The Rivanna Rambler

On a recent weekday in August, I was tromping down a section of Ballinger Creek in Fluvanna County helping StreamWatch put some numbers to the shape and stability of the banks and bottom as part of a watershed wide study. The low water level had the benefit of exposing much of the river bottom to view and making it somewhat easier to walk in the creek. The bedrock outcrops provided firm ground, but were coated in a thin slime of algae that foiled the grip of my river sandals. With each step, I made a careful and studied calculation of the bottom lest I end up on my butt or with a twisted ankle.

And so it was I became acquainted with the nests of the genus Nocomis – those flattened mounds of rocks that dotted the shallow bottom that I had casually and unknowingly trampled. Three of the seven species of Nocomis make the Rivanna their home – the river, bull, and bluehead chubs – and they are fairly common. Once I learned what I was looking for, I saw them everywhere in the creek.

Each spring, males of the Nocomis species get to work, first excavating a pit on the bottom and then building a gravel mound on top of it. Only 4 to 6 inches long, these comely looking fish push, shove, and carry in their mouths small, carefully selected rocks from the surrounding river bed. Piled onto a mound, the nest looks like a small child had whiled away her time making a rock castle in the creek, but indeed it takes the male chub up to 30 daylight hours of hard work collecting the stones of his castle. Then the male chub crafts a small trough in the top — and sets to work attracting his mate, announcing his readiness by a swelled head, horny bumps on his forehead and often a change in color. The name of the bluehead chub is derived from its nuptial coloration, while the river chub turns a bright pink. This takes place in late spring and early summer – each species wired to the spawn by the lengthening days and resulting rise in water temperature.

Once spawning has occurred, the male covers the trough, and the eggs settle into the spaces between rocks where they develop within the safety of the structure. The male chub defends his nest against males of his own species – and other fish such as suckers who would eat the eggs. Like a coral reef in the ocean, chub nests are a hub of activity and play an important role in stream ecology, for the male actually shares his nest with other species such as dace and shiners, who also use it for spawning. Many of these associated species turn brilliant red, transforming the nest into an underwater neighborhood brightly lit like a hot night in the city. All the activity attracts other, larger fish who have their own dinner in mind.

Now in late August, all that’s left is the pile of rubble and my curiosity about these enterprising, engineering fish. Some chub are known to build nests of over a thousand stones – and can carry rocks that are almost half their size. Why do they do it? Besides the safety from predators, the chub males are providing an environment for developing eggs above the river bottom where they might be smothered by sediment. While other fish species use the oxygenated waters of small riffles in which to lay their eggs, chub create their own oxygen rich environment with their nests above the sand and sediment of the bottom.

A Cherokee legend describes the Ugunsteli (or “horned fish”) and his brightly attired band of attendants, holding court under the cold waters of mountain streams, a story which accurately describes the relationship between chub and the species who share the nests. The presence of nest-building chubs indicates that desirable conditions exist – and, in creating their own centers of life, the chub are contributing to the aquatic health of the stream. But Ballinger Creek’s drains an 18 square mile watershed is downstream from Zion Crossroads. Under intense development in Fluvanna County, it’s a good watch for signs of degradation, and like a male chub tending its nest, a good one to watch over.