Fish Assemblage Responses to Different Secondary Channel Designs in the Lower Mississippi River, USA: A Template for River Restoration

Fish assemblages and abundances were compared between permanent secondary channels (with notched dikes) and temporary secondary channels (with unnotched dikes) in the lower Mississippi River (LMR), USA.  Fish assemblages were sampled during 1994-1997 by boat-mounted electrofishing during summer and fall river stages.  Fish sampling was conducted at seven secondary channels spanning from RKm 628 (Louisiana-Mississippi) upstream to RKm 1504 (Kentucky-Missouri).  Fish assemblages were generally dissimilar between temporary and permanent secondary channels throughout the study.  Although species richness was similar between secondary channel types, multivariate analyses indicated assemblage differences.  In particular, Gizzard Shad Dorosoma cepedianum, Threadfin Shad D. petenense, and White Bass Morone chrysops demonstrated preferences for low-current conditions associated with temporary secondary channels.  Blue Catfish Ictalurus furcatus, Flathead Catfish Pylodictis olivaris, Freshwater Drum Aplodinotus grunniens, and Skipjack Herring Alosa chrysochloris exhibited preferences for permanent secondary channels that contained year-round flows.  Gars Lepisosteus spp., Goldeye Hiodon alosoides, Common Carp Cyprinus carpio, River Carpsucker Carpiodes carpio, and buffalofishes Ictiobusspp. showed little preference for either secondary channel type.  Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches, which will provide the greatest biodiversity for the ecosystem.