Verde River Reflections: A tail of two fishes

Common carp like this were found by the thousands in the Verde River. (Adobe/stock)

Common carp like this were found by the thousands in the Verde River. (Adobe/stock)

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Doug Von Gausig

The Verde River Institute uses a new drone technology called photogrammetry to record the Verde’s changes, its health and its ecosystems. These missions produce very high-resolution maps of the river by taking hundreds of aerial photographs and merging them together.

The resulting maps give us a very accurate picture of the river, and we can measure distances, areas, numbers, elevations, and lots of other useful data that make our research more useful and efficient. Over the years, our drones have recorded hundreds of these maps.

A few weeks ago, the Verde River Institute mapped a stretch of the Verde River near Clarkdale, and when we examined the maps, we saw what appeared to be dark, cloudy masses in the water. Zooming in, we could see that these were very dense schools of large fish! The photogrammetry showed that these were fish, but not what kind of fish they were, so we sent the drones back out to take much closer pictures of the schools.

The new images revealed that these were common carp, and thousands of them! The drone took close-ups and videos for our documentation. The schools swirled and moved as if they were a single organism – kind of like an amoeba under the microscope. We knew that carp got together to spawn around this time of year, but we had never seen them in these numbers. We documented the swarms for a few days and produced a YouTube video of them.

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Left: Mixed school of carp and chub. Right: closeup of school; C = carp, R = Roundtail Chub. (Doug Von Gausig)

What the larger female carp are doing is laying their eggs and the smaller males are fertilizing them. This is a random process of scattering millions of eggs in the sandy shallows and hoping some survive! Of the millions of eggs, only a few hundred hatch and grow to adulthood. Carp are good at reproducing and have become perhaps the most common fish in the Verde River.

Then, a few weeks later, we went out to have some fun fishing in our kayaks, and we ran across schools of another large minnow – the roundtail chub. Roundtails (we called them bonytail or Verde trout when I was a kid) grow to 20 inches or so but are usually around a foot long in this stretch of the Verde. They’re the most common of the native fish left in the river, and they are great sportfish.

They take baits of all kinds and are good fighters, but are designated a catch and release species. The schools we found had hundreds of tightly packed fish.

This got us thinking about the carp in our photogrammetry. Since both fish are minnows, and they have similar spawning habits, we thought we could learn something about them by studying the photos of their schools. What a surprise we had when we zoomed in on the carp schools. They were not comprised only of carp but were actually mixed schools of carp and roundtail chub! Since chubs are native to the Colorado River basin and carp are native to Europe, seeing them together in such masses was puzzling. Why would two very different minnows gather together?

Well, W.L. Minkley, the famous Arizona ichthyologist, and my professor at ASU in the 1960s, wrote that roundtail chubs are omnivorous fish that eat just about anything they can get in their mouths -- even their own eggs and the eggs of other fish. Mystery (maybe) solved! The chubs in our pictures were undoubtedly gobbling up the eggs of the carp in the schools.

I thought I knew a lot about the Verde, but the river is always full of surprises and adventures. I guess that’s why I have always loved it. More in a few weeks.

Doug Von Gausig is the executive director of Verde River Institute.


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