Habitat use and feeding ecology of riverine juvenile American shad

We examined premigratory populations of American shad Alosa sapidissima in the upper Delaware River to determine habitat and microhabitat use, differential prey use among habitat types, and habitat suitability indices for this previously unmodeled life stage. Both seining and diving techniques were used to quantify juveniles in six habitat types with six physical habitat covariables. Plankton and drift samples also were compared with stomach contents within habitats. We found no relation between relative abundance of juveniles and habitat type, which suggests general use of most riverine habitats. Physical habitat variables likewise did not affect use of habitat within ranges recorded, with two exceptions: (1) a positive relationship between abundance and water temperature in riffles and (2) a positive relationship between abundance and percent submerged aquatic vegetation (SAV) cover in SAV habitats. Opportunistic use of prey items was apparent; however, juveniles selected chironomid larvae and pupae and adult terrestrial insects and avoided ephemeropterans. Overlap between diets and available prey was high for most habitat types (C_λ mean = 0.71), especially for riffles (C_λ = 0.91). However, overlap for juveniles foraging at tributary mouths, where they strongly selected adult terrestrial insects, was low (C_λ = 0.49).