Flexible‐Pass‐Through Antennas for Half‐Duplex Passive Integrated Transponder Tags in Medium to Large Rivers Used to Study Size‐Selective Reservoir Passage

Abstract

AbstractThe use of passive integrated transponder (PIT) tags for studying fish behavior and demography in medium‐large rivers is hindered by antenna designs that are susceptible to damage in those environments and low detection efficiencies. We designed a vertically oriented, flexible PIT tag antenna for half‐duplex tags that is simple to construct and deploy, resilient to the dynamic river environment, retains the higher detection efficiency of pass‐through antennas, and is suitable for rivers up to 30 m wide and 1.5 m deep. These “flexible‐pass‐through antennas” are economical to build and cost ~US$435 to $680 for a one‐ or two‐winding antenna, respectively. We used two flexible‐pass‐through antennas to test for size‐selective reservoir passage in juvenile steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) and Rainbow Trout. We found that flexible‐pass‐through antennas withstood high flows and debris during a spring out‐migration season and provided data to reject the hypothesis of size‐selective fish passage at the Los Padres Dam and Reservoir on the Carmel River (California, USA).