Comparison of Detection Efficiency among Three Sizes of Half-Duplex Passive Integrated Transponders Using Manual Tracking and Fixed Antenna Arrays

We compared detection efficiency for three lengths (12, 23 and 32mm) of half-duplex (HDX) passive integrated transponder (PIT) tags for both manual tracking and fixed array applications. In a stream we used a wand-type manual tracking antenna and determined that detection efficiency was considerably influenced by tag size (i.e., 20% for 12mm, 43% for 23mm, and 81% for 32mm) and water depth. Vertical and horizontal read range also varied among tag sizes (lower for smaller tags) and orientation (12-mm and 23-mm tags oriented perpendicularly failed to read in the horizontal test). Using a fixed PIT array, we also compared the detection efficiency of the same three sizes of PIT tags in Shorthead Redhorse Moxostoma macrolepidotum released into a fishway. Again, detection efficiency increased with tag size: 12mm = 55.8 +/- 9.2% (mean +/- SE), 23mm = 91.0 +/- 1.8%, and 32mm = 97.0 +/- 1.5%. When using PIT telemetry on smaller fish species and/or life stages, we suggest that researchers consider the tag size, as the diminished detection efficiency of 12-mm tags could introduce a bias and impede the ability to address some research questions. Received July 11, 2012; accepted September 20, 2012