2 2 | C A N YO N V I E W S Green sunfish illustration courtesy © Joe Tomelleri
D
espite dramatic changes to the aquatic ecosystem owing to invasive fish introductions and the construction and operation of Glen Canyon Dam, Grand Canyon National Park (GRCA) currently serves as a stronghold for endemic Colorado River fishes. Declines in native fishes initially occurred following introductions of invasive fishes that began more than 100 years ago and proliferation of cold water predators that thrive in the colder, more stable post-dam era— conditions that also limited native fish reproduction (Figure 1a). Colorado River native fishes require seasonally warm water for eggs to incubate, hatch, and survive. Fifteen large dams that make up the Colorado River Storage Project also fragment migratory routes (Figure 2). Long-distance migratory species like Colorado pikeminnow (Ptychocheilus lucius) were lost from Grand Canyon, as was the bonytail (Gila elegans), and roundtail chub (Gila robusta). Nonetheless, spawning habitat in tributaries sustained important remnant populations of humpback chub (Gila cypha), flannelmouth (Catostomus latipinnis), and bluehead (C. discobolus) suckers. Conditions limiting native fishes in the past have improved over the past decade in the Colorado River. Endangered razorback sucker (Xyrauchen texanus) was considered extirpated in the 1990s, until targeted monitoring rediscovered evidence of spawning in Grand Canyon in 2014. Increases in native fish populations have been documented in scientific publications—native fishes now
Adult humpback chub captured in Havasu Creek. Photo: NPS/Amy Martin.
