HUMAN ALTERATIONS TO LANDSCAPE CONNECTIVITY AND LARGE-RIVER BIOTA: PALLID STURGEON IN THE MISSOURI RIVER

Dams, diversions, and channelization of rivers can alter multiple dimensions of longitudinal and lateral connectivity for fishes. These changes can have severe consequences for anadromous and potadromous fish species that utilize long sections of large rivers for adult migration and young-of-the year dispersal. A thorough understanding of the reproductive ecology of large-river species – how the species’ reproductive life cycles play out in an increasingly fragmented landscape -- is essential for design of effective management and restoration strategies. The objective of this presentation is to illustrate four dimensions of how human alterations can affect reproductive connectivity in a large river, using the endangered pallid sturgeon (Scaphirhynchus albus) and the Missouri River as an example. The pallid sturgeon is a potadromous fish that typically migrates hundreds of kilometers upstream to spawn and whose larvae disperse commensurate distances downstream. The pallid sturgeon is endemic to the Mississippi-Missouri river system, which has been altered by North America’s largest system of storage reservoirs and is extensively channelized for barge navigation. The primary connectivity dimension to the pallid sturgeon is dam-related barriers to upstream migration and access to spawning areas. The secondary, and related dimension, is lack of adequate distance for downstream drift and dispersal in inter-reservoir segments. The third dimension is enhanced longitudinal connectivity because of increased advection and decreased retention of larvae in channelized river segments. The fourth dimension is variable changes in lateral connection with the floodplain due to levees and geomorphic adjustments to the river profile. Understanding of the pallid sturgeon’s needs is complicated by the rarity of the species and the fact that the majority of knowledge gained about the pallid sturgeon has been from a highly altered river system or from laboratories. We will illustrate the state of knowledge about how reproductive ecology, geomorphology, hydrology, hydraulics, and socio-economic context of the Missouri River system combine to determine options for restoring and managing biologically relevant connectivity.