Smallmouth bass have been found in the Colorado River below Glen Canyon Dam in Arizona, which, at first, sounds like good news for anglers.
That’s because smallmouth bass are popular with anglers because they put up so much resistance when they are being caught. The fish typically weigh from 2–6 pounds and can reach lengths of 20 inches or more.
The problem though, is that the fish are invasive. Even more troubling is that smallmouth bass eat the federally endangered humpback chub, a native fish of the Colorado River. Humpback chub, by the way, can be up to 20 inches long and live 30 years or more.
Smallmouth bass, at least until now, hadn’t moved farther south than Lake Powell because Glen Canyon Dam has served as a barrier. As the lake’s water levels continue dropping, smallmouth bass are able to get past the dam and move downstream.
“It’s pretty devastating to see all the hard work and effort you’ve put into removing other invasive species and translocating populations around to protect the fish and to see all that effort overturned really quickly,” said Brian Healy, who has worked with the humpback chub for more than 10 years and founded the Native Fish Ecology and Conservation Program, according to the Associated Press.
A Precarious Balance
While the humpback chub had been close to extinction, its numbers have somewhat climbed thanks to fish biologists, other scientists, and engineers. Indeed, federal agencies spend millions of dollars annually to keep invasive fish in the upper portion of the Colorado River.
Even so, as reservoir water levels drop, non-native fish that live in the warm surface waters of Lake Powell — such as smallmouth bass — are able to swim closer to the dam and its penstocks. Those penstocks are actually submerged steel tubes that are used to move water to the dam’s turbines to, in turn, generate hydroelectric power. The water is then released on the other side of the dam.
Unfortunately, if smallmouth bass and other predatory fish continue to get sucked into the penstocks, and if they survive and reproduce below the dam, they can then feast on humpback chub as well as other native fish. That situation has the potential to undo years of restoration work, as well as change the Grand Canyon aquatic ecosystem, the Associated Press reports.
A Need For Action
Some agencies have been preparing for the arrival of non-native fish. For instance, a task force was assembled earlier this year to address the situation. Federal, state, and tribal leaders working together are expected to release a draft plan outlining possible solutions that could “delay, slow, and respond to the threat of smallmouth bass and other predators” below the dam, according to the Associated Press.
The National Park Service (NPS), U.S. Geological Survey, and Arizona Game and Fish Department are also working to contain the non-native fish. They have collectively decided to increase monitoring efforts in other shallow areas of the river, as well as block off the backwater where the smallmouth bass were recently found so they can’t swim out into the Colorado River.
“Unfortunately, the only block nets we have are pretty large mesh, so it will not stop these smaller fish from going through, but it will keep the adults from going back out,” said NPS fisheries biologist Jeff Arnold, who spotted the smallmouth bass in the Colorado River last week, according to the Associated Press.
Those efforts, however, seem more like a temporary fix. The larger issue, which has been slow to be addressed, is to leave more water in Lake Powell. That approach is difficult as well because Arizona, California, Colorado, Utah, Wyoming, Nevada, and New Mexico all draw water from the Colorado River.
“If we want to protect some of the values for which Grand Canyon National Park was established, we need to really think about how water is stored,” said Healy, according to the Associated Press. “That issue needs to be at the table.”