Effectiveness of Tide Gate Replacements to Increase Habitat Access for Juvenile Salmon at the Julia Butler Hanson National Wildlife Refuge

This research assesses the effectiveness of the tide-gate restoration actions in the Julia Butler Hansen (JBH) National Wildlife Refuge (rKm 55-63) in the LCRE.  Replacement of top-hinge tide gates with new “fish-friendly” tide gates is a common restoration action in the LCRE which managers must weigh against other forms of tidal reconnection.  Colleagues and I performed intensive sampling of water quality, hydrology, channel morphology, plant communities, and fish at restored and reference sites during pre- and post-restoration periods.  We found distinct differences in fish communities and temperature regimes at treatment and reference sloughs before construction (2007 ‐ 2008).  Though juvenile salmonids would enter sloughs through the top‐hinge tide gates, frequency was low when compared to control sloughs.  One season of post‐construction data was collected spring 2010 after three of the five new fish friendly gates were installed.  Two of these gates were installed in sloughs where a levee had previously closed off the historical mouth.  Water temperature profiles within these two sloughs approached that of reference sloughs.  Numerically, more salmon were captured in treatment sloughs after installation of the new tide gates.  More salmon, however, were also captured in a control slough that continues to be disconnected from its historical mouth.  More research is planned to investigate the effectiveness of fish friendly tide gates at JBH.