Endangered fish in the Colorado River face multiple threats. Their survival is linked to the river’s temperature, which is altered both by climate change and by dams. A new study from the U.S. Geological Survey modeled those temperature changes and imagined a future in which water storage is either mostly in Lake Powell or mostly in Lake Mead. KNAU’s Melissa Sevigny spoke with lead author Kimberly Dibble about what those different scenarios mean for native fish.
Were there particular kinds of fish that you were interested in?
We were interested in the big river fishes of the Colorado River, so those are humpback chub, Colorado pikeminnow, and razorback sucker… But we were also really interested in these non-native warm water species… that have found their way into the system, and either compete with or prey on native species like humpback chub or razorback sucker.
So you used computer modelling to look at these different factors, climate change plus how we manage dams on the Colorado River, to create a model that showed you how many days of the year, it would be in the sweet spot, the right temperature for various species of fish, is that right?
That’s correct.
Looking at all of that, what did you find out?
Those decisions on where to store water really do matter. Because if you draw Lake Powell down, for example, you’re going to be warming the environment within the Grand Canyon… The direct effects of climate change are actually pretty low, it’s much more affected by the release temperatures coming from the dam itself. The same goes for Hoover Dam.
Your findings have implications for whether we put most of the water in Lake Powell or most of the water in Lake Mead or some intermediate between those two things. Can you talk more about that?
Sure. There is this debate … over what to do in terms of decreasing watershed runoff that leads to less water in the major reservoirs in the basin. There are debates on whether Lake Mead should be filled first or Lake Powell filled first… If you were to put most of the water theoretically into Lake Powell, it would mean that the Grand Canyon would once again be really cold for fish. It would go back to conditions we saw in the early eighties when the reservoir was really full…. On the flip side if you were to put a lot of water in Lake Mead at the bottom of the Grand Canyon, you would deemphasize storage in Lake Powell… That water would become really, really warm. Which is great for native fish but it’s also great for non-native fish, and since we have a lot of the non-native predators that are problematic in the Upper Basin in Lake Powell, there is a concern that there would be spillover into Grand Canyon. So the best strategy is an intermediate strategy, where you have water that’s not to hot and not too cold… where you can still provide thermal conditions that are conducive to the growth of native fish.
After doing this research how do you feel about the chances of saving endangered fish in Grand Canyon?
I would say fish are pretty resilient, if given the opportunity…. I don’t think all is lost. We do as humans have the ability to do something about the situation, at least for Grand Canyon, and that relates entirely to helping mange the ecosystem in a way that provides that sweet spot for the thermal regime that would help the recovery.
Kimberly Dibble, thanks for speaking with me.
Thank you so much for having me.
