Historical changes in the fish community.
Historical records of the fish community indicate that species richness, species composition, and the abundance of individual taxa have changed dramatically in Lake Mendota from 1900 to 1989. Yet most of the species present in 1900 continued to be present or abundant in the 1980s. Extirpations (species losses), invasions, and introductions are common; populations of individual species such as the cisco and yellow perch have varied repeatedly from high to low numbers. The evidence on which these changes are based is scanty prior to the 1940s and becomes increasingly strong thereafter.