A 2.4- By 6.1-M Flexible Antenna for Detecting Full-Duplex PIT Tagged Fish

We developed a 2.4‑ by 6.1‑m flexible antenna capable of detecting 12‑mm full-duplex PIT-tags. The flexible design was developed to support ongoing studies in the Columbia River estuary that rely on detections of migrating adult and juvenile salmonids.  The antenna wires were housed in a 1.9-cm-diameter water suction hose and the reader was housed in a water-tight PVC capsule.  When deployed, the rectangular shape of the antenna was maintained by light-weight rope frames, PVC spreader bars, and strategically placed weights.  These antennas were used in both a stationary setting, where they were mounted to a pile dike, and in a mobile setting, where they were towed behind two vessels.  Mobile deployment utilized multiple antennas assembled in a horizontal matrix to maximize the detection area. Typical read-range of the flexible antennas from the center plane was 0.75 m in a pass-through orientation and 0.5 m in a pass-by orientation.  These antennas were versatile in application given their large size and ease of handling and had relatively low construction costs compared to traditional PVC antennas.