Decline of the Native Fish Fauna of the Sierra Nevada Foothills, Central California

Abstract

A survey was made of the fishes occurring in streams of the Sierra Nevada foothills above the San Joaquin Valley, California. Twenty-four species were collected, 12 native, 12 introduced. The pres- ent distributions of these fishes were' compared to their pre-1900 distribu- tions, as inferred from old records. Overall, the ranges of introduced species and rainbow trout ha,ve expanded while the ranges of native species, especially California roach, ha,rdhead, Sacramento squawfish and Sacramento sucker, have contracted. Healthy populations of native fishes were foundonly in a rather narrow middle elevation band of compara- tively undisturbed sections of foothill streams. The native fish popula- tions in different foothill stream systems are now isolated from each other and are., thus., in danger of local extinction as foothill development proceeds. The study indicates that populations of native stream fishes, even if they do not contain endangered species., should be protected, to make sure that severe natural conditions, when combined with human alterations of the streams, do not destroy unique assemblages of fishes.