Longitudinal Patterns of the Illinois Waterway Fish Community

Abstract

ABSTRACT The Illinois Waterway can be divided into two segments—an upper region of steep gradient with a rocky substrate and narrow basin and a lower region of shallow gradient with a wide, complex floodplain. We hypothesized that fish abundance and species diversity would be much greater and community structure would differ by species relative abundance and biomass in the lower segment of the waterway given its much greater acreage, habitat availability, and habitat diversity. Patterns in fish species composition and abundance along six reaches of the Illinois Waterway were described from a 15-year (1989–2004). fish monitoring record. Fish numbers in terms of relative abundance and biomass followed expected patterns in most instances; however, overall fish abundances and forage species abundances were greater in the upper river. Longitudinal differences in species relative abundance and biomass were also detected, illustrating a distinct community change between the upper and lower river segments of the system.