A side channel in Glen Canyon National Recreation Area has become a breeding ground for smallmouth bass and other nonnative fish that pose a serious threat to endangered species. Federal officials are working to change that by reconnecting this slough with the Colorado River. Park Service fish biologist Jeff Arnold spoke about the project.
MELISSA SEVIGNY: Tell me about this slough in Glen Canyon and why is it a problem for invasive fish?
JEFF ARNOLD: The slough—a lot of people don’t know what a slough is, or what it means, but a slough is basically a backwater section of the river, or any river…. The slough we’re talking about now is called the “minus twelve mile slough,” meaning it’s about twelve miles up from Lees Ferry boat ramp…. The reason why it’s a concern is a couple years ago, in 2022, the Park Service discovered smallmouth bass that apparently, it looks like they spawned in the slough. And smallmouth bass are a voracious predator which can affect the local rainbow trout fishery and also downstream threatened and endangered fish species like the humpback chub and the razorback sucker.
MS: So, at this moment, there’s this construction work underway at the slough. Tell me what you’re doing and how it’s going to help?
JA: Right now, the slough is minimally connected to the main channel. In the summer,time it gets the heat of the sun all day…. It heats up really fast. Smallmouth bass tend to spawn when the temperature’s around 16 degrees Celsius and with very low velocity, water velocities. The purpose behind channelization is to connect the upper portion of the slough and the down portion of the slough so there’s a continuous current going through. The current going through should discourage any smallmouth spawning and also, what that will do is bring the cold water from the main channel, push it through the slough, and that should also discourage spawning of smallmouth bass.
MS: Okay, so you basically have this mostly disconnected part of the river and you’re going to connect it so the water’s going to be picking up speed and a lot colder. And that will make it unattractive to the fish.
JA: It should…. There’s a lot of scientists out there that say it will.
MS: Sure.
JA: Yeah, and the slough has also been producing some other nonnative fish, like, it’s a great place for green sunfish to spawn [and] common carp.... and so it should discourage all those other fish species from spawning in that location.
MS: Okay. Besides the channelization of the slough, are there other activities that the Park Service is doing to try to get a handle on the invasive fish?
JA: During the summer months, every other week, we are electrofishing. Electrofishing — you can selectively remove fish that you don’t want. It shocks them a little bit, stuns them, you collect them, you can sort through and remove the non-desirable fish like smallmouth bass, green sunfish and carp, and the desirable fish like the native flannelmouth sucker and the rainbow trout you can release back into the water.
MS: Can you tell me, big picture, why is it important to the Park Service and to yourself that we handle this issue?
JA: Glen Canyon is being managed as a rainbow trout fishery. It’s a Blue Ribbon trout fishery. People from all over the country come there to fish. It brings a lot of dollars into the local economy. It’s an important resource for Glen Canyon. The other reason is, we have two endangered fish species downstream in Grand Canyon… And because of the predacious nature of the smallmouth bass and green sunfish, we are worried if they make their way and become established downstream they could decimate those fish populations.
MS: Jeff Arnold, thank you so much for speaking with me.
JA: You’re welcome. Thank you very much.
