PIT-Tag Detection System for Large-Diameter Juvenile Fish Bypass Pipes at Columbia River Basin Hydroelectric Dams

We developed a prototype detection system with increased reading range for passive integrated transponder (PIT) tags. The system eliminates the need to route juvenile salmonids to sampling and collection facilities for detection and allows fisheries management greater flexibility in safely bypassing juvenile salmonids at dams. This technology can be applied to PIT-tag studies elsewhere, especially those directed at recovery of threatened and endangered salmonid populations. The system exceeded the intended goal of 95% tag-reading efficiency and yielded reading efficiencies near 100% for the four antennas combined. In tests using juvenile steelhead Oncorhynchus mykiss and subyearling Chinook salmon O. tshawytscha, the system worked as designed under a variety of release times and densities. Both direct and indirect methods were used to evaluate the system. The direct method used a known number of tagged fish released at a specific location and compared that number to the number of unique tag codes read. Using this method, over 98% reading efficiency was obtained under all test conditions. The indirect method relied upon a statistical comparison of reading performance between antennas during the juvenile migration season. This method showed that the system efficiency ranged between 99.5% and 100%.