The Humpback Chub is Making a Comeback
There was a time when scientists feared the demise of an ugly little fish called humpback chub, which has lived in southwestern rivers for millions of years. One of its last holdouts is in the Grand Canyon section of the Colorado River at a major tributary, the Little Colorado. Glen Canyon Dam took its toll on the little fish, and by the late 1990s, its population plummeted to a few thousand.
But these days, the humpback chub appears to be making a comeback.
Brian Clark is a wildlife specialist with the Arizona Game and Fish Department. These are the sounds of his all-day preparations to head to the confluence of the Colorado and Little Colorado rivers.
“All of our equipment comes in by helicopter, so right now I’m getting everything ready to be carried in a slingload beneath the chopper,” he said. “They used to take boats down in the 90s and carry everything down from the confluence, but as you can see, there will be 800 to 1000 pounds of equipment is going in.”
Three agencies have fish monitoring camps at the confluence: Game and Fish, the U.S. Fish and Wildlife Service and the U.S. Geological Survey. Biologists from all of the agencies have been studying the humpback chub for more than a decade, using increasingly sophisticated techniques.
Clark explains: “… 800 pound of antennas for picking up those tags, and those tags will go in without actually touching the fish, so it’s less stress. Tags are injected with a needle, and inserted into their abdominal cavity.”
All this effort to monitor populations of an endangered fish in the minnow family.
Humpback chub grow up to 20 inches, and as the name implies, each fish sports a large hump on its back. The hump may be protective, making the fish difficult eating for predators. But to humans, they’re just not very pretty. Despite this, scientists believe the chub are invaluable as one of a few remaining native fish in the Colorado River.
“There was a time when we were afraid the chub population was down to about 2100 fish,” said Bill Persons. “We later found out that estimate was too low. They were probably down to about 4500 fish.”
Persons has been studying the chub for 20 years, most recently as a fisheries biologist with the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center.
Biologists used to worry that the chub population was so small, it would disappear completely. That would have meant that out of 8 or 9 fish species once native to the Grand Canyon, only three would be left. Biologists believe the main culprit in the chubs’ near demise has been water temperature. The Colorado River got colder after Glen Canyon Dam, because the turbines pull water from the lower depths of Lake Powell.
But recently, there’s been a change.
“We’ve had 20 years of drought in the Colorado river basin and from about 2003 to 2005, Lake Powell was drawn down, so the turbines were withdrawing water from closer to the surface in Lake Powell,” Persons explains, “ and it appears that period was a good one for humpback chub. We had the second warmest year on record last year. They seem to be doing better than they were in the late 90s when really all we had was cold water coming from the dam.”
Better, meaning the population has increased about 50 percent. Biologists believe anywhere between 7,000 and 10,000 humpback chub swim in the Colorado and Little Colorado rivers.
So drought and warmer temperatures appear to be correcting damage dealt to the chub by Glen Canyon Dam. And the climate forecast calls for more drought, and more warm-water releases from Glen Canyon Dam. So humpback chub may continue to bounce back.
But, of course, the story doesn’t end there. Warm water can also be good for parasites as well as some of the fish species that eat humpback chub. Game and Fish, the USGS and Fish and Wildlife will continue to monitor the chub.
Deep down, Persons admires the perseverance of the unsightly little fish. And he’s not overly worried.
“Humpback chub have survived for millions of years – before Glen Canyon Dam, after Glen Canyon Dam,” he said. “ I think they must be a pretty hardy fish.”
A hardy fish that seems to have gotten by with a little help from its friends.