Instantaneous total mortality rates for planktonic larval freshwater drums (Aplodinotus grunniens) in a channelized stretch of the Missouri River were estimated from analyses of cumulative catch curves. Mortality rates, which ranged from 0.11 to 0.21 per day, were significantly greater in 1976 than in 1974. Basing our interpretation on the underrepresentation of eggs and early larvae in the channelized river samples, we hypothesize that favorable environments upstream represent a more significant source of recruitment of larvae to the freshwater drum population than the channelized river.