Effects of US Army Corps of Engineers Operations on Off-Channel Habitats Used By Oregon Chub and Other Floodplain Fishes in the Willamette Basin, Oregon

Oregon chub (Oregonichthys crameri) are small minnows endemic to the Willamette Valley, Oregon.  In 2009, we initiated a floodplain monitoring study to minimize impacts of Oregon chub under the U. S. Army Corps of Engineers’ Willamette Valley Biological Opinion, with the objective of identifying those conditions (flow levels, temperature regimes, habitat characteristics) that may allow Oregon chub to co-exist with non-native fishes in connected habitats.  In this multi-year study, we are assessing the impacts of altered flow and temperature regimes, floodplain restoration, and reconnection of off-channel habitats on habitat availability and fish assemblages.  Our approach includes mapping the bathymetry and hydrologic points of connection, monitoring water levels and temperatures, and sampling fish assemblages in the study reach.  We are tracking changes in wetted and vegetated habitat areas and volumes and will describe relationships between water levels, temperatures, and hydrologic connection with mainstem river flows (regulated and unregulated).  Over time, we will assess relationships between these physical data and fish assemblage structure in floodplain habitats, including those preferred by Oregon chub.  We will discuss details of our study design, discuss preliminary results from the first four years of monitoring, and provide preliminary results and examples of the application of our methods.