PIT Tag Interrogation
Passive Integrated Transponder (PIT) tags are one of the most common tags used to mark fish. As of 2015, nearly 40 million fish have been marked with PIT tags throughout the Columbia River Basin. PIT tags are small, about the size of a grain of rice, enabling them to be implanted in either adult or juvenile salmonids. PIT tags are relatively inexpensive compared with other types of tags (e.g. radio tags or hydroacoustic tags), which allows researchers the opportunity to mark more fish. Each PIT tag has a number unique to each fish. PIT tags do not have an internal battery, so the fish must pass over or through an antenna in order to ‘energize’ and read out the tag number. When a fish with a PIT tag passes by an antenna, the tag number is read, and the time and date are recorded on a data recorder.
Within the Okanogan subbasin, OBMEP works in conjunction with WDFW to operate and maintain PIT tag antennas on the mainstem Okanogan River and all tributaries used by steelhead. Most antennas are located near the confluence of each tributary to the Okanogan River. Tag detections from these sites are used to estimate both adult steelhead spawning abundance and outmigration of juveniles in each unique tributary. PIT tag antennas are also installed within the Zosel Dam fishways to monitor movements of fish from Washington State into British Columbia. Information derived from PIT tag interrogation sites are also used to define timing of fish migrations, describe spatial distribution of spawning throughout the Okanogan subbasin, and to examine passage success through an impediment (e.g. culvert or small waterfall).