​By Philip Reed​

On April 25-26, Colorado River Storage Project Management Center staff assisted in the Utah Division of Wildlife Resources’ biannual trout electrofishing survey of Green River below Flaming Gorge Dam. Fish Biologist Derek Fryer, who joined WAPA in 2019, led the initiative on CRSP MC’s end.

“I coordinated the volunteers within WAPA and worked with the State of Utah to make sure they had enough people to conduct the survey,” Fryer said. “CRSP MC stays involved with this research to keep these connections going, because it’s important to maintain our relationships with Utah, the guide​s, river users and those who find their livelihoods floating and fly fishing that section of the river.”

Also assisting were Natural Resource Specialist Mark Suchy and General Biologist Tim Langer. This was Suchy’s first electrofishing foray with WAPA, but he has significant experience in marine environmentalism and fisheries, and he was already familiar with the process.

Representatives from other organizations participated as well, including the Bureau of Reclamation, the Forest Service, the Fish and Wildlife Service, Trout Unlimited and Utah State University.

“It’s a diverse group,” said Flaming Gorge Project Leader Ryan Mosley, from the Utah Division of Wildlife Resources. “It’s a huge amount of effort, planning and lining up people to pull it off, having equipment ready and working to make sure that everything goes off without a hitch.”

“It is a big job,” agreed Langer. “You catch and process fish from around 7:30 p.m. to midnight. When you’re catching 400 fish in a night, it takes a bunch of people to process them all.”

The work, however, is worth it. Surveys such as these provide important population estimates, as well as growth and condition data to better understand how daily operations may affect the trout fishery below Flaming Gorge Dam.

Monitoring the fishery occurs each year in the spring and autumn, with the next outing planned for September. The information collected from each event is beneficial to understanding and responding to the health and aquatic life of Green River. As of 2022, the data covers around 30 years of sampling.

“There have obviously been some gaps here and there, just because of high flows or there not being enough water to allow us to sample but, for the most part, it’s a very complete data set,” said Mosley.

“Our studies on the Green River below Flaming Gorge Dam help us better understand the biological effects of winter double peaking on trout and aquatic insect populations,” Fryer explained. “We found that the stomach fullness in trout is much higher immediately following a peak flow discharge than it was after steady flow. The research showed that double peaking was not harming trout. Rather, it helps them maintain weight throughout the winter by scouring the plants below the dam, which releases aquatic insects into the water column for the trout to feed on.”

For each electrofishing event, the team adheres to the same methodology. They set up two sampling locations on Green River, with one immediately below the dam at Tailrace and the other about seven miles downriver at Little Hole.

“We have three one-mile study reaches at each location and we electrofish each side of the river,” said Mosely, referring to the process of shocking the fish in order to collect and catalogue them.

“Electrofishing is a tool that we use to capture and enumerate fisheries populations,” explained Fryer. “It is designed in a way that it doesn’t harm the fish, but it stuns them enough that they are brought up to the surface where you can net them.”

Langer explained that the equipment in the boat is powered by a battery, with shocks delivered via anodes at the end of 12-foot-long poles at the front of the vehicle.

“The anode hangs down from those poles into the water,” he said. “When the operator turns on the battery, the anodes put an electric current into the water. The electric current passes over the fish and they are temporarily stunned. We have two netters at the front of the boat, and they place them into a live well. Then they go back to the front and net some more.”

“Everybody from WAPA was hands on with the whole project,” added Suchy.

The team transfers the trout they catch to live wells inside the boat, and them move them to holding pens on the shore. The fish are anaesthetized, weighed, measured for length and scanned for tags, marks and clips. A black light is used to identify stocked trout, which are marked with ultraviolet dye, allowing biologists to better understand how the stocked fish are surviving and growing.

Biologists measure the relationship between a fish’s weight and length. They compare that to other published trout condition indices, allowing them to assess the condition of local fish as one season ends and another begins.

As they process the night’s catches, the researchers take note of many things. Fryer drew attention to, among other things, the work of the “bug lab,” a collaborative effort between CRSP MC, Utah State University and the Bureau of Land Management.

“We work with bug lab researchers who conduct a gastric lavage of the stomach contents on a subsample of survey fish to determine what they were eating recently,” he said. “The State of Utah also has some hatchery personnel on hand who perform a necropsy on a small sample of last year’s stocked rainbow trout. They look at the overall condition of the fish, internally and externally, to determine how hatchery-stocked fish are holding up.”

He explained that the trout population and the food that the trout rely on are “two big pieces of the puzzle.”

“We are using science to help us understand how our operations may affect those populations and what we can do to mitigate those impacts,” he explained.

“At the end of the night, we tip those recovery tanks into the river and release all of the fish,” Mosley said.

“The fact that the fish are returned unharmed to the river at the end of the night is one of the main benefits of electrofishing,” Fryer said. “It’s an effective tool for assessing fisheries’ populations without harming the fish.”

The purpose of expeditions such as this one is to monitor the continuing health of the river and ensure that hydropower and other activities are not interfering with aquatic lifecycles.

“If we do identify any impacts,” Mosley said, “those could be the result of flows. They could also be a result of our management. For instance, if we are not seeing good performance of rainbow trout, or if we are seeing something that alarms us with their population, we can actually adjust our stocking rates or even change the strains of rainbow trout that we stock and start seeing better returns. Everything we see while electrofishing should complement what anglers see. We are managing it better for river users.”

“Monitoring the river this way ensures that we are having a non-negative impact on the fisheries there,” Suchy added. “That is the main thought process behind this project. I think that it’s important for us to do that and show our involvement to the public in that manner.”

Electrofishing is an interesting and novel enough method of sampling that it attracts a great deal of interest, both from volunteers and from observers.

“A lot of anglers stop by and watch what we’re doing,” said Mosley. “It’s kind of funny to me that some of those anglers could have had poor success on the river that day, and then they stop in and see how many fish we’ve caught in the expedition. They are impressed by the amount of effort that we employ to monitor this fishery.”

Mosley also had great things to say about his experience partnering with WAPA.

“I’ve always had a great relationship with WAPA employees who assist us with these projects,” he said. “It helps things run so much more smoothly. I really appreciate WAPA’s assistance because they have the experience to help out and they know the value of this. Also, they’re helping anglers have lots of opportunity to catch sizable fish on the Green River, and many of them.”

Fryer mentioned that they caught a good number of impressive fish during the survey.

“We shocked up some big fish, some really big German brown trout,” he said. “Those are everybody’s highlights of the whole trip, seeing those fish who survived a lot of years and became really big. They hit seven, eight or nine pounds sometimes, and it’s really impressive.”

Those weren’t just fish stories, either; on the first night, the biggest brown trout they caught was 7.9 pounds. On the second night, it was nine pounds.

“These are the two biggest brown trout in the eight years that I’ve been electrofishing,” Langer said. “They were beautiful fish, too.”

Mosley mentioned that seeing such long-lived fish is reassuring, and it proves that WAPA is able to balance the needs of customers and the river.

“It just highlights what WAPA is doing and the way we operate the dam and pattern the flows for hydropower,” he said. “It can be done in conjunction with maintaining these popular fisheries. From my perspective, that’s kind of the takeaway of what we do out there and why.”

“From the double-peaking study we conducted, we saw some effects of what we call density dependence,” Fryer said.

Density dependence means, in short, that the overall population of trout is limited by factors such as food resources. In previous years, the number of trout may have been high, while the size and condition of the fish could have been less than optimal.

“Now, we see a wide range of trout size classes, good body conditions coming out of winter and some of those big nine-pound browns in the recent surveys,” he said. “This says a lot of good things about how the river and the fishery are being managed. It indicates that the population size is good, allowing some of the fish to get really big, while still having relatively high trout abundance. These surveys show us that we can have a great trout fishery and operate the dam in manner beneficial to hydropower. This is a true win-win scenario for CRSP MC.”

The information gathered from past electrofishing events has allowed CRSP MC to study its release patterns and ensure that it continues to provide reliable power to customers without disturbing the health of the river or its aquatic life.

“We developed a trout individual base model with Argonne National Laboratory, and through these experiments and monitoring with the model, we have been able to show that we are not harming the trout population, but are actually benefitting it,” Fryer said. “These trout models help us understand what’s going on and then explain it to the community of resource users. That allows us to save literally millions of dollars. In the long term, sampling events such as these save everyone lots of money, and CRSP MC is proud to be able to lead the effort.”

Fryer also made particular note of the fact that he is happy to work with interested colleagues on sampling events like this one.

“Contact me if you are interested,” he said. “We are always looking for people, and it’s a chance to see what CRSP MC does and some of the things our biologists work on. You get to get your hands on fish and see what electrofishing is really all about. It’s a good time with a great group of people, and we’d love to see more folks get involved.” 

Man in life vest holding fish

Natural Resource Specialist Mark Suchy holds one of the largest fish caught during the spring 2022 electrofishing trip. 

Smiling man in camo holding fish

General Biologist Tim Langer holds one of the largest fish caught during the trout electrofishing survey in April 2022. 

Image of electrofishing team at dusk

Volunteers from multiple organizations prepare to begin the electrofishing survey April 27. The survey began each night around 7:30 p.m. and concluded at midnight. 

Image of team's station with boat near water

In April WAPA employees participated in the biannual trout electrofishing survey of Green River below Flaming Gorge Dam in Utah.

Man holding fish with headlight image

Jordan Detlor from the Utah Division of Wildlife Resources handles a large nonnative northern pike caught during the trout electrofishing survey below Flaming Gorge Dam in Utah, April 26-27. 

​Note: Reed was a public affairs specialist.

Last modified on September 12th, 2023