Emily Higuera is an Environmental Programs Specialist for the Colorado River Management Section. She participates on behalf of the department in a number of programs, including the Glen Canyon Dam Adaptive Management Program, which focuses on environmental compliance upstream of Lake Mead to Lake Powell, as well as the Lower Colorado River Multi-Species Conservation Program, which provides compliance at Lake Mead to the Southern International Boundary. Emily has always had a bird’s eye view of the Grand Canyon, until her trip with the Glen Canyon Dam Adaptive Management Group in June of 2022. That river experience, she said, “truly encapsulated the depth and wonder that is the Grand Canyon.”
The Grand Canyon is renowned for its geological structures and historic human explorations, but less is known of the endemic fish – the humpback chub - that adapted to survive the grueling pre-dam conditions of the Colorado River.
To truly understand the challenges and what’s at stake for the humpback chub, ADWR staff explored the Grand Canyon through the Glen Canyon Dam Adaptive Management Program
for 10 days in mid-June of last year. The rafting trip began at Lees Ferry and took out at Diamond Creek. ADWR participates in the program as a Colorado River Basin State representative.
The Canyon has sustained species for millions of years. However, much has changed since the installation of Glen Canyon Dam: stocked rainbow trout wait patiently for lunch leftovers and New Zealand mudsnails
litter the banks where nonnative vegetation had often overtaken the shoreline. Some natives still remain: flannel mouth suckers investigate the shallow waters while bighorn sheep graze on the beaches.
Fossils in the canyon walls and 50,000 year-old packrat mittens provide evidence of prehistoric life in the Grand Canyon. Past and present, the canyon teems with life.
Our trip focused not only on the ecosystem, but also its anthropological history. Eleven tribes
historically utilized the Canyon and consider the Colorado River and its tributaries a place of origin, growth, and healing. While our program’s mission is focused on resource management
, the tribes provide traditional knowledge and have been stewards of the Canyon for many years.
We first encountered the humpback chub at the confluence of the Little Colorado River, a point in the river known as River Mile (RM) 61. The fish were visible from the bank, anticipating scraps from dinner. Well-fed, these fish were all too willing to receive food from the hands of campers. They weren’t alone. Among the chub were nonnative fish, including a large common carp, a species that has been shown to feed on larva chub.
After a night under the star-flooded sky at RM 61, it was only a short hike into the canyon of the Little Colorado River. Following heavy rains, the water looked like chocolate milk compared to the beautiful turquoise often seen in picturesque portraits of the area. We could easily see young humpback chub in the shallow waters, indicating a successful spring spawn. This environment was much harsher than the mainstem, with steep walls and narrow beaches, highlighting the conditions these fish have survived for millions of years.
The extraordinary humpback chub has survived periods of low flows to extreme floods and navigated highly turbid waters. As one might guess by the name, the humpback chub
(Gila cypha) evolved to form a distinctive, fleshy hump behind their heads. This adaptation allows the species to stabilize and maintain positions in difficult water conditions, as well as increase survival from co-evolved predators, such as the Colorado pikeminnow. The humpback chub evolved around 3.5 million years ago and remained undiscovered until 1933. Humpback chub can live more than 30 years and reach 20 inches in length.
The humpback chub has experienced many hardships since the damming of the Colorado River and its tributaries. Post-dam conditions
brought stabilized flows and clear water conditions, creating a foreign environment for the large minnow species. The development of reservoirs also provided fishing opportunities that would otherwise be unavailable in the desert, bringing many nonnative, highly predatory fish into the Colorado River Basin. Their introduction has impacted the upper basin’s populations
of the threatened species. The cooler release temperatures from Glen Canyon Dam created a Blue Ribbon Trout Fishery
that has also increased concerns of predation on the humpback chub where the species overlap.
The Grand Canyon’s population of humpback chub has been predominant in the Little Colorado River, with movement into the mainstem and downstream tributaries. Lake Powell’s low elevations have increased water release temperatures, providing more opportunities for humpback chub habitat in the mainstem. This is a double-edged sword, as the lower reservoir elevations have increased the passage of nonnative fish from Lake Powell into the river below. Many of these warmwater fish have the capability to detrimentally effect, and potentially wipe out, this native species from the Grand Canyon.
ADWR has been working with federal, state and external partners to develop strategies
and provide support to protect the Grand Canyon native and ensure the survival of the humpback chub, while maintaining the continued delivery and protection of Arizona’s water resources.