Non-native trout, while prized by anglers who fish the Colorado River below Glen Canyon Dam, threaten to wipe out native species in the river that can't compete with them. While Interior Department officials have a plan to remove the trout, it's effectiveness is being questioned.
With an estimated 1 million trout in the Colorado River within Grand Canyon National Park, Interior's plan to live-trap the fish to dent the population is nothing but a "Band-aid" fix, says Nikolai Lash of the Grand Canyon Trust.
“Obviously, mechanically removing fish, they’re only going to be able to, practically speaking, get tens of thousands of fish, and there are a million," said Mr. Lash when reached Wednesday for his reaction to Interior's plan. "If you remove 30,000, that means you’ll have 970,000 trout left. And maybe it will go over a million, 1.2 million the next time we look at it.
".... The problem is so out of hand now. You can’t mechanically remove trout and think it’s gonna fix the problem."
Anne Castle, Interior's assistant secretary for water and science, announced the fish removal plan on Wednesday when she and Interior Secretary Ken Salazar said high-flow releases would resume from Glen Canyon Dam. She said the efforts would involve live-trapping of trout in different locations of the canyon. Live-trapping is being used instead of lethal means to honor Native American concerns for all living things, the assistant secretary added.
How much the live-trapping effort will cost, or how successful it might be, she did not say. For more than a decade crews in Yellowstone National Park have been trying to rid Yellowstone Lake -- a largely closed system, unlike the Colorado River -- of non-native lake trout with very limited success.
At the Grand Canyon Trust, Mr. Lash said the Colorado River plan, as a means of helping the endangered humpback chub recover, had several problems. Along with only removing a fraction of trout, the live-trapping likely will lead to the deaths of native fish, he said.
Live trapping typically is accomplished by using electro-shock to stun fish, which then float to the surface, said Mr. Lash. While native fish that are stunned are to be thrown back into the river, some will die from the shock, he maintained.
Rather than trapping, Mr. Lash said he'd rather see the river managed for humpback chub; using the flushes proposed by Interior Secretary Salazar would benefit the chub over the trout, he said.
“I think there’s a lot of room still to experiment fundamentally with flows and mix up the interplay between natives and non-natives," he said.
At the Grand Canyon Monitoring and Research Center, a U.S. Geological Survey facility in Flagstaff, Ariz., Scott Vanderkooi said Colorado River researchers have been using electro-shock for years and the fish, both native and non-native, endure it fairly well.
“If it’s done properly it can stun fish, but it generally does not harm fish," said Mr. Vanderkooi, the center's biology program manager. "There certainly are exceptions to that. But by and large natives and non-natives seem to do well when they are handled.”
According to Mr. Vanderkooi, it will be a while before any live-trapping with a goal of denting the trout population is done. A number of "triggers" need to be reached before fish removal begins, he said. They range from the overall population of humpback chub, the trout population, and even water temperatures.
Trout prefer cooler waters than humpback chub, he explained, and so live-trapping would not occur until and unless the water temperature falls below a certain point. Humpback chub, meanwhile, prefer warmer waters and likely would be in the Little Colorado River.
Currently, the USGS biologist said, humpback chub in the Colorado River drainage within the Grand Canyon seem to be on the upswing, number-wise. A decade ago estimates put the population around 5,000, and the latest estimate, made in 2008, raised that number of 7,650, said Mr. Vanderkooi.
According to the USGS official, the bulk of the non-native trout population within the canyon is found just downstream of Lee's Ferry.
"Most appear to be in that reach down to Lee’s Ferry, and the upper parts of Marble Canyon," he said. "The surveys that we’ve done, the catches of trout fall off as you go down river.”
So when live trapping does begin, it will likely be focused on that upper stretch of the river. Captured trout then will most likely be taken by boat to Lee's Ferry and transferred to their final location, said Mr. Vanderkooi.
More troublesome would be removing trout near the confluence of the Colorado River and Little Colorado River, which is the main habitat for humpback chub because its waters are warmer than the main Colorado. As the confluence is roughly 60 miles downstream of Lee's Ferry, said Mr. Vanderkooi, any captured trout most likely would have to be floated down the Colorado River and out of the park.
“The exact method has not been finalized. Likely it would have to be on some sort of raft," he said.
With the vast number of non-native trout in the canyon's waters, trying to tamp down their numbers through live trapping would be difficult, acknowledged Mr. Vanderkooi.
“With the abundance that there is, it would be very challenging," the USGS official said.