Rick Deshler, Michael Pillow, Dennis Stone, Randy Van Haverbeke, Jim Walters, and Kirk Young
The Little Colorado River within the Grand Canyon is home to the largest and most viable of six populations of humpback chub (Gila cypha), an endangered fish native to the Colorado River basin. However, since the early 2000s, the Little Colorado River population has declined to less than 2,000 adults, primarily due to habitat loss from the construction of large dams and reservoirs throughout the basin and predation by nonnative fish.
Biologists commonly use translocation of individual fish or animals from a source population to new locations to conserve or recover imperiled species. But, this technique of expanding the species' range is often unsuccessful, and the reasons are often unclear.
The Service's Grand Canyon Humpback Chub Team determined if and where translocations could be successfully used for chub recovery, quantified that success, and determined cause-and-effect relationships to inform future translocation efforts.
In 2003, the team began an experimental translocation of humpback chub into a previously unoccupied section of the Little Colorado River. The team designed and implemented a successful pilot study for translocating larval humpback chub – instead of juveniles – that reduced the risk of population impacts to the original population. The larval fish protocol is now standard procedure for removing chub for translocations elsewhere.
The Grand Canyon Humpback Chub Team has also been able to demonstrate that translocated chub can grow at unprecedented rates, reach sexual maturity earlier than their downstream source population, remain in the translocation reach years longer than their downstream counterparts, and make a significant contribution toward recovery of this species through increased apparent survival rates.
Moreover, the team uncovered root causes for their translocation success. Both the source and translocated chub populations benefit from suitable water temperatures and food resources. Abiotic factors such as natural floods, extremely high sediment loads, and high dissolved carbon dioxide are believed to control and suppress nonnative predatory fish populations; while humpback chub and other native fish appear to be uniquely adapted to withstand the extreme abiotic conditions and are thus capable of out-competing the current nonnative assemblage.
Successful translocation required innovations in tracking and tagging the fish, including the ability to tag young fish permanently for research on early life stages of humpback chub. The team showed that chub could be tagged with smaller Passive Integrated Transponder (PIT) tags and produce vital data with minimal mortality and tag loss.
The team also pioneered the use of submersible PIT tag antennas, which have substantially improved detection of chub and is enabling new research with the potential to fill key information gaps including spawning return intervals, spawning success causes, and large fish survival rates.
Today, translocations are ongoing in two additional tributaries to the Grand Canyon. The team's experimental translocation program was also recently included as a Conservation Measure in the Biological Opinion for the new 20-year operation plan for Glen Canyon Dam on the Colorado River.
Through their rigorous scientific efforts, the Grand Canyon Humpback Chub Team significantly contributed to an increase in numbers of humpback chub found in the Little Colorado River to over 5,000 adults, and they are making progress toward recovering this endangered species.
Learn more about the Arizona Fish and Wildlife Conservation Field Office
Last updated: March 21, 2017
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