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Ancient Residents of the Grand Canyon Find Their Way Home
by Meagan Racey
Photo Credit: © Amy S. Martin Photography
The waters of the Grand Canyon recently welcomed back a group of old friends—the bizarre, but striking, humpback chub (Gila cypha). Hundreds of the olive and silver colored fish flitted through Arizona's Havasu Creek, a tributary of the Colorado River, in spring 2012 after a yearlong retreat at a national fish hatchery.
The release of 300 endangered humpback chubs to these wild waters was the second of three releases in northwestern Arizona coordinated by the U.S. Fish and Wildlife Service (Service), National Park Service, and Bureau of Reclamation. The three agencies are working together to ensure this native fish continues to call Grand Canyon National Park home.
The humpback chub, a large member of the minnow family, was once one of the most abundant fish species in the Grand Canyon, navigating the rapid Colorado River and three of its tributaries—the Green, Yampa and Little Colorado rivers. Over millions of years, this fish evolved to have large fins and a pronounced hump stabilizing and guiding its movement through whitewater.
Humpback chub populations have declined significantly in response to changes that humans have made to the environment. The construction of dams changed the rivers' flows and temperatures, altering and even eliminating habitat and migration routes for the chub, and other native fish like the endangered Colorado pikeminnow (Ptychocheilus lucius) and razor back sucker (Xyrauchen texanus). Additionally, the introduction of non-native fish tripled the number of species in the chub's habitat, adding the threat of predation, as well as competition for food and habitat.
Biologists saw significant increases in Grand Canyon humpback chub numbers after 2006, however. These increases were likely related to natural warming of the Colorado River in the Grand Canyon because of drought conditions, and a system-wide decline in rainbow trout (Oncorhynchus mykiss), a non-native fish thought to compete with and prey on juvenile humpback chub. This decline was partly assisted by removal of trout near the Little Colorado River inflow.
Today, the largest population of humpback chub in the world is found where the Colorado and Little Colorado rivers meet.
Photo Credit: David R. Van Haverbeke, USFWS
In an effort to further increase humpback chub abundance in the Grand Canyon, the partnering agencies began capturing chub several years ago as fingerlings (young fish) from the Little Colorado River, and transporting them to the Service's Dexter National Fish Hatchery and Technology Center in southeastern New Mexico. Here, they would spend a year growing out before returning to the wild. These steps help to increase growth and survival potential in juvenile chub. To date, biologists have released three groups in Shinumo Creek and two groups in Havasu Creek. Each group has included around 250 to 300 fish.
Biologists hope these experimental releases will help promote the endangered fish's recovery by leading to additional populations throughout the Grand Canyon. According to biologists, the tributaries are good transitional places for the juvenile chub, and as they get larger, the fish are more likely to survive the colder waters of the Colorado River.
The released fish aren't swimming into oblivion, either. Biologists are keeping track of them with passive integrated transponder (PIT) tags, which uniquely identify each fish. In their monitoring, biologists have captured a number of chub released in past years.
So far, these veteran Grand Canyon residents are faring well—an encouraging sign that translocation efforts may be assisting in recovery of the species. However, the species still faces threats to its long-term survival – cold mainstem water in the Grand Canyon and heavy predation by warm water predators in the upper reaches of the Colorado River – that translocation efforts alone cannot overcome.
Meagan Racey, a public affairs specialist in the Service's Northeast Regional Office, can be reached at firstname.lastname@example.org or 413-253-8558.
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