High Conservation Value of the Odonata Assemblage in the Upper Ohio River Mainstem: A Large, Regulated River in North America

Abstract. Like many large rivers in modern industrialized regions, the Ohio River mainstem is a heavily modified riverine habitat comprised of various reservoir-dam series and shaped channels, rather than a free-flowing system. However, many odonate species in such habitats, even species of conservation concern, have been shown to prosper in degraded lotic habitats due to key life history attributes, such as rapid recolonization following large disturbances. In this study we characterize the assemblage of odonates in a Pennsylvania section of the Ohio River mainstem and determined if any species of conservation concern were present. We also tested hypotheses on distributions in the channel by testing if proximity to banks and channel depths helped predict odonate abundance. Samples were acquired as bycatch to benthic fish sampling conducted using electrified benthic trawling, a novel approach for collecting benthic macroinvertebrates in large freshwater rivers. We found seven odonate species, all of which were known to be species of conservation concern in one or more U.S. states. We also concluded that gradients of bank distance and river depth only weakly predicted odonate abundance, suggesting that the Ohio River species regularly use mid-channel habitat that is several meters deep. Life histories of most of the species collected are typical of those living in large lotic, and occasionally lentic, environments. Studies of other large, temperate rivers show that the ability to persist is not uncommon for odonates in these modified environments, and may be due to their ability to use mid-channel resources successfully. Despite the substantial differences between contemporary and historic conditions of habitats in the Ohio River basin, an odonate assemblage worth conserving continues to be present in the mainstem channel.