Stable isotopic indicators of habitat use by Mississippi River fish

The Mississippi River has been highly modified for much of its length, with dredging, channelization, and an extensive levee system disrupting historical connections to inland and coastal floodplains. There are currently many large- and small-scale efforts to restore these historical connections in the Mississippi River basin, often with particular emphasis on restoring fish spawning habitat and the high fisheries productivity of the floodplain systems. To investigate how stable isotopic indicators might be useful in showing fish use of restored floodplain habitats, 118 common, benthic-feeding fish were collected from the lower Mississippi River system in Louisiana. Chemical analyses of amounts and isotopic compositions of C, N, and S in fish tissues showed that fish living in different rivers and floodplain estuaries had distinctly different chemistries that reflected fish use of different habitat types. For example, inland swamp floodplains in the Atchafalaya Basin produced fish with lower δ13C than in the mainstem Mississippi River, and habitats in the coastal floodplain of upper Barataria Bay produced fish with higher δ34S than in the mainstem Mississippi River. In general, floodplain restoration should increase habitat diversity available to river fish, and a good indicator for determining increased habitat use and success of the restoration may be the increase in the C, N, and S chemical isotopic diversity in fish.