​​​WAPA supporting experiment to make more bugs in Grand Canyon

By Lisa Meiman

WAPA’s fish biologists are on a mission to make more bugs below Glen Canyon Dam. 

Diagram showing invertebrate richness by number of genera

Between May and August this year, Glen Canyon Dam will release steady flows through the Grand Canyon on weekends to determine whether or not stabilizing releases for two days a week will help insects complete their lifecycle and reach maturity downstream. 

Nicknamed the “bug flow” experiment, the steady water releases will test a hypothesis that fluctuating river levels cause insect eggs to dry out and die, leaving a major gap at the bottom of the food chain. 

“Many bugs lay their eggs at dusk when the water is high, then, at night, when flows are typically lower, the eggs dry out and die,” said Fish Biologist Craig Ellsworth. “We are going to see if we provide two days of low, steady water, if those eggs have better survival rates.” 

Insect populations downstream of Glen Canyon have sharply decreased since 2012, and insect diversity has also been low. As the primary food source for fish, insect abundance and diversity of species are major concerns. 

“We are seeing fish on a diet. The fish are skinny – all head, and the bodies felt like a piece of cardboard,” said Ellsworth. “This experiment is all about the fish. Fish live off these insect populations. We want to see if we can improve conditions for the bugs, so the fish populations should stabilize.” 

In 2014, the trout fishery at Lees Ferry collapsed due to starvation, with a 90-percent mortality rate over the course of a single winter. The more resilient humpback chub, recently proposed for reclassification from endangered to threatened, was also affected.

“For the first time, we saw skinny humpback chub down at the Little Colorado River,” said Fish Biologist Shane Capron. “This has been a big concern for us.”

Partnerships find win-win solutions

The bug flow experiment was coordinated through the Glen Canyon Dam Adaptive Management Program, a public-private partnership committed to improving the health of the Colorado River below Glen Canyon Dam for the benefit of all the river’s users. It is also the first experiment to be conducted under the Long-Term Experimental and Management Plan Environmental Impact Statement, which included a number of experiments to improve key resources in the Colorado River. 

The Colorado River Storage Project Management Center and preference power customers are active participants in the working group and helped develop the bug flow experiment to limit the impact to hydropower. These bug flows are expected to cost WAPA about $335,000, which is far less than alternative bug flow designs that were proposed during the development of the experiment.

“Having these low, steady flow releases only on the weekends greatly reduces the negative impact to hydropower. Plus, water saved on the weekend gets moved to higher value times during the week, offsetting some of the cost of the experiment,” said Capron. “The working group always looks for win-win solutions. When you look, you can find them.”

The results of the experiment will be monitored in part by rafting companies whose guides will set up insect light traps to collect bugs when they camp for the night. It was these collections over the past few years that led scientists to discover that insect populations appeared to be at their highest numbers where the river was lowest at dusk. 

The Glen Canyon Dam bug flow experiment is part of a multifaceted partnership between the Grand Canyon Monitoring and Research Center, the Utah State University Bug Lab and the Museum of Northern Arizona to study the causes for the reduced insect diversity below Glen Canyon Dam. 

The bug flow experiment is just one of the studies to determine how to improve conditions for fish in Grand Canyon. Many factors may be limiting insect production below Glen Canyon Dam, such as the quality of the habitat on the bottom of the river and nutrient levels in the water being released from the dam. It also might be hard for these insects to proliferate considering the harsh, desert conditions.

“The Colorado River below Glen Canyon Dam is a very different river from other rivers in WAPA’s territory,” said Ellsworth. “The flow may not matter if there isn’t the right habitat for these bugs. We think there is a much more complex story here.”

 “Recovery of endangered fish species is an important goal for WAPA because their conservation currently limits operations at facilities like Glen Canyon Dam.,” added Capron. ” This experiment might increase bug abundance, or it might not. If it does, it may be worth the cost, especially compared to other very expensive options for river management.”​

Top right: The Grand Canyon suffers from a lack of insect diversity as well as low populations compared to other rivers in WAPA’s territory. There could be multiple reasons for this, including the desert-like conditions in the Grand Canyon. (Graphic courtesy of the Glen Canyon Dam Adaptive Management Work Group)​

Below: An illustrative example of Glen Canyon Dam operations during the bug flow experiment. The same volume of water will pass through the dam over the next four months, but flows will be higher on weekdays and low and steady on weekends.

Example bug flows

 

Last modified on September 12th, 2023