

The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture–recapture‐based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid‐1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age‐2 and older fish are age dependent but apparently not time dependent. Back‐calculation of recruitment using the apparent 1990s population age structure implies periods of higher recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and Wildlife Service recovery criterion of stable abundance is not being met for this population. Also, there is a critical need to develop new abundance indexing and tagging methods so that early, reliable, and rapid estimates of humpback chub recruitment can be obtained to evaluate population responses to management actions designed to facilitate the restoration of Colorado River native fish communities.

Colorado River fish monitoring in Grand Canyon, Arizona; 2002–14 humpback chub aggregations

“…The LCR inflow aggregation displayed a pattern similar to the findings of Coggins and Walters (2009) and Van Haverbeke and others (2013). That is, the LCR inflow aggregation experienced a decline in adult humpback chub abundance sometime between Periods 1 and 2 (1994 to 2001).…”

“…They estimated 3,482 adult humpback chub in this area using a multiple pass mark-recapture method. Using an Age-Structured Mark-Recapture (ASMR) model, which includes captures of fish in the LCR, Coggins and Walters (2009) There appears to be little dispersal of humpback chub from the LCR inflow aggregation other than with the nearby Lava Chuar to Hance aggregation. Almost all (99.9 percent) of the humpback chub recaptured in the LCR or the LCR inflow aggregation from 1990 to 2014 were previously tagged in the same area (table 3).…”

“…The LCR aggregation of humpback chub has been studied extensively (Douglas and Marsh, 1996;Marsh and Douglas, 1997;Coggins and others, 2006a,b;Van Haverbeke and others, 2013;Yackulic and others, 2014). Both closed-and openpopulation models are used to estimate abundance of chub in the LCR and near the confluence of the Colorado River (Coggins and Walters, 2009;Van Haverbeke and others, 2013;Yackulic and others, 2014). Reasons for use of areas outside of the LCR vicinity by adult humpback chub is unclear, but most aggregations are associated with seasonally warm tributary streams (LCR, Bright Angel Creek, Shinumo Creek, and Havasu Creek) or warm springs (30-Mile, Pumpkin Spring).…”

Body Condition of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River

“…Fish biologists have intensively studied Humpback Chub in the Little Colorado River and mainstem Colorado River for more than three decades Gorman and Stone 1999;Coggins et al 2006). In order to make temporal and spatial comparisons, we compiled available data from Humpback Chub sampling programs during the 1990s and augmented this dataset with measurements collected in 2011 (Table 1).…”

“…The largest population of Humpback Chub persists around the confluence of the Colorado and Little Colorado rivers in Grand Canyon, Arizona (Coggins et al 2006;Coggins and Walters 2009). Humpback Chub conservation is a major component of the Glen Canyon Dam Adaptive Management Program , which directs operation of the multimillion dollar hydropower facility at the upper end of Grand Canyon.…”