The U.S. Bureau of Reclamation has begun water releases from Glen Canyon Dam to cool the temperature of the Colorado River and slow the reproduction of an unwanted fish. The exotic and predatory smallmouth bass poses a threat to native species like the threatened humpback chub. KNAU’s Melissa Sevigny spoke with Reclamation’s Bill Stewart about the experimental program.
So how often do you anticipate having to do these cool water releases?
We’re in the really early phases of the implementation…and we anticipate intermittently continuing flows are needed to maintain that daily average water temperature below that target of 15.5 degrees Celsius. We’re doing this at locations where we know or suspect smallmouth bass to reside below the dam.
How are you going to find out if it’s successful?
We’re working closely with our partners to monitor and evaluate these flows, particularly with the U.S. Fish and Wildlife Service, also the U.S. Geological Survey, to monitor the populations of warm water nonnative predatory fish like the smallmouth bass in the river below the dam.
What does that involve? Fish counts—you have to go scoop them up and count them?
A whole suite of methods—so yeah, we set nets, there’s electrofishing that goes on, we can use genetic techniques…. We can actually use the age of fish to understand dates of when they hatch. There’s a lot of different techniques that are being used to assess the effectiveness of these flows.
Do you have a sense of how—are you going to be able to figure out pretty quickly if it’s working, or is it going to take a year or two to understand?
It’ll take a little while to understand. There are aspects of this that we’ll learn pretty quickly. The flows are now going. Are we going to see spawning this year? We don’t know. We haven’t seen young of year yet. …. The other thing, is, when you keep the water cold, bass do not grow as fast when it’s cold, and sometimes have a difficult time overwintering into the next year. So we’re also looking at a longer term: do we see a year class that were born in 2024 surviving into 2025? So this will be short and long observations to tell us whether this is working or not.
What are other solutions to this problem of the smallmouth bass are being considered for the future?
Reclamation continues to work with its partners to develop and implement additional preventative actions to combat nonnative species in the Colorado River. It includes supporting the National Park Service in chemical and mechanical treatments, possible modifications to a shallow slough area that is a known prime spawning location for smallmouth bass and other invasive predatory fish. And we’re also considering other methods for preventing or limiting future passage of fish through the dam from Lake Powell.
Is the barrier to doing some kind of physical barrier primarily cost, or is it that this technology is new and we don’t really know how to do it?
I think it’s a combination of really understanding the efficacy…. You know, it’s a unique place, Lake Powell and the forebay above the dam, and so we want to make sure that what we’re putting in there is going to work, should we decide to do something along those lines. So that’s kind of where we’re at. We’re looking at these different options and seeing what’s going to be effective.
Bill Stewart, thank you so much for speaking with me.
Happy to be here, thanks.
