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.
To monitor the native species, which include plump speckled dace and slippery bluehead suckers in addition to the chub, workers bait and set heavy, conical hoop nets and boxy minnow traps for a 24-hour period. After wading through ice-cold and often chest-deep water, the crews haul in the nets, excitedly searching for humpback chub as if they were old friends. "We consider them like children at times because we've seen the whole process and watched them grow," says fisheries technician Amy Martin. "This project is a proactive conservation measure that is helping to protect the genetic populations. It's hard work, but it feels good at the end of the day." Healy agrees: "Chub are part of what make this place unique, so we set the bar high for how we want the park's resources to be managed."
So far, the efforts appear to be paying off. In addition to the new evidence of reproduction in Havasu, the percentage of released chub that remain in Shinumo Creek has nearly doubled from the first to the third years.
Future fisheries management
This conservation work will continue under the park's new 20-year Comprehensive Fisheries Management Plan, which covers the Colorado River from Glen Canyon Dam to Lake Mead. The plan's goals include maintaining the recreational rainbow trout fishery just below the dam as well as continuing to restore native fish populations in the tributaries. As the only endangered fish known to reproduce in the park, the humpback chub will remain the primary focus, but the plan also includes a feasibility study for the reintroduction of the endangered Colorado pikeminnow as well as a research and augmentation plan for the endangered razorback sucker, one specimen of which was found in the park last year for the first time since the 1990s, according to Healy.
Whether this fish tale will have a happy ending, however, is still open to question. The recent government shutdown forced Healy to cancel a fall monitoring trip to Havasu as well as postpone a collection trip to the Little Colorado River and additional electrofishing trips to prepare Bright Angel Creek, the final tributary selected for chub translocations. The resulting data gaps will increase the margins of error in future population models, and the postponed trout removal could cancel out months of previous electrofishing work.
Healy is also concerned about the potential threat to native fish from predators other than trout as the discharge from Glen Canyon Dam warms due to dropping reservoir levels. "Warmer water might increase the numbers of warm water, nonnative fishes such as smallmouth bass, striped bass and channel catfish, which are voracious," Healy says.
Conserving the Grand Canyon's native fish ultimately comes down to choices. "We've made some enormous changes to this whole river system," Trammell says. "We can make the choice to try to undo some of the damage that we've done." Healy, who likens the Grand Canyon ecosystem to an airplane, agrees: "If you're going to be flying an airplane, how many bolts can you afford to lose from the plane before you start feeling nervous?"