Endangered chub conservation sees success in Grand Canyon

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Endangered chub conservation sees success in Grand Canyon
Endangered chub gets help

Each fall for the past 14 years, a group of biologists have waded into the travertine-tinged waters of the Little Colorado River to catch hundreds of silver humpback chub fingerlings.

After slipping the fish into a circular tub filled with river water, they strap the container into a sling and carry the aquatic passengers via helicopter about five miles upriver to a new home.

Thanks to fewer predators and more food at the upriver location, the transplanted fish have come to thrive compared to their downstream brethren, making for a conservation success story that just received national recognition.

The fish-moving process, called translocation, is headed up by a team from the U.S. Fish and Wildlife Service with help from the Arizona Game and Fish Department, the U.S. Geological Survey and the National Park Service. The team received the Fish and Wildlife Service’s 2016 Rachel Carson Award for Exemplary Scientific Accomplishment for its contribution to the recovery of the endangered humpback chub, a distinctive and well-known pillar of the Grand Canyon ecosystem.

Moving fish
Once abundant in Grand Canyon, the humpback chub’s numbers have dwindled due to the introduction of nonnative predators and the construction of Glen Canyon Dam that pulls cooler waters into the Colorado River and blocks the seasonal floods that used to wash through the canyon. Over time, the fish have retreated to the warmer waters of tributaries to the Colorado River. The Little Colorado River now harbors the largest remaining population of the species in the world.

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An adult humpback chub captured in the lower section of the Little Colorado River in 2015. The largest remaining population of humpback chub in the world is found in Grand Canyon National Park and the Little Colorado River is the population's main spawning area.

Mike Pillow, USFWS
Humpback chub congregate in the lower part of the Little Colorado, close to its confluence. Before translocations started the species hadn’t been found above a natural travertine dam 14 kilometers upriver. But that stretch of the river, above what’s called Chute Falls, has warmer water, abundant food sources like insects and the tiny speckled dace and far fewer predators, which for the chub include invasive trout and catfish. Like an in-stream fish hatchery, the area makes for an ideal natural rearing habitat that comes with less disease transmission and genetic challenges, said Randy Van Haverbeke, a senior fish biologist with the Fish and Wildlife Service who is involved in the work. Seeing an opportunity to expand the chub's range and establish another aggregation that could contribute to the population downriver, biologists started translocating humpback chub above Chute Falls in 2003 and now move about 300 baby fish annually, said Mike Pillow, a biologist with the U.S. Fish and Wildlife Service.

More than a decade in, biologists have consistently measured increased growth and survival among the translocated chub compared to non-translocated chub, indicating promise for the conservation tactic to augment the species’ populations in Grand Canyon, Van Haverbeke said.


In the area above Chute Falls, biologists have recaptured an average of 24 percent of fish translocated the year before, Pillow said.

In the bigger picture, he said, the project’s goal is to build up humpback chub numbers to enable the eventual delisting of the species.

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U.S. Fish and Wildlife Service biologist Mike Pillow releases 303 juvenile humpback chubs translocated to an upstream location in the Little Colorado River in November 2013. Chub that were moved upstream have been found to have increased growth and survival rates.

U.S. Fish and Wildlife Service biologist, Mike Pillow, releases 303 juvenile humpback chubs translocated within the Little Colorado River in November 2013.

Nic Medley, NPS
Going beyond the Little Colorado River, the translocation process has been replicated by officials at Grand Canyon National Park as well, where chub from the Colorado River were transported up Havasu and Shinumo creeks. The goal was the same: to establish new population groups of chub within the species’ ancestral habitat where they may be better able to survive. Doing so in more locations creates redundancy, so if something were ever to happen in the Little Colorado River “all our eggs aren't in one basket,” Van Haverbeke said.

Biologists with the National Park Service have seen as much as a five to 10-fold increase in chub in the mainstem of the Colorado River below those two creeks, suggesting translocation is having a positive impact, he said.

Measurable impacts on total chub population numbers in the Little Colorado River are harder to determine because the population is bigger and the fish are affected by other factors like the temperature of water releases from Glen Canyon Dam, Pillow and Van Haverbeke said.

“But the bottom line is we have increased survival and growth rates compared to not translocating (the fish). Then you have to assume it’s a positive (impact),” Van Haverbeke said.

Also important to note is the fact that this is a feasible, doable conservation action proven to help the fish, as opposed to something much harder to influence like modifying dam operations, he said.

The process also involves relatively minimal human impact, Pillow said, instead helping Mother Nature with “little nudges.”
 
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