The Barrier "Tradeoff" in Native Fish Management
Stream fish naturally move. They travel upstream and downstream between feeding and spawning areas, disperse to new habitats, and recolonize areas after disturbances such as flood or wildfire. Biologists believe such movement is important to the resilience of native fish because it allows genetic exchange among population groups and decreases the risk of local extinction. When native fish are threatened by invasion of nonnative competitors, however, biologists face a trade-off: fish barriers such as small dams can stop nonnatives from moving upstream, but those barriers also may isolate and limit movement of the native fish they are intended to protect.