The decline of native fish populations and the invasion of non-native fishes are the most noticeable trends in California's freshwater fish assemblages over the last century (Moyle and Williams 1990, Moyle 2000). Moyle (2000) and Dill and Cordone (1997) date the first introduction of non-native fish into California back to the latter half of the 19th Century. Yoshiyama et al. (1998) place the beginning of the decline of the state's chinook salmon populations also near the turn of the century. The mid-1800's also marks the beginning of a population explosion in California, driven by the discovery of gold in the Sierra Nevada in 1848.