As spring quickly approaches and the migration of fish through the Falls of the James River increases, there is a wealth of information to be gained from a sign on the Floodwall Walk at the overlook to the Manchester Dam on the south bank in downtown Richmond, provided by the Richmond Audubon Society and the James River Park:
The underwater habitat of the Falls of the James provide conditions that support the most dense and rich mix of aquatic life on the entire river.
- The granite bottom is stable so there are few moveable rocks or gravel to grind up small organisms like snails, clams and insect larvae.
- There is a lot of oxygen in the water because of the churning rapids.
- There are many places for creatures to live in the nooks and crannies among the rocks. There is generally a fish behind every rock, resting in the reduced current, waiting for food to wash by.
- Sunlight can penetrate to the bottom in many places because the river is shallow (4 to 6 feet, in most places, for most of the year — except for a few deep holes and deep channels) and single celled algae and diatoms can grow on the rocks. Dense concentrations of aquatic insect larvae like mayflies and stoneflies graze on it at night and they, in turn, feed small fish and predatory insects like hellgrammites. This thin layer of slime is the base of the food chain.
- Inch for square inch there is no more important portion of this river for living things.
The sign also includes information on the wildlife in the river:
- There are several types of shad and herring (American shad are the largest, blue-backed herring are the best eating). While they actually live in salt water, they come up rivers in the spring to lay their eggs because there are fewer predators in fresh water. Moving in huge schools, they travel at night and usually follow the shoreline. They have no teeth and swim with their mouths open to filter the water for plankton.
- Streamlined body, thick muscles and broad tail show that bass are fast-moving predators of small fish. They live at mid depth.
- A slimy coating on the skin allows American eels to keep moist and slip away from predators when they come out of the water on rainy nights to get over dams. Tiny fins and flexible bodies mean they swim slowly and stay out of the current.
- Atlantic sturgeon are the biggest fish in the river (800 pounds) but they are only found in the springtime when they lay huge gobs of sticky eggs among the rocks. Boney plates (instead of scales) show this is a prehistoric fish. A mouth that faces down shows that it lives on the bottom and lips that unroll like a short hose shows that it sucks up food from mud. Native American boys used to ride them here as a Rite of Manhood. It is illegal to catch or hurt them.
- Whisker-like barbells that taste the water and a mouth that points down show that channel catfish live on the bottom and eat a variety of foods, especially dead things.