Feeding and distribution of larval freshwater drum (Aplodinotus grunniens) in Pool 7 of the Upper Mississippi River

Abstract

During the spring and summer of 1981, a sampling program was employed to describe spatial, temporal and diel variations in larval freshwater drum (Aplodinotus grunniens) abundance and distribution in Pool 7 of the Upper Mississippi River as potentially impacted by commercial navigation. In addition food habits were evaluated to determine if seasonal or spatial differences occurred. Freshwater drum eggs first appeared in the samples in late May. The first freshwater drum larvae were collected on 12 June, 1981. Larval freshwater drum were more abundant near the surface at midnight than during the day. Greater densities of larval freshwater drum were collected at main-channel bottom and backwater sites during biweekly daytime collections. Considerable seasonal, spatial and diel variability in abundance of larval freshwater drum existed which would significantly influence the portion of the freshwater drum population potentially impacted by commercial navigation through Pool 7. No identifiable differences in food eaten or growth was discernable by habitat type. Cyclopodid copepods (Cyclops sp.) and calanoid copepods were preferred by larval freshwater drum over cladocerans(Daphnia and Leptodora) primarily because of their body shape and size.