REMOTE DESTINATION: After overwintering at the Southwestern Native Aquatic Resources & Recovery Center, where they were treated to remove any parasites, humpback chub collected from the Little Colorado River were released into this inviting pool at the base of Havasu Creek’s Lower Beaver Falls. Image: © Amy S. Martin
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Some 300 fish took a most unusual trip. Freshly delivered from their winter base camp at a hatchery in southeastern New Mexico earlier this year, the live swimmers—ensconced in aerated coolers—were helicoptered to the base of a dazzling turquoise-blue waterfall in the remote western region of Grand Canyon National Park.
The endangered humpback chub (Gila cypha), endemic to the Colorado River, are distinguished by a large bulge on their sleek, olive-colored backs. They had been collected several months earlier in the Little Colorado River, a tributary that hosts the largest of their known spawning populations. Due to similarities in hydrology, habitat and water chemistry between the Little Colorado and Havasu Creek, the downstream waterway to which the fish were flown, fisheries experts ranked the latter as the creek most likely to support a second reproducing population within the park.
Humpback chub are uniquely adapted to thrive in the turbulent and muddy whitewater environment that characterized the Colorado River prior to the construction of Glen Canyon and other dams throughout the basin. Whereas these dams have provided many benefits, including drinking and irrigation water for over 40 million people, they have also drastically altered the river's chemical and physical environment, including the base of the Grand Canyon's food chain.
Native fishes are considered bellwethers for the entire ecosystem, and of the eight native species once found in Grand Canyon, four—including the humpback chub—are now federally listed as endangered. Should a disaster such as a landslide cut off the Little Colorado chub from the mainstem, the species could quickly become extinct. So this year the National Park Service, in a cooperative effort with the U.S. Bureau of Reclamation, the U.S. Fish and Wildlife Service, and the Arizona Game and Fish Department, carefully sling loaded coolers of chub, each with a transponder tracking tag safely embedded near its belly, for the third time into Havasu and the fourth time into smaller Shinumo Creek, which is located 77 river kilometers to the east, as part of an urgent effort to establish other viable populations.
Chub relocated to these creeks are just beginning to reach maturity, and for the first time in May biologists found evidence that the fish are indeed reproducing: Two juvenile chub without identification tags were captured in Havasu. This discovery, along with the recapture of two female chub in spawning condition, marks a milestone in the multimillion-dollar effort to improve the species's odds of survival. "We can't say for sure whether those juveniles were spawned from the translocated chub," says Brian Healy, Fisheries Program manager for Grand Canyon National Park, "but we found seven ripe males in May last year, and plenty of fish large enough to spawn, so it's certainly possible. Future monitoring should confirm this and will also be necessary to determine whether these juveniles survive to maturity."
Removing nonnative species
Beginning in the early 1900s federal agencies stocked nonnative brown and rainbow trout to enhance sport fishing in the Colorado River and its tributaries according to that era's practices. Unfortunately for the chub, both species are piscivorous, so "the park service is now in the process of trying to remove the nonnative trout that are competitive with and prey on the native fishes," says Melissa Trammell, a fisheries biologist for the National Park Service's Intermountain Region.
Backpack electrofishing, which introduces a weak current into the water to gently stun the trout just long enough for "fish crews" to net them, is operated in conjunction with a weir that blocks trout from entering the tributary. Culling must be repeated for several years before the stream is suitable for chub translocation. After the humpback chub are released, the work crews continue to remove nonnative fishes by several methods including conventional angling, an efficient method that is extremely selective for trout, Trammell says.