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. Passage opportunity is determined by how frequently the tide gate is open, whether or not the tide gate culvert is perched, and water velocity at the tide gate outlet. Fish delayed in their movement by tide gates may experience increased predation risks as they congregate in the vicinity of these structures. We conducted our research in Coos Bay, one of the many Oregon estuaries with extensive use of tide gates. We installed stationary passive integrated transponder (PIT) antennae around a top hinged tide gate to track the movement of PIT tagged juvenile coho and chinook salmon as well as subadult and adult cutthroat trout. A tilt logging device allowed us to pair fish detections with tide gate opening angle.
We found that most coho smolts moved quickly downstream through the tide gate, often during the beginning of the opening cycle. Few subyearling coho moved through the tide gate during the sampling period. However, several subyearling coho from a neighboring system were detected downstream of the tide gate. Fish upstream movement through the tide gate was very limited. This was a pilot study and fish movement and predation risk in two other streams (one with a side-hinged gate and one without tide gates) will be monitored similarly next year.
Additional Research Information:
Performance of a Full-Duplex Passive Integrated Transponder (PIT) Antenna System in Estuarine Channels
Arthur L. Bass , Guillermo R. Giannico and Gabriel T. Brooks