Detection of PIT tagged out-migrating juvenile salmonids in relatively large natural rivers is problematic because available antenna systems are typically incapable of interrogating the upper portions of the water column where fish may travel. Low juvenile detection rates hamper studies of many kinds including those designed to understand population level effects of flow management and habitat restoration.

An antenna system that could detect fish through the whole water column would be invaluable in addressing the ever more specific questions posed by researchers employing RFID technology. We have developed an antenna system dubbed the FIN (Fish Interrogation Nodes) capable of detecting fish through the whole water column at variable river flows and stages. These arrays are composed of individual vertical antenna housings anchored to either the channel bed or an above water support system through an articulated shackle that allows for deflection and passage of debris and ice.

A partial array was recently installed on the Yakima River in the vicinity of Selah. Results to date indicate good debris shedding capability and tolerance for high flows. Significant noise issues initially encountered appear solvable with minor alterations to the anchoring and cabling approaches used in the prototype.