Long-Term Monitoring of an Endangered Desert Fish and Factors Influencing Population Dynamics

Abstract

The lower perennial corridor of the Little Colorado River in Grand Canyon, Arizona, is numerically dominated by endemic desert fishes and therefore significant for conservation of these species. From 2000 to 2012, the U.S. Fish and Wildlife Service conducted monitoring of native fishes in the Little Colorado River near its confluence with the Colorado River. The primary focus of these efforts was to estimate the spring and fall abundance of native fishes, especially the federally endangered humpback chub Gila cypha. Because humpback chub in Grand Canyon are influenced by operations of Glen Canyon Dam, our efforts provide managers of the Glen Canyon Dam Adaptive Management Program with abundance estimates and trends of humpback chub in the Little Colorado River, the most important tributary in Grand Canyon for spawning and production of this species. From 2001 to 2006, the spring abundance estimates of humpback chub ≥150 and ≥200 mm remained relatively low (≤3,419 and ≤2,002 fish, respectively), thereafter significantly increasing to highs of 8,083 and 6,250, respectively, by spring 2010. Also from 2000 to 2006, the fall abundance estimates of humpback chub were substantially below those abundances estimated after 2006. In addition, flannelmouth sucker Catostomus latipinnis and bluehead sucker Catostomus discobolus showed post-2006 increases in relative abundance, suggesting a systemwide event occurred that was beneficial to native fishes. Most of the increases of humpback chub occurred during the spring season in the reaches of the Little Colorado River between 5 and 13.57 km upstream from the confluence. Successful production of age 0 year classes of humpback chub may be partially driven by hydrograph dynamics of the Little Colorado River, whereas water temperatures and predation pressures in the mainstem Colorado River likely influence survivorship of native fishes into subadult and adult life stages.

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

“…It is unknown why Little Colorado River condition increased over this interval, but Van Haverbeke et al (2013) found increasing trends in abundance since 2000 of Humpback Chub, Flannelmouth Sucker Catostomus latipinnis, and Bluehead Sucker Catostomus discobolus in the Little Colorado River, with some of the highest abundance estimates occurring in 2009-2011. These increases in condition and abundance may be the result of improved growing conditions.…”

“…Cross et al (2011) documented that prey consumption rates by fishes in the Colorado River nearly equaled or exceeded invertebrate production, which may cause food limitation that could lead to lower condition. We were only able to estimate length-weight relationships for 1 y (2011) during the time period Van Haverbeke et al (2013) noted increasing abundance for Humpback Chub; but in this one year Humpback Chub showed the most robust size for a given length of all the years we examined (Figures 2 and 3). Despite the increasing temporal trend in Humpback Chub length-weight relationships in the Little Colorado River, condition in this important tributary is still below that of juvenile Humpback Chub occupying the mainstem Colorado River.…”

Surprise and Opportunity for Learning in Grand Canyon: the Glen Canyon Dam Adaptive Management Program

“…A1.3). The 2-year cycle appears to break down after 2009, but the highly variable annual chub production in the Little Colorado River reported by Van Haverbeke et al (2013) between 2001-14, does not bode well for managers who hope to detect recruitment responses quickly after short experimental treatments focused on native chub are started. Net recruitment of native fish to older ages does appear to have responded positively over the 2003-06 treatment period of experimental non-native fish removal from the Colorado River ecosystem mainstem near the Little Colorado River confluence (Coggins et al 2011).…”

Evidence for skipped spawning in a potamodromous cyprinid, humpback chub (Gila cypha), with implications for demographic parameter estimates

“…This sampling program provides data for estimating trends in abundance and recruitment within the LCR using mark-recapture methodologies. Specifically, a Chapman modified Petersen closed population estimator (see Seber, 1982) has been used to estimate seasonal abundance (Van Haverbeke et al, 2013). In more recent years, an age structured open population model was developed to evaluate age-specific annual mortality probabilities as well as abundance and recruitment trends .…”