Introduced Fish in Northeastern USA Lakes: Regional Extent, Dominance, and Effect on Native Species Richness

Abstract
We assessed the effects of nonnative fish on native fish biodiversity, using assemblage data collected during 1991–1996 from 203 randomly selected lakes in the northeastern USA by the Environmental Monitoring and Assessment Program (EMAP) of the U.S. Environmental Protection Agency. An estimated 74% (±17.6%, 95% confidence interval) of the region's 10,608 lakes between 1 and 10,000 ha contain at least one introduced species. Based on our samples, nonnative individuals outnumbered natives in an estimated 31.5% (±11%) of lakes. Regression models indicated that native, introduced, and total species richness were associated with lake surface area, elevation, and lake depth (0.31 ≤ R 2 ≤ 0.81). The intensity of human disturbance in the watershed was positively associated with introduced species richness but not associated with native species richness. The number of nonnative species was a significant variable in the native-species regression models for the entire Northeast and for only one of five sub...