Oregon coast tide gates impact juvenile coho salmon movement

Tide gates are one-way doors integrated into dyke systems that prevent saltwater intrusion to agricultural land and allow freshwater drainage to the estuary during low tide. Tide gates may act as fish passage barriers for juvenile salmonids, limiting movements during migration and access to rearing habitats. We conducted our research in Coos Bay, one of the many Oregon estuaries with extensive use of tide gates. Our objectives were to 1) develop a methodology for recording fish passage at tide gates 2) describe the conditions under which fish passage occurs and 3) compare fish passage behavior between a top-hinged tide gate, a side-hinged tide gate and a non-gated stream. We installed stationary passive integrated transponder (PIT) antennae around a top-hinged gate, a side-hinged gate and in a non-gated reference system to track the movement of PIT tagged juvenile coho and chinook salmon. A tilt logging device allowed us to pair fish detections with tide gate opening angle. Velocity at passage was back calculated to match passage detections based on water surface elevations and opening angle. Results from the 2008 and 2009 field seasons will be presented.