Life of a River - Biology
Adaptations (pg 1 of 3)

Among ecosystems, rivers are unique for the continual flow of water, sediment, nutrients, and organisms (see Spiraling). Stream organisms of all kinds have physical and behavioral adaptations to varying water velocities. Consequently, the plants and animals found in riffles differ from those in pools, even within the same stretch of a river. For example, fish that are adapted to fast water can have a streamlined shape like darters to minimize the force of the current, or fins like a sculpin that anchor them to rocks.

Trout tuck behind a rock or other shelter when feeding to conserve energy. When prey appears, the trout quickly move out into the current to capture it. Smallmouth bass, less streamlined than trout, generally occupy slower water, moving to riffles only when actively feeding. Northern pike, though built for quick acceleration, cannot swim continuously against a strong current. They occupy slack eddies and backwaters in wait of prey.

Flathead catfish have been observed overwintering in slack water on the downstream side of rocks in the Mississippi River. A conspicuous film of sediment that had settled around the fish suggested a motionless state of torpor and the protection that these rocks afforded (Hawkinson and Grunwald, 1979).

Map turtles and softshell turtles are uniquely adapted to larger swift-moving rivers. Softshells have snorkel-like nostrils that allow them to breathe in shallow water while their flat, pancake-shaped shell is nestled in the sand.

Birds and mammals have also adapted to exploit the aquatic habitats. Long-legged herons and egrets effortlessly stalk the backwaters to spear fish and frogs. Mergansers and scaup dive in main channels after fish and fingernail clams. The body profiles and thick fur of otter and beaver allow them to comfortably navigate swift currents and withstand cold water temperatures.

Pictured animals: Brook trout, flathead catfish, smooth softshell turtle, spiny softshell turtle, great blue heron, river otter