David L. Buckmeier, Timothy M. Wetzel, and Elise R. Irwin, USGS Biological Resources Division, Alabama Cooperative Fish and Wildlife Research Unit, 103 Swingle Hall, Auburn University, AL 36849

Abstract. Differences in distributional patterns of larval fishes in large rivers are apparent and may reflect longitudinal changes in habitat and/or managed flow regimes. Upper and lower reaches of the Alabama River were sampled between March and September 1996 and 1997. Within reaches, main channel and tributaries were sampled during day and night with push-nets (N=2006) and tributary margins were sampled at night with light traps (N=645). Initial results (1915 samples processed) indicate that ichthyoplankton in the Alabama River exhibited two distinct peaks in abundance at all sites, including both tributaries and main channel areas within each site. In addition to seasonal patterns, spatial differences in abundance between upper and lower reaches were apparent. Larval abundance was higher at the lower sites during the first season (March through May), whereas abundance during the second season (June through September) did not differ. Initial results reflect our hypothesis that larval abundance will be higher in river reaches where the floodplain is intact and reaches where the natural periodicity of the flood-pulse regime has not been altered. Potential exists for recovery of systems downstream of navigational structures and we intend to test this hypothesis in an unregulated system.